Thermodynamic study on the solute partition coefficients on L/δ and L/δ plus γ phase interfaces for 1215 high-sulfur steel solidification by orthogonal design

The solute partition coefficient (k(i)), characterizing the solute redistribution on the solid-liquid interface, is an important parameter for the study of segregation. Based on thermodynamic equilibrium, the effects of composition fluctuation, phase transition, MnS precipitation, and temperature on the k(i) for the solidification of 1215 high-sulfur steel were investigated by orthogonal design. The results show that there is only L ->delta phase transition for 0.05-0.07 wt% C steel solidification, while there are L ->delta and L+delta ->gamma (peritectic reaction) phase transition in turn for the solidification of steel with 0.07-0.09 wt% C. On the L/delta interface, as the temperature decreases, the k(si) and k(p) increase, the km, decreases, while the k(c) and k(S) both decrease first and then increase because of MnS precipitation. In the L-delta-gamma coexistent phase, the k(i)(L/delta+gamma )is comprehensively determined by k(i)(L/delta) and k(i)(L/gamma). Moreover, the k(i)(L/delta+gamma) for each solute is closer to the k(i)(L/delta) comparing to k(i)(L/gamma), because the mass fraction of gamma Segregation phase (m(gamma)) in the solidified phase (consisting of delta+gamma) is relatively small. The peritectic reaction has small effect on the k(i)(L/delta) and k(i)(L/gamma), but has significant effect on the m(gamma), leading to the discrepancy in k(i)(L/delta+gamma )for the steels with different C contents. The orthogonal analysis indicates that the composition fluctuation in 1215 steel has small effect on the k(i). The Mn and S contents have the greatest effect, followed by C content. Si and P contents have the least effect. The quantitative k(i) in terms of temperature, phase composition, and solute content were fitted. (C) 2019 The Authors. Published by Elsevier B.V.