Environmentally Assisted Cracking Behavior Of Candidate Nickel-based Alloy For 700? USC Boiler In Supercritical Water

Under the interaction of corrosive environment and cyclic stress,the materials of boiler tube in power plant is prone to environmentally assisted crack(EAC)which mainly includes crack fatigue and stress corrosion cracking.EAC seriously threatens the safe operation of power plant.In this paper,corrosion tests under 650? of nickel-based alloy Inconel 617 at the pressure of 8-25MPa,corrosion fatigue(CF)tests of Inconel 617 at the temperature of 550-650?,pressure of 8-25MPa along with slow strain rate tensile(SSRT)tests of Inconel 617 under dry N2,superheated steam and supercritical water at 650? were carried out.All groups of tests were completed on the platform in supercritical water environment self-designed-and-built by the laboratory.The crack growth length during the CF tests was measured using direct current potential drop(DCPD)technique.After the test,the experimental data were collected and analyzed,and the fracture surface of the sample was observed and analyzed.The results of corrosion test show that the oxide film of Inconel 617 formed in the water environment is mainly composed of Cr2O3,and the corrosion in supercritical water environment is more serious than that in superheated steam.The results of corrosion fatigue test show that the corrosion fatigue crack growth rate(CGR)of Inconel 617 alloy increases with the increase of temperature whether in superheated steam or supercritical water environment,and the crack growth rate increases more obviously in supercritical water environment.The results of slow tension test show that Inconel 617 alloy exhibit certain susceptibility to stress corrosion cracking(SCC)in three different high temperature media environments(dry N2,superheated steam and supercritical water),and the fracture behavior of the sample is related to the test medium environment.Inconel 617 alloy has the greatest SCC sensitivity in supercritical water environment,followed by superheated steam environment(under the same dissolved oxygen),and the smallest SCC sensitivity in dry N2 environment.Further analysis of Inconel 617 alloy fracture mode under different environment was carried out.