M2钢连铸冷却条件对裂纹萌生及扩展的影响

Influence of M2 Steel Continuous Casting Cooling Conditions on Initiation and Propagation of Crack

通过扩展有限元法(XFEM),基于Power准则判断裂纹萌生。根据线弹性断裂力学模型描述其扩展方式,采用热力顺序耦合的方式建立圆坯连铸凝固和二冷过程裂纹萌生和扩展数值模型。通过改变冷却条件,优化了连铸冷却参数。结果表明,连铸过程中圆坯表面的热流密度较高,表面径向温度梯度较内部大,造成表面应力集中,形成拉应力裂纹。在二冷区间的第1段,冷却到122 s时距离表面3 mm周向位置处拉应力最大,容易萌生裂纹;裂纹在后续冷却条件下扩展至22 mm长,裂纹末端发展到0.3 mm宽。在裂纹尖端拉应力较大侧,裂纹优先扩展。降低结晶器及二冷各段的换热系数,可降低其拉应力水平,从而消除裂纹的发生。

The extended finite element method （XFEM） was used, and the crack initiation was judged based on Power criterion. The extension mode was described according to the model of linear elastic fracture mechanics, and the crack initiation and propagation models of round billet during the continuous casting solidification and secondary cooling process were built by thermal mechanical sequential coupling method. The cooling parameters of continuous casting were optimized by changing cooling conditions. The results show that the heat flux on surface of round billet is higher, and the radial temperature gradient is bigger than that of internals, which causes concentration of surface stress and the formation of tensile stress crack. In the first section of the secondary cooling zone, when cooling to 122 s, the tensile stress is the largest in circumferential position of 3 mm distance from the surface, and it is easy to initiate crack. The length of crack extends to 22 mm under the subsequent cooling conditions, and the width of crackend extends to 0.3 mm. On the large side of crack tip, the crack propagates firstly. Reducing the heat transfer coefficient of crystallizer and secondary cooling zone can reduce the tensile stress level and eliminate the initiation of crack.