Steel Numbering System

The following is the numbering system for carbon and alloy steels using the SAE numbering system its is recognized globally.

• First two digits indicate the type of steel
• Last two digits indicate the carbon content

Using 4140 Alloy Steel as an example we see its main elements are chromium and molybdenum with a carbon content of 40%.

 Main Element

• 1xxx: Carbon steel
• 2xxx: Nickel steel
• 3xxx: Nickel-Chromium Steel
• 4xxx: Molybdenum Steel
• 41xx Chromium and Molybdenum Steels
• 43xx Nickel, Chromium and Molybdenum Steel
• 5xxx: Chromium Steel
• 6xxx: Chromium-Vanadium Steel
• 7xxx: Tungsten-Chromium Steel
• 8xxx: Nickel-Chromium-Molybdenum Steel