Abstract:The microstructures and high temperature mechanical properties of whole and slices in Inconel 718 thick plate joint obtained by electron beam welding (EBW) were studied. The results show that, in the joint welded by full and cosmetic penetration, dendrites preserve in the top and bottom of welding center and columnar crystals emerge in the middle. The grain size in heat affected zone (HAZ) becomes smaller and smaller from top to bottom of welding line. The δ-phase precipitate in grain boundary and γ″-phase is obtained inside the grain of EBW joint, which was heat-treated with solution and double aging. The most of δ-phases appear in the weld center and the less turn up in HAZ and base material zone (BMZ). The tensile strength σ_b, yield strength σ_s and elongation δ of the whole joint at 650 °C are 1 100 MPa, 800 MPa and 18%, which reach 90%, 80% and 80% of base material’s, respectively. The maximum σ_b, σ_s and δ lie in the bottom of joint and attain 1 170 MPa, 870 MPa and 18%, separately, while the minimum σ_b, σ_s and δ appear in the top of joint and reach 1 080 MPa, 780 MPa and 7%, respectively. The fracture of top weld is brittle; however, the ones of middle and bottom joint are flexible. The microhardness in HAZ and BMZ is higher than that in weld center. The value of microhardness tends to be lower as more δ-phase.

Key words: Inconel 718 superalloy; thick plate; electron beam weld; microstructure; high temperature mechanical property