Silicon as an alloying element in ferrite stainless steels containing 8–13% Cr

A jumpwise improving of the passivation ability and pitting-resistance of the Fe-(8–13)% Cr-(0.32–2.7)% Si alloys upon surpassing the limit of ∼14–15 at % by the chromium and silicon summary concentration is found. It is suggested that the nature of the critical summary concentration CCr + CSi is identical to that in Fe-Cr binary alloys; it is caused by the silicon building-in to the alloy’s crystal lattice and its substitution for chromium in the statistical proportion to its atomic part in alloys. When the summary concentration CCr + CSi approaches ∼14–15 at %, each elementary cell in the Fe bcc lattice must necessarily contain either a Cr atom or the proportional number of Si atoms. The improved passivation ability and pitting-resistance of the Fe-Cr-Si alloy, compared with the Fe-Cr alloys, is explained by the fayalite formation at the alloy surface.