Chromium, Copper, Titanium, Molybdenum, and a few others make stainless steel a highly corrosion-resistant metal alloy. Stainless Steel comes in many grades, but all Stainless Steels contain at least 11% Chromium.
The term 'steel grades' is frequently used when researching steel. Steel's chemical composition is simply described here. For external architectural uses, Grade 304 and Grade 316 are the most common grades.