Glossary

E – Longitudinal modulus of elasticity, used by designers to verify bending stresses during operation. The value can be obtained indirectly from a tensile stress test. The higher the value, the greater will be the rigidity of the structure, and the desired elastic deformation will not materialize.
G – torsional or tangential modulus of elasticity. The value of G can be obtained from the formula below, where E = longitudinal modulus of elasticity
G = (m : (2(m+1))) x E E = Longitudinal modulus of elasticity m = 1/ Poisson coefficient = 3.30 for steel

N – Newton (force)

Rp 0.2 – Unit load of deviation from proportionality, commonly referred to as yield strength at 0.2% (the reference value in case of contestation) and in some cases at 0.02%. The value is obtained from a tensile test and expressed in N/mm². For carbon steels, the higher yield point ReH is normally used.
A% – Percentage elongation after fracture. Value obtained from tensile test
C% – Z% Reduction in area following failure. The value is deduced from the tensile strength test.
Kcu – Impact test with U-notched proportional specimens broken by pendulum hammer, with energy expressed in Joules.
Kv Impact test with V-notched specimens.
HB 10/3000. Brinell hardness (EN 10003), tested on the surface of the material. Useful as a qualitative indication of tensile strength. 10=Ø ball 3000 = kgf pressure.
HRC – Rockwell hardness “C” (EN10109), a hardness test used normally on material of tensile strength between 760 N/mm² and 2420 N/mm²
HV – Vickers hardness, a test used normally on material of tensile strength between 1320 N/mm² and 2500 N/mm² or over.

Properties of a material associated with its elastic and plastic behaviour when stress is applied. Mechanical properties are dependent, for example, on modulus of elasticity, tensile strength, yield, elongation, contraction, hardness, impact strength and fatigue limit.

ACICULAR Describes a needle-like structure.
ACICULAR FERRITE Non-equiaxial, strongly substructured ferrite that forms after continuous cooling
at a temperature slightly higher than the interval in which superior bainite occurs.
ACID BRITTLENESS Brittleness that can be induced in certain metals by treatment with acids.
ACTIVATION ENERGY Energy that must be supplied to a system, or part of a system, so that a particular process can take place. For example, the energy needed by an atom within a crystal, in order to move from one position to another (diffusion).
ADHESION A bond, generally of a physical nature, formed by forces of attraction between the molecules of different substances.
ADJUSTABLE DRAWING-DIES SADDLE OR SHOULDER SHAPE Dies particularly suited to drawing flats. A saddle or shoulder is part of the composite die, which can be adjusted to obtain intermediate settings between the maximum and minimum drawing dimensions of the die. Positioned by means of wedges, plates and screws.
AGGREGATES The atoms of a solid metal bind to form crystals. Aggregates are commonly referred to as grains
AGING A change in the properties of certain metal and alloys (such as steel), usually by precipitation, occurring at ambient or moderately high temperatures after cold working and after heat treatment (300° C). Overaging induced at a temperature higher than ambient one can lead to undesirable changes in mechanical and physical properties (typically hardness, yield strength, tensile strength, ductility, impact value, formability, magnetic properties).
Certain gases, such as nitrogen, can cause steel to age more readily.
AIR HARDENING An alloyed steel can form martensite and develop high hardness if air-cooled starting from an opportune austenitizing temperature. This property is typical of self-hardening steel.
ALKALIS OR ALKALINES Name given to the hydroxides of alkali metals in group 1, period 2 to 7 of the periodic table.
ALLIGATION The blending of various elements to obtain an alloy.
ALLOTROPY The phenomenon whereby a given substance can have different crystalline structures with different properties. Many elements can appear with different forms in the crystalline state, such as sulphur α and sulphur β, white phosphorus and red phosphorus, diamond and graphite. Sulphur α has rhombic crystals, and sulphur β has a monoclinic crystals.
ALLOTROPY Different symmetry of a crystal lattice within metals due to different temperatures.
ALLOY A substance with metallic properties, combining various chemical elements of which one is a metal.
ALLOY STEEL An alloy of iron and carbon with additional elements such as chrome, manganese, nickel, molybdenum, vanadium, tungsten, cobalt, etc.
ALLOYED CAST IRON Cast iron in which resistance to corrosion, oxidation or heat is increased by introducing Si, Ni, Cu and Cr, often in significant proportions.
ALLOYED QUALITY STEEL Steels used in a similar way to non-alloy quality steels, but containing certain alloy elements that warrant their classification as alloy steels. (EN 10020)
ALLOYED SPECIAL STEEL Steels of which the chemical composition and the particular processing and control conditions are governed precisely in order to obtain the widest possible range of cold-forming and application proprieties, in combination and within tight limits (EN 10020).
AMAGNETIC Said of a material hard to magnetize (e.g. austenitic stainless steel). Steel with ferromagnetic characteristics can be demagnetized by heat treatment: the temperature of the metal is raised beyond the critical point of magnetism (770°) and held for an appropriate duration, before cooling in air or in the furnace.
AMORPHOUS Substances having no characteristic crystal lattice (e.g. amorphous coal)
AMORPHOUS STRUCTURE Non-crystalline structure
AMPHOTERIC Said of a substance able to combine both with acids and with bases (base: a substance able to bind hydrogen ions of an acid)
ANCHORAGE Treatment suitable to ease the painting trough modification of the metal surface, by making it macroscopically rough and creating an adherent layer of oxide, phosphates or chromates, that give a micro-roughness, able to steadily anchor the paint layer, that will be applied in the following step.
ANISOTROPIC Describes a substance of which the crystal structure is different along different directions, as also are the physical properties (refractive index, electrical and thermal conductivity, mechanical properties, magnetics etc…), according to the direction.
ANNEALING The main purpose of this heat treatment is to reduce the hardness of hot-worked, hot-rolled and cold-drawn materials, but also to produce a desired microstructure or obtain desired mechanical, physical, or other properties. Annealing is sometimes performed to reduce stresses, but if done only for this purpose, should be referred to as stress relieving.
ANODIZING Anodizing, is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. Anodizing increases corrosion resistance and wear resistance. Anodic films are applied to protect aluminum alloys, titanium, zinc, magnesium and niobium. The anodization is not useful for carbon steel because these metals form oxide bad for this treatment.
ANTIFLAKE HEAT TREATMENT When hydrogen content is greater than 2 ppm, heat treatments are carried out with particularly long pauses at predetermined temperatures (600-680 °C). This allows the hydrogen to migrate toward the outside, without cracks forming inside the metal.
ANTI-WEAR COATINGS These are films of very hard wear and corrosion resistant material deposited on a metal. They include:
CVD Chemical Vapour Deposition: deposition of a chemical in the vapour phase
DLC Diamond-like Carbon
HIP Hot Isostatic Pressing
PCD Poly Crystalline Diamond: synthetic diamond powder (application of graphite mixed with Co or Ni at high pressures and temperatures)
HVOF High Velocity Oxygen Fuel: flame process utilizing the high kinetic energy of compressed gases and the thermal energy of combustion to produce a coating of low porosity, with firm anchorage and low surface roughness.
ATMOSPHERE The environment in which the metal is heated during production. Particular atmospheres are used to protect the surface of the metal or modify the chemical composition of elements on the surface, so as to add or remove carbon, nitrogen, hydrogen ant to add certain elements such as chromium, silicon, etc.
ATOM The smallest fraction of an element that take part in a chemical reaction and retain its chemical characteristics.
ATOMIC ORBITAL Part of space (volume) of the wave function describing the motion of an electron in an atom or a molecule.
ATOMIC PLANES The intersecting planes on which crystals are arranged in a solid.
AUSTENITE A solid solution of cementite (Fe3C) in y-iron, amagnetic, offering excellent resistance to corrosion. When heat is applied, the formation of austenite begins as point Ac1 is exceeded, and this is the baseline structure for quality heat treatments (generally normalization and hardening and tempering). The tendency of Austenite to harden in the course of processing works against machinability.
AUSTENITE GRAIN SIZE The size of austenite grains in steel heated within the austenitic range; can be measured by chemical etching on a section after cooling at ambient temperature.
AUSTENITE STABILIZING A phenomenon reducing or eliminating the possibility of transforming austenite into martensite during cooling at temperatures lower than ambient temperature (supercooling at -70, -80 °C)
AUSTENITIC OR FERRITIC GRAIN Austenitic grain represents the average size of crystals or grains of steel in the austenitic state. In the case of ferritic steels, which cannot be quenched, the grain is described as ferritic.
AUSTENITIC STAINLESS Chrome and nickel steel with an austenitic structure.
AUSTENITIZATION TEMPERATURE The temperature at which steel is made up completely of austenite. This structure is the starting point for all the changes induced during the cooling phase.
AUSTENITIZING The formation of austenite by heating a ferrous alloy to within the interval of transformation (partial austenitizing) or beyond this same interval (complete austenitizing). Used without further qualification, the term refers conventionally to complete austenitizing.
AUTOTEMPERING The tempering that martensite undergoes during hardening. After quenching in water, oil, etc. the core of material is still hot and able to temper the external mass.
BABBITT METAL Antifriction white metal and soft of tin, lead, copper and antimony in several proportions, used in order to fiction reduce, like in the bearings
BAINITE A structural constituent of acicular cementite in a matrix of ferrite, with hardness of between 30 and 55 HRC. At intermediate rates of cooling, carbon diffusion can still take place and cementite will continue to form. Bainite occurs as the result of a trigger action caused by atomic exchanges.
BAINITIC SCALAR HARDENING Heat treatment involving austenitization followed by scalar hardening in which cooling must be fast enough to avoid the formation of ferrite or pearlite, and the material needs to be held at a temperature higher then Ms so that the austenite will transform partially or totally into bainite. There are no particular requirements for final cooling down to ambient temperature.
BANDED STRUCTURE Alignments of microsegregations (C, Mn, P.) parallels to the direction of the plastic deformation. An effect produced occasionally when steel undergoes deformation under heat. The resulting structure creates difficulties in machining.
BANDING Lines of microsegregation running parallel to the direction of plastic deformation.
BATH Liquid mass of metal inside a smelting furnace
BELL FURNACE A heat treatment furnace, generally having a circular base, and at the centre, a diffuser by which the controlled atmosphere is evenly distributed. The bell is a mobile chamber positioned over the base to protect the charge.
BEND Establishes the capacity or otherwise of a material to withstand cold plastic deformation. The bend is followed by analysis of the edges and the outer face of the bent specimen. The material passes the test if there is no evidence of cracks, micro tears or other particular defects specified and agreed at the time of ordering. The bending force has to be slowly applied in order not to obstruct the cold flow of the material.. The UNI 564 and ASTM A 370 standards fix the modalities of the test.
BENDING MACHINE Equipment used for shaping helically coiled pipe or bending plate.
BETA ANNEALING This heat treatment produces the beta phase in certain titanium alloys. The material is heated at an appropriate temperature, then cooled under controlled conditions to prevent decomposition.
BILLET Semi-manufactured product generally of square section with rounded corner edges, produced by continuous casting.
Standard sizes are from 40 to 220 mm.
BINARY ALLOY An alloy containing no more than two elements
BINARY COMPOUND A compound of two elements
BLAST FURNACE A particular type of furnace lined with refractories and reinforced by a metallic structure, in which iron ores are smelted and reduced in preparation for the processing of cast iron.
BLAST FURNACE SLAG Blast furnace slag contains mainly phosphates, silicates and oxides of iron, calcium, magnesium, etc.
BLOOM Semi-manufactured product generally of square section with rounded corner edges, typically hot-rolled from lingots but also produced directly by continuous casting.
Standard dimensions are from 220 to 400 mm.
BLOWHOLE A cavity produced during the solidification of ingots, billets, etc., by gas evolving and unable to escape, which becomes trapped in pockets.
BLOWING IN The insufflation of liquid steel with a gas.
BODY-CENTERED CUBIC LATTICE Between 1392 °C and 1563 °C (melting point), the common lattice structure of metals is body-centered cubic lattice (δ-iron). This same structure is stable below 911 °C (β-iron between 768 and 911 °C, and α-iron below 768 °C). Interatomic spacing at 20 °C=2,48 A (angstrom) = 0.000248 μm. Reticular spacing (side of the cube) at 20 °C = 2.80 A
BOGIE OR TRUCK-HEARTH FURNACE
A heat treatment furnace with a movable hearth rendered independent of the chamber and extractable so as to facilitate charging and discharging operations.
BONDERIZING The preparation of a metal, before cold-drawing, by treating the surface with a solution of zinc phosphate and then soap, to the end of reducing friction.
BORIDE Borides are advanced ceramic compounds, for example titanium boride, wolfram boride, magnesium boride, etc.
BORIDING A thermochemical treatment carried out on ferrous products, resulting in the creation of a hard and wear-resistant boride surface coating.
BORING The removal of material from the bore of a bush or cylinder with a through hole or dead hole, using a tool held in a boring bar.
BOTTLE CAR A special railway wagon lined with refractory bricks, in which liquid cast iron is poured and transported.
BRAZING A permanent joint made between two or more mechanical pieces using a particular type of soldering method (e.g. steel parts joined by fusing brass between the surfaces). Modern brazing normally uses laser beams allowing precise temperature control when heating the base material of the joined parts and fusing the solder rod.
BRINELL HARDNESS TESTING A method of determining the hardness of a material by measuring the area of indentation made by a hard steel ball of given under standard loading conditions. The result is expressed as a Brinell Hardness Number, which can be converted using official tables (experience-based) into values of Failure, Rockwell hardness, Vickers hardness, etc.
BRITTLENESS A notable lack of ductility or toughness, or of both, in a metal.
BURNING An irreversible alteration of the structure and properties of a metal, caused by fusion initiating at the grain boundaries.
BURNISHING An operation performed in an oxidative environment and at a suitable temperature, as a result of which the smooth surface of a ferrous product is covered with a thin oxide layer of dark colour.
CALEFACTION Phenomenon for which small liquid drops succeed in maintaining themselves on a strongly heated metallic surface. It is also used in the heat treatments field to indicate the steam phase persistence or the adhesion to the boll surfaces that are often the reason of insufficient cooling speed..
CALMING AGENT Describes a metal such as vanadium, aluminium, titanium, silicon or calcium which, when added to liquid steel, has the effect of eliminating dissolved gases (killed).
CALORIZING A thermochemical process that involves spraying one metal onto the surface of another metal (typically aluminium onto an alloy of steel) and then applying heat, so as to produce an oxidation-resistant coating.
CARBIDE A binary compound of carbon and another element. Carbides are formed by the union of certain elements with carbon at appreciably high temperatures.
