• Knowledge of materials and monitoring of their quality

For each grade of steel we have defined extremely precise and stringent specifications that concern the following points: • the method of steel production

• the chemical composition 

• the hardness, quenching hardenability 

• the macrostructure and macrographic soundness 

• the microstructure and micro-cleanliness 

• the endurance 

• the product presentation

• the reception and inspection conditions 

The verification of the material is performed by metallographic and spectrographic inspection, completed by bench tests. 

This section details the most currently used materials and surface treatments. Your contacts are at your disposal to study with you the solutions to meet your specifications.

  • Materials and surface treatments
Applications standard

-Requirements

Excellent resistance to fatigue and wear.

Can achieve homogenous hardness throughout.

-Proposals

100Cr6 (AFNOR) high-carbon chromium steel This very commonly used steel displays many advantages: cleanliness (absence of inclusions), quenchability without carburization, heat treatment method flexibility.

Our continuous quality monitoring of materials has enabled us to substantially increase the endurance of this type of steel.

Chemical composition

C from 0.98 to 1.10 %

Si from 0.15 to 0.35 %

Mn from 0.25 to 0.45 %

Cr from 1.30 to 1.60 %

Mechanical characteristics

Coefficient of expansion    : C1=12 x10-6 mm/mm/°C

Modulus of elasticity         : E = 205 000 N/mm2

Poisson ratio                    : η= 0.3

100 Cr6 vacuum re-melted when a gain in performance in a given envelope is absolutely necessary.

XC68 for bearings produced from steel strip.

Special applications

-Requirements

 High resistance to fatigue and wear

 High impact strength at core

 Resistant to high temperatures.

 Improvement in the wear resistance of the bearing external surfaces.

 Improvement in corrosion resistance

 Improvement in fretting corrosion resistance between the shaft or housing and the bearing.

 Lubrication in very low quantities or lubrication by the surrounding environment (petrol,diesel,etc.).

 Improvement in contamination resistance.

- Proposals

100Cr6 steel with localized hardening of the bearing raceways and working surfaces (e.g.contact faces),while the core of the part remains in the initial metallurgical condition.

Case-hardening steels.

100Cr6 steel with stabilization heat treatment. For bearings made in limited quantities:

E80DCV40 (AFNOR) or M50 (AISI) "tool" steel,produced and cast in vacuum when identical hardness at core and surface is necessary;

High-temperature case-hardening steels;

Nitriding steels if the bearings are subject to moderate loads.

Anti-wear surface treatments such as phosphatizing,hard chrome plating, black oxidizing,or others,depending on specifications.

Surface treatments such as electrolytic zinc or others depending on specifications.

Stainless steels.

Surface treatments such as copper or hard chrome plating on the external surfaces of the bearing.

Use of ceramic balls.

Self-lubricating surface treatments such as silver + molybdenum bisulphide or others for lightly loaded bearings.

The collaboration between SNR and the steel manufacturers came up with the development of a bearing steel that is less sensitive to contamination.This steel,which has a special chemical composition and microstructure,requires an appropriate heat treatment.This new material reconciles high surface hardness to resist wear with matrix ductility which reduces the risk of cracking,while maintaining good dimensional stability.

  • Heat treatment

The principle of bearing steel heat treatment is to give a martensitic structure to get: 

• the required hardness (62 HRc approx.), 

• the fatigue resistance, 

• and the dimensional stability, 

necessary to cover the majority of applications. 

It requires a pre-hardening austenilic phase at high temperature above the transformation point.

 Types of treatments

several types of standard hardening of 100 Cr6 steel adapted to the requirements of the application. 

For example: 

Deep martensitic hardening which, by means of judiciously chosen tempering operations, gives perfectly controlled compromises between the ability to withstand Hertz stresses and dimensional stability, and therefore maintaining the geometric precision of the bearings under the most general service conditions. 

Surface hardening of the raceways and working surfaces (e.g. contact faces), while the core of the part remains in the initial metallurgical condition. 

Deep bainitic hardening which gives a good hardness / toughness compromise in the mass and on the raceways.