低碳包晶钢板坯连铸过程枝晶生长和相变行为研究

在低碳包晶钢连铸过程中，包晶相变加剧了枝晶间凝固收缩，极易引发枝晶间热裂，影响铸坯质量和成材率。为此，本研究拟采用实验研究和宏微观多尺度数值模拟相结合的手段，研究低碳包晶钢板坯连铸过程的枝晶生长和相变行为，揭示枝晶间热裂机理。首先，采用高温激光扫描共聚焦显微镜原位观察实验和FactSage热力学计算软件分别研究低碳包晶钢凝固过程相变动力学和热力学。然后，在此基础上，开发多相/多组元枝晶生长数学模型，并耦合宏观凝固传热模型，研究低碳包晶钢板坯连铸过程的形核、枝晶生长、包晶相变和溶质扩散现象，考察冷却速率和钢种成分对低碳包晶钢凝固相界面演变速率、晶间溶质偏析、凝固收缩和凝固组织的影响规律。最后，揭示枝晶生长规律和相变机理，并根据RDG热裂准则建立凝固组织与热裂敏感性之间的定量关系，为控制低碳包晶钢连铸坯热裂提供理论指导。

The peritectic reaction, occurring during the continuous casting of low carbon peritectic steels, could cause a significant solidification shrinkage, which can result in interdendritic hot cracking and deterioration of strand quality. In present study, experiments and multi-scale numerical simulations are all carried out to investigate the dendritic growth and peritectic phase transformation in order to fundamentally reveal the interdendritic hot cracking mechanism. The main studies are listed as follows: Firstly, in situ experimental observations are performed to investigate the kinetics of peritectic reaction and transformation of low carbon peritectic steels using a high temperature laser scanning confocal microscopy (HTLSCM). Secondly, thermodynamic calculations are carried out to investigate the effects of multi-component interactions on the phase equilibrium and solute diffusion coefficient during the solidification of low carbon peritectic steels using the commercial software FactSage. Last but not the least, based on the kinetics and thermodynamics study, a multi-phase/multi-component dendritic growth model will be proposed, and coupled with macro heat transfer and solidification model to investigate the nucleation, dendritic growth, peritectic reaction and transformation, interdendritic solute diffusion, and the effects of the cooling rate and chemical compositions on the phase interface velocity (L/δ，δ/γ and L/γ), solute microsegregtion, solidification shrinkage and characteristic parameters of dendrites (primary dendrite arm spacing λ1, secondary dendrite arm spacing λ2) during the slab continuous casting of low carbon peritectic steels. Based on the above mentioned studies, the dendritic growth patterns and phase transformation mechanism during the slab continuous casting of low carbon peritectic steels are finally revealed, and according to the RDG hot cracking criterion, a quantitative relationship between solidification structure and hot cracking susceptibility is determined to provide theoretical guidance for preventing the interdendritic hot cracking during the slab continuous casting of low carbon peritectic steels.