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Technical Notes

Table of equivalence
Metallurgical state of martensitic steels

Factory-made heat treatments give martensitic steels a high-quality metallurgical state which allows for mechanical machining.
• Annealed state
• Treated state
Each of these states requires the user to offer a range of suitable implementation measures.
• Annealed state: requires a quenching treatment and subsequent tempering after machining; in this case inevitable deforma- tions caused by the quenching operation must be anticipated and machining allowances must be left on the components, in order to achieve optimum treatment with respect to the structure of the steel.
It is also important to monitor the geometry of the parts before quenching and to avoid angles, in order to mitigate the risk of quenching cracks (relaxation of mechanical stresses causing superficial or deep open defects on the surface of the pieces).
• Treated state : allows for direct machining from the martensitic structure obtained at the factory. Its use is limited to the level of mechanical strength and hardness of the material.
In the tooling industry, these grades are pre-treated as much as possible to obtain a hardness of 400HB. At this value machining is still possible under good industrial conditions.
The technical information provided on the grade sheets is for general information; consult us in the case of a special requi- rement.

Equivalence of units of measure

0 degrees Kelvin (0k) = -273 degrees Celsius (° C) = -459 degrees Fahrenheit.
0 degrees Celsius = 273 degrees Kelvin = 32 degrees Fah- renheit.
To convert Celsius to Fahrenheit, multiply the value by 9/5 and add 32.
To convert Fahrenheit to Celsius, subtract 32 from the value and multiply by 5/9.
Pressure; strengths:
Newton (N); Pascal (Pa); kilogramme-force (kgf)
1 Pa = 0,000001 N/mm2 = 0,0000001 kgf/mm2
1N/mm2 = 1 000 000 Pa = 1 MPa = 0,1 kgf/mm2
1 kgf/mm2 = 9,80N/mm2 (1 daN/mm2) = 9,80 MPa (10 MPa)
Millimetre (mm); Inch (’’) 1 mm = 0,039370’’
1’’= 25,4 mm

Metallurgical information

Young’s Modulus: E
The elasticity modulus is the me- chanical deformation constraint required for an elongation of 100% of the initial length of a material.
Since this figure cannot be
achieved on solid materials, the
modulus of elasticity E is defined
by the straight slope of the
deformation curve where the latter is reversible. The unit of measurement is MPa or N / mm2.
Elastic limit: Re
Elongation: A %
Elongation is measured by a tensile test on a standard spec- imen and indicates the stretching deformation capacity of a material before breaking. The ratio is expressed in% between the nominal length and the last length of the specimen before rupture.
Poisson coefficient: V
The Poisson coefficient determines the perpendicular con- traction relative to the maximum pressure force exerted on a material; it has no unit of measurement.
The average value for steels is 0.3.
Density is the ratio of the volume mass of a body to that of pure water at 4 ° C and atmospheric pressure; it is expressed without unit of measure.
Expansion coefficient:
The coefficient of thermal expansion is a measure showing the variation of the volume of a material at 20° C and its volume at a different operating temperature (generally between 100 °C and 600 °C).
Thermal conductivity:
Thermal conductivity is a physical measurement which defines the energy transferred by a material in unit of area and time; it is expressed in watts per metre Kelvin.
This is defined by a tensile test on a standard specimen and indicates the linear elongation of a material between its revers- ible elastic limit and its breaking load.
The unit of measurement is MPa or N / mm2.
Mechanical resistance: Rm
This is measured by a tensile test on a standard specimen and indicates the breaking point of a material.
The unit of measurement is MPa or N / mm2.
Striction: Z %
Striction is the ratio expressed in% between the nominal sec- tion of the standard test piece and that of the last section of the test piece before failure.

Hardness correspondence
Metallurgical state of aluminium and its alloys

The metallurgical state of aluminium alloys is defined by a letter in block capitals which defines its basic state of physical and mechanical characteristics (heat treatment, mechanical treatment, heat and mechanical treatment); this letter is ac- companied by additional figures to subdivide the states according to requirement.
• F = Raw state of hot transformation with no guarantee of properties
• O = annealed state with optimum forming capacity.
• H = Hard state after work-hardening.
• T = quenched and tempered state (series 2000, 6000, 7000).

Purpose of polishing operations

Polishing is a general term for the group of operations which take place after surface machining of a support.
This support is generally metallic (base iron, copper, aluminium), but can also be mineral (glass) or synthetic (plastics) Polishing operations are mainly mechanical. They consist in attaining a homogeneous surface state upon a material support,
defined by criteria of geometry, roughness and visual reflection.

In order to obtain the final surface state of a part, a precise procedure must be followed (chronology, duration of sequences and direction of polishing) using a decreasing range of abrasives and supports.

The table below shows the relative equivalences between correspondences of NFE 05 051 standards; ISO / DIS 2632; the industrial name of the polishing operation; the roughness of the desired surface finishes and the average size of the abrasive particles used in order to obtain Ra.

Raw materials machining allowance

Machining allowance for tool steels:
Raw rolled or rough forged products generally present a decarburised, heterogeneous surface as well a layer of calamine un- suitable for use.

They thus require machining to remove a certain amount of material uniformly distributed on each face. NFA standards 45, 103 and NFA 104 define the minimum machining allowance to be applied to the nominal dimensions of round section, square section, flat and wide flat, non-pre-machined products.

As an indication, certain values are shown in the tables below.
Remarks: the failure to remove surface defects can lead to serious incidents during heat treatment (decarburisation, cracking, deformation, breaking), and after heat treatment (delayed failure on undetected defects).

General tolerances
Adjustment tolerances
Thread correspondence