Effect of medium and pressure on stress corrosion cracking susceptibility of a nickel-based alloy

Nickel-based alloy Inconel 617 is a candidate material for advanced ultra-supercritical units. Stress corrosion cracking (SCC) susceptibility of Inconel 617 under low-pressure superheated steam (0.1 MPa), high-pressure superheated steam (8 MPa) and supercritical water (25 MPa) at 650 °C was studied through slow strain rate tensile tests at strain rate of 5 × 10−7 s−1. The results indicate that Inconel 617 is susceptible to SCC in both superheated steam and supercritical water, with susceptibility increasing with pressure. In a nitrogen atmosphere, fractures were predominantly transgranular ductile. The fracture surface featured dimples and micropores. In three corrosive environments, both intergranular and transgranular fractures were observed. The rock sugar-like morphology becomes more and more obvious as the pressure increases. A large number of cracks perpendicular to the loading axis were found on gauge surface. The SCC mechanism for Inconel 617 in superheated steam and supercritical water conditions is internal oxidation.