CARBON POTENTIAL A measure of the capacity of an environment containing active carbon to alter or maintain the level of carbon in a steel, under standard conditions.
CARBON STEEL An alloy of iron and carbon with a carbon content lower than 1.8%, which can also contain <1.6% manganese and traces of others elements.
CARBONITRIDING A heat treatment for steels, where carbon and nitrogen are diffused interstitially into the surface metal by exposure to an atmosphere rich in these elements, in conditions similar to those of casehardening.
CARBONITRIDING IN SALT BATHS Carbonitriding carried out in salt baths containing cyanide
CARBURIZING Carburizing utilizes chemical and heat treatments to increase the percentage of carbon in an Fe-C alloy.
CASEHARDENING Addition of carbon to the surface of a metal by heating in contact with solid, liquids or gases rich in carbon.
CASEHARDENING DEPTH Distance between the surface and the internal layer where Vickers hardness is HV1 = 550, measured under a load of 9.81 N
CAST A term indicating the quantity of metal discharged from a furnace or blast furnace.
The definition is also given to a set of products having the same chemical composition.
CAST IRON A generic term for a large family of ferrous casting alloys in which the carbon content exceeds the solubility (see solvus) of carbon in austenite at eutectic temperature. Most cast irons contain at least 2% carbon, plus silicon and sulphur, and may or may or not contain other alloy elements. Types include grey iron, white iron, malleable iron, spheroidal iron and alloys.
CASTING The term casting is used to indicate the set of build steels or cast irons by operations at the furnace or blast furnace. The word is also given to a set of products coming from the same chemical composition
CASTING Phase of the production when the liquid steel pass from the ladle to the ingot mold.
CATAPHORESIS The phenomenon whereby particles (colloids: epoxy or acrylic resin) suspended in a liquid will migrate toward the cathode when exposed to an electric field. A surface treatment giving steel or alloys excellent resistance to corrosion, and favouring the firm anchorage of a paint finish
CEMENTITE Cementite is iron carbide (Fe₃C), a constituent of steel having a chemical composition of iron and carbon, in which the percentage of carbon is 6.7%. Hardness can be up to 63 HRc.
It has ferromagnetic properties below 210 °C and is a very hard crystalline substance, but also extremely brittle. Subjected to very slow cooling, it can be decomposed into iron and graphite or graphitic carbon.
Definable as:
● primary, when formed by separation direct from liquid
● secondary, when separated from austenite
● tertiary, when separated from ferrite
The morphology of cementite can be: globular and/or spheroidal, laminar and acicular.
CERTIFICATION Document bearing a declaration released by an accredited agency or professional, certifying the characteristics and quality of a product.
CHAMBER FURNACE A heat treatment furnace. The chamber can be of square or rectangular section, and is lined with refractory bricks. Heat is produced by burning fuel, or electrically, by heating elements. Almost all of these muffle furnaces have a forces air system to ensure a uniform internal temperature.
CHAMFER A bevel formed on sharp edges (normally at the end of bar stock) by means of a cut made at 35° – 45°, etc.
CHAMFERING The operation of producing a chamfer.
CHARACTERIZATION Study and analysis serving to establish the main properties of a material or product.
CHARPY IMPACT TEST An impact test in which the specimen, usually notched, is supported at both ends and broken by a swinging pendulum. The energy absorbed is the measure of resistance to impact offered by the material, expressed generally in Joules.
CHEMICAL ANALYSIS The various methods by which the chemical composition of a substance is determined.
CHEMICAL COMPOSITION Defines the type of material and the percentage quantity of elements making up a product.
CHROMATE TREATMENT Chrome passivation of surfaces, carried out in a special bath
CHROMIUM PLATING Galvanic treatment by which a film of hard chrome is deposited on ground bars. This treatment provides resistance to abrasion and corrosion, and gives a lower coefficient of friction between moving parts, in particular where surfaces are coupled with rubber seals.
CHROMIZING A heat and chemical casehardening treatment where chromium is absorbed by the metal.
CLEAVAGE In mineralogy, synonymous with flaking. Cleavage is fracture caused by the propagation of a crack along crystallographic planes with a low index of slip. In steel, this fracture cuts grains at the boundary, and accordingly, is also known as “brittle transgranular fracture”.
CLEAVAGE A characteristic crystallographic plane or set of planes in a crystal on which cleavage fracture occurs easily
COALESCENCE Geometrical evolution of the particles in a precipitate (see precipitation) by dispersal of the constituent elements across the matrix, from the smaller particles (which disappear) toward the larger (which increase in volume)
COARSENING Coarsening of the grains in a metal: an effect caused by high temperatures, significantly higher than Ac3
COERCIVITY When it refers to some materials, the magnetic force, that has to be applied to a magnetic material in the opposite direction to the residual induction in order to reduce the induction to zero (demagnetization), is named coercive force. Coercivity has to be measured in A/m or in Oersted, Gauss ….
COHESION ENERGY The energy needed to separate one mole of a solid into its constituent parts (atoms or molecules).
COIL Hot-rolled flat strip which, following the final pass or after pickling or continuous annealing, is wound into rolls. A slab rolled in a hot-strip mill will extend more than 400 metres in length; coils are the most efficient way to store and transport steel strip.
COIL A quantity of rolled material wound in ordered turns.
COKE PLANT A plant in which coal undergoes destructive distillation to produce coke. The coal can be riddled, and can then also be crushed. Coal loaded into cells is baked by heat from combustion chambers, transmitted through a wall of refractory material. The higher the temperature, the shorter the distillation time. Heat is generated by burning coke gas, or a mixture of blast furnace gas and coke gas.
COLD DRAWING Cold deformation of hot rolled bar, wire rod, tubes, etc. without any of the material being removed. The metal is forced through a die on a drawbench, deforming in such a way as to emerge with a reduced cross-section
COLD FORMED Describes a material shaped at ambient temperature (by cold drawing, cold forging, etc.)
COLD ROLLED (+CR) Cold rolled. An iron and steel product obtained by deforming previously hot-rolled materials, which in this instance are passed cold through the mill rolls.
COLD TREATMENT Cooling a metal to zero or subzero temperatures in order to induce particular conditions or properties, such as dimensional or microstructural stability. When the treatment involves a transformation of residual austenite, it will be followed generally by tempering. To eliminate the residual austenite, the supercooling temperature needs to be lowered beyond the Mf point as the metal hardens; in practice, temperatures of –70 °C – 80 °C will be sufficiently low.
COMBINED ACTION OF ALLOY ELEMENTS Where two or more alloy elements are present in the steel, their combined action will generally not be equal to the sum of their individual actions.
COMPARATOR An instrument used for taking very precise measurements. A comparator be used to measure surface flatness, out-of-round, roundness, etc., with centesimal or millesimal degrees of accuracy.
COMPOSITE MATERIAL Type of material characterized by a non-homogeneous structure, made up of two or more different substances, with different physical and chemical properties. The individual materials that make up the composites are called constituents: matrix and reinforcement es. fiber glass, carbon fibers, ceramic fibers, wefts steel and rubber.
COMPRESSIVE STRENGTH The capacity of a material to withstand axially directed pushing forces.
CONCRETION Part of a material (e.g. stalactitic rock) having a different composition from the remainder of the formation, or of harder consistency, which has been increased by a progressive addition of matter.
CONDITIONING A treatment designed to eliminate surface defects from semi-manufactured iron and steel products before the process of final transformation. The operation is done by grinding or scarfing.
CONDUCTIVITY The capacity of a material to transmit heat, sound energy or electricity. Conductivity is the inverse of resistivity.
CONFIRMATION OF ORDER A document regulating the supply contract. It contains a description of the merchandise, terms and conditions of sale, and has prevalence over any verbal agreements and/or requests for quotations.
CONSTITUENT A single phase or a blend of phases appearing as an identifiable component when conducting a metallographic test on a structure.
CONTINUOUS FURNACE A furnace used for heat treatments, which operates continuously with metal entering at one end and emerging from the other end.
CONTROLLED COOLING A process whereby metal is cooled from a high temperature at a controlled rate so as to avoid cracking and internal damage and produce a desired microstructure.
CONVERSION Treatment in a converter, by which cast iron is transformed into steel by the injection of oxygen, reducing the carbon, sulphur, phosphorus and silicon content.
COOLING The process of removing heat from a product: dependent on the nature and temperature of the medium and/or environment, relative movements, etc.
COOLING CAPACITY The ability of a medium (air, oil, polymer, water, salt bath, etc.) to bring about a given cooling programme
COOLING CURVE A curve indicating the relationship between time and temperature during the cooling of a metal
COOLING RATE Indicates variation in temperature as related to time and to the cooling medium/environment.
COOLING STRESSES Contraction-related residual stresses caused by a non-uniform distribution of temperatures within the material.
COPPER PLATING A process whereby a layer of copper is deposited electrolytically on a metal surface.
Serves principally to provide good resistance against atmospheric corrosion.
CORE The innermost part of a steel product, which does not change in composition during a thermochemical diffusion treatment
CORE HARDENING Hardening to a depth at least equal to the distance between the surface and the core of the piece.
CORE HEATING The second phase of the heating cycle, where temperature is raised uniformly to the prescribed level across the entire section of a ferrous product.
CORROSION A condition resulting from chemical-physical actions produced on a metallic material by external agents.
CORROSION BRITTLENESS A notable loss of ductility in a metal caused by corrosion, generally intergranular, often undetectable by visual analysis
COVALENCE A chemical bond between two atoms in which electrons are shared between the two nuclei.
CRACK Microscopic or macroscopic discontinuity of a metal where two dimensions are noticeably greater than the third (length – depth – width). When a manufactured item presenting this discontinuity is put under stress, local stresses at the tip of the crack will be intensified.
CRACKS FROM HARDENING The fracture of a metal during hardening at high temperature. It can happen more frequently in the case of carbon steels, alloy steels, or tool steels of appreciable hardness and low toughness. The cracks originate generally from screw threads, holes and sharp edges, or from any point where stresses can be increased locally as a result of the strains induced by an increase in specific volumes connected with the formation of martensite.
CREEP Continuous deformation of a metal under steady load, well within the yield point, proportional limit, or the apparent elastic limit for the temperature.
In a creep test, a specimen is placed in a small furnace and subjected to a predetermined steady load and temperature for a certain number of hours.
CRITICAL COOLING Limit conditions of cooling sufficient to allow the completion of a given transformation, while preventing the appearance of an undesirable preliminary structure. The term should be qualified by the type of transformation in question (martensitic, bainitic, etc.)
CRITICAL COOLING RATE Speed of continuous cooling so that to prevent unwished transformations. In the case of steels, it is the minimum cooling speed at which the austenite is completely transformed into martensite during quenching.
CRITICAL DIAMETER The diameter of a bar that can be completely hardened with 50% of martensite at its centre.
CRITICAL POINT The temperature at which a change in structure starts or finishes
CRITICAL RANGE The temperature interval, for a given metal, between an upper critical point and a lower critical point.
CRYOGENIC Cryogenic steels are steels designed for very low temperature applications.
CRYSTAL LATTICE An array of points representing the centres of equilibrium of ions, atoms or molecules, arranged at regular intervals along three directions in space and in a set order for each crystalline substance.
CRYSTALLINE STRUCTURE A structure having an ordered and periodic organization of atoms or molecules, deriving from the regular repetition of a basic unit, the so-called unit cell, along the three spatial directions. In metallurgy, the term also describes a bright structure that it is visible on impact strength test specimens after failure, or on manufactured items collapsed by fatigue failure.
CRYSTALLIZATION The action by which crystals are formed, including fusion, solution and evaporation, hot solution and cooling.
CRYSTALS Regular three dimensional crystal lattice formed by a sequence of unit cells, each containing an identical distribution of atoms and ions.
CYANIDE HARDENING Hardening in liquid salt baths containing cyanide.
CYCLE ANNEALING Annealing at a selected and closely controlled time-temperature cycle to produce specific properties or a particular microstructure.
CYCLONE Particle accelerator used to obtain beams of positive ions with high kinetic energy, higher than the value necessary to produce some nuclear reactions (transmutations, disintegrations). For example cyclotron super-conductor that employs a super-conductor magnet.
DEALLOYING A corrosive action occurring in copper alloys such as CuZn (brass), CuAl (aluminium bronze), etc.
DECARBURIZATION A typically undesirable and involuntary process whereby carbon is removed from the surface of a steel exposed to certain types of atmosphere, generally at high temperature. Decarburization significantly reduces resistance of the metal to fatigue.
DECARBURIZATION DEPTH Distance between the surface of the ferrous product and a limit characterizing the thickness of the carbon impoverished internal layer. This limit can be defined by reference to a structural state, to a level of hardness or to a percentage of carbon in the unadulterated base metal
DEFECTOMAT An instrument designed to detect flaws on the surface of electrically conductive materials. Using the induced currents method, it will show the principal defects of transverse orientation, while the circograph shows mainly the longitudinal defects.
DEFERRIZATION EQUIPMENT This includes plates, bars and magnetic rollers used to remove or separate ferromagnetic material from other material. Also used to retain objects and ferrous materials advancing on conveyor belts.
DEGASSING Treatment serving to eliminate gases like hydrogen, oxygen and nitrogen from liquid steel.
DEHYDROGENATION A heat treatment designed to eliminate hydrogen occluded in a ferrous product without modifying its structure. Dehydrogenation is carried out after electrolytic coating or after chemical pickling.
DELIVERY BATCH A quantity of steel products, all of one type, from the same pour and of the same size, ordered with the same specifications.
DENDRITE A crystal with a tree-like structure more evident in castings that are cooled slowly within the solidification range. The typical branched growth structure resembles a pine tree.
DENSITY The ratio between the mass of a body and that of an identical volume of water at 4 °C.
DEOXIDATION 1) The removal of oxygen from a bath of molten metal by means of a suitable oxidizers.
2) Deoxidation can also mean the removal of undesirable elements besides oxygen, by introducing elements or compounds that will react swiftly with them
DEPHOSPHORIZING Elimination of phosphorous during the preparation of steel
DESCALING The operation of removing the surface oxide layer from billets when hot, using a high pressure jet of water or air.
DESTRUCTIVE TESTING Testing procedures that involve the destruction of part of a manufactured item (tensile stress, impact strength, etc.)
DESULPHURIZATION Treatment designed to reduce the concentration of sulphur in liquid steel.
DEUTERIUM Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen. The nucleus of deuterium contains one proton and one neutron, and accordingly, its mass is approximately twice that of hydrogen.
DEW POINT The temperature at which water vapour contained in the controlled atmosphere of a furnace (endogas) is converted partially into liquid.
