Abstract: Imported P92 steel was treated by quenching at different temperatures (1040,1060,1080 ℃) and quenching at 1060 ℃ plus tempering at different temperatures (740,760,780 ℃) for different time(1,3,5,7 h).Effect of heat treatment on microstructure,grain size and hardness of the steel was studied.The results show that after quenching,the microstructure of the steel consists of lath martensite and retained austenite.With the increase of quenching temperature,the martensite lath gradually becomes coarser and the average grain size increases from grade 9 to 7.After quenching at 1060 ℃,the hardness of P92 steel gradually decreases with the increase of tempering temperature and the tempering time.The tempered martensite lath gradually merges and transfers to tempered sorbite.During the tempering process,carbides precipitate and grow up at the grain boundaries and inside of the grains.

Key words: P92 steel, heat treatment, microstructure, grain size, microhardness