Effect of Preliminary Heat Treating Cycle on Microstucture and Hardness of 9Cr2Mo Steel

Microstructure,morphology and distribution as well as size of carbides in 9Cr2Mo steel preliminary heat treated by different procedures were investigated by means of metallographic microscope and SEM,and its surface hardness was measured too. The results show that the microstructure of 9Cr2Mo steel after quenching or normalizing consists of martensite,lower bainite and small amount of undissolved carbide and retained austenite,and that amount of martensite in the as-quenched steel is more than that in the as-normalized steel. Furthermore,the microstructure of 9Cr2Mo steel hardened and high-temperature tempered or normalized and spheroidized is ferritic matrix with carbide particles different in size,and the resulting hardness is so low that the steel may be smoothly machined. After heating at 890 ℃ for 30 min and oil quenching followed by tempering at 690 ℃ for 10 h the steel offers fine and uniform carbides which is a proper microstructure developed by preliminary heat treating.