The effects of heating in a vacuum on the surface properties of a low chromium stainless steel

The potential of thermal treatment at intermediate temperatures in a vacuum as a means of enriching exposed surfaces of chromium bearing steels with chromium was investigated. AISI 409 ferritic stainless steel was subjected to heat treatment in the temperature range 400 – 700 °C for 48 h under a vacuum of about 10-6 Pa. X-ray photoelectron spectroscopy analysis showed that the chromium content of the surface alloy was substantially increased by this treatment. The treated surfaces were easily passivated in dilute HNO3. The surface enrichment with chromium in the optimum temperature range is interpreted in terms of the dominance of diffusive segregation of chromium over chromium loss by oxidation and evaporation