本文研究了3Cr3Mo3VNb钢等温淬火后贝氏体回火时的相及组织转变规律。实验结果表明,贝氏体的二次硬化机制和马氏体一样,主要是由Mo_2C,V_4C_3,NbC等细小弥散的合金碳化物析出造成的。回火时,贝氏体中粗大的渗碳体溶解较慢,减慢了合金碳化物的析出速率。贝氏体中的残余奥氏体分解和转变的行为与马氏体中的不同。贝氏体中位错密度较低,不利于合金碳化物的聚集粗化。以上诸因素的共同作用,使贝氏体具有比直接淬火所获得的马氏体更高的二次硬化效应、热强性和组织稳定性。
The phase and structure transformation of bainite during tempering after isothermal quenching were studied on steel 3Cr3Mo3VNb. It was shown that the secondary hardening of bainite is similar to martensite, mainly formed by precipitation of fine dispersed carbides such as Mo_2C, V_4C_3, NbC, etc. The slow dissolution of coarse cemetite in bainite retards the precipitation rate of carbides during tempering. The decomposition and transformation of the retained austenite in bainite differ from that in martensite. The lower dislocation density in bainite is unfavourable for the aggregation and coarsening of carbides. As a result of the coaction of abovementioned factors, the bainite has superior secondary hardening effect, thermal strength and structural stability to martensite formed by straight tempering.
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