Spheroidization of 100Cr6 Bearing Steel by Warm Forging

Warm forging of a (1%C–1.5%Cr) bearing steel at 760 and 800 °C could enable the achievement of a fully spheroidized microstructure comparable to that of the steel spheroidized by long-duration annealing treatment. The deformation-induced spheroidization gave higher hardness, strength, and toughness than the annealed steel. The deformation-induced grain structure and the finer dispersion of the residual carbides at the warm forging temperature promoted divorced eutectoid transformation when the steel was cooled below A1 temperature. A still higher temperature warm forging at 820 °C gave a partially spheroidized microstructure, with a significant fraction of pearlite colonies, resulting in inferior mechanical properties. The lower equilibrium carbide at higher warm forging temperature gave large islands of austenite devoid of carbides, which on cooling below A1 transformed to pearlite. The microstructure evolution and mechanical properties were examined at various stages of processing.