What is the difference between weathering steel (A606-4) and standard carbon steel in terms of corrosion resistance?

• A. Weathering steel corrodes faster always.
• B. Weathering steel cannot be used outdoors.
• C. Standard carbon steel never needs protection.
• D. Weathering steel forms a protective patina in atmospheric exposure, reducing the need for coatings; standard carbon steel requires protection (paint or galvanizing).

Answer: (D)

Weathering steel is designed to develop a tightly adherent patina when exposed to the atmosphere. This protective oxide layer forms after the initial rusting and slows further corrosion, reducing or even eliminating the need for coatings in many outdoor environments. Standard carbon steel, by contrast, lacks this protective patina and will continue to corrode unless it is protected with coatings or galvanizing. So, in atmospheric exposure, weathering steel offers improved corrosion resistance with less maintenance, while standard carbon steel typically requires paint or other protective measures. The other statements misstate the behavior: weathering steel does not always corrode faster, it can be used outdoors, and carbon steel generally does need protection.