Iron is the primary element in stainless steel.
Stainless steel is an alloy whose main ingredient is iron, with a minimum of about 10.5% chromium by mass. Chromium reacts with oxygen to form a thin, self-repairing oxide layer that greatly improves resistance to rust and staining.
Other stainless-steel grades may contain nickel, molybdenum, manganese, or nitrogen. These additions change properties such as strength, corrosion resistance, magnetism, and suitability for high temperatures. The exact composition depends on the grade and intended use.
A common misunderstanding is that stainless steel cannot corrode at all. It is highly corrosion-resistant, but harsh chemicals, salt, poor maintenance, or damage to the protective surface can still cause staining or localized corrosion. Chromium provides the key protection, but iron remains the bulk metal.