Microstructure and Properties of Welded Joints of TWIP Steel Welded by Laser and TIG

Twinning induced plasticity (TWIP) steel was welded by laser welding and TIG welding. Microstructure and properties of welded joints were studied by microstructure observation, tensile test and microhardness test. The results show that grains in the welding line center by lasing welding were small and equiaxial, and microstructure near welding fusion line was columnar crystals, but the heat affected zone could hardly be recognized. The microstructure of TIG welding seam was columnar crystal with nearly consistent-oriented and the crystalline grains were large, and the heat affected zone displayed gross austenite structure. The lasing welding sample fractured in the matrix far from the welding line with tensile strength of 560 MPa and elongation of 67%, and showed typical ductile fracture. The TIG sample fractured in the heat affected zone with tensile strength of 460 MPa and elongation of 48%, and the fracture manifested as brittle fracture. The plastic deformation for TIG sample was clearly lower than lasing welding sample, and the average microhardness of welded joint by lasing welding was higher than TIG welded joint.