【摘要】 微观组织与晶粒尺寸控制对连铸坯乃至最终产品的性能与质量有重要影响，掌握不同连铸冷却条件下微观组织相变规律和奥氏体晶粒生长规律对超高强热成形钢铸坯质量与性能控制具有重要意义。采用高温共聚焦显微镜原位观察的方法，模拟研究了22MnB5钢在不同连铸冷却条件下的微观组织相变规律、相界迁移速率和奥氏体晶粒生长行为，探讨了冷却强度对其组织相变和奥氏体晶粒生长的影响。结果表明，22MnB5钢凝固相变属于过包晶相变，连铸冷速不会影响其凝固相变序列(L→L+δ→L+δ+γ→L+γ→γ);在高冷速连铸固态相变过程中，铁素体从奥氏体晶界析出的温度更低；在高冷速凝固条件下，铸坯相变特征温度和晶粒尺寸都比低冷速过程的小，且相界迁移速率更快，为低冷速凝固条件的3.8倍以上，但相界迁移距离小；在奥氏体生长过程中，奥氏体的晶粒尺寸随着温度的降低而不断增长，其增长速率随着温度下降而减小；低冷速条件下奥氏体晶粒尺寸更大且不均匀。研究结果为超高强热成形钢连铸过程铸坯质量与性能控制提供了理论依据。更多还原

【Abstract】 The control of microstructure and grain size has an important effect on the performance and quality of continuous casting slabs and even the final product. It is important to grasp the microstructural phase transition and austenite grain growth principle at different cooling rates for continuous casting for quality and performance control of ultra-high-strength hot-formed steel slabs. The microstructural phase transition, grain boundary mobility and austenite grain growth behavior of 22MnB5 steel under different continuous casting cooling conditions were simulated using in situ observations with high-temperature confocal microscopy. The effects of cooling intensity on microstructure phase transformation and austenite grain growth were discussed. The results show that the solidification phase transformation of 22MnB5 steel belongs to peritectic phase transformation, and the sequence of solidification phase transformation of 22MnB5 steel is L→L+δ→L+δ+γ→L+γ→γ. The temperature at which ferrite precipitates from the austenite boundary is lower during the solid phase transition of high cooling rate continuous casting. Under the condition of high cooling rate solidification, the characteristic temperature and grain size of the casting slabs are smaller than that of the low cooling rate process, and the migration rate of grain boundary is faster, which is more than 3.8 times faster than that of the low cooling rate, but the migration distance of grain boundary is smaller. During austenite growth, the grain size of austenite increases with decreasing temperature and the growth rate decreases with decreasing temperature. At low cooling rate, austenite grain sizes are large and inhomogeneous. The research results provide a theoretical basis for the quality and performance control of casting slabs in the continuous casting process of ultra-high strength hot-formed steel.更多还原