Research On Welding Process Of 50CrV/SPHE Dissimilar Steel Laser Welding With Filler Wire

In order to solve the exist problems of laser welding 50CrV/SPHE dissimilar steel,a new technology of laser welding with filler wire is adopted.In this paper,the effect of process parameters on the mechanical properties and microstructure of 50CrV/SPHE dissimilar steel joints by laser welding with filler wire was analyzed and to obtain the optimal combination of process parameters.The research results will provide theoretical and technical support for popularizing dissimilar steel laser welding with filler wire.Firstly,in order to investigate the effect of process parameters on droplet transfer of 50CrV/SPHE dissimilar steel laser welding with filler wire and achieve stable droplet transfer mode,high speed camera system was used to observe droplet transfer under different the process parameters,which are divided into four kinds: liquid bridge transfer,explosion transfer,liquid-droplet transfer,droplet transfer.The results show that the liquid bridge transfer mode could improve the stability of the welding process,the quality of the obtained weld is good.The liquid bridge transfer can be obtained when the laser power is 2.8kW~3.4kW,welding speed is 1.0m/min~1.8m/min,defocusing distance is-4mm~0mm,and wire feeding speed is 3m/min~6m/min.The investigation on bead formation of 50CrV/SPHE dissimilar steel laser welding with filler wire shows that weld width and weld reinforcement have a direct relationship with laser power,welding speed,wire feeding speed,defocusing distance and gap width.As the same time,it is found that quenching brittle crack occurs in the heat affected zone of the side of 50 CrV steel when the laser power is higher than 3.4kW.The microstructure and phase analysis of the welded joints were carried out by SEM and XRD.The results indicate that the microstructure of the laser melted zone of 50CrV/SPHE dissimilar steel weld is martensite,and the grain morphology is mainly composed of cellular crystals and cellular dendrites crystals.The microstructure of the heat affected zone of the side of 50 CrV steel is composed of plate martensite,and the microstructure of the heat affected zone of the side of SPHE steel is composed of ferrite and pearlite.The experimental design of laser filler wire welding process for 50CrV/SPHE dissimilar steel is made by using Design-Expert 8.6 software.During the experiment,the maximum tensile strength of the weld are considered as the process responses,the laser power,welding speed,defocusing distance and gap width are presumed as the welding process parameters and the mathematical models correlating the process parameters with the responses are developed.According to the optimization results,the optimum process parameters are obtained as follows: laser power 3.0kW,welding speed 1.6mmin,defocus-2mm,butt clearance 0.6mm.During tensile testing,the specimens from the optimum process parameters fractured through 50 CrV steel base metal.It shows that the mechanical properties of the weld are better than that the base metal.The verification experiment shows that the error range is less than 4%,which proves that the optimization results are effective and the optimization test can be used to guide actual production activities.