Characteristics of rolling contact fatigue of steels produced by thermomechanical processing

0.27C-1.97Cr-1.65Mn-0.30Mo-0.21Ni steels produced by thermomechanical processing were rolling contact fatigue tested in the elastohydrodynamic lubricating condition at the rotating speed of 8,000 rpm under the applied load in the range of 25–100 kgf. A mixture of lower bainite and martensite was formed during thermomechanical processing, and it was found in transmission electron microscopy that fine lower bainite was formed by splitting in two after formation of martensite. The zone of maximum shear stress was found to be 195.0–339.3 m in depth from the contact surface by comparing the regions of hardness increase, microstructural change and the contact width during rolling contact fatigue. Resistance to crack initiation during rolling contact fatigue is the main reason for improved fatigue life. This is confirmed from the result that the shortest fatigue life was shown in the specimen with the largest crack length and crack depth.