Study on Columnar Grain Growth Mechanism of SUS439L Arc Welding

It is well known fact that the columnar grains in fusion zone make problems such as lower strength or crack initiation especially interface plane of columnar grains along longitudinal direction. Generally it is hard to make columnar grains in arc welding comparing to high power density welding method like laser or electron beam welding. However, it is found that lack of shield gas supply affects on the columnar grain growth and limited equiaxed grain generation in STS 439L arc welding. It is proved through comparing cross sections of weldment for lower shield gas feed rate, 5 LPM, and higher case, 20 LPM. Therefore, it is recommended to control the shield gas supply more strictly to prevent columnar grains and its induced defects in STS 439L arc welding as result.