SM490A: Medium-High Strength Welded Structural Carbon Steel
SM490A, designated under the JIS G3106 standard, is a medium-high strength low-alloy carbon steel grade specifically designed for welded structures. With a minimum yield strength of 325 MPa for thicknesses up to 16 mm, it offers an optimal balance of strength, toughness, and weldability, making it ideal for heavy-duty construction and engineering applications. This article explores its chemical composition, mechanical properties, manufacturing processes, applications, and comparisons with related grades.
1. Core Chemical Composition (JIS G3106 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.20% (for t ≤ 50 mm) | Provides basic strength; controlled to ensure good weldability and ductility |
| Manganese (Mn) | 0.60 – 1.50% | Enhances strength and toughness; improves hardenability and deoxidation |
| Phosphorus (P) | ≤ 0.035% | Restricted to minimize brittleness and improve impact resistance |
| Sulfur (S) | ≤ 0.035% | Controlled to prevent hot shortness and ensure sound weld joints |
| Silicon (Si) | ≤ 0.55% | Aids in deoxidation; contributes to strength without excessive brittleness |
| Copper (Cu) | ≤ 0.30% (when specified) | Improves corrosion resistance in atmospheric environments |
| Others (Ni, Cr, Mo, etc.) | ≤ 0.50% combined | Alloying elements for enhanced performance if required |
2. Key Mechanical Properties (Room Temperature)
- Yield Strength (σs): ≥ 325 MPa (for t ≤ 16 mm), ≥ 295 MPa (for 16 < t ≤ 40 mm)
- Tensile Strength (σb): 490 – 610 MPa (ensures high load-bearing capacity in structures)
- Elongation (A): ≥ 17% (longitudinal; provides sufficient ductility for fabrication)
- Charpy V-Notch Impact (KV): ≥ 47 J at 0°C (optional for improved toughness in cold conditions)
- Hardness (HB): ≤ 170 (suitable for welding and machining)
3. Manufacturing Process Characteristics
- Smelting: Basic oxygen furnace (BOF) or electric arc furnace (EAF) followed by ladle refining to achieve low impurity levels and consistent chemistry.
- Hot Rolling: Controlled rolling at 850-1100°C with finishing temperature above 700°C, followed by air cooling to refine grain structure and enhance mechanical properties.
- Normalization (Optional): Heating to 880-950°C and air cooling to improve uniformity and toughness, especially for thicker plates.
- Heat Treatment: Stress relieving at 550-650°C if required post-welding to minimize residual stresses without affecting strength.
- Surface Treatment: Shot blasting and priming for corrosion protection; ultrasonic testing for internal defect detection to ensure quality.
4. Typical Application Fields
Construction & Infrastructure
Bridges, buildings, and high-rise structures; used for beams, columns, and girders requiring high strength-to-weight ratio.
Machinery & Equipment
Heavy machinery frames, crane booms, excavator components, and mining equipment — withstands dynamic loads effectively.
Shipbuilding & Transportation
Ship hulls, railcar underframes, and truck chassis; provides durability in harsh environmental conditions.
Pressure Vessels & Piping
Low to medium-pressure boilers, storage tanks, and pipelines — weldable for seamless fabrication.
5. Difference from Similar Grades (SM490A vs SM490B vs SM490C)
| Grade | Yield Strength (MPa) | Key Advantage | Suitable Scenario |
|---|---|---|---|
| SM490A | ≥ 325 (t ≤ 16 mm) | Cost-effective with good weldability; no mandatory impact testing | General welded structures in mild environments |
| SM490B | ≥ 325 (t ≤ 16 mm) | Requires impact testing at 0°C; enhanced low-temperature toughness | Structures exposed to cold weather or impact loads |
| SM490C | ≥ 325 (t ≤ 16 mm) | Impact testing at -20°C; superior fracture toughness | Offshore platforms, bridges in severe climates |
6. Selection & Usage Precautions
- Welding Recommendations: Use low-hydrogen electrodes (e.g., E5016) and preheating (100-150°C for t > 20 mm) to prevent cold cracking; control heat input to maintain properties.
- Corrosion Protection: Apply suitable coatings or galvanizing for outdoor use; not inherently corrosion-resistant in aggressive atmospheres.
- Thickness Considerations: Properties vary with thickness; verify for plates > 100 mm where yield strength may reduce.
- Quality Assurance: Ensure compliance with JIS G3106 via mill certificates; perform non-destructive testing (NDT) for critical applications.
7. Get a SM490A Steel Quote
If you need customized SM490A steel products (plates, sections, bars) or want to get a detailed price quote, please contact our team directly. Our specialists will provide professional technical support and competitive pricing based on your requirements.