采用双层气流保护TIG焊接方法, 有效地向高氮钢液态熔池过渡活性组元O, 使熔池对流形式由外向对流转变为内向对流, 获得窄深型焊缝; 窄深型焊缝有效降低熔池表面宽度, 减少了焊缝N元素的溢出. 研究了不同热输入下(不同电流下)熔池形貌和焊缝冲击韧性的变化规律, 结果表明, 随着焊接热输入的增加, 焊缝δ铁素体含量增加, 焊缝冲击性能没有明显变化. 冲击断口的SEM观察显示,冲击断口含有大量短而深的裂缝和“骨架状”撕裂的界面, 经EDS分析, 开裂位置为δ铁素体. 高氮钢焊缝中的δ铁素体和奥氏体界面结合强度低, 在承受冲击载荷时两相界面首先开裂, 裂纹沿两相界面迅速扩展, 引起焊接接头脆性断裂.

The high nitrogen stainless steel (HNS) is widespread attention in recent years because of the high strength, good toughness and corrosion resistance. Weld ability and welding efficiency are received extensive attention in the HNS welding. Using the double shielded TIG welding method, the active element, oxygen, was transferred into weld pool so as to change the convection of the liquid metal from outward to inward. This proposed welding process could effectively reduce the width of the pool surface, which is beneficial to reducing the overflow of nitrogen content in the weld. The influence of heat input (different welding current) on the weld pool shape and the impact properties of welds were investigated. The weld penetration increased with the increasing heat input and the 10 mm thick work piece was welded thoroughly under the 250 A welding current. The XRD test and calculation results showed that the δ ferrite content in the welds was increased with the increasing welding current, while the impact properties of welds change little. The poor impact properties of the weld are another focus of this study. The fracture surfaces of the Charpy V-notch specimens were characterized using the scanning electron microscope (SEM).