连铸坯纵裂诱导机制及其数值模拟和热态模拟

The longitudinal cracks frequently occur on the surface of the slab in continuous casting process. It is generally accepted that the formation of the cracks is due to the stress concentration on the thin solidified shell. When the tension of stress exceeds the tensile strength of primary dendritic interfaces, the fine cracks may appear on the slab surface in the mold and expand in the secondary cooling zone, which finally leads to the formation of the longitudinal cracks. However, the above induction mechanism lacks a quantitative numerical criterion. Very little information is available to quantitatively analyze the effect of these factors such as steel grade, the temperature, the stress on the formation of the longitudinal surface cracks. In the present study, the numerical simulation and the hot-state simulation are used to investigate the induced mechanism of longitudinal cracks. Firstly, the high-temperature mechanical properties database for the cracking sensitive steel grades is established by the experimational test and theoretical deduction. Combined with the experimental data, a 3D thermo-machnical model based on the constitutive theory of viscoelastic-plasticity considering the solid phase, liquid phase and fuzzy zone of the steel are developed to clarify the formation mechanish of longitudinal cracks. Furthermore, the independent developed "linear shrinkage-thermal stress" coupled instruments are used to perform the hot-state testing to simulate the solidification process and to represent the deformation of the slab in the different temperature range and track the thermal-mechanical history which can lead to the occurrence of the cracks. The obtained results together with the data from the soft reduction industrial test are used to verify the accuracy of the mathematical model. Finally after the verification, the numerical model is used to obtain the quantitative criterion of the occurrence of the longitudinal surface cracks under different operating conditions by simulating the thermal-mechanical history of the cast slab in the high-temperature, middle-temperature and low-temperature brittleness zone.

厚板坯连铸生产中常出现纵裂缺陷，原因是坯壳应力集中，坯壳中心薄的地方受到拉应力超过一次晶界的抗拉强度，先在结晶器内部形成微小裂缝，进入二冷区后扩展成纵裂纹。但该机制缺少定量判据，也缺乏钢种、温度、应力等要素诱导裂纹的机制分析。本申请拟用数值模拟和热态模拟相结合的方法研究纵裂诱导机制。主要工作包括：⑴通过实验测量及理论推导建立裂纹敏感钢种的高温力学性能资料库；⑵开发涉及固、液、两相区三态的基于黏弹塑性本构的三维热力耦合数值模型、板坯纵裂诱导数值模型；⑶利用自主研制的"线收缩-热应力联测仪"来热态模拟钢从液态开始凝固的过程，再现铸坯在不同温度范围受力产生变形，进而出现纵裂的热-力历程，获得临界数据，并与轻压下试验结合验证数值模型的准确性及精度。⑷数值仿真典型钢种在连铸机历经的过程，得到铸坯在高温、中温、低温脆性区，在不同外力的诱导下产生纵裂的临界判据，完善纵裂机制的定量认识,避免纵裂产生。

当前人们对连铸坯裂纹发生机制多为定性认识，尚缺乏有效的定量判据。本基金在裂纹敏感钢种高温物性参数数据库建立的基础上，依托Marc商业软件开发了涉及固、液、两相区三态的基于黏弹塑性本构方程的热力耦合数值仿真模型，用于定量分析连铸坯凝固过程不同温度范围的热-力行为，再现铸坯在连铸机内的温度场与应力场；利用“线收缩-热应力联测仪”定量测试微合金钢在凝固过程的热应力数值，获得裂纹产生的临界判据，为揭示裂纹的产生，特别是纵裂纹的产生原因，提供一种定量的分析方法。.本基金目前已建立了八个以上钢种的高温物性参数数据库，涉及的材料物性参数包括：比热、潜热、密度、导热系数、液相线温度、固相线温度、T80温度、弹性模量、泊松比、塑性模量、极限强度、极限应变等；基于开发的微合金钢的热-力耦合数值仿真模型，以宝钢的双相不锈钢为应用例开展计算，研究铸坯裂纹产生的时机、产生的部位、临界应力的数值，研究成果《Thermomechanical analysis of triangular zone cracks in vertical continuous casting slabs based on viscoelastic-plastic mode》发表在SCI期刊J. Iron Steel Res. Int.；利用线收缩-热应力联测仪，原位测量了J55、X60、30BF等微合金钢凝固过程热应力值与线收缩值，研究结论撰写论文；通过材料高温物性参数、数值仿真模拟、凝固过程热应力的测量，获得了一种预测微合金钢裂纹发生的临界判据，以及裂纹发生工况的计算测试方法，研究成果在宝钢股份、新余钢铁公司等的生产实践中得到应用。.本基金在四年研究期限内，共在：ISIJ Int.、J. Iron Steel Res. Int.、Metall. Res. Technol.、J Alloy Compd.、RSC Adv.、High Temp. Mater. Pr-ISR.等国际期刊发表SCI论文15篇，在《钢铁》、《上海金属》等中文核心期刊发表论文5篇，在TMS、ICMEA等国际会议发表ISTP收录论文7篇，总计27篇论文，其中，第一标注9篇、第二标注11篇、第三标注7篇，申报专利9项、软件著作权2项，并培养博士后2人、博士生4人、硕士生15人。