The early failure forms of rolling bearings mainly include: rupture, plastic deformation, wear, corrosion, fatigue under normal conditions is the main internal influence factors of contact fatigue: hardness, strength, toughness, wear resistance, corrosion resistance, internal stress state (outside the service conditions)
1. Martensite in quenched Steel
Raw microstructure of high carbon chromium steel: granular pearlite
Quenching + Low temperature tempering: quenching martensite m carbon content, significantly affect the mechanical properties of steel
The GCR15 steel quenching m carbon content is 0.5%~0.56% to obtain the most strong resistance to failure ability of the comprehensive mechanical properties.
M: The amorphous martensite, the measured carbon content is the average carbon content.
2. Residual austenite in quenched steel
High carbon chromium steel after normal quenching, can contain 8%~20%ar (residual austenite).
The AR in the bearing parts is advantageous also has the disadvantage, the AR content should be suitable.
The ar%↑ hardness and contact fatigue life increase with it, and then the favorable effect of decreasing ar after the peak is in AR stable state, if the spontaneous transformation to martensite, the toughness of steel will be reduced and brittle.
When bearing load is small: AR occurs a small amount of deformation, the stress peaks are reduced, the deformation of AR processing and the stress-strain induced martensite phase change are enhanced, and the effect of AR increase on the contact fatigue life is decreased when bearing load is larger: ar larger plastic deformation and base experience partially produce stress concentration and rupture, Thus reducing the life expectancy