Heat Treatment Design of Inconel 740H Superalloy for Microstructure Stability and Creep Properties Enhancement

In this study, three heat treatmentHeat treatment conditions selected from various heat treatment candidates for Inconel 740HInconel 740H, which are considered as materials for A-USC steam turbines, were exposed to long-term thermal conditions at 750 ℃ up to 5,000 h. The stability and mechanical characteristics of heat-treated microstructure were examined, and the optimal heat treatmentHeat treatment to maximize creep property was derived through the creepCreep test (750 ℃/270 MPa). It was confirmed that the content of Cr was concentrated at the boundary of MC carbide without a specific orientation relationship at 750 °C/270 MPa creep, and this was the result of phase transformation by the reaction of MC + γ → M23C6 + γ’. Thus, MC carbide has high resistance to cracks because its temperature and stress during creepCreep contribute to decomposition for phase transformation rather than initiation. Therefore, the higher the fraction of the MC carbide, the more advantageous it is to the creep property.