齿轮钢连铸坯凝固组织与溶质分布均匀性

Evenness of solidification structure and solute distribution in the continuous casting billet of gear stee

分析了20CrMnTi齿轮钢200 mm×200 mm连铸坯凝固组织和溶质分布的均匀性,提出了不同过热度时粗大等轴晶和点状偏析的共生机理,制定了齿轮钢连铸均质性控制策略。结果表明,齿轮钢连铸坯凝固组织受到钢水过热度的直接影响,提高过热度会减小等轴晶面积,降低对中性,减小等轴晶尺寸;齿轮钢连铸坯凝固组织直接影响C元素中心偏析和断面分布均匀性,提高等轴晶率有利于降低中心偏析,但会增大等轴晶区溶质波动范围;齿轮钢连铸坯凝固组织直接影响半宏观尺度的点状偏析,提高等轴晶率会增加大尺寸点状偏析数量,Cr、Mn溶质偏聚程度也会增加。为了同时提高齿轮钢组织和成分均匀性,比较理想的连铸低倍结构特征是等轴晶率低、等轴晶尺寸小而均匀、对中性良好。

The evenness of solidification structure and solute distribution in the continuous casting billet of 20CrMnTi gear steel was experimentally investigated,and the symbiotic relationship and formation mechanism of coarse equiaxed dendrites and spot segregation were proposed.The control strategy on the homogeneity of continuous casting bloom for gear steel was developed.The results indicate that the solidification structure of the bloom is closely affected by superheat during casting.As the superheat increases,the ratio of equiaxed area decreases,the sizes of the equiaxed dendrites reduce,and the alignment of center equiaxed zone worsens.The central segregation and solute distribution evenness are related to solidification structure.The central segregation ratio decreases with the increase in equiaxed ratio,while the solute fluctuation range increases.In addition,the spot segregation is also relevant to the solidification structure.The number of large size spot segregation increases,and the concentration of Cr and Mn in the spot segregation increases,as the equiaxed ratio increases.In order to improve the evenness of microstructure and composition in gear steel,the target solidification structure of continuous casting bloom should possess low equiaxed ratio,small and uniform equiaxed dendrites,and good alignment of equiaxed zones.