Chromium is added to stainless steels to significantly increase which property?

• A. Corrosion resistance
• B. Electrical conductivity
• C. Tensile strength
• D. Thermal conductivity

Answer: (A)

Chromium’s main role in stainless steels is to form a protective, self-healing oxide film on the surface. When the alloy is exposed to oxygen, chromium forms a dense, adherent layer of chromium oxide (Cr2O3) that acts as a barrier to further oxidation and corrosion. This passive film limits the diffusion of iron, water, and ions to the metal, dramatically reducing the rate of corrosion. If the surface is scratched, chromium from the bulk replenishes the film, restoring protection. That passivation is the primary reason stainless steels resist rust and corrosion much more than plain iron or carbon steel. While chromium can influence other properties like strength in certain grades, the fundamental purpose of adding chromium is to boost corrosion resistance.