However, chromium can also be stainless steel’s
Achilles’ heel, and the chloride ion stainless steel’s
nemesis. This is because in the passive layer, the
chloride ion combines with chromium forming a soluble
chromium chloride. As the chromium dissolves, free
iron is exposed on the surface and reacts with the
environment forming rust. However, alloying elements
like molybdenum will minimize this reaction.
Other elements, as illustrated in Table I, may be added
for specialized purposes. For example: high temperature
oxidation resistance, sulfuric acid resistance,
greater ductility, high temperature creep resistance,
abrasion resistance, or high strength.
Again, of all these elements, only chromium is required
for stainless steel to be stainless.