Chromium depletion from stainless steels during vacuum annealing

✍ Scribed by Dr. A. F. Smith; Dr. R. Hales

• Publisher: John Wiley and Sons
• Year: 1977
• Tongue: German
• Weight: 492 KB
• Volume: 28
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.19770280603

✦ Synopsis

Abstract

During selective chromium Oxidation of stainless steels the changes in chromium concentration at the metal surface and in the metal have an important bearing on the overall oxidation performance. It has been proposed that an analogue of chromium behaviour during selective oxidation is obtained from volatilisation of chromium during high temperature vacuum annealing. In the present report the evaporation of chromium from 316 type of steel, vacuum annealed at 1000 °C, has been investigated by menas of energy dispersive X‐ray analysis and by neutron activation analysis. It was established that chromium loss from austenitic stainless steels is rate controlled by interdiffusion in the alloy. As predicted the chromium concentration at the metal surface decreased with increasing vacuum annealing time. The chromium depletion profile in the metal was in good agreement with the previously derived model apart from an anomalous region near the surface. Here the higher resolution of the neutron activation technique indicated a zone within ∼2μm of the surface where the chromium concentration decreased more steeply than expected.