X-ray photoelectron spectroscopy investigation of the carburization of 310 stainless steel

The surface of 310 stainless steel (310SS) samples was investigated by X-ray photoelectron spectroscopy (XPS) after 500 h cyclic exposure to two carburizing atmospheres: CH₄ (2%)–H₂ (98%) at 800 °C, and CH₄ (10%)–H₂ (90%) at 1100 °C. The depth distribution of various elements in the surface region was obtained by XPS after successive cycles of argon etching. The microstructure of the alloy was observed by scanning electron microscopy (SEM) and the phases formed during the exposure were analyzed by X-ray diffraction (XRD). The results showed that the major phases that were formed within few micrometer depth during exposure at 800 °C include both iron and chromium carbides. (Mn, Cr) oxide was also formed as a result of the reaction with the residual oxygen of the atmosphere. A region of few microns width that was relatively depleted of chromium was formed under the surface as a result of the outwards diffusion of chromium. The exposure to the reducing atmosphere at 1100 °C led to the formation of various iron and chromium carbides. No oxide was formed during exposure. In all exposed samples, the surface was Cr enriched while nickel remained buried under the surface region that reacted with the atmosphere.