包晶微合金钢连铸坯表层凝固生成粗大原奥氏体晶粒，致使铸坯尤其是角部频发裂纹缺陷，已成为该类钢连铸生产的共性技术难题。因此，探明包晶微合金钢连铸坯表层粗大原奥氏体晶粒形成机理，并实施高塑化控制具有重要意义。本项目通过深入研究包晶微合金钢连铸结晶器内包晶相变过程初生相细晶及多γ细晶聚合原奥氏体生长行为规律，特别是Ti处理包晶微合金钢凝固过程Ti及其析出物析出行为对初生相细晶以及原奥氏体晶粒生长细化作用规律，全面探明包晶微合金钢连铸坯表层粗大原奥氏体晶粒形成机理与Ti处理原奥氏体晶粒细化作用机制。在此基础上，探究多相变控冷与Ti、Nb等微合金碳氮化物析出行为协同作用下的连铸坯表层奥氏体晶粒相变细化与组织结构转变机制，并开展工业应用实验研究，为开发与应用包晶微合金钢连铸坯角部裂纹控制新技术奠定理论与应用基础。

The slab surface of peritectic micro-alloyed steel forms coarse prior austenite grains during solidification would result in the slab occur cracks especially for corners, which has become one of the common problems for continuously casting the steel. It is significant to study the coarse prior austenite grains formation mechanism and improve the surface hot ductility in the casting strand. In the present study, the growth behaviors of primary fine columnar grains and austenite grains aggregated from multi-γ fine columnar grains during peritectic phase transformation in continuous casting mold will be studied, and the action laws of Ti and its precipitation on the primary fine columnar grains microscopic solidification and the refinement mechanism of prior austenite grains will be systematically investigated especially. Accordingly, the formation mechanism of coarse prior austenite grains at slab surface and the mechanism of grain refinement by using Ti treatment will be comprehensively revealed. On the basis of this, the behaviors of grains restructuring refinement and microstructure transformation of austenite grains at slab surface will be further studied by coupling the effects of cooling condition of multi-phase transformation and the precipitation of the carbides and nitrides of micro-alloys (e.g. Ti and Nb) at high temperature. The industrial trials will also be carried out correspondingly. The theory and application foundation would be laid for the new technology development and application of peritectic micro-alloyed steel slab corner cracks control.