304不锈钢管TIG焊接头凝固行为及热力耦合研究

目的 对2mm厚不锈钢管的焊接工艺参数进行优化，并基于模拟仿真软件对接头的热应力场进行模拟，以解决薄壁管件接头应力测试不方便的问题。方法 以TIG焊对2 mm不锈钢管进行焊接，通过对接头宏观形貌、微观组织、显微硬度等结果进行优化进而得到最佳焊接工艺参数，采用双椭球热源和温度-位移耦合方法结合最优工艺参数进行数值模拟。结果 当焊接电流为150 A、焊接速度为66 cm/min时，焊接接头全部熔透，且正面及背面焊道均匀致密，成形良好。焊缝中心上部区域和下部区域均呈现等轴晶形貌，下部区域尺寸较上部区域尺寸略大，熔合线附近为柱状晶组织。焊接接头显微硬度整体分布呈现U形，其中热影响区显微硬度（197HV）大于焊缝区域硬度（162HV），熔合线附近显微硬度达到最低值（145HV）。模拟结果显示，在焊接过程中，当纵向残余应力从母材向焊缝中心过渡时，由压应力逐步转化为拉应力；焊缝中心横向应力呈现为压应力，向两侧母材过渡时应力值逐渐趋近于0，径向应力值变化幅度较小，模拟数据变化趋势与实测数据变化趋势接近。

Solidification Behavior and Thermodynamic Coupling of TIG Welded Joint of 304 Stainless Steel Pipe

The work aims to optimize the welding parameters of 2 mm thick 304 stainless steel pipe and simulate the thermal stress field of the joint based on simulation software to solve the problem of inconvenient stress testing for thin-walled pipe joints. The 2 mm thick stainless steel pipe was welded by TIG technology, and the optimal welding parameters were obtained by optimizing the macro morphology, microstructure and microhardness of the joint. The numerical simulation was carried out by using double ellipsoid heat source and temperature-displacement coupling method combined with the optimal parameters. When the welding current was 150 A and the welding speed was 66 cm/min, the welded joint was completely penetrated and the front and back weld passes were uniform and dense, which was well formed. The upper and lower regions of the weld zone exhibited equiaxed crystal morphology, while the size of the lower region was slightly larger than that of the upper region. The columnar crystal structure appeared near the fusion line. The overall trend of the microhardness of the welded joint presented a "U" shape, in which the microhardness of the head-affected zone (197HV) was larger than that of the weld zone (162HV), and the microhardness near the fusion line was the lowest (145HV). The simulation results showed that the longitudinal residual stress gradually transformed from compressive stress to tensile stress when transitioning from the base metal to the center of the weld seam. The transverse stress at the center of the weld seam bore compressive stress, and the stress value gradually approached 0 when transitioning to the base metal on both sides. The radial stress value in the thickness direction of the weld seam changed slightly, and the changing trend of simulated data was close to that of the measured data.