The standard designation for plain carbon steel in SAE is?

Plain carbon steel is designated in the SAE system based on its carbon content, which is represented by a four-digit code where the first digit or digits indicate the steel type, and the remaining digits specify the carbon content. For plain carbon steels, the initial digit is typically '1' or '10', which indicates it as a carbon steel.

In the case of plain carbon steel, the designation '10XX' indicates that it is a carbon steel with a carbon content ranging from 0.10% to 1.0%. The 'XX' part represents the additional alloying elements, which are negligible in plain carbon steels, meaning this designation is specifically categorized for those steels that do not include significant alloying elements beyond carbon.

This classification is important for material selection in engineering design, as it helps in understanding the material properties, including hardness, tensile strength, and ductility, which are typically more dependent on the carbon content in these steels.