Brittleness of high-chromium ferritic stainless steels

Abstract

1. Ferritic chromium steels with 10–30% Cr and grain size≥grade 8 with cleanness typical of openmelted steels undergo brittle fracture at room temperature. 2. The use of vacuum melting for high-chromium ferritic steels reduces the concentration of impurities (C+N+O) by an order (total concentration of interstitial impurities drops from tenths to hundredths of one percent), which lowers the transition temperature by 130–170° for steels of grade 8 and 220–295° for steels of grade 4. 3. Raising the chromium content from 10 to 30% in both open and vacuum heats raises the transition temperature additively, which is described by the equation T50=k·% Cr+b. 4. The transition temperature of high-chromium ferritic steels, both open and vacuum heats, increases with the grain size, which conforms with a relationship of the Hall-Petch type: T50=M+N·d−1/2.