What two metals are most commonly found in stainless steel?

At its core, all steel is an alloy, a mixture of metals, with iron serving as its primary component. The problem with iron, however, is its natural tendency to rust when exposed to oxygen and moisture. To create the famously corrosion-resistant material we know as stainless steel, a second key element is added: chromium. By law in the United States, stainless steel must contain a minimum of 10.5% chromium by mass.

The true genius of this combination lies in how chromium protects the iron. When exposed to oxygen in the air or water, the chromium forms an incredibly thin, transparent, and tough layer of chromium oxide on the surface of the steel. This "passive layer" acts as an invisible shield, preventing oxygen from reaching the iron underneath and stopping rust before it can even start.

What makes this protective shield so effective is that it is self-healing. If the stainless steel is scratched or cut, the newly exposed chromium immediately reacts with oxygen to instantly reform the barrier, maintaining its protective qualities. While other elements like nickel and manganese are often added to enhance certain properties, it is the fundamental partnership between iron and chromium that gives stainless steel its signature "stainless" quality.