Effect of Cr Content On Pitting Behavior of Fe-Cr Alloys

Immersion and applied current studies are used to investigate the pitting behavior of binary Fe-Cr alloys formed both by conventional melting techniques and by diffusion of chromium into mild steel (chromizing). Experiments on both sets of materials show that a chromium content of 28-30 percent is critical for elimination of room-temperature pitting corrosion. It is proposed that chromium acts to improve the pitting resistance of Fe-Cr alloys by stabilizing passivity, thus reducing pit initiation and slowing pit growth. The relationship between polarization measurements and pitting is discussed. It is shown that in a simple immersion test pitting occurs at potentials quite different from the “critical” potentials predicted by polarization measurements.