The elimination of pores in laser welds of AISI 304 plate using different shielding gases

A laser power of 10 kW was used to weld 304 stainless steel. Different shielding gases including Ar, N2 and no gas were used. The porosity in the laser welds was examined. The metallic plume, liquid melt pool and laser keyhole were observed by a high-speed video camera. Bubbles were produced in all the laser welds. Many pores were retained in the 304L stainless steel laser welds made in Ar. Almost no pores were found in the laser welds made in N2 or no shielding gas. The dissolution of N2 bubbles in the liquid melt pool led to the elimination of the pores in the 304L laser welds. The retention time of liquid melt pool was 1.1 s at a laser power of 10 kW and a welding speed of 0.8 m/min. It took 30 μs to absorb all the N2 bubbles in the liquid melt pool. The increase of the nitrogen content in weld metal was 3.4 × 10−5 wt.%.