| Heat treatment of high-carbon chromium bearing steel, STB 2 (AISI 52100 or JIS SUJ 2), with excellent resistance to rolling contact fatigue was attempted in this study by spheroidized annealing, partial austenitizing and then isothermal transformation. The rolling contact fatigue test was conducted at a shaft speed of 1700 rpm under axial load, 506 kgf, circulating the lubricant using thrust-type rolling contact fatigue testing machine. It was found that lower bainite was formed after isothermal transformation. Strain hardening of lower bainite occurred due to formation of tangled dislocations, which resulted from accommodation of severe plastic deformation in lower bainite during rolling contact fatigue. It was also observed that propagation of subsurface crack leading to flaking during rolling contact fatigue in the isothermal transformed specimen was retarded by deflection due to tough lower bainitic matrix, just under the raceway surface subjected to rolling contact stressing. Consequently, the rolling contact fatigue life of the isothermal transformed steel was improved in comparison with that of the conventional quench-tempered steel. |
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