In the designation 4130, what does the first digit indicate?

• A. Basic alloying element
• B. Carbon content
• C. Heat treatment
• D. Manufacturing process

Answer: (A)

In SAE/ASME steel designations, the digits encode composition, and the first digit flags the principal alloying element that defines the steel’s family. For the designation shown, the first digit signals chromium as the base alloying element, so the steel is a chromium-based alloy (with molybdenum and carbon content specified by the remaining digits). This is why the first digit is described as indicating the basic alloying element. The other digits describe additional elements and approximate carbon content, not the first digit’s element.