Laser welding phenomena of mild steel with oxide film. Influence of oxide film on high power CO sub 2 laser welding of mild steel (Report 1)

Influence of oxide film, such as laser cutting edge or mill-scale, on CO sub 2 laser welding phenomena and weld characteristics of mild steel was investigated. Laser welding of butt joints, which were different in location and thickness of oxide film, were performed. Examinations were made on the weld characteristics; which were bead geometry, defect and microstructure. Light emitted from laser induced plasma was also analyzed to understand welding phenomena. The results of these experiments lead to understanding that oxide film especially on joint face causes substantial spatters, under-filled surface, disappearance of nail-head, porosity formation and reduction of hardness. It is considered that these are attributed to oxygen which reduces surface tension of molten metal and react with carbon, manganese and silicon. These results suggest that reduction of oxide film thickness or killing oxygen activity by supplementary deoxidizing elements may produce acceptable weld.