观察和比较了油淬热处理和等温热处理４０ｃｒＮｉ２Ｓｉ２ＭｏｖＡ钢的显微组织。研究表明，两种热处理后钢均得到回火马氏体＋贝氏体＋残余奥氏体的混合组织，但贝氏体及残余奥氏体形态有所不同。等温热处理后钢的韧性相较多而对韧性有益，主要表现为裂纹起始功的提高。 The microstructure of 40crNi2Si2MovA steel treated by oil quenching and isothermal heat treatment was observed and compared. The results show that the mixed microstructure of tempered martensite + bainite + retained austenite is obtained in both steels after heat treatment, but the shapes of bainite and retained austenite are different. After isothermal heat treatment, the toughness of the steel is more beneficial to the toughness, mainly for the improvement of the initial work of the crack.