Effects of heat treatments on the microstructure of IN792 alloy

The microstructure of IN792 alloy were investigated at the as-cast state, annealed state at 845 °C for 24 h, HS1220 and HS1120 heat treatment states (the material was solution heat treated at 1220 and 1120 °C, respectively, followed by a two-stage ageing process with 4 h at 1080 °C and 24 h at 845 °C, which were named HS1220 and HS1120, respectively). The incipient points of eutectic and solution temperature of carbide are 1230 and 1260 °C, respectively, which are measured by metallographic examination. Chinese script MC-type carbides, rose-shaped γ′/γ eutectic and cubic γ′ phase are observed in the as-cast IN792 alloy. The annealed microstructure is the same as that of as-cast alloy because the annealing treatment only removes the residual cast stress. After HS1120 solution treatment, MC-type carbides and rose-shaped γ′/γ eutectic partly dissolves into γ matrix, and M23C6 carbide that has a cube–cube orientation relationship with γ matrix forms near γ′/γ eutectic and MC-type carbides. After HS1220 solution treatment, rose-shaped γ′/γ eutectic completely dissolves into γ matrix, but morphology of carbides does not change. The subsequent aging treatments make γ′ phase arrange regularly, and induce re-precipitation of profuse fine γ′ particles throughout γ matrix channels.