Study On Microstructure And Mechanical Performance Of Tilt Laser Welded 301LN Stainless Steel

The paper was based on the study of the stainless steel 301LN, and the 301LN stainless steel which adding N elements could weaken or even eliminate the intergranular corrosion of stainless steel, at present, they are main materials to manufacture lightweight rail passenger. The effect of laser welding on its solidification mode and microstructure were studied. Systematically, in order to improve its properties, the influence of tilted welding structure on its tensile ductility and fatigue strength were also investigated, by comparison of vertical welding structure. The materials involved in this study were main 1.5mm301L-HT,2.0mm301L-DLT and 0.8mm301L-DLT sheet.The results showed that, tilt laser welds were constituted by austenite and delta ferrite dendrites, weld columnar crystals was FA mode which delta ferrite primary crystal phase and the size of columnar grain less than lOum.Microstructures of the columnar crystals were homogeneous, and heat affected zone of microstructures were narrow, what’s more, the weld lines were clear and no shrinkage defects in the tilt laser welds; the content of ferrite were different from positions, and the content of ferrite in the weld center were more lower;In the tensile test, compared with remained three combinations, tensile ductility of 1.5+0.8 combination was higher, closed to 20mm.During tensile test, plastic deformation were produced in the vicinity of the weld interface, and the deformation of the lower plate welds greater than the upper plate welds, While the amount of plastic deformation were large, interfacial shear stress exceeded the shear strength at the weld interface, it was fractured; compared to the vertical welding, the fracture ductility and tensile strength of tilt welds were higher to a certain extent;The fatigue test showed that the location of fracture of four combined specimens were at the lower plate, and the macroscopic fracture were showed three parts of the source region, the expansion area, and the final short-break zone; the fatigue life of crack initiation were the vast majority of the total, the microscopic fracture mechanism of crack propagation were transgranular and intergranular hybrid fracture mode. Compared with the fatigue properties of vertical welds, the tilt welding structural had changed the path of crack propagation, increasing the resistance of fatigue crack, and the fatigue performance had improved.To some extent, compared with the vertical welds, the tensile properties and fatigue performance of tilt welding specimens were improved, and the safety of body were enhanced. So the tilt welding structure were feasible in vehicle applications.