SM570: Ultra-high strength welded structural carbon steel
SM570 steel, designated under the JIS G3106 standard for rolled steels for welded structure, is a high-strength low-alloy (HSLA) carbon steel renowned for its exceptional tensile strength and weldability. With a minimum yield strength of 570 MPa, it is ideal for heavy-duty applications requiring robust structural integrity, such as bridges, buildings, and machinery. This article explores its chemical composition, mechanical properties, manufacturing processes, applications, and comparative advantages in the steel industry.
1. Core Chemical Composition (JIS G3106 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.18% | Provides basic strength; controlled to ensure good weldability without brittleness |
| Silicon (Si) | ≤ 0.55% | Enhances deoxidation and improves elasticity and strength |
| Manganese (Mn) | ≤ 1.60% | Increases hardenability and tensile strength; aids in desulfurization |
| Phosphorus (P) | ≤ 0.025% | Minimized to prevent brittleness and improve ductility |
| Sulfur (S) | ≤ 0.015% | Strictly controlled to reduce hot shortness and enhance weldability |
| Niobium (Nb) | ≤ 0.05% (optional micro-alloying) | Refines grain structure for improved toughness and fatigue resistance |
| Vanadium (V) | ≤ 0.10% (optional) | Boosts precipitation hardening for higher yield strength |
2. Key Mechanical Properties (Room Temperature)
- Yield Strength (ReH): ≥ 570 MPa for t ≤ 16 mm (superior to standard structural steels for load-bearing)
- Tensile Strength (Rm): 570-720 MPa (high ductility under tension)
- Elongation (A): ≥ 17% (adequate for forming and welding without cracking)
- Impact Toughness (KV2): ≥ 47 J at 0°C (excellent low-temperature performance for seismic zones)
- Hardness (HB): ≤ 230 (balanced for machinability and wear resistance)
3. Manufacturing Process Characteristics
- Smelting: Basic oxygen furnace (BOF) or electric arc furnace (EAF) with vacuum degassing to achieve low impurity levels and uniform composition.
- Continuous Casting: Slab casting followed by reheating to 1200-1250°C to ensure homogeneity and prevent segregation.
- Hot Rolling: Controlled rolling in the 900-1100°C range with finishing at lower temperatures to refine microstructure and achieve high strength via controlled rolling and cooling.
- Heat Treatment: Normalized at 880-920°C or quenched and tempered (Q&T) for enhanced toughness; air cooling to avoid distortion.
- Quality Control: Ultrasonic testing (UT) for internal defects and surface inspection per JIS standards to guarantee weldability and structural reliability.
4. Typical Application Fields
Construction and Infrastructure
Bridges, high-rise buildings, offshore platforms, and seismic-resistant structures — leverages high strength-to-weight ratio for efficient designs.
Machinery and Equipment
Heavy machinery frames, crane booms, mining equipment, and pressure vessels — withstands dynamic loads and fatigue.
Automotive and Transportation
Truck chassis, railcar components, and shipbuilding hull sections — provides durability in harsh environments.
Energy Sector
Wind turbine towers, pipelines, and power plant supports — resists corrosion and maintains integrity under stress.
5. Difference from Similar Grades (SM570 vs SM490 vs SM520)
| Grade | Yield Strength (MPa) | Key Advantage | Suitable Scenario |
|---|---|---|---|
| SM570 | ≥ 570 | Ultra-high strength with good weldability | High-load, space-constrained structures like bridges |
| SM490 | ≥ 490 | Cost-effective medium strength | General buildings and moderate-stress components |
| SM520 | ≥ 520 | Balanced strength and formability | Machinery frames and welded assemblies |
6. Selection & Usage Precautions
- Welding Considerations: Preheat to 100-150°C for thicknesses >20mm; use low-hydrogen electrodes (e.g., E7018) to prevent cold cracking.
- Corrosion Protection: Not inherently corrosion-resistant; apply galvanizing or coatings for outdoor exposure in humid or saline environments.
- Thickness Limits: Optimal for plates up to 100mm; for thicker sections, consult normalized vs. Q&T variants for toughness.
- Compliance Verification: Ensure certification to JIS G3106; request material test reports (MTR) for traceability and property confirmation.
7. Get a Steel Quote
If you require customized SM570 steel products (plates, sections, bars) or a detailed price quote for wholesale, contact our team. We offer professional guidance and competitive rates tailored to your project needs.