In the designation '4130' for chromium molybdenum steel, the first digit indicates what aspect of the alloy?

In the designation '4130' for chromium molybdenum steel, the first digit indicates what aspect of the alloy?

• A. Percentage of Basic Element in the Alloy
• B. Percentage of Carbon in Hundredths of a Percent
• C. Basic Alloying Element
• D. Carbon Content

Answer: (C)

In SAE/AISI steel numbering, the digits encode composition, and the first digit marks the general alloy family by its major alloying element. For chromium–molybdenum steels, that category is indicated by the first digit. So in 4130, the initial 4 tells you the steel belongs to the chromium-molybdenum group, with the remaining digits (the 1, 3, and 0) refining the specific elements and the carbon content. The carbon content is actually shown by the last two digits (30 → 0.30%), not by the first digit. Therefore, the first digit represents the basic alloying element category.

In SAE/AISI steel numbering, the digits encode composition, and the first digit marks the general alloy family by its major alloying element. For chromium–molybdenum steels, that category is indicated by the first digit. So in 4130, the initial 4 tells you the steel belongs to the chromium-molybdenum group, with the remaining digits (the 1, 3, and 0) refining the specific elements and the carbon content. The carbon content is actually shown by the last two digits (30 → 0.30%), not by the first digit. Therefore, the first digit represents the basic alloying element category.