It measures the stretching of the material when taken to rupture point using tensile testing.
it is a data that allows engineers to know how much steel can be stretched before reaching the rupture point.
It’s a steel showing ferromagnetic properties and that can be demagnetized with adequate heat treatment, which consists of exceeding the magnetism critical point (769 °C), remaining at that point for a period of time, and cooling normally in air or furnace.
The crystal shape is different in all directions as well as the physical properties (refraction index, thermal conductivity, mechanical and magnetic properties, etc.) which vary depending on the direction taken.
The specific physical properties inside a material have different values in different directions.
Heat quantity necessary to raise temperature of a mass unit by 1 °C.
The specific heat capacity at 20 °C of ferritic and martensitic steels is slightly less than that of austenitic steels, but grows quicker with raising temperature.
Magnetic field forming around a magnet or an electrical circuit. It’s marked by H and measured by Ampere/meter.
The ultimate strength determined by stress proportional samples, measured in N/mm2.
This occurs within a solid subject to stress causing the molecular bonds to break.
This testing is used by engineers for dimensioning supporting structures.
Load corresponding to a non-proportional extension, widely used as yield strength at 0.2%.
The value is obtained from tensile testing, measured in N/mm2 and is useful to engineers to determine sections and safety margin to adopt for structures of a determined construction.
It’s the property of a material’s ability to conduct heat or sound energy or electric current.
Symbol: Siemens • m/mm2.
Thermal conductivity is the W / (m • K) measurement of a body’s ability to conduct heat. It depends from the nature of the material and not from its shape.
This property is a lot higher in carbon steels ~ 50 W / (m • K) and bonded steels ~ 40 W / (m • K), it lowers to ~ 30 W / (m • K) in stainless steels at chromium 15% and lowers ~ 15 W / (m • K) in nickel and molybdenum steels.
Thermal conductivity proportionally increases to the part heating and it is a parameter used in heat treatments to define the heat rate.
Defines the variation of magnetic properties at temperature variation. Normally expressed in variation % of the part for each degree of temperature.
Automatic instrument used to measure coercive force of steel samples of any shape (regular or irregular) and of specific manufacture products alone or assembled with other materials.
Normative widely used for checks: ASTM 341 or IEC 404-7.
Defined as the magnetic field, expressed by Hc, needed to reduce induction B or magnetization M to value zero. Normally measured in Oersted or Ampere/meter. Needed to measure resistance to demagnetization of a magnetized material.
It’s the property of a material’s ability to conduct heat or sound energy or electric current.
Physical size equal to the inverse of resistivity.
Graphic representation of the curve obtained by measuring induction B (air + material) or magnetization M in presence of a magnetic field H. It describes a complete cycle between defined limits for induction or magnetization saturation from the first to third quadrant. 

B = Magnetic flow density Br = Residual magnetic induction
H = Magnetic field Hc = Coercive force
Graphically it is the curve sector of the hysteresis cycle of the second quadrant, which defines the main magnetic characteristics of a magnetized material. The demagnetization curve describes the induction change or emanation of the residual value at zero applying a negative magnetic field.

This ratio m/v between the mass (m) of a body and its volume (v) is also called specific weight and is measured in Kg/dm3.
The iron specific weight is 7.86 Kg/dm3 and its atomic mass is 55.847 while that of the main elements of stainless steel is: 51.996 for chromium, 58.69 for nickel and 95.94 for molybdenum.
Thereby alloys rich in chromium are lighter than iron, while nickel and molybdenum alloys are heavier. The following example compares the estimated weight of three bars sized 180 mm square and 1500 mm long.
Density values are reported in the data sheets specifications.
42CrMo4 steel (1,80 • 1,80 • 7,85 • 15,00) = Kg 381,51
1.4006 steel (1,80 • 1,80 • 7,70 • 15,00) = Kg 374,22
1.4567 steel (1,80 • 1,80 • 8,027 • 15,00) = Kg 390,11
Defines the induction field as magnetic lines of force per unit area.
Is an electrical insulator that can be polarized by an applied electric field with accumulated energy. It has the function of separating parts with different potentials and forcing the current into one single direction.
Characteristic depending on molecular cohesive forces. Measured through various sizes (HB, HRC, HV, etc.) within empirical tables, among which only some correlation exists, all in ratio with traction rupture load.
The thermal expansion or growth is the physical phenomenon which appears when material has a volume increase, due to temperature increase during heat treatment, function or welding.
The value can be determined by dilatometer testing or according to data sheet specifications contained in the volume Designing with steel by Lucefin Group.
This data lies within the formula for the theoretical linear e volumetric growth in mm, that steel will endure when heated at temperatures between: 20 and 100 °C, 20 and 200 °C, 20 and 300 °C, etc. 

