针对已有板形瓢曲浪形缺陷冷轧高强钢板的淬火过程,应用ABAQUS有限元分析平台及其UMAT二次开发功能,建立淬火过程温度-组织-应力应变多场耦合的有限元仿真模型,研究淬火过程高强钢板的弹塑性变形行为及其对初始板形瓢曲缺陷的改变。通过热模拟实验结果对该有限元仿真模型进行了验证,模拟再现了已瓢曲高强钢板的淬火过程及弹塑性变形,获得了板形瓢曲浪形在淬火过程中的演变规律,指出钢板宽度方向上的温度梯度以及依先后顺序相变所引起的钢板纵向延伸变形沿宽度方向上分布不均匀,导致原有板形瓢曲浪形发生改变,甚至可以生成新的瓢曲浪形。定义了描述板形瓢曲浪形改变程度的指标,如浪高变化率、浪宽变化率、浪距变化率,定量揭示横向温差、张力等工艺参数对冷轧高强钢板淬火过程板形变化的影响规律。搭建实验室冷轧钢板淬火实验研究系统,开展具有单边浪板形瓢曲缺陷钢板的淬火实验,实验结果与仿真计算结果取得定性一致。
Quenching is a key process in cold-rolled high strength steel manufacturing for the improvement of the material strength and plasticity. The quenching, however, may bring initial flatness defects of the steel strips, which causes problems for subsequent production process. It is thus necessary to study the flatness defects evolution during the quenching process. Using the secondary development of ABAQUS subroutine UMAT, this work establishes a temperature-microstructure-stress coupling finite element modeling (FEM) model to simulate the quenching process of the high strength steel with initial buckling defects. Thermal simulation experiments are further conducted to verify the present FEM model. Then, the elastic-plastic deformation behavior of the steel plates and its effects on flatness buckling during the quenching process is investigated using the FEM model. As a consequence, the buckling defect evolution mechanism in heat treatment process is obtained for the cold-rolled high strength steel. The flatness change or the forming of new flatness defect is mainly caused by the longitudinal extension arising from temperature gradient and the sequential phase transformation different in width and transverse directions. Change rates of the wave height, width, and length are used to describe the flatness change degree, quantifying the influence of the tension and initial transverse temperature difference on flatness change. The simulation shows that the tension has a positive correlation with the improvement of initial bucking defects. The initial edge waves become more severe after quenching along with the appearance of the new quarter waves, when the initial temperature of strip center is higher than that of the edge. On the contrary, the initial central waves become more serious when the initial temperature of strip center is lower. Meanwhile, joint impact of the tension and the initial transverse temperature difference on wave height is revealed for the application of industrial practice. Furthermore, quenching experiments of the high strength steel plates with initial single edge wave buckling defects are carried out using the experiment system in lab. Different sides of the plates quench into the water tank to reproduce the sequence of the phase change. The simulation and experiments produce consistent results qualitatively. This work makes connections between technological parameters and flatness change during quenching process, which can provide support to industrial heat treatment of high strength steel.
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