Steel is fundamentally an alloy of two factors: iron and carbon. On top of that, stainless steel adds somewhere around 13%+ chromium, depending on the exact steel, to the alloy to make it resistant to rusting when in contact with acids.   I say resistant because no steel is really rust proof. Stain resistant is more accurate than stainless. If you leave it dirty and wet overnight in the sink, even stainless knives will rust eventually. Therefore, the next time you read a review where someone complains that their stainless knife rusted, you can safely ignore it; that’s a user error.

Knowledge is power and all we need to know here was covered in Chemistry 101. All steel has iron and that is what has an oxidation reduction reaction with oxygen to make the iron oxide we know colloquially as rust. I won’t ask you to balance the equation, but here is the equation that creates rust. Iron and atmospheric oxygen react to make rust:

The big problem with rust is its insidious nature of spreading to more rust. It’s a rough surface, thus creating more surface area for oxygen to react and make more rust. If left unchecked, eventually you’ll have a deep pit in your knife. When you sharpen up to that point you’ll have a hole in the edge! There are a number of ways to limit and contain rust on steel that I want to discuss. This level of vigilance is mostly only required for carbon steel knives.