The early failure forms of rolling mill bearings mainly include: rupture, plastic deformation, wear, corrosion, fatigue. Under normal conditions, contact fatigue is mainly the main internal influencing factors: hardness, strength, toughness, wear resistance, corrosion resistance, internal stress state (outside service conditions).

1. Martensite in hardened steel

High carbon chromium steel original structure: granular pearlite

Quenching + low temperature tempering: the carbon content in quenched martensite M obviously affects the mechanical properties of steel

When the carbon content of quenching M is 0.5% ~ 0.56%, the mechanical properties of GCr15 steel with the strongest failure resistance can be obtained.

M: cryptic martensite, the measured carbon content is the average carbon content.

2. Residual austenite in hardened steel

After normal quenching, high carbon chromium steel can contain 8% ~ 20% Ar (residual austenite).

The Ar in bearing parts has advantages and disadvantages, and the Ar content should be appropriate.

Ar % ↑ hardness, contact fatigue life are increased, after reaching the peak and then reduce the Ar favorable effect must be in the Ar stable state, if the spontaneous transformation into martensite, will make the toughness of steel sharply reduced and embrittlement.

When bearing load is small, a small amount of Ar deformation occurs, which not only reduces the stress peak, but also strengthens the deformed Ar processing and the stress-strance-induced martensitic transformation. The influence of increasing amount of Ar on the contact fatigue life is reduced. When bearing load is large, the plastic deformation of Ar and the matrix will locally produce stress concentration and rupture, thus reducing the life span

3. Undissolved carbides in hardened steel

The quantity, morphology, size and distribution of undissolved carbides in hardened steel are affected by the chemical composition of steel and the original microstructure before quenching and the austenitizing conditions.

When bearing the load (especially when the carbide is non-spherical), the stress concentration with the matrix will cause cracks, which will reduce the toughness and fatigue resistance.