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Around the world, a variety of organizations have developed standards for steel grading, including British Standards, Japanese Industrial Standards, and Germany’s GB Standard. However, SAE International’s steel grading system is the most common. Started in the 1930s as a joint effort between SAE and the American Iron and Steel Institute (AISI), the two designed a number system that is still used today. Here are SAE’s basic designations for carbon and alloy steel:
- 1xxx: Carbon Steel
- 2xxx: Nickel Steel
- 3xxx: Nickel-Chromium Steel
- 4xxx: Molybdenum Steel
- 5xxx: Chromium Steel
- 6xxx: Chromium-Vanadium Steel
- 7xxx: Tungsten Steel
- 8xxx: Nickel-Chromium-Molybdenum Steel
- 9xxx: Silicon-Manganese Steel
How does the number grading work?
These steel alloys are distinguished with a four-digit number. As seen in the list above, the first digit represents the primary alloying element. In some cases, there are multiple elements, such as nickel-chromium-molybdenum steel (8xxx). If there are secondary elements, they are represented by the second digit in the sequence. Here are a few examples:
- 10xx: Plain Carbon Steel
- 13xx: Manganese Steel (Mn 1.75%)
- 32xx: Nickel-Chromium Steel (Ni 1.25%, Cr 1.07%)
- 34xx: Nickel-Chromium Steel (Ni 3%, Cr 0.77%)
- 72xx: Tungsten-Chromium Steel (W 1.75%, Cr 0.75%)
Finally, the last two digits in the grading system are devoted to the alloy’s carbon percentage (in hundredths, by weight). If the last two digits are 45, that means the carbon content is 0.45 wt%.
How is stainless steel graded?
Unlike carbon and alloy steels, stainless steel has its own grading system. With three digits instead of four, there are less stainless steel alloys to categorize. Similar to the previous grading method, the first digit represents the primary alloy composition. Here are the main categories:
- 1xx: Austenitic General Purpose Alloys
- 2xx: Austenitic Chromium-Nickel-Manganese Alloys
- 3xx: Austenitic Chromium-Nickel Alloys
- 4xx: Ferritic and Martensitic Chromium Alloys
- 5xx: Heat-Resisting Chromium Alloys
