A comparative investigation on the microstructure and mechanical properties of laser and arc fillet welding of dissimilar steels with flux-cored wire

Flux-cored arc welding (FCAW) is a matured welding technique utilized in fabrication of structural components in industry. However, the high heat input induced by the FCAW process results in large distortion and wide heat-affected zone, which in turn cause the degradation of mechanical performance of the welded joints. In this study, a novel laser fillet welding technique with flux-cored wire was developed to weld the Q235B and 65Mn dissimilar steels for mining machinery applications. According to the comparative investigation between the FCAW and flux-cored laser welding (FCLW) techniques, it was suggested that the welding speed for the FCLW process was ∼1.5 times that of FCAW process. The microstructure in the weld metal of the FCLW specimen was dominated by lath martensite mixed with ferrite. However, the weld metal of FCAW specimen was consisted of a mixed microstructure of bainite and ferrite. The coarse grained heat affected zone and fine grained heat affected zone at the 65Mn steel side experienced quenching hardening for both the FCAW and FCLW specimens. The FCLW specimen exhibited maximum hardness value of ∼830 HV 0.5 in the hardened regions, which is approximately 170 HV 0.5 higher than that in the hardened regions of the FCAW specimen. The FCLW specimens exhibited superior shear strength in both the Q235B and 65Mn steel side loading directions compared to the FCAW specimens. This study tested the feasibility to utilize the novel and high efficiency FCLW technique to substitute the traditional FCAW technique to fabricate structural components in the future.