Microstructure and Rolling Contact Fatigue Strength of Induction Heated AISI 52100 Bearings

In the present work the microstructure and the rolling contact fatigue properties of induction heated AISI 52100 bearings are investigated. The bearings were heat treated by using a flat coil at 30 kW power and 60 kHz frequency, cooled with water and subsequently tempered for 1 hour at 180 °C. The hardness at the surface of the material was close to 900 HV0.3kgf/15s. The hardening depth of the induction heated sample was higher than 5 mm. The retained austenite content was around 18% at the surface and decreases along with the depth. The samples were rolling contact fatigue (RCF) tested up to 107 and 4.5x107 cycles, at Hertzian stress 4 GPa. No flaking failure was observed on the bearing races. For tests up to 107 cycles the track size was around 690 um and this remained unchanged up to 4.5x107 cycles. The residual stresses at the material surface before testing were close to zero and became highly compressive after the RCF testing. Stress induced transformation occurred at the surface and the retained austenite content after testing reached around 10%. Induction heating was successfully applied to induce martensitic transformation in AISI 52100 steel and the bearings showed very high fatigue strength under rolling contact.