The corrosion behavior of ferritic stainless steels is reviewed. The intergranular corrosion behavior of commercial purity ferritic stainless steels had been believed to be quite different from that of austenitic stainless steels. The heat-treatment that would make ferritic alloys susceptible makes the susceptibility of austenitic alloys to become minimum. Recently, however, it has been shown that the behaviors of both ferritic and austenitic stainless steels can be explained by the chromium depletion theory. The difference in their behavior described above is considered to be due to the very low solubility and rapid diffusion rate of carbon and nitrogen in the ferrite phase compared with the austenite phase. The effects of heat-treatment and alloy composition on the susceptibility to intergranular corrosion are also outlined.
The increase in chromium and/or molybdenum contents of Fe-Cr alloys markedly increases the resistance to pitting and crevice corrosion in chloride environments. Ferritic stainless steels are known to be highly resistant to stress corrosion cracking, but when the alloys contain nickel or copper, they become susceptible to stress corrosion cracking. The susceptibility of ferritic stainless steels to hydrogen embrittlement is also discussed briefly.
