SB450: Carbon Steel for Medium-Pressure Boilers and Pressure Vessels
SB450 carbon steel, specified under the JIS G3103 standard, is a low-alloy carbon steel plate designed for use in medium-pressure boilers and pressure vessels. With its controlled composition, it offers good weldability, moderate strength, and sufficient toughness to withstand internal pressures up to approximately 2.5 MPa at elevated temperatures. This grade is widely adopted in industrial applications requiring reliable performance under thermal and mechanical stress. This article explores its chemical composition, mechanical properties, manufacturing processes, applications, and comparative advantages.
1. Core Chemical Composition (JIS G3103 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.20% | Provides basic strength; limited to ensure weldability and ductility |
| Manganese (Mn) | ≤ 1.35% | Enhances strength and toughness; improves hot workability |
| Phosphorus (P) | ≤ 0.035% | Controlled impurity; minimizes brittleness and cracking |
| Sulfur (S) | ≤ 0.035% | Restricted to prevent hot shortness and improve forgeability |
| Silicon (Si) | ≤ 0.55% | Aids deoxidation; supports strength without reducing ductility |
2. Key Mechanical Properties (Room Temperature)
- Tensile Strength (σb): ≥ 450 MPa (for thickness ≤ 16 mm; JIS G3103 standard)
- Yield Strength (σ0.2): ≥ 245 MPa (adequate for medium-pressure containment)
- Elongation (δ): ≥ 21% (ensures formability for fabrication and assembly)
- Hardness (HB): ≤ 170 (Brinell; suitable for welding without excessive brittleness)
- Impact Toughness (Charpy V-notch): ≥ 27 J at 0°C (maintains integrity in moderate-temperature service)
3. Manufacturing Process Characteristics
- Smelting: Basic oxygen furnace (BOF) or electric arc furnace (EAF) followed by ladle refining to achieve low impurity levels and uniform composition.
- Hot Rolling: Controlled at 1100-1200°C, with finishing temperatures above 850°C to refine grain structure and ensure plate flatness.
- Normalization: Heat treatment at 880-950°C followed by air cooling to improve uniformity, strength, and resistance to stress corrosion.
- Inspection and Testing: Ultrasonic testing for internal defects; tensile and bend tests to verify compliance with JIS G3103 requirements.
- Surface Preparation: Shot blasting and priming for corrosion protection during storage and transport.
4. Typical Application Fields
Boiler Manufacturing
Shells, drums, and headers for medium-pressure steam boilers operating at temperatures up to 450°C and pressures around 2.5 MPa.
Pressure Vessels
Cylindrical bodies and heads for storage tanks and reactors in petrochemical and power generation industries.
Industrial Piping
Flanges, fittings, and supports for steam lines and hot water systems in manufacturing plants.
Structural Components
Supports and enclosures for heat exchangers and furnaces requiring moderate strength and weldability.
5. Difference from Similar Grades (SB450 vs SB410 vs SB480)
| Grade | Tensile Strength | Key Advantage | Suitable Scenario |
|---|---|---|---|
| SB450 | ≥ 450 MPa | Balanced strength and weldability for medium-pressure use | Boilers and vessels up to 2.5 MPa and 450°C |
| SB410 | ≥ 410 MPa | Lower cost for low-pressure applications | Light-duty boilers and general structures |
| SB480 | ≥ 480 MPa | Higher strength for elevated pressures | High-pressure vessels and critical components |
6. Selection & Usage Precautions
- Temperature Limits: Suitable for service up to 450°C; beyond this, opt for higher-grade alloys like SB480 or low-alloy steels.
- Welding Guidelines: Use low-hydrogen electrodes (e.g., E7018); pre-heat to 100-150°C for thicknesses >20 mm to avoid cold cracking.
- Corrosion Protection: Apply coatings or linings in corrosive environments; not inherently corrosion-resistant like stainless steels.
- Quality Assurance: Verify with mill test certificates (MTC) ensuring JIS G3103 compliance, including NDT reports.
7. Get a Carbon Steel Quote
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