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用穆斯堡尔谱技术研究了高Ｃｏ－Ｎｉ二次硬化马氏体钢（Ｇ９９）在不同回火制度下的组织结构变化．实验结果表明，随着回火温度的升高，起初奥氏体量有所降低，在４８０℃回火５ｈ奥氏体量达到最低．随后，随着回火温度的升高，奥氏体量又较快地增加．碳化物含量也随回火温度变化而有所变化．值得注意的是马氏体中Ｃｏ和Ｎｉ替代铁原子而成为Ｆｅ－Ｃｏ和Ｆｅ－Ｎｉ近邻，也随回火温度变化而变化，在４８０℃处出现较高的峰值，且与屈服强度峰位一致．这说明Ｃｏ，Ｎｉ分布状态可能与屈服强度有着密切的联系
The microstructure changes of high Co-Ni secondary-hardenable martensitic steel (G99) under different tempering regimes were studied by Mössbauer technique. The experimental results show that with the increase of tempering temperature, the amount of austenite initially decreases, and the amount of austenite reaches the minimum after tempering at 480 ℃ for 5h. Subsequently, as the tempering temperature increases, the amount of austenite increases more rapidly. Carbide content also varies with tempering temperature. It is noteworthy that in the martensite, Co and Ni substitute Fe atoms to form Fe-Co and Fe-Ni neighbors, and also change with the tempering temperature. Peaks appear at 480 ℃, Consistent. This shows that Co, Ni distribution may have a close relationship with the yield strength