Property Analysis of Laser Welded Dissimilar Q345D/20Mn2 Steel Joints

A fibre laser was used to weld Q345D/20Mn2 dissimilar steel with and without a Ni60 powder filler. Finite element (FE) simulation of the temperature and stress fields in the laser beam welding (LBW) was conducted COMSOL. Experimental investigation determined the effect of Ni-based powder filled welding on the microstructure, morphology, element content, microhardness and fracture morphology of the weld cross-section. The results show that when the laser power was 2700 W, the scanning speed was 1 mm/s and the out-of-focus amount was 0 mm, the tensile properties of Q345D/20Mn2 steel welds were optimal and deformation was minimal. Under such conditions the depth of the weld pool can reach 2.7 mm and the width 2.8 mm. After the Ni-based powder melts and penetrates the bottom of the base material (BM) along the weld seam, small cytosolic, equiaxed and columnar crystal grains can be observed near the fusion line, and the Ni-based filler powder can achieve a good metallurgical bond with the BM. The location of tensile fracture is at the weld and small tough nests can be observed in the cross-section leading to judgment that the fracture mode is ductile.