DIAMAGNETIC A material not attracted by a magnet.
DIE A drawing tool with an orifice of selected cross sectional profile through which a deformable material is forced usually at ambient temperature; drawing is therefore classified as a cold working process. Dies are made of hard metals pressed from powders, or of high speed steels hardened by PVD processes. The entry angle serves to guide the material through the die, but more importantly to feed in the lubricant. The approach angle is where the actual deformation occurs, and where the highest stresses are localized.
DIFFUSION LAYER Surface layer formed during a thermochemical treatment, containing elements added during the course of the treatment. The concentration of these elements decreases progressively from the outer surface toward the core. Precipitates in the diffusion layer can be nitrides, carbides, etc.
DIMENSIONAL DEFORMATION Alteration of the shape and initial dimensions of a product during heat treatment or in the course of a heating step.
DIMETRIC In crystallography, system of trigonal, hexagonal or tetragonal symmetry in which there are two equal parametric constants and a third unequal.
DIRECT QUENCHING An operation in which casehardened items are quenched directly at casehardening temperature
DISLOCATION A crystallographic defect or irregularity in the lattice that occurs during solidification. When the metal is stressed, dislocations are produced internally and can increase in density, inducing processes of plastic deformation and work hardening at a microscopic level.
DISSOCIATION The breaking up of a chemical compound into simpler compounds or into elements.
Among the most common examples of dissociation is the separation of ammonia (NH3) into nitrogen and hydrogen (N + H).
DOG HOUSE A system for soundproofing the furnace shell and evacuating flue gases generated when melting scrap in electric furnaces.
DOUBLE SKIN An overlap of material connected partially to the base material. Generally, in a double skin, there is a preponderance of not metallic inclusions
DOUBLE TEMPERING A treatment in which hardened steel undergoes two complete tempering cycles, the second usually at a lower temperature than the first, so as to ensure the transformations are completed and maximize the stability of the resulting microstructure.
DRAWING Operation of cold-forming a thin sheet of metal, accomplished by pressing in a steel or cast iron mould.
DRAWING SCRATCHES Mechanical damage to the surface of a manufactured item. The defect arises from friction between the piece and parts of the production machinery
DRAWN PRODUCTS Products of various cross section shapes obtained, after descaling, by drawing of hot rolled bars or rod on a draw bench (cold deformation without removing material). This operation gives the product special features with respect to shape, dimensional accuracy and surface finish. In addition, the process causes cold working of the product that can be eliminated by subsequent heat treatment. Products in lengths are delivered straightened regardless of size.
DUAL PHASE STEEL Structural mild or low alloy steels subjected to thermomechanical treatments performed on the production line in such a way as to control the formation of a dual-phase structure (fine grain ferrite, and martensite islands). This produces a steel with high static mechanical strength and a high resistance to fatigue.
DUCTILE Ductility is the property of a metallic material to deform plastically without fracturing.
DUCTILE FRACTURE A fracture characterized by a clear plastic deformation of metal, which in progressing consumes a notable amount of energy.
ELASTIC LIMIT The maximum stress that a material can bear without presenting residual deformation after the source of the stress has been completely removed.
ELECTRIC ARC FURNACE A furnace with a refractory hearth on which scrap metals are placed. Thermal energy is produced by electric arcs struck between electrodes and the charge of material.
ELECTRO SLAG REMELTING (ESR) ESR (Electro Slag Remelting) is a process used in manufacturing special steels and alloys. It involves remelting steels (generally round section ingots, used in the manner of electrodes) by immersion in a bath of liquid slag. The advantage of the process is that it improves the internal integrity of the ingots and enhances the purity of the metal.
ELECTROFORMING Production of mechanical parts by electroplating in a mold, on a specific model for example dies, molds, etc.
ELECTROLYSIS Chemical decomposition. This process, brought about by passing an electric current from cathode to anode through a solution of iron chloride, can bs used to obtain pure iron.
ELECTROLYTIC GALVANIZATION ZINC PLATING The process of plating a base metal with zinc by electrodeposition
ELECTRON The electron is a fundamental subatomic particle carrying a negative electric charge; a basic constituent of the atom, distributed around the nucleus.
ELECTRON DISCHARGE MACHINING The removal of metallic materials by means of electric discharges. Hundreds of thousands of discharges per second create micro-craters in the work, with maximum precision. The discharges are controlled by highly sophisticated mechanical and electronic systems. A continuously filtered dielectric fluid flushes away the metal removed by the process.
ELEMENT A chemical element is a type of atom that is distinguished by its atomic number (the number of protons in its nucleus). Elements are ordered in the periodic table by their atomic weight and their chemical proprieties; they include metals, semi-metals and non-metals.
ELEMENTARY CELL Symmetry of the crystal lattice
ENDOGENOUS These inclusions (e.g. manganese sulphides) form during solidification to the inside of the steel.
ENDOTHERMIC Describes a chemical reaction involving the absorption of heat
END-QUENCH HARDENABILITY TEST (JOMINY TEST) A test for determining the hardenability of steel or cast iron, in which a standard specimen is heated to a value above its critical temperature. The specimen is then cooled rapidly by a water jet, starting from the hardened end. Once the specimen is at ambient temperature, a series of hardness tests is conducted, starting from the cooled end. The results are indicated on a hardness-distance graph.
ENTHALPY A state function of a system, expressing the amount of energy it can exchange with the environment. In a chemical reaction, for instance, the enthalpy exchanged by the system is the heat absorbed or released during the reaction. When a transition of state occurs, like the transition of a substance from liquid to gas, the enthalpy of the system is the latent heat of vaporization
ENTROPY Thermodynamic function that identifies the tendency of systems to achieve a state of greater disorder. It is a state function and changes ΔS depend only on initial and final states.
EPOXIDE A term for thermosetting resins obtained by condensation, used in the manufacture of paints, adhesives and laminates, and as a matrix for compounds together with fibre glass and carbon.
EQUIAXIAL GRAIN A grain of polyhedral form, not laminar
EQUILIBRIUM DIAGRAM A graph showing temperature and composition of the limits of existence of the phases in an alloy, under conditions of complete equilibrium.
EQUIVALENT DIAMETER 1) Reference diameter for the heat treatment of pieces having a square or rectangular section, quenched in oil or water. Standards provide correlation graphs, e.g. EN 10083-1 figure A.1
2) An equivalent diameter is also used in ultrasonic testing. Defects are compared with flat bottomed holes (‚fbh‘) formed in specimen blocks, of varying diameters and depths: e.g. defects with equivalent diameter of 3mm max.
EUTECTIC 1) A reversible isothermal reaction in which a liquid solution is transformed by cooling into two or more intimately mixed solid solutions. The number of solid phases obtained is equal to the number of components in the system.
2) An alloy structure consisting in a blend of solid solutions that form as the result of a eutectic reaction.
EUTECTOID STEEL Steel with a carbon content of 0.8%
EXHAUSTED, SPENT A term often associated with liquids such as quenching oils, chemical pickling baths, etc. when their properties have been lost.
EXOGENOUS These are inclusions trapped in the steel that have come from outside, for instance, from refractory bricks
EXOTHERMIC Said of a process or reaction that releases energy in the form of heat.
EXTRUSION A process whereby a plastic or metallic material is forced through a die of selected cross-section to produce a given profile. The equipment is known as an extruder.
EXUDATION The emergence of liquid steel through cracks or fissures in the solidified skin
FACE-CENTERED CUBIC LATTICE From 911 °C up to 1392 °C, the stable lattice structure of metals is face-centred cubic (γ-iron or austenite). Austenite describes the solid solution of γ-iron with carbon and other elements. Interatomic spacing at 916 °C = 2,573 A ; Reticular spacing 916 °C = 3,639 A
FANTINA A holder for drawing die tools (saddles, shoulders, wedges), in which they can be ground so as to remove deformations and scoring, and restore them to optimum condition
FATIGUE FRACTURE Failure due to the propagation of a crack that is stressed repetitively by loads, each inducing a macroscopic deformation.
FATIGUE LIMIT The maximum stress to which a material can be subjected repeatedly, for a virtually infinite number of load cycles, before failure occurs.
FATIGUE TEST Mechanical test where the piece has to be stressed many times by a lighter load at the elastic limit.
FEEDER HEAD A special receptacle positioned above an ingot mould, containing molten metal on which the cooling ingot can draw to compensate for shrinkage during solidification, and serving to collect any impurities floating on the metal.
FERRITE For practical purposes, pure iron, with a body-centered cubic crystal structure. It can occur in two forms: acicular ferrite (a fine lamellar structure, like pearlite, of ferrite and cementite) or free ferrite resulting directly from the decomposition of austenite during cooling, without cementite being formed. Ferrite is a very ductile constituent and tends to form a built-up edge when machined (the chip sticks to the tool and does not break easily). Mild steels containing high percentages of ferrite are relatively hard to machine.
FERRITIC STAINLESS Low carbon steel containing high percentages of chromium. The structure is ferritic , and not hardenable.
FERRITIZING ANNEALING A treatment carried out on grey irons after casting, or on spheroidal cast irons, in order to obtain a predominantly ferritic matrix.
FERROMAGNETIC Describes a material of high magnetizability; magnetization can be removed by means of demagnetizers, or by heating the metal to a temperature above 769 °C (Curie point).
FIRST FURNACES In 4000 B.C., iron was obtained from certain meteorites. In 1500 B.C. the Hittites (in the hill country of northern Syria and Asia Minor) began extracting iron from minerals found abundantly in nature. The earliest smelting furnace was the bloomery, essentially a pit in which alternating layers of iron ores and wood or charcoal were laid, and through which air was forced with bellows. The blooms produced in this way absorbed small quantities of carbon from the fuel, and were the first form of steel.
FISSILE MATERIAL Fissile materials are those that undergo fission when exposed to slow neutrons in the fuels of nuclear reactors.
FISSION A process in which the nucleus of an atom bombarded with neutrons is caused to split into two approximately equal parts.
FLAT Flat rolled steel of thickness between 6 and 60 mm and width between 150 and 1250 mm.
FLAT BLOOM A semi-manufactured item of rectangular section produced by continuous casting, which will be hot rolled by the mill train.
FLAT PRODUCTS Products presenting a right section, of which the width is greater than the thickness. Included in this category are: uncoated flat products, uncoated hot rolled flat products, uncoated cold rolled flat products, electrical steels, oriented-grain electrical steels, blackplates, tinplates, coated hot or cold rolled flat products, flat products with metal coating, flat products with organic coating, flat products with other coatings, profiled sheets, composite products. Standard EN 10079/94
FLUX Material added during the casting of a metal, serving to fluidize the oxides and form slag.
FORCED AIR HARDENING Hardening treatment carried out by forced air such as fans.
FORGING MANIPULATOR A machine that can be either automatic (running horizontally on rails) or controlled manually by skilled operators, used to facilitate the handling of ingots and semi-manufactured items products during forging operations.
FORGING, FORGED A product obtained by deforming metals when hot. The work is done by hammering, pressing, swaging, etc.
FORMABILITY A property indicating the ease with which a metal can be worked to a given shape or form by plastic deformation
FRACTURE TOUGHNESS TEST (KIC) A procedure serving to determine the ability of a metal containing a crack to resist fracture.
FREE CARBON Indicates the fraction of carbon occurring as graphite, in steel or cast iron.
FULL ANNEALING A treatment in which a steel is austenitized by heating to 20 – 50 °C above the upper critical temperature Ac3 (hypoeutectoid steel) or above Acm (hypereutectoid steel), then held at this temperature for 2-3 minutes per mm of thickness, before being cooled within the critical range Ac3– Ac1. The metal is cooled finally to ambient temperature at a given rate (5 – 30 °C/h), according to the CCT curves.
FULLERENES A family of molecules discovered in 1895, consisting of carbon atoms united by covalent bonds, in the form of a hollow sphere, ellipsoid, tube, or plane. Fullerenes are the fourth solid structure of carbon, together with graphite, diamond and amorphous carbon.
GALVANIC Refers to a range of coating techniques using electrolysis.
GALVANIC TREATMENT Deposits or coatings designed to give base metals a bright appearance or resistance to corrosion. The voltage applied to the electrolyte solution in the baths (copper, silver and nickel silver, nickel, palladian gold, platinum, ruthenium, etc.) is no more than 6 – 8 V.
GALVANIZATION, ZINC PLATING Process of coating items manufactured in steel so as to improve their corrosion resistance.
GAS CASEHARDENING Casehardening by exposure to a gaseous medium.
GAUGE A precision measuring instrument used for checking dimensions, particularly during machining.
GEMINATE CRYSTAL A union, according to precise laws, of two or more differently oriented crystal portions in such a way as to determine lattice continuity between the portions.
GETTER A volatile metal with the power to absorb neutrons or gases (e.g. for cleaning the vacuum in valves). Zirconium is a metallic absorber.
GHOST – LINE Ghost lines. They are segregation bands born in the continuos casting and then lengthened in the direction of hot rolling. These alignments can negatively influence the mechanical properties of the steel products.
GRAIN A single region in an alloy or a polycrystalline metal. The term describes both crystals of pure phase, and aggregated crystals having a eutectic structure.
GRAIN BOUNDARY The separation interface between crystals, usually presenting an irregular symmetry.
GRAIN GROWTH The growth of some grains at the expense of others, producing an overall increase in grain size throughout the manufactured item.
GRAIN REFINING A heat treatment designed to refine the grain. It consists in heating the metal to a temperature slightly higher than Ac3 (or Ac1 for hypereutectoid steel), without holding this temperature for any significant duration, then cooling in air at a suitable rate.
GRAIN SIZE The number of grains per unit of surface area.
GRANULAR FRACTURE A type of irregular surface produced when metal fractures, characterized by a rough and granular morphology, as opposed to smooth and fibrous. Can be classified as transgranular or intergranular. Often referred to as a „crystalline fracture“
GRAPHITIZING Precipitation of carbon in form of graphite (graphite is the stable phase of carbon at ambient temperature and pressure)
GREY CAST IRON Cast iron that solidifies according to the stable phase diagram, where carbon appears in free form as graphite. Can be obtained by increasing the percentage of silicon and other graphitizing elements, or by slowing the rate of solidification and cooling.
GRINDING A finishing operation carried out with grinding wheels or abrasive belts, whereby minimal quantities of metal are removed from a piece to ensure close dimensional tolerances (h 6) and an optimum finish with surface roughness Ra 0.4 µm.
GRINDING The process of removing superficial discontinuities from bar or billet stock with grinding wheels.
GROUND PRODUCTS Drawn or turned round bars given an improved surface quality and dimensional accuracy by grinding or grinding and polishing.
