K-TIG焊接中厚板的工艺窗口改进

针对穿孔深熔氩弧焊(K-TIG)工艺焊接8 mm厚Q235低碳钢板时焊接过程不稳定、焊接工艺窗口小等突出问题，首次提出在焊接工件背部铺加保护焊剂的方法改善焊接过程。采用对接焊的方式，在不开坡口、焊接过程不添加焊丝的情况下，达到单面焊双面成形的效果。最终成功的采用430～480 A范围内的直流电流对8 mm厚的Q235低碳钢进行了焊接，将焊接电流窗口扩大到50 A同时也显著的提高了焊接过程的稳定性。同时，在扩大焊接电流窗口之后，系统研究了不同焊接电流下焊接接头的组织性能。研究结果表明:在不同焊接电流下得到的焊接接头中，组织分布以及力学性能分布呈现出相同的状态。焊缝区的组织均由铁素体+珠光体+魏氏组织组成；熔合区由魏氏组织组成；热影响区由铁素体+少量的珠光体组成；此外随着焊接电流的增加，焊接接头背部的熔宽有略微增加；在焊接接头中，熔合区处硬度值最高，其次是焊缝区，之后是热影响区，母材的硬度值最低；焊接接头最终的拉伸断裂位置是在热影响区处。 

Improvement of process window for medium and thicker plates welded by K-TIG

The welding of 8-mm thick Q235 low-carbon steel plates by keyhole tungsten inter gas welding (K-TIG), a deep penetration argon arc welding technique with tungsten electrode, is associated with many problems, including an unstable welding process and a small welding current window. To solve these prominent problems, the method of adding shielding flux on the back of the welding workpieces was proposed for the first time in this paper. This method can improve the stability of the welding process. The butt welding method was used to achieve the result of single-sided welding and double-sided forming without adding welding wire or prefabricating groove during the welding process. The results show that direct current (DC) in the range of 430–480 A is successfully used to weld the 8-mm thick Q235 low-carbon steel. The welding current window is expanded to 50 A, and the welding process stability is significantly improved. After expanding the welding current window, the microstructures and properties of welded joints obtained under different welding currents were systematically studied. The results show that the distribution of microstructures and the mechanical properties of the welded joints under different welding currents present the same states. The microstructures of the weld zone are composed of ferrite + pearlite + widmanstatten structure; the microstructures of the fusion zone are composed of Widmanstatten structure; the structures of the heat-affected zones are composed of ferrite + a small amount of pearlite. In addition, with the increase in the welding current, the fusion width of the back of the workpiece increased slightly. In the welding joint, the hardness value of the fusion zone is the highest, followed by the weld zone, and the heat-affected zone. The base material has the least hardness, and the final tensile fracture position of the welded joint is in the heat affected zone.