Wet Corrosion

The molybdenum-alloyed ferritic steels, e.g. 4521, have largely the same corrosion resistance as AISI 316 but are superior to most austenitic steels in terms of their resistance to stress corrosion cracking. A typical application example for these steels is hot-water heaters.

For chlorine-containing environments, where there is a particular risk of pitting, for instance in seawater, the high-alloy steel S44635 (25Cr 4Ni 4Mo) can be used.

High Temperature Corrosion

Ferritic steels with high chromium contents have good high-temperature properties. As mentioned previously, the steels readily form a brittle sigma phase within the temperature range 550-950 °C, but this is of minor importance as long as the product, such as a furnace, operates at its service temperature.

Grade 4762 with 24% chromium has a scaling temperature in air of about 1070 °C.