Alloy corrision?

Question

Why alloy can prevent corrision?
I know that Chromium atoms are added among Iron atoms.
But how can they appear on the surface of the Iron in the oxide form to prevent corrision?

Based on what Wikipedia says, chromium oxide is formed ( in stainless steel) on metal surface to prevent rusting. But chromium atoms are added among Fe atoms. Therefore, chromium layer is not directly painted. Then, how chromium oxide appears on the whole surface while chromium is not wholely painted on surface but among Fe ions?

Answer 1

They dont have to appear as an oxide of chromium. Chromium oxide is only formed at hight temperatures, and chrome oxidize will not form at earth conditions. Chrome on surface as you describe is PLATED chromium and a thin layer plated over a layer of plated copper onto steel. Of course, pure chrome will not oxidize.

The high chrome steel is known as StainLess Steel and the chrome content is sufficiently high to prevent rusting by normal atmospheric conditions creating a very molecular tightly filled and packed structure with nearly no iron exposed as a rough surface that can oxidize.. However, stainless steel with a marginal quantity of chrome will indeed oxidize the iron present and appear as rust.