SS400 Carbon Structural Steel  

SS400 steel is a widely used carbon structural steel grade specified under the Japanese Industrial Standard JIS G3101. At Aobo Steel, with our extensive experience in steel forging and supply, we understand the importance of precise material specifications. Let’s break down what defines SS400.

1. What Does the “SS400” Designation Mean?

The JIS G3101 standard provides clear naming conventions:

• “SS”: This stands for “Steel Structure,” indicating its primary use in structural applications.
• “400”: This number represents the minimum guaranteed tensile strength of the steel in megapascals (MPa). So, SS400 steel must have a minimum tensile strength of 400 MPa.

JIS G3101 covers hot-rolled steel plates, sheets, strips, bars, and sections for general structural use. Remember that standards like JIS G3101 are updated over time (e.g., 1995, 2004, 2010 editions exist). Always verify requirements against the specific standard edition being used.

2. Key Mechanical Properties of SS400 steel

The performance of SS400 is defined by its mechanical properties, which can vary based on the product’s thickness or diameter.

2.1 Tensile and Yield Strength

• Tensile Strength (Rm​): As noted, the defining characteristic is its tensile strength, which falls within the range of 400 to 510 MPa for most common thicknesses.
• Yield Strength (ReL​or 2​): The minimum yield strength depends on the material’s dimensions:

• ≤16 mm thickness/diameter: Minimum 245 MPa
• >16 mm up to 40 mm thickness/diameter: Minimum 235 MPa
• >40 mm up to 100 mm thickness/diameter: Minimum 215 MPa
• >100 mm thickness/diameter: Minimum 205 MPa

2.2 Elongation (Ductility)

Elongation at fracture (A) measures ductility and also varies:

2.2.1 Plates/Sheets/Strip (Thickness):

• ≤5 mm: Min 19%
• >5 mm to ≤16 mm: Min 19%
• >16 mm to ≤50 mm: Min 21%
• >50 mm: Min 21% (Note potential overlap in ranges depending on specific standard table)

2.2.2 Bars/Angle Sections (Diameter/Thickness):

• ≤25 mm: Min 20%
• >25 mm: Min 24%

2.3 Bend Test Requirements

Bend tests confirm formability:

• Plates/Sheets/Strip: 180-degree bend. Inner radius (r) = 1.5× thickness (a) for a≤25 mm; r=2.0×a for a>25 mm.
• Bars/Angle Sections: 180-degree bend. Inner radius (r) = 1.5× diameter/thickness (d/t) for d/t≤25 mm; r=2.0×d/t for d/t>25 mm.

3. SS400 steel Chemical Composition (Example: JIS G 3101:1995)

Chemical composition is crucial for properties like weldability. Based on the 1995 version of the standard, the maximum limits for SS400 are generally:

• Carbon (C): ≤0.23%
• Silicon (Si): Not specified (typically low)
• Manganese (Mn): ≤1.40%
• Phosphorus (P): ≤0.050%
• Sulfur (S): ≤0.050%

Note: Always refer to the specific standard certificate for the exact chemical composition of a supplied batch.

4. Important Considerations of SS400 steel

• Suffixes: Sometimes SS400 may have suffixes (e.g., SS400-D2) indicating specific processing like cold drawing or tolerance levels.
• Related Standards: For welded structures, JIS G3106 (e.g., SM490A) covers steels specifically designed for weldability.
• International Equivalents: While SS400 is sometimes compared to grades like ASTM A36 or certain ISO 630 grades, direct equivalence isn’t guaranteed. Differences in composition or required properties often exist. Always check the specific requirements of each standard for accurate comparison.

SS400 is a reliable, general-purpose structural steel defined by its minimum tensile strength and governed by JIS G3101. Its specific mechanical properties depend on the product form and dimensions. For precise applications, consulting the relevant JIS standard edition is essential.

At Aobo Steel, we leverage our 20+ years of forging experience and deep knowledge of materials like tool steel and alloy steel to ensure our customers receive materials that meet their exact specifications. Contact us for your steel requirements.