研究了新型高合金超高强度钢 (2 3NiCo)中M2 C的回火析出机制。结果表明M2 C以非均匀形核方式析出 ,有两种形核机制 ,一种是自基体位错上直接析出 ,即单独形核 ;另一种是在渗碳体上形核 ,即原位形核。以单独形核机制析出的M2 C与基体高度共格 ;以原位形核机制析出的M2 C与基体非共格。 The mechanism of tempering precipitation of M2 C in a new type of high alloyed ultra high strength steel (2 3NiCo) was studied. The results show that M2 C precipitates in a heterogeneous nucleation mode. There are two nucleation mechanisms, one is the direct precipitation from the matrix dislocations, that is, nucleation alone; the other is nucleation on the cementite, that is, in situ nucleation. The M2 C precipitated by a single nucleation mechanism is highly consistent with the matrix; the M2 C precipitated by the in situ nucleation mechanism is non-coherent with the matrix.