SS400: Medium-strength General Structural Carbon Steel
SS400, a standard grade under the Japanese Industrial Standards (JIS G3101), is a versatile medium-strength carbon steel widely used for general structural purposes. Known for its good weldability, machinability, and cost-effectiveness, SS400 features a simple chemical composition with low alloying elements, making it suitable for construction, machinery, and fabrication applications. This article explores its key properties, production methods, applications, and comparative advantages.
1. Core Chemical Composition (JIS G3101 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.25% | Provides basic strength; controlled to ensure ductility and weldability |
| Manganese (Mn) | ≤ 1.50% | Improves hardenability and toughness; aids in deoxidation |
| Phosphorus (P) | ≤ 0.050% | Limited to prevent brittleness and maintain impact resistance |
| Sulfur (S) | ≤ 0.050% | Restricted to avoid hot shortness and ensure good hot workability |
| Silicon (Si) | ≤ 0.50% | Enhances strength and oxidation resistance during processing |
| Iron (Fe) | Balance | Primary matrix element for structural integrity |
2. Key Mechanical Properties (Room Temperature)
- Tensile Strength (σb): 400-510 MPa (JIS G3101 standard; adequate for general loading)
- Yield Strength (σ0.2): ≥ 245 MPa (for thicknesses ≤ 16mm; supports moderate structural demands)
- Elongation (δ): ≥ 21% (good formability for bending and shaping)
- Hardness (HB): 120-170 (Brinell hardness; facilitates machining and assembly)
- Impact Toughness: Not specified in standard but typically ≥ 27 J at 20°C (suitable for non-critical low-temperature use)
3. Manufacturing Process Characteristics
- Steelmaking: Basic oxygen furnace (BOF) or electric arc furnace (EAF) followed by ladle refining to achieve low impurity levels and uniform composition.
- Hot Rolling: Rolled at 850-1100°C to produce plates, sheets, or sections; controlled cooling to refine grain structure and achieve desired mechanical properties.
- Normalization: Optional heat treatment at 880-950°C followed by air cooling to improve uniformity and relieve internal stresses.
- Cold Forming: For thinner sections, cold bending or drawing with annealing (650-700°C) to restore ductility if work-hardening occurs.
- Surface Treatment: Pickling in acid solutions to remove scale; optional shot blasting or priming for corrosion protection in outdoor applications.
4. Typical Application Fields
Construction and Infrastructure
Beams, columns, bridges, and building frameworks — ideal for welded structures requiring economical strength without high corrosion demands.
Machinery and Equipment
Frames for agricultural machinery, conveyor systems, and general machine bases — excellent weldability for fabrication.
Automotive and Transportation
Chassis components, trailer frames, and railway parts — balances strength and formability for vehicle manufacturing.
Fabrication and General Use
Pipes, tubes, angles, and channels for shelving, platforms, and storage racks — cost-effective for non-specialized structural needs.
5. Difference from Similar Grades (SS400 vs A36 vs S235JR)
| Grade | Yield Strength (MPa) | Key Advantage | Suitable Scenario |
|---|---|---|---|
| SS400 (JIS) | ≥ 245 | Superior weldability in Asian standards; economical | General structural fabrication in construction and machinery |
| A36 (ASTM) | ≥ 250 | Well-established in North American markets; similar properties | Buildings, bridges, and riveted/welded structures |
| S235JR (EN) | ≥ 235 | European compliance; good cold formability | Offshore platforms and lightweight structural components |
6. Selection & Usage Precautions
- Corrosion Protection: Not inherently corrosion-resistant; apply coatings (galvanizing, painting) for outdoor or humid environments to prevent rusting.
- Welding Guidelines: Suitable for all common welding processes (SMAW, GMAW); use low-hydrogen electrodes to minimize cracking risks.
- Thickness Considerations: Properties vary with thickness (e.g., yield strength decreases above 16mm); select based on structural calculations.
- Quality Assurance: Verify with material certificates confirming JIS G3101 compliance, including chemical and mechanical test results.
7. Get a Carbon Steel Quote
If you need customized SS400 carbon steel products (plates, sections, pipes, bars) or want a detailed price quote, contact our team. Our specialists offer professional support and competitive pricing tailored to your needs.