Microstructures and Mechanical Properties for Laser Tailor Welded Blanks of DP590 and Low Carbon Steels

This research characterizes the microstructures and mechanical properties of laser TWBs of DP590 and DP590, DP590 and IF steel (a low carbon steel). For the joint of DP590 and DP590, the laser welding results in a significant increase of microhardness in the weld caused by the formation of martensite in large quantity. HAZ shows a relatively higher microhardness than that of the base metal except for the local softened zones. But no martensite is observed in the weld of DP590 and IF steel, which is mainly composed of ferrite and granular bainite. Highest microhardness is observed at the fusion line of DP590 side. For both of the two TWBs, the transverse joints have the lower strength and elongation, and the longitudinal joints show the higher strength and lower elongation than those of the base metals. The properties of weld metal and HAZ are obtained by the miniature sample testing, and also the theoretical results of HAZ properties are calculated based on the rule of mixture. It is concluded that the weld metal has limited ductility, and the deformation of the joint is concentrated on the base metal. HAZ plays an important part in the joint properties, but its softening does not seriously affect the mechanical properties.