The evolution and oxidation of carbides in an Alloy 601 exposed to long term high temperature corrosion conditions

Abstract Inconel 601 alloy has been studied after 2 years exposure in a commercial methanol plant. Carbon penetration leads to precipitation of nanometer-scale M 23 C 6 and coarser M 7 Cr 3 , tens of microns below and within several microns of the alloy surface respectively, as predicted by thermodynamic calculations. Previously unreported M 3 C 2− x precipitates form between the M 23 C 6 and M 7 C 3 in the C-concentration gradient and sometimes outcrop the surface. Carbides are Cr-rich, the smallest may contain Fe, orientated with respect to the matrix and oxidize when exposed to the corrosion product and synthesis gas. The Cr 2 O 3 formed is not optimal for protection from carbon ingress.