JIS G3106 High-Strength Carbon Steel for Welded Structures
JIS G3106 specifies high-strength low-alloy (HSLA) carbon steels, primarily the SM series (e.g., SM400, SM490, SM520), designed for welded structures requiring superior strength and toughness. These grades feature controlled alloying elements like manganese and silicon to enhance weldability and mechanical performance, making them ideal for heavy engineering, bridges, and machinery. This article explores the chemical composition, mechanical properties, manufacturing processes, applications, and comparisons with related grades.
1. Core Chemical Composition (JIS G3106 Standard)
| Element | Content Range (e.g., SM490A) | Function |
|---|---|---|
| Carbon (C) | ≤ 0.20% | Provides basic strength; limited to ensure good weldability and avoid brittleness |
| Manganese (Mn) | 0.60 – 1.50% | Improves hardenability, strength, and toughness; enhances deoxidation and hot workability |
| Silicon (Si) | ≤ 0.55% | Aids deoxidation; contributes to strength and resistance to atmospheric corrosion |
| Phosphorus (P) | ≤ 0.035% | Controlled impurity; excess reduces ductility and increases cold shortness |
| Sulfur (S) | ≤ 0.035% | Minimized to prevent hot shortness and ensure weld integrity |
| Copper (Cu) | ≤ 0.30% | Optional; improves corrosion resistance in atmospheric environments |
2. Key Mechanical Properties (Room Temperature, e.g., SM490A)
- Tensile Strength: 490 – 610 MPa (high yield-to-tensile ratio for structural efficiency)
- Yield Strength: ≥ 325 MPa (for thicknesses ≤ 16mm; supports heavy load-bearing)
- Elongation: ≥ 17% (adequate ductility for forming and impact resistance)
- Charpy V-Notch Impact Toughness: ≥ 47 J at 0°C (ensures toughness in low-temperature applications)
- Hardness (HB): ≤ 170 (balanced for machinability and weld preparation)
3. Manufacturing Process Characteristics
- Steelmaking: Basic oxygen furnace (BOF) or electric arc furnace (EAF) followed by ladle refining to control inclusions and achieve fine grain structure for enhanced toughness.
- Hot Rolling: Controlled rolling at 850-950°C with finish rolling above Ar3 temperature to refine austenite grains, followed by accelerated cooling to improve strength without quenching.
- Normalization: Optional heat treatment at 880-950°C to homogenize microstructure, relieve internal stresses, and ensure consistent mechanical properties across plates.
- Ultrasonic Testing: Non-destructive testing per JIS G 0992 to detect internal defects, ensuring quality for welded fabrications.
- Surface Conditioning: Shot blasting and priming for corrosion protection during storage and fabrication.
4. Typical Application Fields
Bridge and Civil Engineering
Bridge girders, highway structures, and earthquake-resistant frameworks — leverages high strength-to-weight ratio for durable, cost-effective designs.
Heavy Machinery
Crane booms, excavator frames, and mining equipment — provides weldability and fatigue resistance under dynamic loads.
Shipbuilding and Offshore
Ship hull sections, offshore platforms, and pressure vessels — offers toughness in marine environments with proper coatings.
Construction Equipment
Building scaffolds, steel towers, and industrial silos — supports large-scale welding with minimal preheat requirements.
5. Difference from Similar Grades (SM400 vs SM490 vs SM520)
| Grade | Yield Strength (MPa) | Key Advantage | Suitable Scenario |
|---|---|---|---|
| SM400 | ≥ 235 | Cost-effective entry-level strength; excellent weldability | General welded structures (buildings, light machinery) |
| SM490 | ≥ 325 | Balanced strength and toughness; suitable for thicker sections | Bridges, heavy vehicles, and medium-load applications |
| SM520 | ≥ 365 | Higher tensile strength; improved fatigue resistance | High-stress environments (cranes, offshore rigs) |
6. Selection & Usage Precautions
- Welding Considerations: Preheat to 100-150°C for thicknesses >20mm to prevent cold cracking; use low-hydrogen electrodes (e.g., E5016) and control heat input below 2.5 kJ/mm.
- Corrosion Protection: Apply shop primers or galvanizing; not inherently corrosion-resistant — avoid prolonged exposure to chlorides without coatings.
- Thickness Limitations: Properties vary with plate thickness; consult JIS G3106 for adjustments in yield strength beyond 100mm.
- Quality Assurance: Verify compliance with JIS G3106 via mill certificates; perform weld procedure qualification (PQR) for critical applications.
7. Get a Steel Quote
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