Study Of The Mechanical Performance And Fracture Mechanism Of Laser Welded301L Cold Rolled Plates

ABSTRACT:In stainless steel type A and type B car body structure, the body wall panels are1.5mm and2mm low strength cold rolled plates, and frame materials are below1mm and1.5-2mm301L high strength cold rolled plates. In this paper301L-DLT,301L-HT and EN1.4318, three kinds of cold rolled plates with the above thicknesses are selected as test materials. Through metallurgical observations, tensile test, fracture analysis and finite element simulation, microstructure and properties of austenitic stainless steel301L cold rolled plates laser weld, as well as the relationship between laser weld geometry, plate strength and plates combination and failure behavior and service performance of the laser butt and lap welding joints with the same thicknesses and different thicknesses.The results showed that the diameters of columnar crystals in laser weld were10-20μm and the distribution of the small amount of ferrite in weld was uneven. The laser welded301L-DLT was of higher plasticity than301L-HT; the laser lap welded301L-DLT was of higher strength than301L-HT, moreover, the larger weld depth and width of lap welded plates with the same thicknesses were, the plastic deformation was. Tensile strength of butt laser welded301L-HT exceeded800MPa, higher than301L-DLT plates. Mechanical properties of lap welded plates with different thicknesses were related to plates combinations, and301L-DLT welded plates with different thicknesses had large plastic deformation. Mechanical properties of301L-DLT and301L-HT lap welded sheets combination were connected with the plates’thicknesses and the1.5mm301L-HT and0.8mm301L-DLT combination had good mechanical properties.The fracture modes of the lap laser welding were two species, plate fracture and interface weld tensile-shear fracture, which were caused by differences of micro-hardness and tensile strength around the weld. The lap welded301L-HT and301L-DLT plates with outer plate penetration rate40%were plate fracture and weld fracture, which with the lower penetration rate were all weld tensile-shear fracture. The fracture strength of overlapping structure for plate fracture was higher. The microstructure of the longitudinal section of the weld fracture and the finite element analysis showed that the main reason why tensile fracture occurred in the outer plate and weld interface, rather than inner plate was the excellent bending and tensile properties of laser welding columnar crystals, though stress concentration also existed in weld.