GROWTH The crystallization of atoms on endogenous nucleation.
HAMMER A machine with a striking head, used to shape steel while hot.
HARDENABILITY The extent to which steel can be changed to assume a martensitic and/or bainitic structure. Generally, the depth and distribution of hardness that can be induced in a ferrous alloy by quenching. The higher the percentage of carbon, the greater the hardenability.
HARDENED LAYER A surface layer of steel having a composition that has been modified by the addition of carbon, nitrogen, chromium or other elements at high temperature.
HARDENER An element added when the steel is liquid and having the property of being able to increase the hardness of the metal as it passes to the solid phase. Examples of hardeners are: C, Cr, W, Mo, Co, Nb Ni and certain rare earths (lanthanides)
HARDENING Increasing the hardness of a metal, usually by heating and then cooling.
HARDENING AND TEMPERING Heat treatment that consists in the operations of quenching and tempering, performed in sequence.
HARDENING DEPTH The extent to which a ferrous product is hardened by quenching, considered from the outer surface toward the core.
HARDNESS A property of solid materials, connected with the strength of interatomic or intermolecular bonds. Expressed in terms of the resistance opposed by the material to penetration.
HARDNESS DEPTH The distance between the surface and the internal layer at which Vickers hardness, measured under a load of 9.81 N, is equal to 80% of the maximum specified surface hardness.
HARMONIC STEEL An alloy of iron and carbon with additional manganese and silicon, having elasticity and strength. Used for manufacturing springs.
HEAT INPUT The electrical energy transferred by a torch (plasma torch: a device that converts electrical energy into thermal energy applied to a gas, which ionizes into plasma) to the workpiece.
HEAT PROPAGATION Heat conduction is the spontaneous transfer of thermal energy through matter, from a region of higher temperature to a region of lower temperature. Convection is the transfer of heat within or by the motion of a fluid. Heat radiation is the propagation of thermal energy emitted in the form of electromagnetic waves from an object raised to a given temperature, with no contact.
HEAT TINTING OR BLUEING A previously notched specimen is caused to fracture and then heated to around 300 °C in a muffle furnace. The structure of the material turns bluish, and the presence of nonmetallic inclusions is demonstrated by a clear and bright colour.
HEAT TREATMENT A sequence of thermal operations designed to bring about a change in the properties and/or structure of a ferrous material.
HEAT TREATMENT ENVIRONMENT The environment to which a product is exposed during a heat treatment; can be a solid, liquid or gaseous medium.
HEAT TREATMENT FURNACE A particular type of furnace in which the temperature of the heating chambers is rigorously controlled so that steel can be produced with predetermined technological characteristics.
HEATING Raising the temperature of a product, applying a predetermined thermal gradient.
HEATING TIME The time taken for the product to be raised from a given start temperature to a desired process temperature at the specified point.
HETEROGENEITY A heterogeneous compound, mixture, reaction or other object is one having different constituents that are not easily sorted or separated, yet are clearly distinct.
HEXAVALENT CHROME A highly carcinogenic chemical element having a valence state of 6, written Cr 6+. Chrome can also be bivalent Cr 2+ and trivalent Cr 3+
HIGH ANNEALING (LARGE- GRAIN ANNEALING) High annealing, also called large-grain annealing, involves heating metal to a temperature above hardening temperature, followed by a suitable cooling step to obtain a large grain size. The purpose of large-grain annealing is to improve machining and profiling. Temperatures between 950 and 1200 °C are used, with a holding time long enough to bring about the desired increase in grain size.
HOLDING (OF TEMPERATURE) Phase of the heat treatment cycle when the temperature is maintained at a selected level for a given duration (holding time).
HOLDING TIME The step of a heat treatment cycle in which the temperature is maintained constant.
HOLDING TIME The duration for which a piece is held in a furnace at a selected heat treatment temperature.
HOMOGENEOUS NUCLEATION The transformation of a metal from liquid to solid phase, with a reduction of free energy. Solid metal is stable only below the temperature of equilibrium (solidification) , when it has less free energy.
HOMOGENIZING A process in which ingots are heated to and held at temperatures near the solidus temperature (> 1000 – 1200 °C) for varying lengths of time. Serves to reduce microsegregation and improve workability.
HOMOGENIZING ANNEALING Annealing at high temperature (1100-1200 °C), so as to bring about a diffusion that will reduce heterogeneity of the chemical composition caused by the effects of segregation.
HOT FORMED Describes a material shaped at high temperatures (hot rolled, forged, etc.)
HOT GALVANIZATION, ZINC PLATING Galvanization of metals by a hot dip process.
HOT ROLLED +AR (as-rolled). These are iron and steel products obtained by deforming blooms, billets, etc. while still hot, in a rolling mill.
HYDRATE The combination of a single or compound substance with one or more molecules of water.
HYDROGEN (H) The first chemical element of the first group in the periodic table, and lightest element known to science. Its nucleus contains a single proton, with a single electron orbiting the proton
HYDROGEN BRITTLENESS Brittleness of steel as a result of hydrogen being absorbed during solidification or during plating processes.
HYDROLYSIS A chemical reaction in which water reacts with a compound to produce other compounds; involves the splitting of a bond and the addition of the hydrogen cation and the hydroxide anion from the water.
HYDROXIDE A compound of a metal oxide with water.
HYPEREUTECTOID STEEL Steel having a carbon content of between 0.8% and 2.06%
HYPOEUTECTOID STEEL Steel with a carbon content of < 0.80%
HYSTERESIS This term is used to indicate the phenomena whereby the state of a system depends not least on the succession of its previous states.
IMPACT ENERGY The amount of energy required to fracture a metal, measured generally by Charpy impact tests (Kv). The characteristics of the test specimens and the conditions in which the test is conducted will greatly influence the values obtained, consequently the type of specimen must be specified (Kcu, DVM etc.).
IMPURITY In any solid, there are always extraneous atoms present in concentrations significant to a greater or lesser degree. An „super clean“ solid, in reality, will contain 1012 impurities per cubic centimetre
INCLUSIONS Particles of impure matter (usually oxides, sulphides, silicates, alumina and the like) that separate from the liquid metal. In certain types of steel, the quantity is kept intentionally high in order to improve machinability.
INDUCTION FURNACE A heat treatment furnace in which the heating is produced by currents induced in the body of the material by means of an induction coil.
INDUCTION QUENCHING A type of quench in which the material is heated by currents from induction coils. The temperature has to be higher than Ac3. Induction quenching cannot generally be used for thicknesses under 6 mm, and is preferable for diameters between 14 and 150 mm
INDUCTION TEMPERING A tempering procedure in which the steel is heated by low frequency induction currents.
INGOT A mass of steel or alloy cast in a mould (an ingot mould) ready for subsequent plastic working.
INGOT MOULD A receptacle in which liquid steel solidifies.
INITIAL HEATING The first phase of heating, when the temperature rises.
INSTILLATION The process of introducing a liquid of appropriate composition, drop by drop, into the chamber of a heat treatment furnace, in a controlled atmosphere. Used in gas carburizing procedures, for example.
INTERATOMIC Existing or operating between atoms.
INTERCRITICAL ANNEALING Annealing at a temperature within the range Ac1 and Ac3
INTERCRITICAL HEAT TREATMENT Heat treatment whereby a hypoeutectoid steel is heated to and held at a temperature between Ac1 and Ac3, then cooled in such a way as to obtain given characteristics.
INTERGRANULAR Between crystals or between grains. Also intercrystalline
INTERGRANULAR CORROSION Corrosion occurring preferably at the grain boundary, generally attacking adjacent grains either negligibly or not at all.
INTERGRANULAR CRACK Crack or fracture occurring between the grains or the crystals of a polycrystalline aggregate.
INTERGRANULAR FRACTURE A brittle fracture in a metal, where the fracture occurs along the grain boundaries, within the microstructure.
INTERMEDIATE ANNEALING Annealing carried out in one or more stages during the course of production.
INTERMETALLIC COMPOUNDS Chemical compounds having a specific crystalline structure, formed by uniting two or more metals in different ratios (e.g. copper and tin, in bronze)
INTERMETALLICS Two metallic elements blended in an exact proportional relationship whereby they can be stacked in a crystalline structure different from their original individual structures; CrAl, for example, giving resistance to oxidation.
INTERMOLECULAR Located or occurring between molecules.
INTERNAL OXIDATION Precipitation internally of a ferrous product, to a greater or lesser depth, of dispersed oxides formed with oxygen spreading from the surface.
INTERRUPTED QUENCHING Interruption of the cooling cycle at a given temperature, whereupon this same temperature is held for a specific duration before cooling to ambient temperature. The effect of the interruption is to trigger an autotempering step by which tensions are relieved in part.
INTRINSIC PROPERTY A property that depends only to a limited extent on the presence of lattice defects or impurities in the material. Examples of intrinsic properties are specific heat, latent heat of sublimation, elastic modulus and bond energy.
INVERTER Power supply circuit for the conversion of alternating current to continuous. A converter is a circuit that changes the frequency of alternating current. In industrial applications, inverters are used principally to control the speed of electric motors.
ION An electrically charged particle, consisting in an atom or a group of atoms that has captured or lost one or more electrons.
ION NITRIDING An ion-bombardment process, with a luminescent discharge taking place in a gas mixture, under a pressure lower than atmospheric. The ferrous metal product acts as the cathode.
IRON An element making up one of the three triads in group 8 of the periodic table, iron is a light grey solid, ductile and malleable, the toughest of the metals in common use, and the most abundant among magnetic metals. It has the drawback of being easily attacked by moist air containing carbon dioxide, changing to rust (hydrated iron oxide). Specific weight at 20 °C is 7.874 g/cm3. Melting point 1536 °C
IRON AND STEEL METALLURGY The sector of metallurgy concerned with techniques for the production and initial processing of cast iron, steel and iron alloys obtained from iron ores.
ISOCHRONOUS A term describing periodic motions that occur in the same time period; it is associated with the curves providing values indicative of the unit load that will produce 1% hot creep, and failure after 100,000 hours.
ISOMORPHISM Informally, an isomorphism is a kind of mapping between objects, which shows a relationship between two properties or operations. If there exists an isomorphism between two structures, we call the two structures isomorphic. In a certain sense, isomorphic structures are structurally identical, if you choose to ignore finer-grained differences that may arise from how they are defined.
ISOMORPHOUS Describes phases with crystal structures of the same type.
ISOTHERMAL Pertaining to changes or other phenomena occurring at a constant temperature.
ISOTHERMAL ANNEALING Annealing carried out at 20-30 °C above Ac3 (hypoeutectoid steel) or Ac1 (hypereutectoid steel). This heat treatment allows regeneration of the structure and completely eliminates any work hardening. The temperature is raised at a gradient of 50 °C/h, and held for 1 hour per inch of thickness. Furnaces must be equipped with forced air circulation. Once below Ac1, the metal must be cooled swiftly down to the temperatures indicated in the data sheets. A holding time of at least 2 hours is then required to complete the transformation of austenite (see TTT-curve), before final cooling in air.
ISOTHERMAL TRANSFORMATION The transformation of one phase to another phase at constant temperature.
ISOTOPE Isotopes of an element have nuclei containing the same number of protons ( Z ) but different numbers of neutrons ( N ). Every chemical element is characterized by an atomic number Z and has several isotopes that present the same chemical proprieties but a different atomic weight, indicated by the number A = Z+N
ISOTROPY Having the same physical properties (mechanical properties, for example) in all directions.
JOMINY See end quench hardenability test
LADLE Metal receptacle often lined with refractories, used for transporting and pouring molten metal take from a smelting or refining furnace.
LANTHANIDE The lanthanide series, now lanthanoid, comprises the fifteen elements with atomic numbers 57 to 71, from lanthanum to lutetium
LAP Zones that have overlapped one with another during hot or cold deformation without the surfaces fusing completely together. A lap resembles a flat metal tongue welded in part to the surface beneath; distinguishable from a longitudinal crack in that it forms a fold at an acute angle to the surface.
LASER Light Amplification by Stimulated Emission of Radiation. Lasers are thought of typically as emitting light with a narrow wavelength spectrum („monochromatic“ light). In manufacturing, lasers are used for cutting, bending, and welding metal and other materials, and for „marking“ — producing visible patterns such as letters by changing the properties of a material or by inscribing its surface.
LATENT HEAT Thermal energy absorbed or released when a substance undergoes a change of state, from solid to liquid or from liquid to vapour.
LEDEBURITE Aggregation (see aggregate) of crystals of the solid phases of austenite and cementite in a striped structure
LIQUATION A separation that occurs during the solidification phase of alloys formed from elements with very different melting points.
LIQUID CASEHARDENING Casehardening in liquid salt baths.
LIQUID SALT BATHS A single molten salt, or a mixture of such salts, providing a high temperature liquid medium in which steel is immersed. This allows the material to be heated faster than in air, also with greater uniformity and precision, and protects against oxidation and decarburization.
LIQUID STEEL Statistical data on liquid steel production is based on the weight of liquid steel ready for pouring that is obtained directly from the melting of raw materials or scrap.
LIQUIDMETAL Not a liquid metal (like mercury), but an alloy based on platinum, copper, nickel and phosphorus. It has a shiny appearance like glass, and characteristics (yield point, hardness, failure, elastic limit, resistance to corrosion and wear) superior to steel. Liquidmetal is an amorphous metal with a disordered atomic-scale structure. In contrast to most metals, which are crystalline and therefore have a highly ordered arrangement of atoms, amorphous alloys are non-crystalline. This minimizes shrinkage during cooling, and provides resistance to plastic deformation. The absence of grain boundaries (a weak spot in crystalline materials) results in better resistance to wear and corrosion. These alloys are well suited for casting technologies used to produce complex shapes.
LIQUIDUS A completely liquid alloy.
LONG PRODUCTS Products of constant section defined by a standard that establishes the current range of dimensions as well as geometrical and dimensional tolerances. Long products include: rods, wires, hot finished bars, rolled bars, forged bars, hollow mining drill bars, bright products, drawn products, turned products, ground products, grooved or ribbed products for reinforcing and prestressing of concrete, hot formed sections, rail track products, sheet piling and pilling, mining frame sections, heavy sections, other profiles, welded sections, cold formed long profiles, tubes, welded tubes, hollow sections, hollow bars. Standard EN 10079/94
MACHINABILITY The ease with which a material can be machined to a given surface finish.
MACHINING ALLOWANCE Limited thickness of metal left after a first operation of roughing in such a way that distortions and other surface defects produced by heat treatments or other operations can be eliminated when machining subsequently to a finish.
