聚变堆用奥氏体不锈钢不同激光输出模式熔丝特征

针对聚变堆用316LN奥氏体不锈钢材料，分别在连续激光和脉冲激光模式下进行了激光填丝焊接试验。主要研究了不同焊接工艺参数下的焊丝熔入特征及其对焊缝质量的影响，并对连续激光与脉冲激光焊接熔池流动及熔池形貌、接头的显微组织进行了研究。结果表明，连续激光填丝焊和脉冲激光填丝焊在合适的焊接工艺参数下均能获得焊丝液桥过渡，且熔池铺展均匀、焊缝成形良好。与脉冲激光填丝焊相比，连续激光填丝焊在坡口中的熔池长度约是脉冲激光填丝焊的3倍，温度梯度较大，更易产生侧壁未熔合和贯穿焊缝中心的凝固裂纹等缺陷。连续激光填丝焊的焊缝显微组织以柱状晶为主，由焊缝两边向焊缝中心生长，方向性强。脉冲激光填丝焊的焊缝两侧显微组织以柱状晶为主，各个区域都受到了相邻脉冲的重复作用，具有周期性，产生二次结晶，有助于熔池的搅动和晶粒细化，打乱了枝晶生长的方向性；焊缝中心区域为方向各异的柱状晶和等轴晶，枝晶间距减小，能够抑制裂纹的产生。 创新点： 首次提出通过脉冲激光调控结晶形态以抑制厚板焊接中裂纹的焊接工艺，可在不添加任何外部设备的基础上实现对裂纹的有效控制，打破了传统焊接工艺带来的局限性。

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.