The Sulfidation of Inconel 738 in H2/H2S/Ar Gas Mixture at 500–900°C

Abstract

The sulfidation behavior of the cast nickel-base superalloy Inconel 738 (IN-738) was studied over the temperature range 500–900°C in three various ratios of H2/H2S/Ar atmospheres having sulfur partial pressures in the range 10−4–102 Pa. The sulfidation kinetics followed the parabolic rate law in all cases, and the sulfidation rates increased with increasing temperature and sulfur partial pressure. In general, the scales formed were heterophasic and duplex, consisting of an outer layer composed mostly of nickel sulfides (mostly NiS and Ni3S2, and minor Ni7S6 detected at T > 750°C) plus some CoS2/Co3S4, CoMo2S4, NiCo2S4, and minor chromium sulfide (Cr2S3/Cr3S4), while the inner layer contained a mixture of nickel sulfides and minor amounts ofA12S3 and Cr2S3/Cr3S4. The amount of NiS decreased and that of Ni3S2 increased with increasing temperature. The dependence of the sulfidation rate constants (K p ) and Ps(2)(the n value) was significantly higher at T ≥ 850°C as compared to that measured at lower temperatures (T ≤ 850°C).