随着微合金钢技术的进步，对铸坯裂纹的控制迫切需要突破传统“躲避”脆性区的温控策略，寻求改善高温塑性的根本性解决方案。控制第二相颗粒由晶界析出转为晶内弥散析出有助于从根源上消除铸坯裂纹缺陷。本课题借鉴国内外研究成果，系统将界面自由能理论引入第二相形核-长大过程研究，深入剖析促使第二相颗粒晶内形核及尺寸演变的影响要素，从而实现钢中第二相颗粒的灵活控制。主要研究内容包括：凝固过程中第二相粒子析出热力学研究，Mg处理对第二相颗粒的改性及定量表征，第二相粒子长大过程的原位观察与数学解析，高温塑性的协同调控与试验验证。本研究旨在确定有利于促进第二相粒子晶内形核和晶粒细化的微细夹杂类型与成分区间以及抑制粒子过度长大的冷却制度，揭示钢中微细夹杂诱导第二相粒子晶内弥散形核的界面参数和作用机制，为第二相弥散化析出指明方向。Mg处理对第二相粒子和凝固组织的双重控制可为抑制铸坯裂纹提供新的解决思路。

With the rapid development of micro-alloyed steel production technology, the study of surface transverse crack is urgent need for breaking through the conventional control method and searching fundamental solution to improve hot ductility. The precipitation location of secondary phase particles transferred from grain boundary into matrix is contributed to inhibition of crack. With references of the pertinent research results, this present project puts forward using the theory of interface free energy to study nucleation and growth of secondary phase particles. After some factors of size evolution of secondary phase particles are obtained, they can be used to achieve the aim control of particles. The main research contents are follows. (1) thermodynamics of precipitation of secondary phase particles; (2) quantitative characterization of secondary phase particles by Mg treatment; (3) in-situ observation and mathematical analysis of size evolution of particles; (4) synergistic control and verification for hot ductility. This study is to found the inclusion type and suitable cooling rate in favor of enhancing precipitation in matrix, also it can be used to reveal the interface parameters and reaction mechanism between inclusion particles and secondary phase, which can give us more directions for the study of dispersed precipitation. The research results not only perfect the control theory of precipitation, but also supply newer thinking for inhibition of surface transverse crack.