Precipitation and growth behaviors of MnS inclusions during the solidification of non-quenched and tempered steel have been experimentally and thermodynamically investigated. Effects of cooling method and cooling rate on the morphologies, size distributions, number densities, and average diameters of MnS inclusions in steels were systematically revealed. Coupled with thermodynamic calculation of MnS precipitation, two solute element micro-segregation models, Clyne–Kurz model and Ohnaka model, were introduced and improved by taking the micro-segregations of silicon, oxygen, and other solute elements into account during the steel solidification. The MnS inclusion growth was estimated according to the model calculation results. A non-linear fitting curve equation for describing the relationship between cooling rate of molten steel v and average inclusion diameter d was acquired by experiments: d = 10.726v^−0.438. At the cooling rate of R_c = 1.26 K s⁻¹, the solidification fraction values for MnS precipitation in the two models were 0.929 and 0.931, respectively. Precipitation and growth of the MnS inclusions during solidification were well predicted by the improved Clyne–Kurz and Ohnaka solute element micro-segregation models by comparison of experimental and calculated results. Both the two models were validated and could be judged as equal in this work.

通过实验和热力学研究了非调质钢凝固过程中 MnS 夹杂物的析出和生长行为。系统地揭示了冷却方法和冷却速率对钢中 MnS 夹杂物的形貌、尺寸分布、数量密度和平均直径的影响。结合MnS析出的热力学计算，引入并改进了两种溶质元素微偏析模型，Clyne-Kurz模型和Ohnaka模型，考虑了钢凝固过程中硅、氧等溶质元素的微观偏析。根据模型计算结果估算MnS夹杂物的增长。描述钢水冷却速率关系的非线性拟合曲线方程v和平均夹杂物直径d通过实验得到：d  = 10.726 v ^-0.438。在R _c  = 1.26 K s ^-1的冷却速率下，两种模型中 MnS 沉淀的凝固分数分别为 0.929 和 0.931。通过比较实验和计算结果，改进的 Clyne-Kurz 和 Ohnaka 溶质元素微偏析模型很好地预测了凝固过程中 MnS 夹杂物的析出和生长。这两个模型都经过验证，在这项工作中可以判断为相等。