Retained austenite produced by induction hardening of cast iron

Induction hardening is one kind of surface hardening process and can improve the wear resistance of components for the combination of high surface hardness and high toughness core. However, it may contain noticeable amount of retained austenite in the matrix of martensite, affecting the structural and dimensional stability of rails. The research focuses on the analyses of the amount of the retained austenite of FC350 cast iron obtained in different proceeding conditions. The hardness value of the induction hardened case is 750±50 HV
_0.3
and the hardness of core is 300 HV
_0.3
. The white area, retained austenite, distributed in the black martensite plate was observed in the microstructure of the induction hardened case. The flake dispersed in the martensitic microstructure of hardened FC350 case was dominant in the cryogenic treated specimen. The volume percent of retained austenite existed in specimen is 15.0, 3.7 and 2.4 vol% for the induction hardened, subzero treated at -50°C and cryogenic treated at -150°C, respectively. It is believed that the cryogenic treatment can noticeably decrease the amount of the retained austenite.