SAPH370: Medium-Strength Carbon Steel for Automotive Structures
SAPH370, specified under the JIS G3113 standard, is a medium-strength, hot-rolled carbon steel grade designed primarily for automotive structural components. With a minimum yield strength of 370 MPa, it offers an optimal balance of strength, formability, and weldability, making it ideal for cold forming applications in vehicle frames, chassis, and reinforcements. This article explores its chemical composition, mechanical properties, production methods, applications, and comparisons with related grades.
1. Core Chemical Composition (JIS G3113 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.25% | Provides basic strength; controlled to ensure good formability and weldability |
| Manganese (Mn) | ≤ 0.60% (max 1.50% for certain thicknesses) | Enhances hardenability and tensile strength; improves deoxidation during rolling |
| Phosphorus (P) | ≤ 0.030% | Limited to prevent brittleness and ensure ductility in cold forming |
| Sulfur (S) | ≤ 0.020% | Restricted to minimize hot shortness and improve transverse properties |
| Silicon (Si) | ≤ 0.55% | Aids in deoxidation; contributes to strength without sacrificing toughness |
2. Key Mechanical Properties (Room Temperature)
- Yield Strength (σs): ≥ 370 MPa (for plates ≤ 16 mm; decreases for thicker gauges)
- Tensile Strength (σb): 430-560 MPa (ensures adequate load-bearing in structural use)
- Elongation (δ): ≥ 26% (longitudinal; supports deep drawing and bending operations)
- Hardness (HB): ≤ 197 (suitable for forming without excessive springback)
- Charpy Impact Toughness: Not specified; generally good at ambient temperatures for automotive crash resistance
3. Manufacturing Process Characteristics
- Steelmaking: Basic oxygen furnace (BOF) or electric arc furnace (EAF) followed by ladle refining to achieve low impurity levels and consistent chemistry.
- Hot Rolling: Rolled at 850-950°C with controlled reduction ratios; finished at ≥ 700°C to refine grain structure and promote uniform properties.
- Cooling and Coiling: Controlled cooling on runout table to avoid excessive hardness; coiled for thicknesses up to 20 mm.
- Heat Treatment: Optional normalizing at 880-950°C for stress relief in heavy sections; no quenching required for standard applications.
- Surface Conditioning: Pickling in acid solution to remove scale; edging and oiling for protection during storage and transport.
4. Typical Application Fields
Automotive Chassis and Frames
Wheel arches, cross members, and suspension components — provides high yield strength for crash energy absorption and lightweight design.
Body-in-White Structures
Reinforcements, floor panels, and side sills — excellent formability for complex stamping and hemming in vehicle assembly.
Heavy Vehicle Parts
Truck frames, trailer hitches, and agricultural machinery brackets — balances strength and cost for durable, weldable parts.
General Pressed Steel Components
Brackets, mounts, and housings in industrial equipment — suitable for high-volume production with consistent performance.
5. Difference from Similar Grades (SAPH370 vs SAPH310 vs SAPH410)
| Grade | Min. Yield Strength | Key Advantage | Suitable Scenario |
|---|---|---|---|
| SAPH370 | 370 MPa | Balanced formability and medium strength; weldable | Medium-stress automotive structures (chassis, panels) |
| SAPH310 | 195 MPa | Higher ductility for deep drawing | Low-stress components (inner panels, fenders) |
| SAPH410 | 410 MPa | Enhanced tensile strength for higher loads | High-strength reinforcements (bumper beams, pillars) |
6. Selection & Usage Precautions
- Forming Limits: Suitable for bending radii ≥ 1.5t (t=thickness); avoid excessive strain rates to prevent cracking in cold forming.
- Welding Guidelines: Use low-hydrogen electrodes (e.g., E7018); preheat for thicknesses >10 mm to control heat-affected zone properties.
- Corrosion Protection: Apply zinc coating (galvanizing) for exposed automotive parts; not inherently corrosion-resistant in humid or salted environments.
- Quality Assurance: Verify compliance with JIS G3113 via mill certificates; inspect for surface defects like seams or laminations before processing.
7. Get a Carbon Steel Quote
If you need customized SAPH370 carbon steel products (sheets, coils, plates) or require a detailed price quote for your automotive or industrial projects, contact our team. We offer professional technical advice and competitive pricing tailored to your specifications.