Mild Steel vs Stainless Steel

Main alloying element

This is the main factor that distinguishes mild steel from stainless steel. Mild steel is alloyed using carbon whereas stainless steel has chromium as its alloying element. The 2 different alloys produce very different results in corrosion resistance, malleability and ease of fabrication and cost.
It is this key difference that separates the 2 different kinds of steel.

Does mild steel rust?

Because stainless steel is alloyed with chromium, this metal has a much higher corrosion resistance than mild steel. The chrome in the stainless reacts with the oxygen in the air producing a natural ‘chromium oxide’ protective skin on the surface of the metal which means that as long as this layer is undamaged, the metal is naturally corrosion resistant. Different stainless steel grades contain different elements to make them more suitable for different environments, such as a marine environment. Mild steel on the other hand does not have this chromium oxide protective layer and so the iron present reacts with the moisture in the air to produce iron oxide or ‘rust’. Mild steel therefore requires further processing such as galvanizing in order to give it a protective surface.

Fabrication

As chrome is a hard alloy, stainless steels are much more impact resistant compared to mild steel and (although relatively easy to fabricate) are not as easy to fabricate as mild steel. Mild steel is much more malleable compared to stainless and so is used a lot in general fabrication.

Cost

The price of the metal is a large factor when choosing stainless steel or mild steel. Although stainless offers far superior life span and corrosion resistance over its mild counterpart, the various alloying elements (particularly chromium) make it more expensive. Coupled with the additional work required to fabricate, stainless steel is the more expensive however the benefits are an aesthetic metal with superb corrosion resistance and low maintenance.