Nickel-chromium-molybdenum steel corresponds to which SAE designation?

Nickel-chromium-molybdenum steel is designated by the SAE (Society of Automotive Engineers) system with a specific set of numbering that indicates its composition. The correct designation, SAE 49XX, reflects a steel that typically contains nickel, chromium, and molybdenum as its primary alloying elements.

The '49' in the designation signifies that it has a significant nickel content, which enhances toughness and resistance to impact, while chromium is known for improving hardenability and corrosion resistance. Molybdenum further contributes to strength at high temperatures and resistance to softening. Together, these elements make 49XX steels highly suitable for applications requiring strength and durability, like crankshafts and gears.

Understanding the SAE numbering scheme is essential, as it categorizes various steel grades based on their alloying elements. The absence of nickel, chromium, or molybdenum in the other options provides clarity on why these specific designations do not correlate with the described steel.