The influence of microstructure on the oxidation of duplex stainless steels in simulated propane combustion products at 1000°C

A low nickel Type S32101 duplex stainless steel has been oxidised in simulated industrial reheating conditions. The surfaces have been studied using optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Observations show that local breakaway regions (LBRs) form on the austenitic regions whereas thinner oxides are observed on the ferritic regions of the substrate. The reason proposed for these differences is the formation of a continuous oxide layer on the ferrite region and a discontinuous layer on the austenitic region during the early stages of oxidation. The chemical composition of these LBRs have been shown to be oxide islands of iron and manganese and oxide craters of chromium rich oxides. The more protective regions consist of chromium and manganese rich oxides. A silica layer formed below the oxide which may be attributable to a slight enrichment of silicon in the ferritic regions or due to faster rates of diffusion in ferrite.