包晶微合金钢连铸坯表层原奥氏体晶粒生长行为及高塑化控制研究

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.

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。

包晶微合金钢连铸坯表层凝固生成粗大奥氏体晶粒，致使铸坯表面（特别是角部）频发裂纹缺陷，已成为该类钢连铸生产的共性技术难题。本项目通过数值模拟仿真手段，研究了板坯结晶器内凝固坯壳动态热/力学行为演变规律，并基此自制快速定向凝固装置，研究了包晶钢凝固过程粗大柱状奥氏体生长行为，以及在不同Ti含量和Nb-Ti复合作用下，包晶钢凝固过程碳氮化物析出和奥氏体晶粒生长行为、以及Ti与Nb-Ti复合细化粗大柱状奥氏体晶粒的作用机制。在此基础上，采用Gleeble热模拟检测，定量探究了Ti处理含铌微合金钢循环相变晶粒细化关键控冷参数，开发形成了Ti处理与铸坯二冷高温区角部组织循环相变晶粒细化协同控制新工艺及其控冷新结构，并在宝钢梅钢、天津钢铁、唐钢中厚板以及攀钢等企业应用，为包晶微合金钢连铸坯表面无缺陷连铸生产奠定了坚实的理论与应用基础。项目执行过程相关创新理论与结果在MMTA、MMTB等冶金行业顶刊与学术会议上发表学术论文22篇，其中SCI检索9篇、EI检索2篇，2篇论文分别入选年度优秀论文和中国精品科技期刊顶尖学术论文—领跑者5000，并在国内外学术会议上做开幕式大会报告、特邀报告、主题报告、以及分会场报告9次。授权发明专利7项，获省部级科技奖励3项（其中2项一等奖），出版学术专著1部（国家出版基金资助，冶金工业出版社，校稿中），已培养硕士与博士生各1名。

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