MAGNETIC PARTICLE INSPECTION The exam consists in distorting the lines of force extending along a magnetized body when there is a break in continuity of the material interrupts their path. Two magnetic poles are created in the area of the crack, to which coloured magnetic particles are attracted as a means of showing the detail of the defect.
MAGNETIC RETENTIVITY OR RESIDUAL MAGNETISM A phenomenon, quite commonplace in steel, can create problems not so much in terms of workability, but more typically with the finishing of surfaces. During lapping or grinding, fine filings often continue to be attracted by metal that has been magnetized by overheating or by the removal pof material (hacksawing, roughing, etc.), with the result that very poor honed finishes are produced. The problem can be remedied using demagnetizers or by including a stress relieving heat treatment step before final machining.
MAGNETIC VISCOSITY A term describing the delay with which magnetization in a ferromagnetic material varies when the intensity is altered suddenly by an external magnetic field.
MAGNETOSTRICTION Magnetostriction is defined as the property of ferromagnetic materials to modify their dimensions when subjected to magnetic fields
MALLEABLE Said of a material that can be deformed plastically under compressive stress; typically a metal that can be hammered or rolled into a thin sheet.
MALLEABLE CAST IRON Cast iron made by a prolonged anneal of white cast iron involving decarburization (for whiteheart malleable) or graphitization (for blackheart malleable), or both, to eliminate some or all of the cementite. The graphite is in the form of temper carbon. Ferritic or pearlitic malleable cast irons present a mainly ferritic or a mainly pearlitic matrix, respectively.
MALLEABLIZATION An annealing heat treatment that transforms the structure of a white cast iron by eliminating some or all of the cementite through decarburization or graphitization, or both, so as to obtain a malleable cast iron.
MARAGING STEEL Steel with high ductility and yield point, optimum hardenability, and good weldability. Not susceptible to deformation and decarburization during heat treatment. Has good toughness at low temperatures. Undergoes a simple martensite-aging process at 400-500 °C, which increases the hardness and raises the breaking point of the metal. Solution heat treatment is required before machining. Applications: dies, diecasting equipment and mechanical components.
MARKS (GROOVES) Abnormalities forming mainly when certain defects in a semi-manufactured item are elongated and widened during rolling.
MARTEMPERING (INTERRUPTED QUENCHING) A hardening treatment in which steel is cooled swiftly from austenitizing temperature to a temperature slightly higher than Ms, then held at this temperature so as to render the entire structure homogeneous, before final cooling in air. An important aspect of martempering is that no transformation product other than martensite should form.
MARTENSITE A product of transformation, extremely hard and brittle, that forms when steel is cooled rapidly from austenitizing temperature to a temperature lower than Mf (martensite finish, usually ambient temperature). Tempered martensite is the best and the most common structure present in hardened and tempered alloy steels. The temperature at which the transformation of austenite to martensite begins (martensite start), during cooling, can be determined by empiric formulas. Martensitic transformation is characterized by an expansion of the steel, and can induce stresses liable to generate ruptures (internal cracks)
MARTENSITIC SCALAR HARDENING Heat treatment involving austenitization followed by scalar hardening in which cooling must be fast enough to avoid the formation of ferrite, pearlite or bainite, and the material needs to be held slightly higher than Ms for a duration long enough to establish a uniform temperature throughout the matrix, at the same time, short enough to avoid the formation of bainite. Final cooling takes place in air, with martensite forming practically at the same rate across the entire section of the product.
MARTENSITIC STAINLESS Steels with an martensitic structure
MARTENSITIC TRANSFORMATION A reaction that takes place in some metals during cooling, with the formation of an acicular structure known as martensite.
MASS A quantity of homogeneous or heterogeneous solid or fluid material forming a compact whole. It can be: nominal mass, weighed mass or theoretical mass.
MASS EFFECT The influence of the volume of a piece on the rate at which it cools: the greater the mass, the greater the resistance to cooling.
MATRIX Term used to indicate the basic material containing a given metallic structure.
MECHANICAL ANCHOR Means an anchor between two metallic elements through the contribution of metal flanges, nuts and bolts, welds etc..
MECHANICAL CHARACTERISTICS FATT – Fracture Appearance Transition Temperature: transition temperature at which the area of intergranular fracture is 50 % of the original area, measured on Charpy V-notch test pieces following fracture. Various temperatures can be used, from -180 °C (liquid nitrogen) to +150 °C and higher.
Em – Failure energy in pendulum hammer test for impact strength, types: Kv – KCU – DVM – Mesnager
J – Joule (energy)
ksi – kilogram per square inch
lbf – pound force
Rm – R – Tensile strength calculated with proportional tensile specimens, expressed in N/mm²
MESOPHASE Intermediate aggregation state between crystalline solid and liquid, characterized by a lower order than the solid state but a higher order than the solid state.
METAL A solid (except for mercury, which is liquid at ambient temperature), appearing shiny and with high thermal and electrical conductivity. The mining and working of metals is referred to as metallurgy
METALLIC In metallurgy, indicates the aggregation of atoms firmly united within molecules forming a structure.
METALLIZATION The coating of a surface with a metallic layer. The metal finish can be applied by electric arc or by gas.
METALLOGRAPHIC STRUCTURE The morphology assumed by two or more phases of a metallic system when aggregated. The term also describes a structure observed and photographed under the optical microscope.
METALLOID Improper name used for a nonmetal. The term is no longer in use.
METALLURGY The science and art of separating metals and metallic minerals from their ores by mechanical and chemical processes. It studies the internal structures and properties of metals and the effects of various processing methods.
METASTABLE 1) Describes a state of pseudo-equilibrium characterized by free energy higher than that of true equilibrium, but from which a system does not change spontaneously (e.g. Martensitic transformation)
2) Having a structure other than stable.
METASTABLE STATE A state of non-equilibrium where changes tending toward the stable state are imperceptible and extremely slow (centuries).
MICROHARDNESS The hardness of microscopic areas or of the individual microconstituents in a metal, measured by methods such as Tukon, Knoop, or scratch.
MICROMETER A gauge type instrument with a micrometric device, used for taking precision measurements (micron µm).
MICROSEGREGATION Segregation within a grain, crystal, or particle of microscopic size.
MICROSTRUCTURE The structure of polished and etched metal and alloy specimens as revealed by the microscope at a magnification of 50x, 100x , 500x, 1000x and greater.
MILLING Removing or shaping metal with a milling cutter.
MIREX dissimilarly to a blast furnace, metallic iron is produced by chemical reaction rather than by smelting ores An industrial process in which iron oxide is reduced by a chemical reaction of hydrogen and carbon monoxide with iron oxide to obtain metallic iron. This method is employed where the price of natural gas is very low (e.g. Argentina, etc.). The reducing gas rises to the top of the shaft furnace at a temperature of 350-450 °C and causes part of the carbon monoxide and hydrogen to convert to carbon dioxide and water vapour, respectively, while the ore fed into the furnace (pellets or granular material, as for a blast furnace) becomes metallic iron. The resulting product is put into an electric furnace together with scrap in percentages of 30% and 70% to make steel.
MODULUS OF ELASTICITY The ratio of stress to corresponding strain under given conditions of load. As there are three kinds of stresses, so there are three kinds of modulus of elasticity for any material: in tension, in compression, and in shear. In the case of tension, it is referred to as Young’s modulus. The higher the value, the stiffer the structure.
MOLE An SI (International System base unit indicating amount of substance (formerly gram-atom and gram-molecule in older systems).
MOLECULAR WEIGHT The sum of the relative atomic masses of the constituent atoms of a molecule
MOLECULE The smallest particle of a substance that can exist in the free state and which has the same composition as any larger mass of the substance.
MONOCLINIC Crystal architecture in which the three axes are of unequal length, with one intersection oblique and the other two at right angles.
MONOMETRIC System of crystallization in which the three axes are of equal length and at right angles to each other, and where the cut-off parameters on the three axes of the basic face (cubic) are equal.
NANOMETER The nanometer (symbol nm) is a unit of measure for length, corresponding to 10-9 meters.
NANOTECHNOLOGY A field concerned with the control of matter on an atomic and molecular scale. Nanotechnology deals in general with structures 100 nanometers or smaller, and involves developing materials or devices within that size.
NATIVE ELEMENT An element that occurs in nature uncombined, having a distinct mineral structure.
NATIVE STATE Said of an element not yet separated from the mineral containing it, e.g. sulphur from gypsum or limestone
NATURAL STATE Describes a material that has not undergone heat treatment following hot or cold deformation.
NATURAL, or RAW Unannealed material, in the natural state of transformation (cold-drawn, hot rolled, forged)
NEUTRINO Neutrinos are subatomic particles with no electrical charge and having a mass 100,000 to 1 million times less than that of an electron. They can pass through space and ordinary matter almost undisturbed and are therefore difficult to detect.
NEUTRON An electrically uncharged nuclear particle of approximately the same mass as a hydrogen atom. Neutrons and protons make up the nuclei of all chemical elements.
NICKEL-PLATING The process of coating a metal surface with a layer of nickel, electrolytically or by chemical reduction, so as to provide a protective and/or decorative finish, which can be shiny or dull.
NITRIDING A thermochemical treatment for steel that involves heating in a atmosphere of ammonia or in contact with a nitrogen-bearing material so as to promote the absorption of nitrogen. Nitriding produces an extremely hard case (< 1000 HV).
NITRIDING DEPTH Distance between the surface and the innermost limit the nitrogen-enriched layer. This limit has to be specified at the time of ordering (expressed as depth in µm or as a hardness value)
NITROCARBURIZATION A thermochemical diffusion treatment in which carbon and nitrogen are absorbed by the surface of a steel, in conditions similar to those of nitriding. Produces a considerable increase in fatigue strength.
NODE Intersection of straight lines representing the crystal lattice
NOMINAL Not actual, not real, as in the case of a nominal reference thickness, for instance.
NON-ALLOY QUALITY STEEL Steels for which there is no requirement, generally speaking, as regards uniform response to heat treatments, and none regarding purity in respect of non-metallic inclusions (EN 10020).
NON-ALLOY SPECIAL STEEL Compared to quality steels, these have a higher purity, particularly with regard to non-metallic inclusions. In most cases, non-alloy special steel will be hardened and tempered (EN 10020).
NON-ALLOY STRUCTURAL STEEL Steels for which there are no quality requirements dictating the adoption of special precautions during the manufacturing process (EN 10020).
NONDESTRUCTIVE TEST Testing or inspection that does not destroy the object under scrutiny (ultrasound, magnetic particle inspection, penetrant liquid, etc.)
Non-destructive tests include various methods of checking for irregularities in items manufactured from steel without impacting on their shape or characteristics. The most common are visual inspection, liquid penetrant testing (PT), Ultrasonic testing (UT), Radiographic testing (RT), Electromagnetic testing (ET)
NORMALIZATION A heat treatment applied to steel, performed at a temperature slightly higher than Ac3 (Ac1 for hypereutectoid steel C% > 0.83), followed by cooling in still air. Its main purpose is to produce a homogeneous crystalline structure and refine grains swollen by previous hot transformation steps. Not recommended for tool steels and self-hardening steels.
NORMALIZATION ROLLING A rolling process in which the final deformation is carried out within a limited temperature range, followed by cooling in still air, in order to develop the material to a state equivalent to that obtained by normalizing heat treatment.
This also gives the rolled product an essentially better surface quality than when normalized in the furnace.
NUCLEUS The very dense region consisting of nucleons (protons and neutrons), at the centre of an atom, where the greater part of its mass is concentrated.
OSMONDITE Obsolete term once used to designate a ferrous microstructure not so well defined as Troosite.
OVALIZATION OUT-OF-ROUND In items of round section, a deviation from true circular outline. Out-of-round tolerance is the difference between maximum and minimum diameters, divided by 2. This value must be equal to or less than the IT value corresponding to the nominal dimension divided by 4.
OVERCARBURIZING, OVERCARBURIZATION A level of carbon in excess of the prescribed percentage, after casehardening.
OVERHEATING Heating of a steel or an alloy to a temperature so high that the combination of its properties is significantly altered. Overheating can lead to melting of grain boundaries with consequent loss of the initial properties was not fixed in a subsequent heat treatment, in this case it called „burning“.
OVERHEATING Heating to a temperature and for a duration such that abnormal grain growth is induced.
OXIDATION 1) A chemical reaction in which the valency of the atoms involved is raised, resulting in a loss of electrons
2) A passivation reaction in which the metal forms the oxide
3) A chemical reaction in which an element or a chemical compound combines with oxygen
OXIDE A compound created when oxygen is combined with another element, for example aluminium oxide, nitrogen oxide, etc.
OXYGEN LANCE CUTTING A system for profiling and cutting sheets and blooms with torches. Preheating temperature is selected according to carbon equivalent Ceq = C+ Mn/ 6+(Cr + Mo + V)/ 5 + (Ni + Cu)/ 15
PARAMETRIC Each of the lengths of the segments cut by the face of a crystal on three crystallographic axes x, y and z
PARTICLE A constituent of matter, subatomic in size, characterized by a given value of mass than can even be zero, as in the case of the photon and the neutrino.
PASSIVATION The property of some metallic elements and alloys (stainless steels) to oxidize on the surface: the resulting thin oxide film protects the metal from corrosion.
PATENTING Treatment of steel, usually wire, in which the metal is gradually heated to about 1000 °C and then cooled, usually in air, in a bath of molten lead, or in a liquid salt bath at between 425 °C and 565 °C.
PEARLITE Aggregate of ferrite and cementite obtained from the transformation of austenite above the bainitic interval. Can occur as lamellar pearlite (flakes) and, if uniformly distributed in the ferritic matrix, will provide good machinability particularly for casehardening steel and H&Tcarbon steel.
The structure guaranteeing the longest tool life consists generally in ~10% pearlite and 90% ferrite. Globular pearlite (spheroidal) gives good machinability where steels have a high percentage of carbon. Chromium steels for bearings are annealed to a ferritic-cementitic spheroidal structure (globular) so as to provide good machinability.
PEARLITISATION Heat treatment designed to produce a thin microstructure, performed particularly on hot-working tool steels. After hot deformation, the material is cooled to 500 °C in still air, then placed in a furnace heated to 730 °C and held for duration of one hour per inch of thickness.
PENETRANT TESTING A method of revealing surface defects exploiting the law of capillarity. A liquid (red) penetrates very thin cracks, then the piece is cleaned and another liquid (white detector) shows up the defects.
PERIOD Constant interval of time after which, during the evolution of a recurring physical phenomenon, a quantity always assumes the same value. Period is the inverse of frequency.
