Comparison of processing window in full penetration laser welding of thick high-strength steel under atmosphere and sub-atmosphere

In order to show the advantages of laser welding under vacuum or sub-atmosphere in fabrication of thick section structures, fiber laser welding of thick high-strength steel was performed under atmosphere and sub-atmosphere, respectively. The effect of ambient pressure on penetration depth and cross section was investigated, and the processing window in full penetration welding of 10 mm thick high-strength steel under atmosphere and sub-atmosphere was compared. The results showed that the processing window of full penetration laser welding under atmosphere (101 kPa) was very narrow because of the appearances of various weld defects. Full penetration sound welds could only be achieved in a small processing window near the parameter of 10 kW laser power and 1.5 m/min welding speed. It was found that there was a sharp increase in penetration depth and a significant change of cross section from “nail-head” shape to parallel shape with a decrease in ambient pressure. Full penetration welds joint under sub-atmosphere (0.1 kPa) displayed high weld quality with extreme smooth surface appearances. The processing window under sub-atmosphere with laser power ranging from 4 kW to 6 kW and welding speed ranging from 0.5 m/min to 1.5 m/min was much wider than that under atmosphere.