大断面连铸圆坯中心裂纹的成因和控制研究

Research on causes and control of central cracks in large section continuous casting round billets

针对某钢厂Φ600 mm AISI4130钢连铸大圆坯存在的中心裂纹,通过低倍观测到裂纹分布在V型偏析区内,采用原位分析发现中心主要为碳、硫偏析,采用扫描电镜观察裂纹形貌发现裂纹为凝固前沿卵形树枝晶开裂形成的空隙,分析裂纹成因是凝固末期低熔点元素富集芯部,同时凝固收缩使铸坯中心产生较大的拉应力使卵形树枝晶开裂。运用ANSYS软件建立大圆坯传热和应力模型,计算铸坯的温度场和应力场,模拟计算结果表明,凝固末端铸坯中心拉应力超出抗拉强度。提出在凝固末端施加强制冷却工艺,通过模拟计算验证了末端强冷可加速铸坯外部向中心收缩,抑制铸坯中心凝固收缩产生较大的拉应力,有效降低大断面圆坯中心裂纹的产生风险和概率。

In view of the central cracks in the Φ600 mm AISI4130 steel continuous casting round billet of a steel plant, in-situ analysis found that elemens C and S segregation existed in the center of the round billet. The morphology of the crack was observed by scanning electron microscope and it was found that the crack formed at the end of solidification, and the cause was the low melting point elements were enriched in the core at the end of solidification The solidification shrinkage of the cast billet causes a large tensile stress in the center. The heat transfer and stress model of the round billet was established using ANSYS software, and the temperature field and stress field of the billet were calculated. The simulation results showed that the central tensile stress of the billet at the solidification end exceeded the tensile strength. A process of applying forced cooling at the end of solidification is proposed. It is verified by simulation calculation that the process of forced cooling at the end can accelerate the shrinkage of the round billet from the outside to the center, inhibit the solidification and shrinkage of the center of the round billet from generating large tensile stress, and effectively reduce the risk of center cracks and probability.