Lo = Initial length of the bar or the part in mm
ro = Initial radius in mm
E = Constant value from data sheet specification (i.e. as 10-6 • K-1 equal to 10.4 insert 0.0000104)
Δt = Temperature difference between the part to be heated and the environment
L = Length in mm after heating at °C.
V= 3 mm volume after heat treatment
Linear expansion L = Lo • (1 + (E • Δt))
Volumetric expansion V = 3,14 • r2 • Lo • (1 + (2 • E • Δt)) • (1 + (E • Δt)

Number of magnetic lines of force measured in Gauss o Tesla. The lines can seen using dry iron powders or in humidity.
Consist of non metallic materials made of iron oxides and a bivalent metal (Mg, Mn, Zn, Cu, etc.) and can be assimilated to ceramic materials for its harness and brittleness. They have a very low conductivity, thus are suitable to form ferromagnetic nuclei for high frequency applications (5 – 500 kHz). The most common ferritics are Mn-Zn, Ni.Zn, Mg-Mn.
It is the magnetizing or demagnetizing force, generally measured in Oersteds, which determines the ability of an electric current, or a magnetic body, to induce a magnetic field at a given point.
Devised used to measure change of magnetic induction flow.
Demagnetizing force necessary to reduce residual induction to zero, as measured on a saturated magnet. Calculated in Oersted or A/m and KA/m. Symbol: Hc.
Measures the resistance of a magnetic material to demagnetization and shows its stability degree at high temperatures. Symbol: Hci.
Unit of measure of magnetic induction in the CGS electromagnetic system. It shows flow lines for cm2.
Device used to measure the instantaneous value of magnetic induction and residual magnetism.
Is the magnetic field induced by an applied field resulting from the laid down field and from the matter. Also defined as magnetizing or demagnetizing force measured in Oersted, which determines the current ability or of a magnetic material to induce a magnetic field in a given point. B = µo • H
In any given material: B = µr • µo • H
A magnet is isotropic when its properties are identical in all directions. In the metal material field, magnetic orientation of particles does not have a preferred direction thus allowing an all round magnetization.
It is a ferromagnetic substance characteristic, in which magnetization intensity does not uniquely depend from the magnetic field applied, but also from the previous evolution in the magnetic field. It is defined as the tendency of a magnetic material to retain its magnetization in a demagnetizing energy presence.
Is a ferromagnetic body artificially or naturally magnetised. Only certain types of substance are able to acquire a satisfying permanent magnetization, after adequate treatments.
It is the remaining magnetism in a steel material after having been in contact with an applied magnetic field (usually lift magnets, induction processes, etc.). Its intensity depends on several factors, some of the most important are: chemical structure, magnetic field intensity at source, temperature of material.
Magnetism for each volume unit, measured in Ampere/meter.
It is a property that can cause changes of shape or dimension during the process of magnetization.
In the hysteresis curve it is represented by the point of maximum out come between magnetizing force H and induction B. Also defined as the energy that a magnetic material can transfer to an external magnetic circuit in a given point of the demagnetization curve. Symbol: BH max.
The magnetic structures a and b inside anti-ferromagnetic materials, are precisely equal but opposite, resulting in null magnetization.
Hematite is the best anti-ferromagnetic material.
Are those materials whose magnetization is inversely inducted to that of the inductive field. They are composed of non magnetic atoms placed in complete orbitals without free electrons. This causes an opposition when in a magnetic field. In other words, a negative magnetization is created, exactly the opposite of what happens in ferromagnetic materials. Among these diamagnetic materials are quartz, calcite, water and organic substances.
One of the main characteristics of these materials is the spontaneous magnetization without a magnetic field and can be increased until it reaches magnetic saturation. Saturation is at high temperatures and moderate magnetic fields.
In particular, each ferromagnetic material at a given temperature called Curie temperature, which differs from material to material, loses the electrons configuration and becomes paramagnetic. Furthermore, ferromagnetic materials can retain a magnetic memory from previously. The best ferromagnetic elements are: iron, nickel and cobalt. Ferritic and martensitic stainless and duplex steels are among this category.
These are made of atoms and ions with unpaired electrons and incomplete orbitals. They have a net magnetism and can magnetize when exposed to a magnetic field. However it is a weak magnetization, which disappears when the magnetic field is taken away. Liquid oxygen, aluminium, biotite, pyrite, siderite are among the paramagnetic materials. Austenitic stainless steels belong to this category (stable austenitic structure).
The measurement unit of the flux produces by a intensity magnetic field in the CGS system in an area of 1 cm2. One Maxwell is 10-8 Weber and equals one line of magnetic flux. Symbol: Mx.
Defined as the strain stress and deformation ratio, in mono-axial loads and elastic behaviour of material. Used by engineers for flexural strain verification, under exercised stress, to establish the maximum load factor of a construction. The longitudinal elastic modulus for each steel and the different temperatures to which a stainless steel product can be worked at, all are reported in the data sheet specification.
m = 1/Poisson coefficient (the Poisson coefficient is reported within some data sheet specification contained in the volume Stainless Steels by Lucefin Group © 2011).
