Quality descriptors are applied to steel products in broad categories such as merchant, industrial, or structural quality. These labels mark certain steel as being suitable for specific applications and fabrication processes, allowing for faster market navigation and decision making. Steel is placed in specific categories based on several different factors:

• Internal soundness
• Chemical composition and uniformity
• Degree of surface imperfections
• Extent of testing during manufacturing
• The number, size, and distribution of inclusions
• Hardenability

Steel grading systems

Specifications, such as those issued by ASTM, AISI (American Iron and Steel Institute), and SAE, provide a standard language for engineers, fabricators, and consumers to communicate the properties of steel. Grading is often very specific—including everything from chemical compositions, physical properties, heat treatments, fabrication processes, and forms.

SAE

The AISI/SAE numbering system uses a 4-digit number for classification. The first two numbers indicate the steel type and alloying element concentration, and the last two numbers indicate carbon concentration.
For example, SAE 5130 describes a steel containing 1% Chromium and 0.30% Carbon. Letter prefixes are used as quality descriptors for merchant quality.

ASTM

The ASTM system uses a descriptive letter followed by a sequential number. For example, ‘A’ indicates a ferrous metal, and ’53’ is the number assigned to galvanized carbon steel.
ASTM A53 would have the following properties:

• Chemical composition, Max %
• Carbon: 0.25 (Grade A), 0.30 (Grade B)
• Manganese: 0.95 (Grade A), 1.20 (Grade B)
• Phosphorous: 0.05
• Sulfur: 0.045
• Mechanical properties
• Tensile Strength, UTS: 330 MPa or 48,000 psi (Grade A), 414 MPa or 60,000 psi (Grade B)
• Tensile Strength, Yield: 207 MPa or 30,000 psi (Grade A), 241 MPa or 35,000 psi (Grade B)
• Form and treatment
• Pipe NPS 1/8 – NPS 26
• Galvanized steel
• Black and hot-dipped
• Zinc coated
• Welded and seamless