Abstract: Effect of quenching and tempering temperature on microstructure and property of new stainless steel 940X were investigated and mechanism of high hardness of steel 940X after heat treatment was analyzed.The results show that the optimal quenching temperature of steel 940X was 1 030 ℃.The gained hardness was about 57.3 HRC and the microstructure was martensite and dispersed precipitates.With the increase of tempering temperature,the hardness of steel 940X decreased slowly from 150 ℃ to 300 ℃,then increased slowly from 300 ℃ to 500 ℃,and finally decreased greatly from 500 ℃ to 750 ℃.The change of tempering microstructure with temperature resulted in the change of the hardness of steel 940X.