Effects of keyhole-assisted gas jet on microstructure and microhardness of stainless steel laser weld

Slab CO₂ continuous wave laser welding of HR-2 hydrogen-resistance stainless steel was carried out with different keyhole-assisted gas jet.During welding,the incident angle of the keyhole-assisted gas jet was 60° with a nozzle put ahead of the laser beam.The experimental results show that the layout with gas nozzle ahead of laser beam obtained better weld appearance and had little perturbation on the welding pool than that with gas nozzle behind the laser beam in gas jet-assisted keyhole laser welding.Compared with traditional laser welding,penetration depth increased significantly while penetration width decreased, and the weld shape became gourd-like with narrow middle part and wide upper and lower parts in the enhanced laser welding,because more plasma was suppressed within the keyhole and the keyhole deepened.Shorter columnar grains formed near the fusion line while equiaxed grain existed in the center of weld in enhanced laser welding,and the weld solidified by following ferrite-austenite (FA) mode.The reason for less ferrite precipitated in the weld could be resulted from the introduction of keyhole-assisted gas jet which improved the cooling condition of the weld metal.