GB/T11251 1345 Alloy Structural Steel Plate Material Overview & Core Advantages
GB/T 11251 1345 alloy steel plates deliver 650 MPa+ yield strength for mining equipment and rail vehicle components, combining boron-enhanced hardenability with water-cooling stable toughness. These hot-rolled plates achieve HRC 28–32 surface hardness while maintaining 16% elongation (50B grade).
Key Differentiators:
- Wear Resistance: 3x higher than AISI 1045 under abrasive conditions.
- Global Equivalency: ASTM A534 (45Mn2), DIN 17200 46Mn7 (27SiMn).
- Processing Flexibility: 85% cold-forming capability without edge cracking.
Technical Specifications
1. Chemical Composition (GB/T 11251-2023 Revision)
| Grade | C Range | Mn Range | B Range | CEV* |
|---|---|---|---|---|
| 45Mn2 | 0.42–0.49% | 1.40–1.80% | – | 0.68 |
| 40B | 0.37–0.44% | 0.60–0.90% | 0.0005–0.0035% | 0.54 |
| 50B | 0.47–0.55% | 0.60–0.90% | 0.0005–0.0035% | 0.72 |
*CEV = C + Mn/6 + (Cr + Mo + V)/5
2. Mechanical Performance
| Grade | Yield (MPa) | Tensile (MPa) | Elongation (%) | Impact (-20°C) |
|---|---|---|---|---|
| 45Mn2 | ≥600 | 850–1000 | 13 | 45 J |
| 40B | ≥500 | 700–850 | 20 | 55 J |
| 50B | ≥550 | 900–1100 | 16 | 35 J |
Physical Properties:
- Thermal Conductivity: 45.6 W/m·K (20–300°C)
- Linear Expansion: 12.8 µm/m°C (25–200°C)
Manufacturing & Processing
1. Heat Treatment
- Quenching: 830–860°C water cooling (45Mn2/50B).
- Tempering: 550–600°C × 2h (prevents white spot defects).
2. Machinability
| Process | Parameter | Surface Finish (Ra) |
|---|---|---|
| Turning | 180–220 m/min | 3.2–6.3 µm |
| Grinding | 35 m/s wheel speed | 0.8–1.6 µm |
Industrial Applications
1. Heavy Machinery
- Crusher Hammers: 50B grade (hardness HRC 32–35).
- Excavator Pins: 45Mn2 with 50–55 HRC surface.
2. Transportation Equipment
| Component | Material Grade | Service Life |
|---|---|---|
| Rail Axles | 27SiMn | 1.2M km |
| Gear Blanks | 40B | 80,000h |
3. Energy Sector
- Wind Turbine Shafts: 50B (IEC 61400-6 certified).
- Hydraulic Cylinders: 40B (ISO 6020/2 compliant).
Quality Compliance
- Testing Protocols:
- Ultrasonic inspection: GB/T 2970 Class II.
- Hydrogen content: <2ppm (prevent white spots).
- Certifications:
- China Compulsory Certification (CCC).
- ISO 630:2019 structural steel compliance.
Delivery & Storage
- Dimensions:
- Width: 1,500–3,200mm (max length: 18m).
- Thickness Tolerance: ±0.2mm (ground edges).
- Packaging: Rust-inhibitive oil + PE wrapping.
Welding Guidance: Use GB/T 5117 E6013 electrodes with 150–180°C preheat*
Technical Footnotes:
- 40B achieves 0.2% proof strength of 420 MPa @ 150°C.
- Maximum service temperature: 350°C (prolonged exposure).
Why Choose GB/T 11251 1345?
Compared to SAE 4340, 50B grade provides 15% higher surface hardness while maintaining equivalent impact toughness. The boron microalloying (0.0035% max) enhances hardenability depth by 40% in oil-quenched components.
Environmental Note: 88% recycled content with 6.8kg CO₂/t production footprint (GB 17167-2012).
Global Material Equivalents:
| GB/T 11251 | ASTM | DIN | JIS | Application Focus |
|---|---|---|---|---|
| 45Mn2 | 1345 | 46Mn7 | SCMn3 | Mining Equipment |
| 27SiMn | – | 27MnSi5 | – | High-Stress Fasteners |
| 50B | 50B46H | 50B2 | SB49 | Gear Shafts |
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