Co-Ni型超高强度钢的微观组织结构与力学性能

Microstructure and mechanical properties of Co-Ni ultrahigh strength steel

利用透射电镜、扫描电镜等试验手段研究了回火温度对2000 MPa和2200 MPa两种强度级别Co-Ni超高强度钢的微观结构、断口形貌与力学性能的影响。结果表明,两种强度级别Co-Ni超高强度钢的强化均与M2C碳化物有关。Co-Ni超高强度钢在400～450℃回火韧性出现谷值,产生的原因与板条边界存在Fe3C、M3C及M2C处于共格状态,使马氏体基体产生强烈静畸变有关,冲击试样断口微观形貌表现为准解理断裂。Co-Ni超高强度钢在480～510℃回火,马氏体板条内析出细小、弥散的M2C,粗大片状Fe3C被细小、弥散的MC取代,使其具有比较好的强韧性配合。

The effect of tempering temperature on microstructure and mechanical properties in the two strength levels of Co-Ni ultrahigh strength steel were examined by means of transmission electron microscope（TEM）and scanning electron microscope（SEM）.The results show that the strengthening for the two strength levels of Co-Ni ultrahigh strength steel is related to the M2C carbides.The impact toughness and fracture toughness of the steel tempered at 400～450 ℃ are low.It is related to that there are Fe3C,M3C and M2C on the boundary of martensite lath and appear as-coherent which makes the martensite matrix possess strong static distortion.The fracture morphology of impact toughness sample shows quasicleavage character.The steels tempered at 480 ℃ to 510 ℃ have high strength and good impact toughness,which is attributed to the formation of fine M2C carbides in the martensite lath and the coarse Fe3C precipitate is replaced by a fine dispersion of M2C carbides.