JIS G3101 General Structural Carbon Steel: Versatile Rolled Steel for Construction and Engineering
JIS G3101 is a Japanese Industrial Standard specifying general structural rolled steels for welded structures, widely used in construction, bridges, and machinery due to their excellent weldability, formability, and cost-effectiveness. Key grades include SS400 (most common), SS490, and SS540, offering varying strength levels. This article covers chemical composition, mechanical properties, manufacturing processes, applications, and comparisons to guide material selection in structural engineering.
1. Core Chemical Composition (JIS G3101 Standard)
| Element | Content Range (SS400 Grade) | Function |
|---|---|---|
| Carbon (C) | ≤ 0.25% | Primary strength contributor; controlled to balance ductility and weldability |
| Manganese (Mn) | ≤ 1.50% | Improves strength and toughness; aids in deoxidation during smelting |
| Phosphorus (P) | ≤ 0.050% | Impurity limited to enhance ductility and prevent brittleness |
| Sulfur (S) | ≤ 0.050% | Restricted to minimize hot shortness and ensure good weldability |
2. Key Mechanical Properties (Room Temperature, SS400 Grade)
- Tensile Strength (σb): 400-510 MPa (provides robust load-bearing for structural elements)
- Yield Strength (σ0.2): ≥ 235 MPa (for plates ≤ 16mm thickness; supports deformation resistance)
- Elongation (δ): ≥ 21% (ensures formability for bending and riveting)
- Hardness (HB): ≤ 170 (Brinell; facilitates machining and fabrication)
- Impact Toughness: Not specified in standard, but typically ≥ 27 J at 20°C for welded applications
3. Manufacturing Process Characteristics
- Smelting: Basic oxygen furnace (BOF) or electric arc furnace (EAF) followed by ladle refining to control impurities and achieve uniform composition.
- Hot Rolling: Rolled at 850-1100°C into plates, sections, or bars; controlled cooling to refine grain structure and meet strength requirements.
- Normalizing: Optional heat treatment at 850-900°C for stress relief and improved uniformity in heavy sections.
- Cutting and Shaping: Flame cutting or shearing for plates; hot forging for sections to enhance weldability without cracking.
- Surface Treatment: Shot blasting to remove scale; priming for corrosion protection in outdoor applications.
4. Typical Application Fields
Construction and Infrastructure
Building frameworks, steel beams, columns, and bridge girders — ideal for seismic zones due to ductility and weldability.
Machinery and Equipment
Heavy machine bases, crane structures, conveyor frames, and agricultural implements — cost-effective for moderate-strength needs.
Automotive and Transportation
Chassis components, trailer frames, and railway parts — balances strength with formability for fabrication.
General Fabrication
Welded pipes, storage tanks, and structural supports — versatile for non-corrosive environments with protective coatings.
5. Difference from Similar Grades (SS400 vs SS490 vs ASTM Equivalents)
| Grade | Yield Strength | Key Advantage | Suitable Scenario |
|---|---|---|---|
| JIS SS400 | ≥ 235 MPa | High ductility and weldability; economical | General construction and light structures |
| JIS SS490 | ≥ 285 MPa | Enhanced strength for heavier loads | Bridges and high-stress frameworks |
| ASTM A36 | ≥ 250 MPa | Similar properties; global availability | International projects requiring U.S. standards compliance |
6. Selection & Usage Precautions
- Environmental Considerations: Susceptible to corrosion in humid or marine environments — apply galvanizing or painting for protection.
- Welding Guidelines: Use low-hydrogen electrodes (e.g., E7018); preheat for thick sections (>25mm) to avoid cold cracking.
- Thickness Selection: Properties vary with thickness; verify yield strength de-rates for plates >40mm.
- Quality Assurance: Require mill test certificates (MTC) confirming JIS G3101 compliance, including tensile tests and chemical analysis.
7. Get a Steel Quote
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