A new approach to improve the ductility of non-penetrating laser-welded lap joints of cold-rolled 301LN stainless steel

The aim of this work is to improve the fracture ductility of non-penetrating laser-welded lap joints. The 1.5 + 2.0 and 2.0 + 2.0 lap plates of cold-rolled 301LN stainless steel tilted 15° in the load direction and in the reverse load direction were welded by a vertical laser beam to prepare a positive-tilt weld (PTW) and negative-tilt weld (NTW). The tilt weld had a regular geometry, and the solidification centerline was tilted by approximately 15°. The laser-welded 301LN stainless steel was solidified by the primary ferritic mode with good resistance to thermal cracking, and the weld metal with ultrafine grains had excellent plasticity. The main weld in the penetrating plate of the NTW joints has a greater bending moment than that of PTW joints under tensile loading conditions, so the plastic deformation of the NTW is due to uniform bending, while that of the PTW is due to approximate parallel stretching. The bending deformation of the main weld of the NTW joint leads to a greater tensile stress ratio (decomposed normal stress to shear stress) in the interfacial weld metal than that of the PTW joint, so the interfacial fracture ductility of NTW joints is much greater than that of PTW joints.