Effect of oxygen content in He–O2 shielding gas on weld shape in ultra deep penetration TIG
Effect of oxygen content in He–O2 shielding gas on weld shape in ultra deep penetration TIG
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DOI：
10.1179/174329307x238425
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发表时间：
2007-11
影响因子：
3.3
通讯作者：
S. P. Lu;H. Fujii;K. Nogi;T. Sato
中科院分区：
文献类型：
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作者：
S. P. Lu;H. Fujii;K. Nogi;T. Sato
研究了SUS 304不锈钢在He-O2混合气体保护下平板移动焊道TIG焊时保护气体浓度对焊缝成形的影响。通过向氦基保护气体中添加少量的氧，可以精确地控制熔池中的氧含量和焊缝形状。氧是不锈钢的表面活性元素。当熔池中的氧含量超过临界值1070 ppm时，由于熔池表面Marangoni对流由外向内的变化，焊缝形状突然由宽浅型变为深窄型。系统研究了纯He和He-0.4%O2混合气体保护下焊接速度、焊接电流和电极尖端工作距离等焊接参数对焊缝形状变化的影响。研究结果表明，TIG焊焊缝的最终形状在很大程度上取决于熔池表面Marangoni对流的形式和大小，而Marangoni对流是由熔池中氧含量、表面张力温度系数（dσ s/dT）和熔池表面温度梯度（dT/dr，r为熔池表面半径）的综合作用决定的。据认为，焊接参数的变化改变了熔池表面的温度分布和梯度，从而影响Marangoni对流的大小和最终的焊缝形状。
The effect of the shielding gas concentration on the weld shape was studied for the moving bead on plate TIG welding of SUS304 stainless steel under He–O2 mixed shielding. The small addition of oxygen to the helium base shielding gas can precisely control the oxygen content in a liquid pool and the weld shape. Oxygen is a surface active element for stainless steel. When the oxygen content in the liquid pool is above the critical value of ∼ 70 ppm, the weld shape suddenly changes from a wide shallow type to a deep narrow one due to the change in the Marangoni convection from the outward to inward direction on the liquid pool surface. Weld shape variations influenced by the welding parameters including welding speed, welding current and electrode tip work distance under pure He and He–0.4%O2 mixed gas shielding were systematically investigated. The investigation results showed that the final shape of the TIG weld depends to a large extent on the pattern and magnitude of the Marangoni convection on the pool surface, which is governed by the combined effect of the oxygen content in a liquid pool, temperature coefficient of the surface tension (dσ s/dT) and the temperature gradient on the pool surface (dT/dr, r is the radius of the weld pool surface). It is considered that the change in welding parameters alters the temperature distribution and gradient on the pool surface, and thus, affects the magnitude of the Marangoni convection and final weld shape.