Effect of C Content on Microstructure and Mechanical Properties of GH4079 Alloy

Three kinds of GH4079 alloys with carbon content of 0.018 wt %, 0.038 wt % and 0.051 wt % were prepared using duplex smelting, homogenization, forging and heat treatment. The equilibrium phase precipitation behavior of GH4079 alloys with different C contents was investigated through thermodynamic calculations. In addition, the effects of C content on the microstructure and mechanical properties of GH4079 alloys were studied by combining EDS component analysis,microstructure observation, room temperature tensile testing and endurance performance testing at 650 ℃/863 MPa. The results show that the increase of C content can promote the precipitation of MC-type carbides in GH4079 alloys. The amount of carbides enriching in Nb, Mo and Ti increases linearly with carbon content increasing, but has no significant effect on the precipitation of γ’ phase. With the increase of carbon content, the grain size of GH4079 alloy bars after the same forging deformation and heat treatment significantly decreases. The room temperature tensile strength and yield strength increases,while the elongation after fracture decreases. The endurance life significantly increases, and the endurance plasticity is comparable. These carbides and their hindrance to dislocation movement and inhibition of grain boundary sliding are the main reasons for the improvement in mechanical properties of GH4079 alloy.