Basics on Steel Classification and Numbering

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Basics on Steel Classification and Numbering

Within the world of metal, steel is a very broad category. There are several general types of steel out there, plus additional ways of classifying them and number systems used for this classification.

At Wasatch Steel, our experts can help you with anything you need to know when it comes to steel categorization and classification. Let’s take a look at the basics here.


According to the American Iron and Steel Institute (AISI), steel is broken into four basic categories based on chemical composition:

  • Carbon steel
  • Alloy steel
  • Stainless steel
  • Tool steel

There are several different grades that have different properties – physical, chemical and environmental. In reality, all steel is made of at least some iron and carbon; it’s the actual amount of carbon and the additional alloys used that change the properties between styles.


In addition, steel can be classified using a few important factors:

  • Composition: Carbon range, alloy, and stainless properties
  • Production method: Continuous cast, electric furnace, others
  • Finishing method: Cold rolling, hot rolling, cold drawing, etc
  • Form or shape: Bar, tube, pipe, plate, sheet, others
  • De-oxidation process: Killed, semi-killed, etc
  • Microstructure: Ferritic, pearlitic, martensitic, others
  • Physical strength (using ATSM standards)
  • Heat treatment: Annealed, quenched, tempered, others
  • Quality nomenclature: Commercial quality, drawing quality, pressure vessel quality, others

Numbering Systems

There are two major numbering systems in the steel industry. One was developed by the AISI, and the other by the Society of Automotive Engineers. Both use four-digit code numbers to identify base carbon and alloy steels, with certain selections of alloys that have five digits instead.

In general, if the first digit is a 1, this indicates carbon steel in both numbering systems. The first digit then moves down in order of other alloy steels, with nickel labeled as number 2 and the list running all the way down to 9, where silicon-manganese steels and other SAE grades are found. The second digit generally indicates the concentration of the major element, while the last two digits indicate carbon concentration. So for instance, SAE 5130 is a chromium alloy steel that contains about 1 percent chromium and about 0.3 percent carbon.

For more on steel classification, or to learn more about any of our steel services, speak to the pros at Wasatch Steel today.