超高强耐磨钢NM500多层多道对接接头残余应力的研究

Study on Residual Stress of Multi-layer and Multi-pass Butt-welded Joint for Ultra-high Strength Wear-resistant Steel NM500

基于SYSWELD软件平台,以新型NM500钢的多层多道对接接头为研究对象,开发一种考虑固态相变的“热-冶金-力学”耦合计算方法来模拟对接接头的温度场、组织体积百分数以及焊接残余应力。同时,采用光学显微镜观察对接接头的显微组织,采用显微硬度计测量接头硬度分布,以及采用小孔法测量对接接头表面残余应力。数值模拟结果与试验测量结果的比较表明:使用实际焊接热输入模拟得到的对接接头超过冶金熔点以上的温度区域与实际焊接接头熔化区吻合较好;纵向残余应力峰值位于紧邻热影响区的母材上,其值约为1600 MPa,与母材的常温屈服极限相当;横向残余应力在焊缝厚度方向呈现“拉-压-拉”的分布形态。总体而言,数值模拟得到纵向及横向残余应力的大小及分布与试验测量结果吻合较好,验证了“热-冶金-力学”耦合计算方法的有效性。基于数值模拟结果,探讨了NM500钢多层多道对接接头焊接残余应力的形成机理。

Based on SYSWELD software,a“thermo-metallurgical-mechanical”coupling computational approach with consideration of solid-state phase transformation is established to simulate temperature field,fraction of phase and welding residual stress in a multi-layer and multi-pass butt-welded joint of wear-resistant NM500 steel.Meanwhile,microstructure,hardness and surface residual stress distribution of the joint were observed by optical microscope,measured by micro-hardness tester and by hole-drilling method,respectively,and the measured data are compared with the corresponding simulation results.The results show that the simulated melting zone above the melting point of the NM500 steel butt-welded joint is in a good agreement with the actual melting zone,and this proves that the numerical simulation method reproduced the actual welding heat input for the butt-welded joint.For NM500 steel butt-welded joint,the peak value of longitudinal residual stress located the base metal adjacent to the heat-affected zone,and its value is about 1600 MPa,which is similar to the yield strength of base metal at room temperature.The transverse residual stress distributed in the thickness direction in the shape of“tension-compression–tension”.In general,the magnitude and distribution of longitudinal and transverse residual stresses obtained by numerical simulation are in good agreement with the experimental measurements,which verified the effectiveness of the“thermo-metallurgical-mechanical”coupling computational method.Based on the numerical simulation results,the formation mechanism of welding residual stress in NM500 steel multi-layer multi-pass butt-welded joint is also investigated.