Evenness of solidification structure and solute distribution in the continuous casting billet of gear steel
The evenness of solidification structure and solute distribution in the continuous casting bil-let of 20CrMnTi gear steel was experimentally investigated,and the symbiotic relationship and forma-tion 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 super-heat 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 even-ness 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 align-ment of equiaxed zones.
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