Study of the solute micro-segregation behaviour of bainite rail steel in the continuous casting process

A coupled model of micro-segregation and macro-heat transfer was established to study the solute microsegregation behaviour of bainite rail steel in the continuous casting process. The effects of solute elements, effective cooling rate of the mushy zone (Ceff), and MnS precipitation on the solute micro-segregation and characteristic solidification temperatures were analysed. The results show that Ceff gradually decreases from the surface of the bloom to the centre as the solidification of the molten steel progresses, and the maximum effective cooling rate is in the corner of the bloom. During the solidification of bainite rail steel, the micro-segregation degree of P and S is more serious, followed by C, Si, Mo, etc. At the later stage of solidification, the precipitation of MnS leads to a decrease in the micro-segregation degree of S and Mn. Carbon mainly affects the solute micro-segregation behaviour by changing the solidification mode of molten steel, while the initial S and Mn contents in molten steel have no obvious effect on the micro-segregation degree of C, Si, Cr, Ni, Mo, and P. Ceff has different effects on the micro-segregation behaviors of different solute elements. An increase in C, Mn, and S content and in Ceff will advance the MnS precipitation time and lead to an increase in the amount of MnS precipitation. Increasing the initial C, Mn, and S content in molten steel leads to a decrease in both ZST and ZDT.