St37-2 Carbon Steel: Older/Alternative Grades for Structural and General Applications
St37-2 carbon steel, a non-alloy structural steel under the DIN EN 10025-2 standard (equivalent to S235JR in modern nomenclature), is a versatile low-carbon grade widely used in construction and engineering. With its mild composition featuring a maximum carbon content of 0.17%, it offers good weldability, machinability, and moderate strength, making it suitable for load-bearing structures, pipes, and machinery components. This article explores its chemical composition, mechanical properties, production processes, applications, and comparisons with alternative grades.
1. Core Chemical Composition (DIN EN 10025-2 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.17% | Provides basic strength; low content ensures good weldability and ductility |
| Manganese (Mn) | ≤ 1.40% | Improves strength, toughness, and hardenability; aids in deoxidation |
| Phosphorus (P) | ≤ 0.045% | Controlled impurity; limits brittleness and cold shortness |
| Sulfur (S) | ≤ 0.045% | Restricted to enhance hot workability and prevent hot shortness |
| Nitrogen (N) | ≤ 0.009% | Minimizes aging effects and improves impact toughness |
| Silicon (Si) | ≤ 0.55% | Acts as a deoxidizer; supports strength without reducing ductility |
2. Key Mechanical Properties (Room Temperature, Thickness ≤16mm)
- Yield Strength (ReH): ≥ 235 MPa (adequate for structural beams and frames)
- Tensile Strength (Rm): 360-510 MPa (balances strength and formability)
- Elongation (A): ≥ 25% (high ductility for bending and fabrication)
- Impact Toughness (KV): ≥ 27 J at 20°C (Charpy V-notch; suitable for moderate impact loads)
- Hardness (HB): ≤ 120-170 (Brinell; easy machinability for general purposes)
3. Manufacturing Process Characteristics
- Smelting: Basic oxygen furnace (BOF) or electric arc furnace (EAF) with ladle refining to control impurities and achieve homogeneous composition.
- Hot Rolling: Rolled at 900-1100°C to form plates, sections, or bars; controlled cooling to normalize microstructure and avoid excessive grain growth.
- Heat Treatment: Normalizing at 850-900°C followed by air cooling to refine grain structure and enhance uniformity for structural use.
- Cold Forming: For thinner sections, cold drawing or bending with minimal springback due to low yield strength.
- Surface Treatment: Pickling in acid solutions to remove scale; optional galvanizing for corrosion protection in outdoor applications.
4. Typical Application Fields
Construction & Infrastructure
Structural beams, columns, bridges, and building frameworks — provides reliable support in non-corrosive to mildly corrosive environments.
Piping & Mechanical
Pressure vessels, boiler tubes, automotive chassis parts, and machinery frames — excellent weldability for assembly.
General Fabrication
Storage tanks, conveyor systems, agricultural equipment, and shipbuilding components — cost-effective for moderate-duty uses.
Heavy Equipment
Crane booms, earthmoving machinery parts, and transmission towers — durable for dynamic loading conditions.
5. Differences from Similar/Alternative Grades (St37-2 vs S235JR vs ASTM A36)
| Grade | Key Specification | Yield Strength | Suitable Scenario |
|---|---|---|---|
| St37-2 (DIN 17100) | Older German standard; C ≤ 0.17% | ≥ 235 MPa | Legacy structural projects; general European fabrication |
| S235JR (EN 10025-2) | Modern EU equivalent; similar composition | ≥ 235 MPa | Current structural steel for welding and forming; bridges and buildings |
| ASTM A36 (US) | High-strength low-alloy; C ≤ 0.26% | ≥ 250 MPa | American construction; higher strength for riveted or bolted assemblies |
6. Selection & Usage Precautions
- Environmental Limitations: Not ideal for highly corrosive settings (e.g., marine or acidic); opt for galvanized or higher-alloy alternatives like S355.
- Welding Guidelines: Preheat to 100-150°C for thicknesses >20mm; use low-hydrogen electrodes (E7018) to prevent cracking.
- Fatigue & Load Considerations: Suitable for static loads; for cyclic fatigue, perform stress-relief annealing post-fabrication.
- Quality Assurance: Verify with material certificates (EN 10204 3.1) ensuring compliance with DIN EN 10025-2 mechanical and chemical specs.
7. Get a Carbon Steel Quote
For customized St37-2 carbon steel products (plates, sections, bars) or competitive pricing, contact our team. We offer expert advice tailored to your project needs.