On the Chromium Depletion near Grain Boundaries of Austenitic Stainless Steels

Auger spectroscopic analysis and thermodynamical calculations were conducted, in order to determine the chromium concentration profiles near grain boundaries of austenitic stainless steels.Of several kinds of environmental sensitive cracking of austenitic stainless steels, the intergranular corrosion, the intergranular stress corrosion cracking and the intergranular hydrogen embrittlement were discussed with particular respect to the chromium depletion occurring near grain boundaries.Results obtained are as follows.(1) The local chromium concentrations in the chromium depleted zone at grain boundaries could be quantitatively determined by Auger spectroscopic analysis.(2) The local chromium concentrations in austenite at interface with Cr23C6 particles were calculated by using the chromium and carbon activities. The calculated results were in good agreement with the experimental results.(3) The intergranular corrosion attack and the intergranular stress corrosion cracking susceptibilities were found to have strong dependence on the minimum chromium concentration in the chromium depleted zone at grain boundaries.(4) The intergranular hydrogen embrittlement, however, was affected mostly by chromium carbide precipitation and not affected much by the minimum chromium concentration.