Fuse characteristics under different laser output modes of austenitic stainless steel for fusion reactor

Laser wire filling welding experiments of 316LN austenitic stainless steel for fusion reactor were carried out under continuous laser mode and pulse laser mode respectively. Fusing characteristics of welding wire under different welding parameters and its influence on weld quality were studied, and flow and morphology of molten pool and microstructure of welded joints by continuous laser welding and pulse laser welding were studied. The results showed that both continuous laser wire filling welding and pulse laser wire filling welding could obtain wire liquid bridge transition under appropriate welding parameters, and molten pool spread uniformly and formation of weld was good. Compared with pulsed laser wire filling welding, length of molten pool in the groove of continuous laser wire filling welding was about 3 times that of pulsed laser wire filling welding, and temperature gradient was large, which was more likely to produce defects such as incomplete fusion of side wall and solidification crack penetrating through weld center. Microstructure of weld by continuous laser wire filling welding was mainly columnar crystals, which grew from both sides of weld to the center of weld and appeared intense direction. Microstructure of weld by pulsed laser wire filling welding was dominated by columnar crystals on both sides, and each zone was affected by repeated action of adjacent pulses, it showed periodicity and produced secondary crystals, which was conducive to stirring molten pool and refining grains, and then disrupting directionality of dendrites. Center of weld was columnar crystals and equiaxed crystals with different directions, and spacing between dendrites was reduced, which could inhibit generation of cracks.Highlights: It was the first time to put forward welding process of controlling crystal morphology by pulse laser to restrain cracks in thick plate welding, which could realize effective control of cracks without adding any external equipment and break limitations form traditional welding process.