GB/T11251 1345 Alloy Structural Steel Coil: High-Strength Steel for Heavy-Duty Machinery Components
GB/T11251 1345 Alloy Structural Steel Coil Product Overview
GB/T11251 1345 is a hot-rolled alloy structural steel optimized for high-stress parts like gears, shafts, and bearings. Combining 600–800 MPa tensile strength with 18–22% elongation, it balances wear resistance, machinability, and weldability. Grades like 45Mn2, 27SiMn, and 40B meet ISO 683-18 and ASTM A322 standards, serving automotive, mining, and heavy machinery industries. With controlled boron content (≤0.0035%), it achieves uniform hardness in heat-treated components like hydraulic rods and gearboxes.
Key Technical Specifications
1. Manufacturing & Dimensions
- Process:
- Hot-rolled: 2.75–100mm (±1.2% thickness tolerance per GB/T 709)
- Cold-rolled: 0.2–3mm (±0.25% tolerance for precision stamping)
- Width: 45–2,200mm (CNC-ready for gear teeth/threads)
- Surface: Annealed (Ra ≤1.6μm) or phosphated (3–8μm coating)
2. Chemical Composition
| Grade | C (%) | Si (%) | Mn (%) | B (%) | Key Alloy Features |
|---|---|---|---|---|---|
| 45Mn2 | 0.42–0.49 | 0.17–0.37 | 1.40–1.80 | – | High Mn for impact toughness |
| 27SiMn | 0.24–0.32 | 1.10–1.40 | 1.10–1.40 | – | Si-enhanced fatigue strength |
| 40B | 0.37–0.44 | 0.17–0.37 | 0.60–0.90 | 0.0005–0.0035 | Boron for hardenability |
Trace elements:
- P/S: ≤0.035% (45Mn2), ≤0.025% (40B)
- Cr/Ni: ≤0.30% (all grades)
Mechanical Properties
| Grade | Yield (MPa) | Tensile (MPa) | Elongation (%) | Impact Energy (J @ -20°C) | Hardness (HBW) |
|---|---|---|---|---|---|
| 45Mn2 | ≥600 | 800–1000 | 13 | 25 | 200–250 |
| 27SiMn | ≥550 | 750–950 | 18 | 30 | 180–220 |
| 40B | ≥500 | 700–900 | 20 | 35 | 170–200 |
Test standards:
- Tensile: GB/T 228.1 (strain rate 0.008/min)
- Impact: GB/T 229 (Charpy V-notch, 10x10mm)
- Hardenability: Jominy test (40B: HRC 45 at 10mm depth)
Performance Advantages
- Wear Resistance:
- Surface hardness: HRC 50–55 after carburizing (40B)
- Abrasion rate: ≤0.05 mm³/Nm in ASTM G65 testing
- Machinability:
- Cutting speed: 120 m/min (27SiMn with TiN-coated tools)
- Chip control: ISO M4 classification for continuous chips
- Heat Treatment:
- Quenching: 850–880°C oil cooling (45Mn2)
- Tempering: 500–550°C to reduce brittleness (HV 300–350)
- Weldability:
- Preheat: 150–200°C for SMAW (E7018 electrodes)
- Crack resistance: CET ≤0.45% (40B for low-HAZ cracking)
Applications
| Industry | Use Case | Recommended Grade |
|---|---|---|
| Automotive | Transmission gears (HRC 58–62) | 40B |
| Mining | Excavator drive shafts (950 MPa) | 45Mn2 |
| Railways | Axle boxes (ultrasonic-tested) | 27SiMn |
Global Equivalents
| GB/T11251 | ASTM | DIN | JIS | EN |
|---|---|---|---|---|
| 45Mn2 | 1345 | 46Mn7 | SMn433 | 1.1213 |
| 27SiMn | – | 27MnSi5 | – | 1.5140 |
| 40B | 14B35 | 35B2 | SB49B | 1.5530 |
Sustainability & Compliance
- Recycled Content: 78% (certified per GB/T 38216)
- RoHS Compliance: Lead-free, Hg <0.005%
- Certifications: ISO 9001, IATF 16949 (automotive)
Packing And Delivery
