Metallographic study on rolling contact fatigue of 0.44%C-1.71%Mn induction-hardened bearing steels

Microstructural changes and propagation of subsurface cracks during rolling contact have been studied to clarify rolling contact fatigue of 0.44%C-1.71%Mn induction-hardened bearing steels, using the specimens with different induction-hardened layer. The specimens were pretreated to form lower bainite and induction-hardened to form fine martensite in shallow induction-hardened layer or coarse martensite in deep hardened layer. Rolling contact fatigue tests were conducted under maximum a Hertzian contact stress of 508 kgf mm(-2) with circulating lubricant through a filtered-pump feed system. Heavy plastic deformation of fine martensite in shallow induction-hardened layer and propagation of subsurface crack across grain boundaries were observed with superior resistance to fatigue. On the other hand, intergranular crack along grain boundaries in coarse martensite of deep hardened layer were observed with poor resistance to fatigue. Deformed martensite and dense tangles of dislocations in ferrite were observed by transmission electron microscopy for a shallow induction-hardened layer which was heavily deformed during rolling contact fatigue.