S355J2 Carbon Steel: Structural Steel from the EN 10025 Series
S355J2 carbon steel, designated under the EN 10025-2 standard (yield strength of 355 MPa), is a non-alloy structural steel widely utilized in construction and engineering. With a balanced composition featuring low carbon, manganese, and trace elements, it offers high strength, good weldability, and impact toughness at low temperatures (-20°C). This grade is ideal for load-bearing structures, bridges, and heavy machinery. This article explores its chemical makeup, mechanical properties, production methods, applications, and comparative advantages.
1. Core Chemical Composition (EN 10025-2 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.22% | Provides basic strength; controlled to ensure weldability and ductility |
| Manganese (Mn) | 0.90 – 1.60% | Enhances strength and toughness; improves hardenability during cooling |
| Silicon (Si) | ≤ 0.55% | Aids deoxidation; supports scaling resistance in hot working |
| Phosphorus (P) | ≤ 0.025% | Limited impurity; minimizes brittleness and cold shortness |
| Sulfur (S) | ≤ 0.025% | Controlled to prevent hot shortness and promote machinability |
| Niobium (Nb) | ≤ 0.05% | Micro-alloying element; refines grain structure for improved strength |
| Vanadium (V) | ≤ 0.12% | Enhances precipitation strengthening; boosts fatigue resistance |
2. Key Mechanical Properties (Room Temperature, Thickness ≤ 16 mm)
- Yield Strength (ReH): ≥ 355 MPa (guarantees structural integrity under load)
- Tensile Strength (Rm): 470 – 630 MPa (high load capacity for engineering applications)
- Elongation (A): ≥ 22% (adequate ductility for forming and fabrication)
- Charpy V-Notch Impact (KV): ≥ 27 J at -20°C (Charpy V-notch toughness for cold environments)
- Hardness (HB): ≤ 163 (suitable for welding and machining without excessive wear)
3. Manufacturing Process Characteristics
- Steelmaking: Basic oxygen furnace (BOF) or electric arc furnace (EAF) followed by ladle refining to achieve low impurity levels and fine grain control.
- Hot Rolling: Rolled at 900-1100°C to produce plates, sections, or bars; normalized or controlled cooling to refine microstructure and meet impact requirements.
- Heat Treatment: Normalizing at 850-900°C for stress relief and uniform properties; optional quenching and tempering for enhanced toughness in critical sections.
- Cooling and Finishing: Air cooling post-rolling; surface inspection and shot blasting to remove scale, ensuring compliance with EN 10163 standards.
- Quality Control: Ultrasonic testing (UT) per EN 10160 for internal defects; mill certification to verify mechanical and chemical specs.
4. Typical Application Fields
Construction and Infrastructure
Beams, columns, and girders in buildings; bridge components, offshore platforms, and crane structures — supports heavy static and dynamic loads.
Mechanical Engineering
Machine frames, pressure vessels, and conveyor systems; gears and shafts where weldability and toughness are essential.
Heavy Equipment
Earthmoving machinery, agricultural implements, and mining equipment — withstands impact and fatigue in harsh conditions.
Pipelines and Transmission
Oil and gas pipelines, transmission towers, and storage tanks — reliable performance in moderate corrosive environments with proper coatings.
5. Difference from Similar Grades (S355J2 vs S355JR vs S355J0)
| Grade | Impact Test Temperature | Key Advantage | Suitable Scenario |
|---|---|---|---|
| S355JR | +20°C (≥ 27 J) | Cost-effective for ambient conditions | Indoor structures and general fabrication |
| S355J0 | 0°C (≥ 27 J) | Balanced toughness for mild climates | Outdoor non-critical applications like sheds |
| S355J2 | -20°C (≥ 27 J) | Superior low-temperature performance | Cold regions, bridges, and heavy machinery |
6. Selection & Usage Precautions
- Corrosion Protection: Not inherently corrosion-resistant; apply galvanizing, painting, or weathering coatings for outdoor exposure to prevent rust.
- Welding Guidelines: Preheat to 100-150°C for thicknesses >20 mm; use low-hydrogen electrodes (e.g., E7018) to avoid hydrogen cracking; post-weld heat treatment if required.
- Fatigue Considerations: Design with safety factors for cyclic loading; avoid sharp notches to maintain impact toughness.
- Compliance Verification: Ensure CE marking and EN 1090 certification for structural use; request material test certificates (EN 10204) for traceability.
7. Get a Carbon Steel Quote
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