Which option describes unprotected steel with only mill scale on the surface?

• A. Black Steel
• B. Galvanized Steel
• C. White Steel
• D. Stainless Steel

Answer: (A)

Mill scale forms on hot‑rolled steel as a dark oxide layer on the surface. When the steel is unprotected and the only surface present is this mill scale, the proper label is black steel. This description is specific to uncoated carbon steel that still carries the oxide layer from rolling, rather than having any protective coating.

This helps distinguish it from galvanized steel, which has a zinc coating providing corrosion protection; from white steel, which refers to a scale-free or bright, cleaned surface; and from stainless steel, which contains chromium and other alloys that form a protective passive film and resist corrosion. In practice, recognizing black steel signals higher corrosion risk due to the absence of durable protective coatings.