E = Longitudinal elastic modulus G = Tangent elastic modulus
The result is measured in GPa (GigaPascal).
E = G / (m / 2 • (m + 1)) G = (m / (2 • (m + 1)) • E
It is measured in Am2 (Ampere for each m2).
When a material is compressed in one direction, it usually tends to expand in the other two directions perpendicular to the direction of compression. This phenomenon is called Poisson effect. The Poisson ratio is the ratio of the percent of expansion divided by the percent of compression. It is often used when calculating elasticity and structural projects.
Unit of measure for the intensity of the magnetic field and measuring the magnetic force.
1 Oe = 1 Gauss = 0,79 A/cm. Symbol: Oe.
Is the propagation ability of the magnetic flux in a classical vacuum:
µo = 1,26 • 10-6 • H/m
µr < 1 Diamagnetic materials (if the magnetic field is weakened inside the material)
µr > 1 Paramagnetic materials (if the field is strengthened inside the material)
µr >> 1 Ferromagnetic and ferromagnetic materials (if the field is strengthened a lot inside the material)
Is the ratio between field B and field H measured when H has a zero tendency. Relative permeability or ratio from material and free space (air) permeability is more useful. Used to indicate weak ferromagnetic steels used for transformers.
Is the parameter of all materials given by the ratio between magnetic induction B produced inside the material by the magnetic field and intensity H of the applied field.
Symbol: m. The 1/m opposite of permeability is called specific reluctance.
In physics terms it defines the ability of a substance to be magnetized by a magnetic field. Symbol: µr and it is the ratio between absolute permeability µ of a generic material and the permeability µo of free space (vacuum). Ferritic and martensitic stainless steels are defines magnetic (a magnet attracts them) when at room temperature and they lose this characteristic when heated over 769 °C. Austenitic steels are classified as non-magnetic and their permeability is around 1.02 µr. They can be slightly magnetized during cold drawing treatment, but a later re-crystallization return them to the initial non-magnetic state.
A device able to do hysteresis cycles and measure magnetization of mild magnetic steels (i.e. stainless for electro-valves and nuclei). It performs in automatic and determines the following parameters: Br, Hc, Bsat, Jsat, µmax. Standards used for checking: ASTM 341 or IEC 404-4 for straight samples or bars.
A substance exposed to a magnetic field directs its atoms magnetism to magnetize for induction. Generally, term used to describe an alteration of physical state, where some phenomena from isotropic become vector.
Indicates material tenacity when exposed to violent shocks. Resistance measured in J (work – energy), it is determined through previously cut samples and usually of Kv types. This value also indicate steel predisposition for certain uses.
It is the resistance of a conductor of unit length and area section unit, measured in Ω • mm2/m. The resistivity of a conductor depends on its nature, temperature, and in some cases on the intensity of magnetic field in which it is. Under heat treatment the resistivity of the material is null (absolute zero) and increases by 6% each 100 °C. The increase of resistivity in a material can be obtained by altering its composition (i.e. 4-4.5% silicon increase).
It represents residual magnetism when the magnetic field applied is zero. In the graph it is the intersection of the curve with the y-axis. Symbol: Mr.
Phenomenon occurring when, in a ferromagnetic substance subject to a sufficiently intense magnetic field, magnetization remains practically constant to every increase of magnetic field.
The tendency of a solid material to deform under the influence of constant stresses at high temperatures. The sample is subject to a determined constant load and temperature for long periods. The obtained results simulate steel behaviour in time.
This unwanted magnetic force (found in products for grinding, lapping and polishing, galvanic treatments, etc.) attracts filings or iron powder and causes unacceptable surface finishes. It can be diminished or removed by bringing steel at temperatures above 769 °C or let it through demagnetizing tunnels. Another rather efficient method is the stress-relieving heat treatment for long periods.
It is a coil wound into a tightly packed helix, mounted on a cylindrical support bigger than the helix diameter.
It is the temperature above which ferromagnetic materials become paramagnetic. It normally depends on the chemical composition of the magnetic material, once the material reaches it, loses all of its permanent magnetic properties and can no longer keep magnetism. Symbol: Tc = 769 °C.
The maximum temperature of exposure that a material can resists without mechanical or structural changes.
Density unit of magnetic flux: 1 T = 10000 Gauss.
It describes the variation of magnetization delay in a ferromagnetic material when the external magnetic field abruptly changes intensity.
It is the unit for magnetic flux which when linked at a uniform rate with a single turn electric circuit during an interval of 1 second, will induce an electromotive force of 1 volt. 1 Weber = 10-8 Maxwell. Simbol: Wb.