采用激光焊打底和冷金属过渡(CMT)焊填充的工艺对FV520B钢进行焊接,研究了不同工艺参数下接头的组织和性能。激光打底焊后,焊缝熔化区的组织主要包括原奥氏体晶粒内平行排布的板条马氏体以及分布于原奥氏体晶界和马氏体板条界的δ铁素体;激光焊熔合线位置存在呈连续和离散状分布的δ铁素体。随着CMT填充焊热输入的增加,熔宽、熔深及热影响区的宽度均增加,激光打底焊热影响区和熔化区的组织特征逐渐消失;当CMT填充焊的热输入较低时,在紧靠填充焊熔合线的受热影响的激光焊熔化区(HALWFZ)内,晶粒在高温热影响下变为等轴状,并且随着到熔合线距离的增加而变小;当热输入量较高时,激光焊熔化区的柱状晶组织均转变为等轴晶且晶粒较大。与激光焊相比,填充焊后焊缝横截面在水平方向各区域的硬度分布更加均匀;随着填充焊热输入增加,HALWFZ的平均硬度先增大后减小。填充焊熔化区(FWFZ)的平均硬度低于激光焊熔化区(LWFZ);LWFZ在靠近熔合线处的硬度最低。填充焊后激光焊区域的强度大于母材,填充焊区域的强度小于母材。随着填充焊热输入增加,激光焊区域的冲击韧性增加。电化学腐蚀试验表明,随着热输入增加,LWFZ的腐蚀电位先升高后降低;填充焊前和填充焊后LWFZ的耐蚀性均高于母材。

Herein, an FV520B steel joint is formed through laser backing welding and cold metal transfer (CMT) filler welding. Microstructures and properties of the joints at different processing parameters are studied. Microstructures of the fusion zone (FZ) obtained using laser backing welding mainly comprise lath martensites, which are arranged in a parallel form in the primary austenite grains, and δ ferrites, which are situated at the primary austenite grain boundaries and lath martensite interfaces. Some continuous and discrete δ ferrites are located at the fusion line of laser welding. The weld width, weld penetration, and the width of heat-affected zone (HAZ) increase with the increase of the heat input of the CMT filler welding. Moreover, the microstructural characteristics of the HAZ and FZ of laser backing welding gradually disappear. When the heat input of CMT filler welding is lower, the grains in the heat-affected laser welding fusion zone (HALWFZ) close to the filler welding fusion line exhibit an equiaxed shape because of the high temperature reheating. Furthermore, the size of the equiaxed grains decreases with the increase of distance to the filler welding fusion line. When the heat input of CMT filler welding is higher, the columnar grain microstructures in the laser welding fusion zone transfer into the larger equiaxed grains. Compared with the single laser welding, the hardness of the weld cross-section exhibits more uniform distribution in the horizontal direction after the filler welding. With the increase of heat input of filler welding, the average hardness of HALWFZ initially increases and then decreases. The average hardness of the filler welding fusion zone (FWFZ) is lower than that of the laser welding fusion zone (LWFZ). Moreover, the average hardness of the LWFZ presents the lowest value in the vicinity of the filler welding fusion line. After filler welding, the strength of laser backing welding area is higher than that of the base metal, whereas the strength of filler welding area is lower than that of the base metal. The impact toughness of laser backing welding area increases with the heat input of filler welding. Electrochemical corrosion results show that with the increase in the heat input, the corrosion potential of LWFZ initially increases and then decreases. The LWFZs before and after filler welding both exhibit a superior corrosion resistance than the base-metal substrate.