Difference between milled steel and stainless steel?

Milled steel is a cheap form of iron-carbon alloy that is subject to corrosion but is malleable and does not suffer from the brittleness issues of Stainless steel. Stainless steel contains additional compounds that reduces atmospheric and hydro-corrosion and increases the hardness of the steel. This makes it more expensive, less malleable and is more likely to suffer from stress fatigue and stress fractures