Chromium is added to carbon steel primarily to

• A. Increase the resistance to rust and corrosion
• B. Increase the hardness
• C. Decrease brittleness
• D. Improve electrical conductivity

Answer: (A)

Chromium is added to carbon steel to form a protective surface film that resists rust and corrosion. It tends to create a stable chromium oxide layer (a passive film) on the steel surface, which slows down ongoing oxidation and can even self-heal if damaged. This is the same principle that makes stainless steels corrosion resistant. While chromium can influence hardness or other properties in different contexts, the primary reason in carbon steel is to boost its resistance to rust and corrosion.