中碳CrMo钢中Ti、Nb液析形貌及生成机理分析

Analysis of Morphology and Formation Mechanism of Ti and Nb Liquid Precipitation Phase in Medium Carbon CrMo Steel

通过观察微合金Ti、Nb、V在42CrMo钢连铸坯中的液析形貌,以及液析经加热轧制后的变化,同时,采用热力学计算的方式推导液析生成机理。结果表明,在含w[Ti]0.012%、w[Nb]0.030%、w[V]0.030%、w[N]0.003 5%的42CrMo钢410 mm×530 mm连铸坯中,可观察到Ti、Nb以复合碳氮化物的形式析出,形成微米级液析,w[Ti]较高(70%~83%)的多呈多边形块状,w[Nb]较高(70%~85%)的多呈薄膜状或不规则块状,液析中基本不含V元素;Ti和Nb的碳氮化物液析可互溶并共同生长,Nb含量较高的液析以Ti含量较高的液析为核心长大为块状,部分液析以含硫夹杂物为核心形核并长大;连铸坯心部的碳氮化物液析较多,并且尺寸较大(最长达35μm),连铸坯表面的数量较少,尺寸较小(10μm以下);连铸坯经1 200℃加热并轧制后,液析可部分回溶,数量减少,尺寸减小,并且在轧制过程中破碎。

The morphology of the liquid precipitation phase of micro alloys Ti,Nb,and V in 42CrMo steel continuous casting billets was observed,as well as the changes of the liquid precipitation phase after heating and rolling,then the formation mechanism was derived by using thermodynamic calculations.The results showed that Ti and Nb precipitated in the form of composite carbonitrides can be observed in 42CrMo steel 410 mm×530 mm continuous casting billets with Ti 0.012%,Nb 0.030%,V 0.030%,N 0.0035%,which was formed a micrometer scale liquid precipitation phase.Those with higher Ti content(70%-83%)were mostly polygonal blocks,while others with higher Nb content(70%-85%)were mostly thin films or irregular blocks,and no significant V segregation in the liquid phase;The carbonitrides precipitation phases of Ti and Nb can dissolve and grow together,the liquid precipitation with higher Nb content grew into blocks with the liquid precipitation with higher Ti content as the core,while some phases nucleate and grew with sulfides as the core or basal planes;There were many carbonitrides liquid precipitation phase in the center of continuous casting billets,and their sizes were relatively large(up to 35μm),but its quantity and size under the surface were relatively small(below 10μm);After heating and rolling the continuous casting billet at 1200℃,liquid precipitation phase can be partially dissolved,resulting in a decrease in quantity and size,and it will break during the rolling process.