Influence of laser power on microstructure and mechanical properties of laser welded TWIP steel butted joint

• The adjustment of laser power can effectively improve the properties of TWIP steel laser welding butt joint. • The formation mechanism of joint and the relationship between weld microstructure and mechanical properties were analyzed. • The formation mechanism of microsegregation and shrinkage porosities are analyzed. The twinning-induced plasticity (TWIP) steel is a newly developed which possesses fantastic mechanical properties and high potential for anti-crash weight-optimized structural applications. In this study, the weldability of 2 mm thick TWIP steel plate by laser welding method was investigated. The welded joint exhibited fully austenitic structure, and the weld seam consisted three types of solidification structures: columnar dendrite, cellular crystal and equiaxed dendrite. The microsegregation of C and Mn elements occurred in the interdendritic regions during the solidification of the weld seam. The toughness of the heat-affected zone (HAZ) was higher than that of the weld seam. The microhardness diagram of cross-section of welded joints presented V-shaped under different laser power. The microhardness of equiaxed dendrite zone was higher than that of the weld seam and coarse grain heat affected zone (CGHAZ). The average strain and tensile strength increased first and then decreased with the rising of laser power. Further study demonstrated that the fracture of the laser welding TWIP steel joints during tensile test presented ductile mode characteristics. The results show that the appearance and performance of the welded joint are optimal with laser power of 1800 W in present study, and the tensile strength and total elongation are 915 MPa and 48%, respectively.