Effects of beam-offset on microstructure and properties of laser welded Nb/304 SS joint

In this work, the Nb/304 SS joint was welded by laser welding. The joint fractured immediately due to continuously distributed Fe₂Nb intermetallic compounds when the laser was directed to the Nb/steel interface. In order to solve the problem, the laser beam-offset welding procedure was proposed. The amount of melted niobium was reduced by the laser offset effect. Finally, the formation of Fe₂Nb intermetallic compounds was controlled. The results showed that laser beam-offset welding was an ideal way to control the joint crack which occurred in laser centered welding condition. The joint microstructure was mainly consisted of γ austenite phase and a certain amount of Fe₂Nb intermetallic compounds with little δ ferrite phase. The tensile strength of the joint was 221 MPa, the fracture occurred in the Fe2Nb intermetallic compounds layer. The highest microhardness existed in Fe₂Nb intermetallic compounds layer with a value of 1 143 HV.