易切削非调质钢凝固过程及钢中MnS析出规律

Solidification process and sulfide precipitation behavior in free-cutting non-quenched and tempered steel

利用Thermo-Calc热力学软件计算研究YF45MnV钢中MnS的平衡析出规律及凝固过程中各元素的偏析行为对MnS析出的影响。结果表明:MnS平衡初始析出温度为1421℃,初始析出温度随C、Si、Al含量增加而降低,随Mn、S含量增加而升高;Scheil凝固过程中,计算得到Mn、S的平衡分配系数分别为0.70、0.02,二者随着凝固过程进行在剩余液相中不断偏析富集,达到平衡浓度积后析出MnS。真空感应炉冶炼不同S含量(0.025%~0.065%)的实验钢,发现钢中硫化物主要为大量细小II类MnS+少量尺寸较大的III类MnS。随S含量的提高,大尺寸MnS数量增加,沿晶界偏聚分布的情况更为严重。

Phase diagram and sulfide precipitation behavior of YF45MnV steel were investigated by simulation using Thermo-Calc thermodynamic software combined with the related TCFE6 database,and the effects of segregation of C,Si,Al,Mn and S on sulfide precipitation in the steel were studied.The Scheil-Gulliver solidification model was implemented to predict the solidification mode and the segregation behavior of various elements in the solidification process.The results show that the initial precipitation temperature of MnS decreases with increasing of C,Si,Al content and decreasing of Mn and S content.The calculated equilibrium distribution coefficients of Mn and S are 0.70 and 0.02,respectively.With the concentration of Mn and S enriched in remaining liquid,MnS precipitates at the end of solidification process.Also,the increase in S concentration would obviously enlarge the precipitated MnS,which distributes along the grain boundaries.