PERMANENT MOULD A long-life mould used repeatedly to produce many castings. Not an ingot mould.
PERMEATION In physics and engineering, the penetration of a permeate (such as a liquid, gas, or vapor) through a solid, indicative of a material’s intrinsic permeability; for example, the permeability of steel by hydrogen at a given temperature.
PHASE The sum of all portions of a material system that are identical in chemical composition and physical state, and separated from the rest of the system by a distinct interface (the phase boundary).
PHASE TRANSITION Microstructural modifications such as allotropic transformations, recrystallization, grain growth. These transformations involve processes of diffusion, but no modifications of the number or composition of the phases present.
PHOSPHATING The application of an electrochemical phosphate conversion coating to the surface of a metal to protect against corrosion and provide increased resistance to wear. Applied cold or hot, typically before painting, the coating consists in an aqueous solution containing acid phosphate of a heavy metal such as manganese, zinc, etc.
PHOTON In physics, the photon is an elementary particle, the quantum of the electromagnetic field and thus the basic unit of light and all other forms of electromagnetic radiation.
It propagates in a vacuum at ~ 300.000 km/s, carrying energy that depends on its frequency, and zero mass when at rest.
PHYSICAL PROPERTIES Properties of a metal or an alloy, relatively independent of its microstructure, which can be measured without the application of a force, (e.g. density, electrical conductivity, coefficient of thermal expansion, lattice parameters, magnetic permeability)
PICKLING A treatment designed to remove layers of oxide that form on the surface of a metal when hot-worked. Pickling procedures can be chemical or mechanical.
PIT FURNACE A heat treatment furnace with a vertical chamber, often used for vertical treatments in order to minimize the dimensional deformations that occur with horizontal treatments.
PITTING A form of extremely localized corrosion that leads to the creation of small holes in the metal.
PLASMA Gas in which all the atoms are ionized.
PLASMA – NITROGEN TRANSFERRED ARC Plasma is deposited by an electric arc within a flow of gas, obtaining optimum hardening at an extremely fast rate. In this way, the metal powder is fused and directed onto the surface being coated. The powders most widely used are chromium oxide, aluminium oxide, titanium oxide and carbides.
PLASMA – SEMI-TRANSFERRED ARC This technology is used in the field of hot coating. It can be used to deposit alloys of stellite, carbides, etc.
PLASMA NITRIDING This process of plasma nitriding/nitrocarburization is based on the dispersion of nitrogen and or carbon within ferrous metals. The operation takes place in a vacuum. A low energy plasma is generated, whereupon nitrogen is added and ionizes on contact with the plasma. The ionized nitrogen penetrates the metal to a depth of around 0.8 mm. This technique, combined with controlled oxidation, provides an alternative to chromium plating.
PLASMA SPRAY A spray technique by which molten particles of powder material are deposited onto a surface as a coating. The energy carried by the hot plasma is sufficient to melt any powdered material coming within the envelope. The microscopic droplets of melted powder are projected onto the surface at a velocity comparable to the speed of sound.
PLASTIC DEFORMATION A permanent type of deformation induced by the application of external stresses, and in microscopic terms, represented by displacement (slip) of specific atomic planes. Plastic deformation can be generated in a hot or cold material.
PLASTICITY The propensity of a material to undergo permanent deformation under load.
PLATING A process serving to protect or enhance the appearance of a material, which generally involves coating the surface of the material with a layer of other material, metallic or not-metallic.
POISSON’S RATIO (0.25-0.30 for steel ) Absolute value of the ratio between transverse deformation per unit breadth and longitudinal deformation per unit length of a body subjected to a longitudinal stress, usually within the elastic range. Used to calculate the modulus of rigidity.
POLYCRYSTALLINE A solid composed of many crystallites, or grains, varying in size and orientation-
POLYHEDRON A three-dimensional solid made up of a finite number of polygonal faces that are parts of planes.
POLYMER Synthetic fluid comprising water and organic products of high molecular weight (polymers). The severity of hardening with a 35% solution is marginally higher than that of oil, so that the great majority of steels can be treated without risk of failure. Polymer baths are replacing traditional hardening oils, which produce more pollution and are more expensive.
POLYMORPHISM The ability of a crystalline substance to assume different forms without any change in chemical composition.
ppm (parts-per-million) The expression “1 ppm” means that a given property is present in a proportion of one part per million parts examined. The proportion of hydrogen, oxygen and nitrogen in steel is expressed in ppm (e.g. 2 ppm = 0.0002%)
PRECIPITATION Precipitation is the formation of a practically insoluble product — the precipitate — during a chemical reaction in solution. The precipitate can also be formed when the solution is supersaturated by a compound. Where steel contains elements having great affinity with nitrogen, such as Mn, Mo, Cr, Al, V, and Ti, they combine to form fine nitride precipitates and thus bring about an increase in hardness of the nitrided layer, accompanied by a state of surface compression due to the greater volume of the precipitated compounds.
PRECIPITATION HARDENING Hardening produced by the precipitation of a constituent from a supersaturated solid solution.
PRECIPITATION HEAT TREATMENT Any of various aging treatments conducted at high temperatures to improve certain mechanical properties in a material through precipitation from solid solution.
PREHEATING A general term used to describe heating applied as a preliminary to some further mechanical or heat treatment. In the case of welding, the preheating step immediately precedes the welding operation.
PRESSING, FORGING A manufactured item produced by hot or cold forming.
PRIMARY STRUCTURE The first type of crystal that separates from a melt during solidification, considered anomalous, and typical of materials not transformed sufficiently in the course of rolling or forging
PRODUCT MARK Every product has to be marked. Semi-manufactured, bar and profile stock of dimensions greater than 35 mm are marked by: painting, labels, electric pen or punching; bar and profile stock of dimensions smaller than 35mm by labels or by another of the methods mentioned; wire rod by a label attached to the roll. Minimum elements of information to be indicated are: name of manufacturer, steel type designation, casting number and, in case of specific control requirements, an identification number linking the product with the relative test certificate.
PRODUCTS OF POWDER METALLURGY Steel powder: particles of steel smaller than 1 µm. Sintered pieces: products formed from agglomerated powders that are sintered initially and sometimes undergo a pressing again thereafter. Pieces with full density: products obtained from powders by the simultaneous action of temperature and pressure (hot isostatic compression, extrusion, etc.)
PROEUTECTIC FERRITE Proeutectic or structurally free ferrite is obtainable through the decomposition of hypoeutectoid austenite during cooling, without the simultaneous formation of cementite.
PROEUTECTOID The constituent that separates out of a solid solution before the formation of eutectoid.
PROTON Stable elementary particle of positive electric charge who ago part of all the atomic nucleus.
PWHT Post Welding Heat Treatment
PYROLYSIS (CRACKING) A chemical reaction that consists in heating a substance or mixture of substances to a high temperature so as to bring about its decomposition into smaller molecules.
PYROMETER A temperature-measuring device, originally designed to measure temperatures beyond the range of thermometers. Now also, a device that measures thermal radiation in any temperature range. Contact and non-contact types exist.
QUATERNARY A quaternary alloy is one containing four principal elements.
QUENCH SEVERITY Characterized by the H value, relating to the rate of temperature change during quenching.
QUENCHING Rapid cooling of a piece from an high temperature (austenitization) by immersion in a suitable medium: water, oil, polymer, etc.
QUENCHING An operation in which a ferrous product is cooled more rapidly than in still air. As a rule, the quenchant shouldn’t cool no faster than is effectively necessary, since the faster the rate of cooling, the greater will be the stresses internally of the material. Baths of quenching fluid need to be agitated so that steam bubbles will not cling to the material. Quenchants most widely used are: gas mixtures (for treatments below zero), water, liquid salt baths, polymers (water and additives), oil, forced air or still air.
The weight of the bath mut be at least 10-15 times that of the material to be quenched. On completion of the quench, the temperature of the bath must be no higher than 49 °C
QUENCHING BATHS The weight of the bath mut be at least 10-15 times that of the material to be quenched. On completion of the quench, the temperature of the bath must be no higher than 49 °C
RADIOGRAPHIC INSPECTION The principle is based on the changes that electromagnetic radiation undergoes, when directed though a material, on encountering a defect in its path. Thicknesses up to 60 mm can be examined using X-rays, and thicknesses up to 180 mm using gamma rays.
RAW MATERIALS Materials used for the production of alloys, including iron ore, scrap metal, metallurgical coke, fluxes (e.g. limestone) and oxygen.
RAW, BLANK Said of material such as rolled, forged or as-cast items, that have not been machined
RECALESCENCE Temperature rise caused by the emission of heat accompanying the transformation of austenite during cooling.
RECARBURIZING A thermochemical treatment that serves to restore the carbon content of a surface layer decarburized during a previous heat treatment.
RECRYSTALLIZATION ANNEALING Recommended for cold-rolled material, this type of anneal is carried out at temperature Ac1. Its purpose is to regenerate crystals by reforming the microstructure, without any phase transformation. When steel is rolled, the structure tends to align on the direction of the main deformation, increasing the hardness of the metal and reducing its ability to undergo further deformation, such as drawing.
RED-SHORTNESS In the steel-rich sulfur has significant presence of iron sulfide, which melts at 988 °C (temperature included in the field of hot plastic working eg. Hot-rolling and forging). This compound, if in quantities greater than 0,10% give a liquid film to the joint of the grains and damage the cohesion of the crystals.
REDUCING Said of a substance or a set of substances that gains one or more electrons when caused to react with other substances (e.g. carbon with carbon monoxide, or with aluminium or with ferro silicon). Reduction is always accompanied by oxidation.
REDUCTION RATIO In its raw solidified state, steel does not have mechanical properties that will enable it to withstand stresses generated during use. Consequently, ingots, billets, etc. need to undergo a reduction sufficient to render the structure refined and compacted. The recommended reduction for forged steels is 3.5:1 and for rolled steels, 6:1. The reduction ratio is obtained dividing the initial section by the final section.
REFINING To optimize productivity, steel that has reached the liquid state is poured into a ladle so as to free up the melting furnace for another cycle. Refining takes place in the ladle furnace, and it is here that the steel takes on its final identity (chemical composition, purity) and, in the majority of cases, undergoes a vacuum treatment to eliminate gases such as hydrogen, oxygen and nitrogen.
REFINING (LADLE) FURNACE The part of a mill where liquid steel is refined.
REFRACTORY A material with a significantly high melting point (~ 1580 °C), often used for lining furnaces and ladles.
REGENERATIVE QUENCHING A hardening and tempering treatment carried out twice, in order to improve the yield strength of the steel.
REGULAR ARRAY A crystalline material consists of a regular array of atoms, arranged on lattice planes
RESIDUAL AUSTENITE Untransformed austenite, which remains at ambient temperature after a quench hardening treatment.
RESIDUAL STRESSES Internal strain not caused by external stresses associated with work hardening, phase transformations or very high temperature gradients, but attributable for example to thermal expansion or impeded deformation.
RESISTIVITY An intrinsic property of a material determining its resistance to the flow of current. The resistivity of a conductor depends on the nature and temperature of the material, and the intensity of the electromagnetic field in which it is placed.
RESTORATION A heat treatment that serves to restore, at least in part, the physical or mechanical properties of a strain-hardened ferrous product, without any apparent modification of the structure.
RESULPHURIZED STEEL Steels with a sulphur content greater than 0.10% (high sulphur) Sulphur is added intentionally at the casting stage in order to improve chip removability for machining purposes.
RHOMBOHEDRAL Primitive cell of the face-centered cubic system. A rhombohedron is a crystal form of the trigonal system with six similar faces, each a rhombus or parallelogram.
ROAK (or ROKE) A longitudinal surface defect (an elongated fissure) caused by a blow that is not welded up during rolling and has perforated the surface and become oxidized.
ROD Hot rolled long product having a nominal size generally of 5,5 mm or above and wound into irregular coils.
ROLL MARKS Wear on rolls or cold-drawing guide rollers can produce defects located at regular distances or randomly along the length and across the width of pieces.
ROLLED AND PEELED Bars of round section produced by a peeling machine, straightened and polished.
ROLLED-IN-SCALE Marks on a rolled surface, varying in shape, depth and frequency. The extent and character of the defect depends on the intrinsic formation of scales on the surface of the piece before or during hot-rolling
ROLLING Hot or cold plastic deformation of a material produced by mill rolls.
ROTARY HEARTH FURNACE A heat treatment furnace with a rotating hearth of annular shape. Generally used as a preheating furnace.
ROUGHING The operation of trimming a block of metallic material, synonymous with turning and milling.
ROUND Semi-manufactured item or product of circular section.
ROUNDNESS In items of round section, a deviation from true circular outline. Out-of-round tolerance is the difference between maximum and minimum diameters, divided by 2. This value must be equal to or less than the IT value corresponding to the nominal dimension divided by 4. The IT tolerance has to be specified at the time of quoting or ordering (Standard UNI ISO 286/1)
SAMPLE A portion of material taken from a steel product, on which to perform physical tests.
SANDBLASTING A mechanical pickling operation in which very hard grit is projected onto pieces at high velocity.
SCALAR HARDENING A quench during which the cooling stage is interrupted momentarily by placing the material in a medium/environment (air) at an appropriately selected temperature.
SCALE (CALAMINE) The mixture of ferrous oxides that forms during hot deformation or heat treatment at high temperature. Removable by pickling or by machining.
SCARFING External/internal removal of a welding bead by machining.
SCATTER (ATOMIC DIFFUSION) The movement of atoms within a lattice by distances greater than interatomic distances.
SCRAP Recyclable materials generated as waste from industrial processes and discarded or phased-out consumer goods (vehicle parts, building materials, etc.). Unlike ores, their availability is linked to industrial activity.
SCRATCHES Mechanical damage to the surface of a manufactured item. The defect is caused by frictional contact between the piece, and parts of the machinery employed in manufacture.
SECONDARY HARDENING Some alloy steels develop higher levels of hardness when tempered at predetermined temperatures.
SECONDARY HARDENING Hardening induced by one or more tempering heat treatments that result in the precipitation of a compound or give rise to the formation of martensite or bainite from residual austenite.
SEGREGATION Often used to indicate liquation. The non-uniform distribution of alloying constituents, impurities and inclusions in a mass of solidified metal that were distributed uniformly in the liquid mass. Often caused by the primary crystallization of one phase with the subsequent concentration of other elements in the remaining liquid.
SELECTIVE HEATING Heating confined intentionally to certain parts of an item only (superficial hardening of a particular area, for example).
SELECTIVE QUENCHING Cooling limited to certain parts of a piece only.
SELF-HARDENING Cooling that occurs by thermal conduction toward parts that have not been heated.
