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 gamma matrix, gamma' precipitates, MC carbide and gamma/gamma' eutectic. The microstructure of the conventional solution treatment, 1120 degrees C/2h/accelerated air cooling (AAC), contains a bimodal gamma' precipitate. Solution treatment at several temperatures of 1120, 1180, and 1220 degrees C for 1.5 h as well as 1180 degrees C/1.5h + 1220 degrees C/2h 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 degrees C was carried out for all solutioning conditions followed by WQ. Solution treatment at 1180 degrees C/1.5h + 1220 degrees C/2h gives the best homogeneity for different alloying elements and a uniform size for the fine gamma' precipitates. AAC increases the volume fraction and tends to agglomerate gamma' precipitates compared to WQ. (C) 2007 Elsevier B.V. All rights reserved.