Q275 Carbon Steel: A Low-Carbon Structural Steel for General Engineering Applications
Q275 carbon steel, designated under the Chinese GB standard (equivalent to ASTM A283 Grade D or EN S275JR), is a low-carbon structural steel widely used in construction, machinery manufacturing, and general engineering applications. With a minimum yield strength of 275 MPa, this grade offers a balanced combination of strength, weldability, and machinability at an economical cost. This article provides a comprehensive analysis of its chemical composition, mechanical properties, manufacturing processes, and practical applications.
1. Chemical Composition (GB/T 700 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.22% | Primary strengthening element; low content ensures good weldability and ductility |
| Manganese (Mn) | 0.30 – 0.65% | Enhances strength and hardenability; improves deoxidation during smelting |
| Silicon (Si) | ≤ 0.30% | Deoxidizer; improves strength without compromising ductility |
| Sulfur (S) | ≤ 0.045% | Impurity; controlled to prevent hot cracking during rolling and welding |
| Phosphorus (P) | ≤ 0.040% | Impurity; restricted to maintain toughness and prevent cold brittleness |
| Chromium (Cr) | ≤ 0.30% | Residual element; minimal impact on properties at this concentration |
| Nickel (Ni) | ≤ 0.30% | Residual element; negligible effect on mechanical properties |
| Copper (Cu) | ≤ 0.30% | Residual element; may improve atmospheric corrosion resistance slightly |
2. Mechanical Properties (Room Temperature)
- Yield Strength (σs): ≥ 275 MPa (minimum guaranteed strength for structural applications)
- Tensile Strength (σb): 410 – 560 MPa (varies with thickness and heat treatment)
- Elongation (δ₅): ≥ 23% (for thickness ≤ 16mm; ensures formability)
- Impact Energy (AKV): ≥ 27 J at 20°C (standard Charpy V-notch test)
- Hardness (HB): ≤ 163 (Brinell hardness; suitable for machining and drilling)
- Density: 7.85 g/cm³ (standard for carbon steels)
3. Manufacturing and Processing Characteristics
- Smelting: Basic oxygen furnace (BOF) or electric arc furnace (EAF) with ladle refining to control sulfur and phosphorus levels. Continuous casting produces slabs or blooms for rolling.
- Hot Rolling: Heated to 1100-1250°C and rolled to final dimensions. Controlled cooling prevents grain coarsening and ensures uniform mechanical properties.
- Cold Forming: Suitable for bending, stamping, and deep drawing due to low carbon content. Maximum cold deformation ratio typically ≤ 70% without intermediate annealing.
- Heat Treatment:
- Normalizing: 880-940°C, air-cooled to refine grain structure and improve toughness.
- Annealing: 600-700°C for stress relief after cold working.
- Quenching & Tempering: Rarely applied; not cost-effective for this grade.
- Welding: Excellent weldability with all standard methods (SMAW, GMAW, FCAW). Preheating not required for thickness ≤ 20mm. Use E43xx or ER70S-6 filler materials.
- Machining: Machinability rating of ~60% (relative to AISI 1212). Recommended cutting speeds: 20-30 m/min for turning, 15-25 m/min for drilling.
4. Typical Applications by Industry
Construction & Infrastructure
Structural components for low-rise buildings (beams, channels, angles), bridge parapets, and highway guardrails. Compliant with GB 50017 for steel structure design.
Machinery Manufacturing
Frames for agricultural equipment, conveyor systems, and light industrial machinery. Used in gearboxes, shafts, and couplings where high strength is not critical.
Automotive & Transportation
Chassis components for commercial vehicles, trailer frames, and railway wagon underframes. Meets GB/T 3273 for automotive structural steels.
General Fabrication
Storage tanks (non-pressure), platforms, staircases, and handrails. Often galvanized (Z120-Z275 coating) for enhanced corrosion resistance in outdoor applications.
Shipbuilding
Secondary structural parts for inland waterway vessels and small coastal ships (non-classified). Used in decks, bulkheads, and superstructures.
Energy Sector
Support structures for solar panels, wind turbine towers (non-critical sections), and transmission pole bases. Often paired with hot-dip galvanizing for longevity.
5. Comparison with Similar Carbon Steel Grades
| Grade | Standard | Yield Strength (MPa) | Key Differences | Typical Use |
|---|---|---|---|---|
| Q275 | GB/T 700 | ≥ 275 | Balanced strength and ductility; economical | General structural applications |
| Q235 | GB/T 700 | ≥ 235 | Lower strength; better formability | Light structures, sheet metal work |
| Q345 | GB/T 1591 | ≥ 345 | Higher strength; lower ductility | Heavy structures, cranes, pressure vessels |
| SS400 | JIS G3101 | ≥ 245 | Japanese equivalent; similar properties | General construction in Asia |
| S275JR | EN 10025-2 | ≥ 275 | European equivalent; guaranteed impact at 20°C | EU structural projects |
| A36 | ASTM A36 | ≥ 250 | US standard; wider chemistry range | North American construction |
6. Selection Guidelines and Practical Considerations
- Thickness Limitations: Mechanical properties degrade for thicknesses > 40mm. For heavier sections, consider Q345 or normalized Q275.
- Corrosion Protection: Uncoated Q275 rusts in humid environments. Specify hot-dip galvanizing (ISO 1461) or paint systems (ISO 12944) for outdoor use.
- Welding Procedures:
- For thickness > 20mm, preheat to 100-150°C to avoid cold cracking.
- Use low-hydrogen electrodes (e.g., E4316) for constrained joints.
- Post-weld stress relief at 550-650°C for critical applications.
- Machining Tips: Use carbide tools for high-speed machining. Avoid built-up edge formation by maintaining sharp tool edges and proper coolant flow.
- Quality Certification: Verify mill test certificates (EN 10204 3.1) for chemical composition and mechanical properties. Ultrasound testing (UT) recommended for thick plates.
- Alternative Grades: For improved toughness at low temperatures, consider Q275GNH (normalized) or Q345E. For corrosion resistance, specify Q275NQR (weathering steel).
7. Request a Carbon Steel Quote
Baoli Iron & Steel supplies Q275 carbon steel in various forms, including hot-rolled plates (3mm-150mm), coils, angles, channels, and beams. Our inventory meets GB, ASTM, EN, and JIS standards with third-party inspection available. For customized sizes, surface treatments, or bulk pricing, contact our technical sales team with your specifications.