SELF-HARDENING STEELS Steels hardenable in such a way as to maintain a martensitic structure when cooled in air.
SEM – Scanning Electron Microscope With this instrument, chemical analysis (microanalysis) is performed by measuring the energy and intensity of x-rays directed by an electronic beam at the test piece, using an EDS (Energy Dispersive Spectrometry) detector. Given that the portion of space excited by the electronic beam measures only a few microns, SEM+EDS provides a powerful system for examining chemically non-homogeneous solids on microscopic scale.
SEMI-MANUFACTURED PRODUCT A hot-worked iron/steel product that has been subjected to a partial transformation process and requires a further stage of processing to become a finished item. It can be of square, rectangular or round section (billets, blooms, etc.).
SENSITIZATION A particularly important process for austenitic stainless steels in which, by holding the metal at around 600 °C, chromium carbides can be precipitated at the grain boundary. If the free chromium content drops locally below 10,5%, the grain boundary becomes susceptible to intergranular corrosion. The term is also used to denote the mechanism by which certain stainless steels are rendered vulnerable to intergranular corrosion. In addition, sensitization describes a specific heat treatment serving to verify the potential of a material to reach predetermined values.
SERENDIPITY The discovery of something unexpected and useful while searching for something else entirely.
SHAVED In mechanical engineering, refers to a product shaved by a linear shaving unit. The machine tool is known as a shaver, and measurements are laser-controlled.
SHEAR STRENGTH The capacity of a material to withstand a stress applied parallel or tangentially to a face of a material, as opposed to a stress applied perpendicularly.
SHEARING Cold cutting of sheet, strip and similar materials using machine tools.
SHEARING A process by which metal bars are cut cold, mechanically, to the prescribed stock length.
SHEET PILING A construction material consisting in hot or cold rolled steel sheets with interlocking edges that are joined one to the next when driven into the ground to form a continuous wall. Its functions are to retain earth, prevent seepage and withstand possible overloads.
SHEET, PLATE A flat hot rolled product with deformation of the edges left free, supplied either as-rolled or pickled, mostly in pieces of square or rectangular outline (not excluding others) and minimum width 600 mm. Material under 6.5 mm thickness is referred to as sheet; material thicker than 6.5 mm as plate. Edges are as-rolled or sheared, flame-cut or chamfered. Sheet material can also be cold-rolled.
SHERARDIZING A thermal diffusion coating process in which zinc powder applied to the surface of a metal is caused to vaporize and form a zinc-alloy layer.
SHRINKING-ON A rigid connection between two mechanical components, disallowing relative motion. Steel parts can either be heated (e.g. 300 °C) to induce thermal expansion, or cooled (e.g. -180 °C using liquid nitrogen) to induce contraction, so that an interference fit is produced when temperatures return to normal.
SILICIZATION A thermochemical treatment designed to enrich the surface of a metal with silicon.
SINTER-HARDENING A combined sintering and heat treatment operation completed in one pass through the furnace. Hot-pressed powders with an appreciably high alloy content undergo rapid cooling (using the same protective atmosphere already circulating in the furnace) within a suitable hardening temperature range. Sinter-hardened products offer advantages in terms of mechanical, static and fatigue strength, at competitive prices.
SINTERING The conversion of metal powder into a continuous mass by heating to a temperature of up to 1500 °C) usually after a preliminary pressure-compacting step. Sintering incorporates the technique of Hot Isostatic Pressing (HIP).
SKIN PASS A hot or cold rolling pass affecting only the surface of the product, giving it a uniform and shiny look. As a rule, the structural and mechanical characteristics of the material remain unchanged.
SLAG A mixture produced during the refining step in the converter, which floats on the liquid steel. From the reactions between slag and steel, process controllers can monitor the percentage of certain constituents in the metal: elements such as phosphorus, sulphur and silicon, and to an extent, inclusions.
SMELTING A thermal process serving to separate metal, by fusion, from nonmetallic materials or other undesired metals with which it is associated.
SMELTING FURNACE A furnace in which ores, scrap or alloys are smelted or reduced.
SOFTENING ANNEALING A heat treatment serving to reduce the hardness of a ferrous product to a predetermined requisite level.
SOLID CASEHARDENING Casehardening treatment carried out in a solid medium, using metal enclosures (no longer in use).
SOLID SOLUTION A solid and homogeneous crystalline phase containing two or more chemical species.
SOLIDIFICATION RANGE Temperature interval between the liquidus and solidus curves where liquid and solid metal phases coexist.
SOLIDUS Temperatures at which solidification is completed; for all alloys
SOLUBILITY The maximum quantity of solute, in grams, that can be dissolved in one hundred grams of solution.
SOLUTE In a solution having two components, the minor component in terms of quantity.
SOLUTION HEAT TREATMENT A process in which an alloy is heated to a suitable temperature long enough to allow a certain constituent to enter into solid solution, and than cooled rapidly to hold the constituent in solution.
SOLUTION HEAT TREATMENT A treatment in which material is heated to 1000 – 1100 °C, then cooled rapidly in water or in air (hardening of austenitic steels).
SOLVENT In a solution having two components, the major component in terms of quantity.
SOLVUS Curves representing the mutual solubility of two solid state components, related to temperature.
SORBITE An aggregate of ultrafine cementite or carbide globules (not visible under the optical microscope) in the ferritic matrix. It has the classic structure of hardened and tempered steels, which, however, is not readily machinable.
SPECIFIC CONTROLS These are the various controls agreed at the time of quoting or ordering. The chemical analysis of the pour can be considered a non-specific control, whereas that of the product is a specific control. Other specific controls are: mechanical tests, hardness, decarburization, non-metallic inclusions, non-destructive testing, grain, Jominy, etc.
SPECIFIC HEAT The heat required to raise the temperature of 1 gram of a substance by 1 °C. Equivalent to thermal capacity.
SPHEROIDAL CAST IRON Cast iron which in the molten state is treated by adding magnesium or cerium, resulting in the formation of nodular or spheroidal graphite and consequently increased ductility.
SPHEROIDIZING Geometrical evolution of carbon particles, such as flakes of cementite, toward a stable spherical form.
SPRAY FORMING A method of casting near net shape metal components with homogeneous microstructures via the deposition of semi-solid sprayed droplets onto a shaped substrate. Technologically, an intermediate step between conventional metallurgy and powder metallurgy.
SQUARE A hot-rolled, forged or cold-drawn product, appearing generally as bars of square section.
STABILIZING TREATMENT A heat treatment designed to ensure that material worked mechanically will not undergo dimensional changes subsequently.
STAINLESS Describes a material resistant to oxidation.
STAINLESS STEEL Alloy steel containing at least 10,5% chromium, making the finished metal resistant to oxidation and corrosion.
STANDARDS A series of documents, approved and published by national or international official organizations, including specifications or requirements, practices, guides, test methods, etc., covering various materials, products, systems or services.
STAY TIME The time from when the material reaches the predetermined temperature at the core, to the subsequent variation in temperature. The stay time normally adopted is &frAc12; h per 2.5 mm of thickness during quenching and 1 h during tempering. These parameters are correct for thicknesses above 50 mm.
STEEL An alloy of iron and carbon, with a carbon content less than 2,11%, which can take on particular physical characteristics when heat treated.
STEEL MILL A plant for the production and processing of steel. Steel mills using liquid cast iron are defined as operating an integral cycle, as opposed to mills where scrap iron is melted in electric furnaces.
STEEL WITH CONTROLLED PERCENTAGE OF SULPHUR Like resulphurized steel, but containing a percentage of sulphur between 0.020 and 0.040%. Sulphur has a marked embrittling effect under shear stresses, which will cause chips to break and separate more easily. Examples: C45R with sulphur content specified in the range 0.020 – 0.040%, or C45E with maximum specific sulphur content of 0.035%
STEELMAKING Types of steelmaking process
LD a process in which the charge consists of liquid cast iron, scrap and calcium oxide CaO
OLP a process whereby cast iron containing up to 2% phosphorus can be refined by insufflating lime mixed with oxygen
OBM and LWS processes based on the old Thomas process. Pure oxygen is insufflated by tuyeres at the bottom of the converter (see blast furnace).
BOF process using a Basic Oxygen Furnace. Lime is used to remove phosphorus, sulphur, silicon and to an extent manganese.
EBT Eccentric Bottom Tapping process. Scrap is loaded into the furnace from the top, with molten metal emerging through a hole at the bottom of the shaft furnace, so that no slag is entrained when casting.
Thomas process. Designed originally as a method of dephosphorizing cast iron made with phosphorous-bearing materials.
EAF Electric Arc Furnace. A modern process, generally with scrap as the charge.
AOD Argon Oxygen Decarburization process. A technique similar to VOD but with the difference that the gas insufflated through porous baffles at the bottom of the furnace is a mixture of argon and oxygen. The furnace normally has an automatic alloy charging system, controlled by software allowing 100% reproducibility of the process.
VIM Vacuum Induction Method. A steelmaking process that uses a vacuum induction furnace.
VOD Vacuum Oxygen Decarburization. A process whereby steel (usually stainless steel) can be ‚improved‘ by reducing carbon to minimal values (< 0,03%). Carbon is removed by insufflating the liquid steel with oxygen.
VAD Vacuum Arc Degassing. This process, usually combined with the VOD process, has a deep degassing action (hydrogen < 1,2 ppm) and limits slag basicity.
VDG Vacuum Degassing process in which the charge is insufflated with argon
VAR Vacuum Arc Remelting
ESR Electro Slag Remelting
EBR Remelting of a consumable Electrode Bombarded with electrons
VIM + VAR , VIM + ESR, ASLD + WIR Combined process
STELLITE Hard-facing wearprooff in order to resist to high temperatures.
STIRRING / STIRRER Electromagnetic Stirrers situated on the tundish and/or on the casting ways in order to stir the liquid and limit the segregations formation.
STRAIGHTENING Correction of curvilinear or wavy profiles in rolled, forged and cold-drawn bars, etc. Generally a cold-working operation using horizontal or vertical presses, rolling or other equipment capable of re-establishing the desired straightness, expressed in ‰ (e.g. 1mm/m). Highly elastic or alloyed steels are straightened by hot-working (~300 °C), when possible exploiting the heat in the material on the completion of tempering. Besides facilitating the mechanical action, the material will be free of tensile stresses (in contrast to the situation created with cold straightening, where pieces remain slightly in tension). The hardness of materials straightened post-anneal by rolling will increase by 10 HB (average value for alloy steels and carbon steels).
STRAIGHTNESS All bar products (round, square, hexagonal, flat, wide and special profiles) have a permissible straightness tolerance that varies depending on the type of process they undergo. The tolerance is measured on pieces 1 metre in length and expressed in ‰. E.g. 1.5 ‰ max
STRESS RELIEVING Material is heated to a temperature (600-650 °C) sufficient to reduce stresses, then cooled slowly in the furnace down to 250-300 °C, so as to minimize the risk of internal and external stresses being reintroduced. Hardened and tempered materials usually undergo stress-relieving at a temperature 50 °C below that of tempering. When carried out in furnaces in a controlled atmosphere (e.g. nitrogen), known also as bright stress-relieving.
STRESS RELIEVING Material is heated to a temperature between 600 and 650 °C (preferably 650 °C), then cooled in the furnace down to 250-300 °C, before final cooling in air.
STRESSES Residual stresses are stresses that remain after the original cause (external forces, temperature gradient) has been removed and derive from the action of intermolecular forces seeking to balance externally applied forces. Residual stresses occur for a variety of reasons, including non-elastic deformation and heat treatment.
STRUCTURALS A group of steel products including I-beams, H-beams, wide-flange beams and sheet piling. Obtained by extrusion, cold drawing or rolling. Structurals have standard dimensions based on standard reference tables ( L,V,T structurals), or are designed on a case by case basis.
SUB ZERO TREATMENT See supercooling
SUBCRITICAL ANNEALING This heat treatment is not recommended for hypoeutectoid steels (C < 0.8%) to be machined by chip removal, but is the only one by which hypereutectoid steels (C 0.80 – 2.06%) can be rendered machinable. The material is heated to a temperature near Ac1 (-10 °C) but notably long stay times are required: 1h per 10mm thickness of the bundle of bars or rolled and forged stock making up the charge. The treatment is excellent for materials that will be cold-forged or extruded. Subcritical annealing can be used for spheroidizing cementite.
SUBLIMATION The transition of an element or compound from solid phase to gas phase with no intermediate formation of a liquid.
SULPHUR-CARBON-NITRIDING A thermochemical treatment designed to enrich the surface layer of a metal with sulphur, carbon and nitrogen.
SUPER CLEAN STEEL Steel that is ultra clean from the inclusions.
SUPERCLINC STEEL Steel designed to minimize brittleness over time. Used for the manufacture of rotors. Elements Si, Al and Mn are maintained at particularly low levels.
SUPERCOOLING Cooling to a temperature below the temperature at which phase transformation equilibrium occurs, normally below ambient temperature (between -70 °C and -80 °C).
SUPERFICIAL HARDENING (FLAME HARDENING) Heating of a surface using an oxyacetylene torch or another type of flame at high temperature, followed by rapid cooling, so as to induce hardening.
SUPERFICIAL HARDENING (INDUCTION HEATING) A hardening operation in which material is heated by means of electric coils generating a magnetic field, and then cooled in water.
SUPPLY CONDITIONS Detailed description of the material supplied: type of steel, heat treatment, surface quality, etc.
SURFACE The outermost part of a body. The envelope delimitating the space occupied by a body and separating it from the surrounding space.
SURFACE HARDENING A generic term covering several processes applicable to ferrous alloys, in which a piece is quenched to produce a surface layer harder or more wear resistant than the core. Processes commonly used include casehardening, carbonitriding, nitriding, induction hardening, flame hardening, shell hardening, laser hardening, etc.
SURFACE HARDENING Hardening treatment in which the quench is preceded by surface heating. See also SURFACE HARDENING
SURFACE QUALITY The desired surface layer must be indicated at the time of requesting a quote and placing an order, by referring to the quality categories specified in industry standards: e.g. as-rolled, surface quality class D, EN 10221
SURFACE ROUGHNESS The overall effect produced by microgeometric errors on the surface of worked material. Measured transversely to the direction of the predominating fissures, and expressed normally in microns (µm)
SYMMETRY A physical system is symmetrical when it appears identical before and after rotation about a hypothetical segment (a crystal reappears with the same faces).
SYNTHETIC DIAMOND Synthetic diamond is obtainable by heating carbon to over 2000 °C and applying pressure of around 102 Mpa.
