基于结晶器角部快速冷却控制微合金钢连铸坯角横裂纹的应用基础研究

Micro-alloyed steel slabs occurring transverse corner cracks is a common technical problem that limits the steel high quality production. Refining the size of austenite grains and control the precipitation behaviors of carbonitrides and proeutectoid ferrite film in slab surface prior austenite grain boundaries are the key factors to prevent the cracks occurrence. In the present study, on the basis of the intense research on thermal and mechanical behaviors of shell solidification and the austenite grain growth and evolution laws of the shell corner surface in continuous casting mold, a new curved surface taper and cooling structure of mold wide and narrow face corners are designed to prevent the mold flux film and air gap concentrated forming around it and accelerate the copper plate heat transfer. The mold corner fast cooling process that may cause the shell corner generate fine austenite grain is proposed. Based on these, the influence laws of second cooling mode on the precipitation behaviors of carbonitrides and proeutectoid ferrite film in grain boundaries and the grain size growth and evolution laws under the condition of mold corner fast cooling process are syudied. A new technology of control micro-alloyed steel slabs transverse corner cracks is put forward innovatively based on mold corner fast cooling process and the control of the precipitation behaviors of carbonitrides and proeutectoid ferrite film in grain boundaries and the grain size growth and evolution.

微合金钢连铸坯频发角横裂纹是限制其高质与高效化生产的共性技术难题。铸坯角部表层生成细小奥氏体晶粒并全流线控制其晶界碳氮化物和先共析铁素体膜析出行为，是控制微合金钢连铸坯角横裂纹发生的关键。本课题通过深入研究典型微合金钢在结晶器内坯壳凝固热/力学及其角部初凝奥氏体晶粒生长与演变行为，设计可有效抑制坯壳角部保护渣膜与气隙集中分布并加速其冷却的新型结晶器宽、窄面角部曲面锥度与铜板冷却结构，形成可实施微合金钢连铸坯角部初凝奥氏体晶粒细化的结晶器角部快速冷却工艺。在此基础上，自制连铸坯凝固模拟装置，全面开展结晶器角部快速冷却条件下二冷不同冷却行为对微合金钢连铸坯角部凝固全流线表层晶界碳氮化物与先共析铁素体膜析出以及晶粒生长与演变等关键行为的影响规律研究，创新提出基于结晶器角部快速冷却、全流线控制铸坯角部表层晶界碳氮化物与先共析铁素体膜析出和晶粒生长演变行为的微合金钢连铸坯角横裂纹控制技术。

微合金钢广泛应用于石油化工、海洋工程、交通运输等领域，是当前国内外钢铁企业生产的主力产品之一。然而，微合金钢连铸坯生产过程却频发角部裂纹缺陷，已成为限制微合金钢高质与高效化生产亟待解决的共性技术难题。.本项目通过采用数值模拟与检测分析相结合方法，系统了研究微合金钢连铸坯角部裂纹产生机理、微合金碳氮化物析出行为规律、连铸坯在结晶器及二冷高温区凝固热/力学行为，基此开发出了基于内凸型曲面结晶器与铸坯二冷高温区角部晶粒多相变超细化控冷相结合的原创性裂纹控制技术，并成功获得规模化推广应用，结果如下：. (1) 定量化揭示了微合金钢连铸过程结晶器内坯壳动态变形与传热行为规律，探明了限制微合金钢凝固坯壳角部高效传热的关键因素，并基此研制出了高效传热内凸型曲面新型连铸结晶器，实现了微合金钢连铸过程铸坯角部碳氮化物弥散化析出与原奥氏体晶粒细化生长。. (2) 探明了微合金钢凝固过程多相变晶粒超细化与组织结构转变机制，研发出了铸坯角部晶粒超细化控冷新技术，实现铸坯角部皮下20mm范围晶粒超细化至≤20μm，并形成“铁素体+珠光体”高塑性组织结构，从根本上强化铸坯角部抗裂纹能力。. (3) 项目技术先后在鞍钢、宝钢、河钢集团、韩国现代钢铁等国内外10家企业17条产线规模化推广应用，成功消除各应用产线含Nb、V、Al、B等微合金钢铸坯角部及皮下裂纹缺陷，实现铸坯无清理热送轧材平均边部裂纹率≤0.08%的先进指标。. 项目执行过程申请发明专利6项（授权5项），发表各类学术论文11篇，获天津市科技进步二等奖1项、教育部优秀科研成果技术发明二等奖1项、“国际领先”科技成果评价1项，其研究结果对完善微合金钢连铸高温凝固及其高效连铸理论、保障应用企业微合金钢稳定、低成本生产和促进我国高端微合金品种钢高质、高效化生产具有十分重要意义。