Effects of Austenitizing Temperature and Cryogenic Treatment on Microstructure and Mechanical Properties of GCr15 Steel

The effects of austenitizing temperature and cryogenic treatment on the microstructure and hardness in GCr15 steel were studied by microstructural observation and Rockwell indentation test. The results show that, as the austenitic temperature increases, the proportion of carburics less than 0.5 μm gradually decreases in quenching microstructure and more above 0.5 μm. Meanwhile, the average particle size and primary austenitic grain size of the carburina are increasing. At 820-860 ℃, the hardness after austenite increases as the austenitic temperature increases. However, at 880℃ and 900 ℃ austenitic, more residual austenite is enched in the austenitic matrix, decreasing the hardness of GCr15 steel. Cryogenic treatment can improve the quenching hardness, but the long-time cryogenic treatment does not significantly improve the hardness.