Effect of various heat treatment conditions on microstructure of cast polycrystalline IN738LC alloy

The microstructure of cast polycrystalline Inconel 738LC (IN738LC) under different heat treatment conditions was investigated. The cast microstructure of this alloy consists of austenitic γ matrix, γ′ precipitates, MC carbide and γ/γ′ eutectic. The microstructure of the conventional solution treatment, 1120 °C/2 h/accelerated air cooling (AAC), contains a bimodal γ′ precipitate. Solution treatment at several temperatures of 1120, 1180, and 1220 °C for 1.5 h as well as 1180 °C/1.5 h + 1220 °C/2 h has been carried out under argon atmosphere. Accelerated air cooling (AAC) and water quenching (WQ) were applied after solution treatment. Moreover, aging treatment at 845 °C was carried out for all solutioning conditions followed by WQ. Solution treatment at 1180 °C/1.5 h + 1220 °C/2 h gives the best homogeneity for different alloying elements and a uniform size for the fine γ′ precipitates. AAC increases the volume fraction and tends to agglomerate γ′ precipitates compared to WQ.