December 19th, 2022

Most people are unaware that there are over 3,500 different grades of steel. You can find a steel's grade by measuring the amount of carbon in the steel, its other alloys, and how the manufacturer processes it. Steel is graded and categorized into four groups; Carbon, Alloys, Stainless, and Tool. Steel Grading systems help differentiate types of steel based on properties and their different uses.

How the ASTM Steel Grading System Works

The American Society for Testing and Materials (ASTM) grading system consists of around 12,000 different codes that classify various metal grades on the market. It assigns each metal a letter or prefix based on category ("A" is the designated letter for iron and steel). Each metal is also assigned a corresponding number that represents the specific properties of that metal. 

For example, A351 is the standard specification for austenitic steel castings. So, if a customer would like their steel to be cast, you would refer to this specific ASTM standard. The ASTM is responsible for setting product development and manufacturing standards across all industries.

AISI/SAE Standards for Steel Grading

The American Iron and Steel Institute (AISI)/Society of Automotive Engineers (SAE) is another steel grading system. It differs from the ASTM numbers in the sense that it exclusively covers product standards while only considering steel and iron.

Alloy steels and carbon steels are assigned specific grades through a four-digit AISI/SAE numerical index system. The first two digits indicate whether the material is plain carbon steel or if it may contain alloying elements. The last two digits indicate what percentage of the steel is made up of carbon. 

For example, let's look at AISI/SAE No.1020: the first digit (1) indicates that this is plain carbon steel, the second digit (0) means there are no alloying elements, and the last two numbers (20) shows that that steel contains about 0.20 percent carbon, classifying it as a low-carbon (or mild) steel.

Understanding Steel Grading

Steel grading standards are fundamental and used in various fields, including science, architecture, engineering, and even in some government agencies. They provide standard terms to ensure the properties and specifications of steel and steel alloys are aligned throughout all industries while providing standard processing and application procedures for all manufacturers.

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