Effect of energy input on the microstructure and properties of butt joints in DP1000 steel laser welding

Highlights: • The inharmonious deformation of welded joint led to a significant decline in ductility of the entire welded joint. • The softening existed in sub-critical zone and inter-critical zone of HAZ. • The existing of softening can make the mechanical properties degradation. This paper investigated the effect of energy input on the microstructure and properties of DP1000 steel butt joint using laser welding. As the energy input decreased, the weld bead width narrowed and the width of the softening zone became narrowed, and the mechanical properties increased as the energy input decreased. Demarcating different areas of the welded joint and testing the change in length due to the tensile tests indicated that only the HAZ of the welded joint had an apparent extension, the base metal and weld metal zone had no clear deformation, and the inharmonious deformation led to a significant decline in ductility of the entire welded joint. The HAZ hardness analysis of the welded joints revealed that apparent softening existed in the sub-critical and inter-critical zones of the HAZ.