Laser beam welding of 316L T-joint: microstructure, microhardness, distortion, and residual stress

Abstract

Austenitic stainless steel 316L is welded by laser beam with T-joint in this paper. Microstructures of fusion zone consist of a large amount of austenite and a small amount of ferrite; heat-affected zone (HAZ) width is about 10 μm. The fine-equiaxed dendrites existing as network morphology locate at the center of fusion zone, and columnar structures are near HAZ. Microhardness at the top of the cross-section of welded joints is higher than that at the bottom, and the hardness of the second pass is higher than that of the first pass. The numerical result of maximum deformation (2.67 mm) keeps a good line with that of the experiment result (2.52 mm). The maximum value of the longitudinal compressive stress is 306 MPa, while the residual stress of the first pass is slightly released during the second pass welding process. The transverse residual stress along line 1 always presents a compressive state. At the 3.5 mm position far from the bead center, a large fluctuation of angular deformation and longitudinal residual stress are induced by the high-temperature gradient. Maximum values of angular deformation and equivalent residual stress for the whole sample are 1.37 mm and 452.3 MPa, and these both locate at the end-start zone of the welding path.