Microstructure and mechanical properties of electron beam welded joint of Nb refractory metal to 304 austenitic stainless steel

In this study, the microstructure and mechanical properties of electron beam welded dissimilar joint of Nb to 304 austenitic stainless steel were analyzed. The results showed that the joint obtained were asymmetric due to the large difference in physical properties between the Nb and the 304 austenitic stainless steel. The weld mainly consisted of eutectic structure and brittle intermetallic compounds reaction layer. The eutectic phase was composed of α-Fe ferrite and ε(Fe₂Nb) intermetallic compound. The brittle phases in the reaction layer were ε(Fe₂Nb) and μ(Fe₇Nb₆). The microhardness of the reaction layer of the joint was up to 1065 HV, and the presence of ε(Fe₂Nb) in the eutectic region contributed to its high microhardness as well. The tensile strength of the welded joint was 137 MPa, which was 53 % of that of the Nb base metal. The joint failed at the reaction layer by brittle cleavage fracture.