SYSTEM A combination of interdependent parts combining to produce a given outcome, or joined so as to form a consistent whole.
TANDEM MILL A rolling mill in which the stands operate in tandem, so that material can be rolled in one pass.
TEMPER BRITTLENESS Brittleness occurring when high strength steels are tempered at temperatures between 200 and 400 °C, during the tempering treatment. Attributed to the attendant precipitation of cementite at the grain boundaries of primitive austenite (thereafter becoming martensite).
TEMPERING Heat treatment to which a ferrous product is subjected after quench hardening so as to obtain the desired mechanical properties. After hardening, the material is affected by strong stresses that need to be eliminated, otherwise their force could exceed the ultimate tensile strength of the material and cause it to rupture. Tempering also serves to reduce the strength of the metal so as to reach a favourable compromise between UTS and toughness values.
TEMPERING DIAGRAM Graphic representation of the relation between mechanical properties and tempering temperature for a given stay time.
TENSILE TEST A test in which material is subjected to an increasing tensile pull until it fractures.
TETRAGONAL OR
TETRAHEDRAL
Describes a polyhedron having four triangular faces. In the tetrahedral bond typical of diamond, silicon and germanium, an atom at the centre of the tetrahedron is linked to the four atoms at the vertices.
TETRAVALENT Describes an atom capable of forming four covalent bonds with other elements.
THERMAL CAPACITY The heat needed to raise the temperature of a body by 1 °C. In homogeneous bodies, equal to the product of the mass of the body multiplied by the specific heat of the substance from which the body is made.
THERMAL CENTRE OF GRAVITY The last zone of a casting to solidify, where the concentration of impurities is highest. Where ingots have a feeder head, coincides with the part that will be cut off so as to eliminate the polluted part.
THERMAL CONDUCTIVITY When two ends of a body are held at different temperatures, or two bodies are placed in contact, thermal energy will pass from the hotter to the cooler without any movement or macroscopic change in the body or bodies themselves..
THERMAL CYCLE Evolution of temperature related to time.
THERMAL EXPANSION The tendency of matter to change in volume in response to a change in temperature.
THERMAL GRADIENT Indicates the rate °C / h at which thermal energy increases or decreases during heat treatments in reaching prescribed temperatures.
THERMAL QUENCH Heat treatment that consists in austenitizing and cooling material in a liquid salt bath in such a way as to overcome the critical quenching speed.
THERMAL SHOCK Thermal shock occurs when a thermal gradient causes different parts of an object to expand by different amounts. This causes the material to crack as a result of the sudden change in temperature.
THERMAL SHOCK Development of a particularly swift temperature gradient (heating) by which high stresses are induced in the structure.
THERMAL STRESS Stresses in a metal caused by non-uniform distribution of temperature
THERMOCHEMICAL TREATMENT A process conducted in an appropriately selected medium/environment, serving to bring about a change in the chemical composition of the base material.
THERMOCOUPLE Instrument used to measure temperature, consisting of two metals or alloys connected electrically at one end and connected to a voltmeter at the other end. When one of the two junctions is warmer than the other, the effect is to produce a potential difference approximately proportional to the temperature difference between the junctions.
THERMODYNAMIC EQUILIBRIUM A thermodynamic system is in equilibrium when the variables characterizing its condition do not change over time.
THERMODYNAMIC POTENTIAL Essentially, the capacity of a system to perform work (free energy). One of several extensive quantities determined by the instantaneous state of a thermodynamic system, independent of its previous history, and which are at a minimum when the system is in thermodynamic equilibrium under specified conditions.
THERMODYNAMICS The study of how heat is converted into work (e.g. mechanically, chemically, electrically). For example, a change in volume of a system can produce work mechanically.
THERMOMECHANICAL TREATMENT A hot-forming process during which temperature and forming are monitored and regulated in such a way as to bring about a predetermined structural condition, and consequently obtain predetermined characteristics of the material.
THERMOPLASTIC Defines a rigid material that becomes soft temporarily when heated and can then be moulded to a shape that it retains on cooling
THERMOSETTING Defines a material that reacts chemically on heating (curing) and is then resistant to deformation when reheated
THERMOSPRAY Equipment using a powder feeder, a spray gun and remelters to provide an economically advantages, good quality coating.
TITANIUM A metal with similar properties to silicon and tin. Chemical symbol Ti, density 4.51 (steel 7.85). The best-known titanium alloy is made with 90% titanium, 6% aluminium and 4% vanadium.
TOLERANCE A range within which the dimensions and shape of a product can deviate from the order specification and still meet the essential requirements.
TORSION Strain set up in a bar, rod, profile, etc., by twisting. The external twisting effort is opposed by the shear stresses induced in the material.
TOTAL CARBON The total amount of carbon in an alloy having a ferrous matrix, representing the sum of free carbon and alloy carbon.
TOUGHNESS The ability of a metal to absorb energy and to deform plastically before fracturing.
TRAIN OF ROLLS In a hot-rolling system, the “train” is the complete line from the reheating furnace, through roughing and descaling stations to the finishing train of rolls proper, comprising 6 or 7 stands each with 4 cylinders.
TRANSFORMATION DIAGRAM A set of time-temperature curves showing the initial and final instant of isothermal austenite transformation at each temperature level. The curves are typical of each steel and will vary according to the chemical composition and grain size of the particular steel.
TRANSFORMATION TEMPERATURE Acm. In hypereutectoid steel, the temperature at which the solution of cementite in austentite is completed during heating.
Ac1. Temperature at which austenite begins to form during heating.
Ac3. Temperature at which the transformation of ferrite to austenite is completed during heating.
Ac4. Temperature where austenite transforms to δ ferrite during heating.
Aecm, Ae1, Ae3, Ae4. Temperatures of phase changes at equilibrium.
Arcm. In hypereutectoid steel, the temperature at which the precipitation of cementite begins during cooling
Ar1. Temperature at which the transformation of austenite to ferrite (hypoeutectoid steel) or to ferrite plus cementite (hypereutectoid steel) is complete during cooling.
Ar3. Temperature at which austenite begins to transform to ferrite during cooling.
Ar4. Temperature at which δ ferrite transforms to austenite during cooling.
A2 Critical point of magnetism (~ 770 °C). Above this temperature, residual magnetism dissolves
Ms. Temperature at which transformation of austenite to martensite begins during cooling (martensite start)
Mf. Temperature at which the formation of martensite is completed during cooling (martensite finish)
All these changes, except for the formation of martensite, occur at lower temperatures during cooling than during heating.
Temperatures at which there is 10%, 50% and 90% of martensite can be deduced from the following formulas:
M 10% = Ms – 10 °C ± 3
M 50% = Ms – 47 °C ± 6
M 90% = Ms – 103 °C ± 12
M f = Ms – 215 °C ± 15
TRANSFORMATION TEMPERATURE The temperature at which a change of phase occurs. The term indicates the limit of a transformation temperature range.
TRANSGRANULAR CRACK Crack or fracture occurring through or across a crystal or grain.
TRANSGRANULAR FRACTURE Fracture propagating through the grains.
TRANSITION CURVE Variation of impact test values obtained by inducing failure in test specimens at high and low temperature, known also as FATT (Fracture Appearance Transition Temperature). It can show the brittleness of the steel and its point of transition (sudden decay of ductility or toughness).
TRANSITION POINT The temperature range within which impact strength abruptly decays. For the majority of steels, this range is lies below 0 °C.
The transition point (°C) is important for materials required to function at low temperatures
TRANSURANIC It refers to chemical elements that stay after the uranium in the periodic classification.
TRIMMING A mechanical operation performed on the ends of manufactured items to eliminate burrs left by cutting.
TRIP Transformation-Induced-Plasticity, associated with high strength steels. The particular microstructure of these steels is obtained by conducting two heat treatment steps after cold plastic deformation of the rolled material, or directly after hot-rolling. The resulting mechanical proprieties are superior to those of dual phase steels. Indicative chemical composition: C% 0.10 – 0.60, Mn% 1.50 – 2.10, Si% 1.50 – 1.70, Al% 0.030 – 0.050
TROOSTITE At very low rates of cooling, iron atoms migrate and take on a new lattice structure (gamma → alpha), and at the same time, carbon atoms migrate to form cementite. This product of transformation is named pearlite (ferrite plus cementite).
TUBE A hollow wrought product, long in relation to its cross section, which can be round or of other shape (regular hexagonal or octagonal, elliptical, or square or rectangular with sharp or rounded corner edges), and is of uniform wall thickness except where radiused along angles. Obtained by cold drawing, rolling, extrusion, or welding sheets and strips.
TUMBLING A mechanical surface treatment, serving typically to remove casting or forging residues. Items are rotated wet or dry in a barrel, often with abrasives such as glass granules, grit, ceramic or corundum.
TUNDISH A receptacle used in metal foundries to hold molten metal, typically in continuous casting processes, and for filling moulds. The tundish holds a reserve of hot metal from which to feed the casting machine while ladles are switched, thereby ensuring continuity and uniformity of the flow, regulating feed to the moulds, and keeping the metal clean.
TURNED PRODUCTS Round bars produced by turning on a lathe where the product can be further processed by straightening and polishing This operation gives the bar special features with respect to shape, dimensional accuracy and surface finish.
The removal of metal is carried out in such a way that the bright product is generally free from rolling defects and surface decarburization.
For technical reasons some bars ordered as hot rolled products may be delivered roughly turned (peeled), nevertheless such products are treated as hot rolled products and not bright products.
TURNING The removal of metal from a workpiece revolving on a lathe.
ULTIMATE STRENGTH The maximum tensile, compressive, or shear stress that a material can sustain, calculated on the basis of the ultimate load and the original or unstrained dimensions.
ULTRASONIC INSPECTION A technique used principally to look for internal defects, although external defects can also be examined using angle probes. The principle is based on the propagation of sound waves through liquid or solid substances. Special probes transmit and receive a beam of waves directed through the material; when the sound waves encounter a discontinuity, a signal will be reflected and displayed on imaging equipment. This visual information is then interpreted and evaluated by operators.
UNITARY DEFORMATION Unitary deformation is the ratio between the initial length of a component, and its linear length measured post-stress.
VACANCY The absence of atoms at the nodal positions of the crystal lattice.
VACUUM ANNEALING Annealing carried out at a pressure lower than atmospheric.
VACUUM TREATMENT Steel will absorb hydrogen during manufacture and casting, leading to the formation of minute internal cracks referred to as flakes (see antiflake heat treatment). The hydrogen content can be reduced by treating the liquid steel with degassing systems.
VALENCY The number of electrons an element can release to, acquire from or share with other elements in a chemical compound. The maximum valency of an element is given by the number of the group to which it belongs in the periodic table. For example, alkalines (first group) are monovalent, alkaline-earth metals are bivalent (second group), noble gases (eighth group) are non valence. Monovalent (1), bivalent (2), trivalent (3), quadrivalent (4), pentavalent (5), hexavalent (6), heptavalent (7).
VANADIZING A thermochemical treatment applied to a ferrous material in order to obtain a vanadium-enriched surface.
VERTICALIZATION Development of an industrial operation in such a way as to avoid the marketing of generally less profitable semi-finished products and gear the manufacturing system as far as possible to the production of end-use items.
VISCOSITY The resistance of a fluid to shear forces, and therefore to flow.
WATER QUENCHING Hardening carried out by means of cooling water.
WEAR A parameter principally associated with inclusions in steel (abrasive oxides such as alumina and silicates), and the possible presence of carbides. When brought into contact with a cutting tool, these components cause wear.
WELDED TUBE Tube obtained by working a flat rolled product (sheet or strip) into a tubular shape and then welding the joined edges. The welded seam can be longitudinal or helical.
WELDING A process used to join two metal pieces permanently by the application of heat or high pressure. In fusion welding (gas, arc, and resistance processes), the joined metals are melted without any mechanical pressure.
WELDLESS TUBE, COLD-WORKED Tube obtained by cold-drawing or cold-rolling previously hot-worked weldless tube.
WELDLESS TUBE, HOT-WORKED Tube rolled or extruded hot from billets or blooms.
WETTABILITY A general term used also in welding to indicate the presence of binders in the hard metal, which are able to absorb the weld material and ensure a strong connection.
WHITE ANNEALING An anneal that takes place in a controlled atmosphere so as to retain the initial appearance the metal and prevent oxidation.
WHITE CAST IRON This cast iron solidifies according to the metastable phase diagram, where carbon is present in an alloy form such as cementite. It can be produced by reducing the percentage of silicon and other graphitizing elements, or accelerating the rate of solidification and cooling. Extremely brittle, white cast iron provides the starting material for the production of malleable irons.
WHITE LAYER A surface layer 35 – 40 µm thick, which forms as a result of nitriding treatment. Composed of nitrides only as a rule, having a tetragonal crystal structure.
WHITE NITRIDING A simulation treatment that consists in reproducing the thermal cycle of nitriding without any specific medium or atmosphere.
WIDE FLAT Flat product of width over 150 mm up to and including 1250 mm and thickness generally over 4 mm, always supplied in lengths, i.e. not coiled , and the edges are square i.e. hot rolled on the four sides (or in box passes)
WIDMANNSTÄTTEN FIGURES Structure resulting from the formation of a new phase in some crystallographic planes of a solid mother solution, appearing in hypoeutectoid steels as needles of ferrite on a pearlitic background, and in hypereutectoid steels as needles of cementite. The structure is also detectable by ultrasonic inspection, appearing on the screen of the instrument in clustered patterns. To eliminate the effect, the steel must be hot-deformed again and then undergo suitable heat treatments, such as normalization, etc.
WIRE A cold-drawn product of solid and constant section, generally cylindrical, that can be wound onto reels either in ordered coils or randomly.
WIRE ROD A hot-rolled product, measuring generally between 5 and 52 mm, wound in coils. See rod.
WORK HARDENING Plastic deformation of a metal at a temperature low enough to avoid activation of the recrystallization process, with the result that the hardness and mechanical strength of the metal increase.
WORKABILITY ANNEALING Annealing carried out at 30-50 °C below the critical point Ac1. This treatment does not alter the internal structure but softens the metal suitably (see softening annealing) and eliminates stresses induced by previous working. The metal can be cooled in the furnace or in air.
YIELD Term used to quantify the effectiveness of a transformation or steelworking operation.
α IRON (alpha) The stable state of pure iron below 911 °C. The crystal structure is body-centred cubic.
γ IRON (gamma) Stable state of pure iron between 911 and 1392 °C. The crystal structure is face-centred cubic.
δ IRON (delta) Stable state of pure iron between 1392 °C and melting point. The crystal structure is body-centred cubic, like that of α-iron.