枝晶生长抑制因子及其对晶间应力累积耦合影响机制

The slab quality is restricted by many crack defects which was affected by solute segregation, dendrite growth and stress obviously. Therefore, the related research has been widely concerned by researchers. Dendrite growth, controlled and inhibited by multicomponent and multi-field during solidification of thick slab, has very little study. The effect of inhibitory factor on the intergranular strain accumulation and interdendritic crack remains unclear. In this research, the wide thick slab of microalloyed steel was selected as the research objects. Correlation researches should be carried out with the method of thermodynamic simulation and lab experiments under the condition of mold cooling and secondary cooing zone. The main objectives of this study are:1) to establish and improve the solute segregation model under the coupling effect of dendrite growth and precipitation. 2) to explore the influence mechanism of thermodynamics and kinetic of dendrite growth and solid-liquid interface growth, which was affected by dendrite growth inhibitory factor, such as solute segregation and temperature fluctuation.3) to illustrate the couple mechanism between intergranular strain accumulation, interdendritic intensity and interdendritic crack. 4) to clarify the crack formation law of interdendritic crack. The research achievement not only provide a theoretical basis for reveal the mechanism of crack initiation, but supply data for the thermodynamics and kinetic of dendrite growth.

裂纹缺陷制约着铸坯质量的进一步提升，而溶质偏析、枝晶生长及铸坯受力对晶间裂纹形成影响最为显著，相关研究已得到广泛关注，但厚板坯凝固过程中多组分（溶质偏析）、多场(浓度场、温度场)耦合作用下枝晶生长受到的抑制/控制作用研究较少，枝晶生长抑制因子对晶间累积应力和枝晶间裂纹的影响机理尚未明晰。因此本项目以微合金钢宽厚板坯为研究对象，采用理论分析与实验研究相结合的方法，以结晶器冷却及二冷工艺参数为基础，建立并完善铸坯凝固前沿枝晶生长和析出物耦合作用下的溶质偏析模型，探索溶质偏析、温度波动等枝晶抑制因子对凝固前沿固/液界面及枝晶生长热力学和动力学的影响机制，阐释抑制因子对枝晶间累积应力、晶间强度及晶间裂纹的耦合作用，明晰其对枝晶间裂纹的影响规律，研究结果不仅为揭示铸坯启裂机理奠定理论基础，也为完善枝晶生长热力学和动力学理论提供支撑。

铸坯裂纹的形成机理是近年来讨论的热点问题之一，其中钢液溶质元素偏析行为易引起初凝坯壳晶界富集，进而生成低熔点液相薄膜，降低初凝坯壳晶界的高温强度，对连铸坯凝固前沿的裂纹敏感性产生显著性影响，从而引发连铸坯表面和皮下裂纹。本以微合金钢为研究对象，采用Thermo-calc热力学软件对平衡态微观偏析模型（杠杆模型）与非平衡态微观偏析模型（Scheil模型）及修正后的Scheil模型下固相线温度及残留液相中C、N、S、P、Mn、Ti、Nb、V元素偏析程度及析出物进行了模拟研究。结果表明：考虑元素扩散行为对凝固期间元素质量分数变化存在影响规律。凝固末期固相率增大，元素扩散行为使固相线温度升高、残留液相中偏析程度降低。凝固过程析出相主要包括MnS相、AlN相、铁素体相及奥氏体相、富钛相碳氮析出相、富铌相碳氮析出相与碳化钒析出相。利用Procast软件模拟分析了溶质元素含量与切面凝固组织中晶粒数量、晶粒大小与单位长度晶界数的影响规律，通过对凝固过程中热力学计算数据的整理，构建溶质元素凝固过程中偏析行为与二次枝晶臂间距的关系，通过二次枝晶臂间距大小表明凝固前沿凝固组织的影响规律。另外，结合实际工艺，构建了铸坯凝固过程本构关系模型，深入解析了铸坯启裂机制。相关研究结果不仅为揭示铸坯启裂机理奠定理论基础，也为完善枝晶生长热力学和动力学理论提供支撑。