The standard designation for Molybdenum steel in SAE is which of the following?

Molybdenum steel is identified in the SAE (Society of Automotive Engineers) system through specific designations, which denote the alloying elements and their percentages used in the steel. In the case of Molybdenum steel, the correct designation is 40XX.

The '40' in the designation indicates that the steel has a carbon content of approximately 0.40%, while the 'XX' indicates the presence of alloying elements, specifically molybdenum in this case. The last two digits typically provide additional information about other alloying elements or specific heat treatment characteristics, but the first two digits are key to identifying the primary alloying element.

Molybdenum steel exhibits desirable properties such as improved strength, hardness, and wear resistance compared to non-alloyed carbon steels. Its applications often include components that require these enhanced properties, making the designation of 40XX particularly relevant in the context of machine design and engineering applications.