Here’s a professional English comparison of QT400, QT500, and QT600 ductile iron materials (per ISO 1083 standard):
Classification & Composition
| Grade | Type | Composition (wt.%) | Microstructure |
|---|---|---|---|
| QT400 | Ferritic | C 3.6-3.8, Si 2.2-2.8 | 85% ferrite + 15% pearlite |
| QT500 | Ferritic-Pearlitic | C 3.5-3.7, Si 2.0-2.5 | 50% ferrite + 50% pearlite |
| QT600 | Pearlitic | C 3.4-3.6, Si 1.8-2.2 | 20% ferrite + 80% pearlite |
Mechanical Properties
| Property | QT400 | QT500 | QT600 |
|---|---|---|---|
| Tensile Strength (MPa) | 400-450 | 500-600 | 600-750 |
| Yield Strength (MPa) | 250-300 | 320-380 | 420-480 |
| Elongation (%) | 18-22 | 7-12 | 3-6 |
| Hardness (HBW) | 130-180 | 170-230 | 190-270 |
| Impact Energy (J, -20°C) | 14-18 | 10-14 | 6-9 |
| Elastic Modulus (GPa) | 169 | 173 | 176 |
Physical Properties
| Property | QT400 | QT500 | QT600 |
|---|---|---|---|
| Density (g/cm³) | 7.10-7.15 | 7.10-7.15 | 7.10-7.15 |
| Thermal Conductivity (W/m·K) | 36-42 | 34-40 | 32-38 |
| Specific Heat (J/kg·K) | 460-480 | 450-470 | 440-460 |
| Damping Capacity | Excellent | Good | Moderate |
Key Performance Advantages
QT400:
- Best impact toughness (maintains ductility at -40°C)
- Superior vibration damping (6-10× better than steel)
- Good weldability (200°C preheat sufficient)
QT500:
- Optimal strength-ductility balance
- Best machined surface finish (Ra 1.6μm achievable)
- 40% better wear resistance than QT400
QT600:
- Near-steel strength properties
- Best wear resistance (comparable to low-alloy steels)
- Upgradeable to QT900 via ADI heat treatment
Processing Characteristics
| Process | QT400 | QT500 | QT600 |
|---|---|---|---|
| Castability | Excellent (low shrinkage) | Good | Fair (requires feeding) |
| Machinability | Easy (long tool life) | Optimal | Difficult |
| Heat Treatment | Annealing only | Normalizing possible | Requires alloying |
| Welding | Best (cold welding possible) | Preheating required | Special filler needed |
Typical Applications
QT400:
- Wind turbine hubs
- Heavy truck chassis
- Cryogenic valve bodies
QT500:
- Hydraulic valves
- Machine tool beds
- Gear pump housings
QT600:
- Diesel engine crankshafts
- Rolling mill rolls
- Mining crusher teeth
Corrosion Resistance
- General: Similar for all grades (passive film formation)
- Special Environments:
- QT400 performs best in acidic conditions
- QT600 more suitable for erosion-corrosion conditions
Material Selection Guide
- High toughness required → QT400
- Balanced properties needed → QT500
- High-strength/wear applications → QT600
- Cost ranking: QT400 < QT500 < QT600 (15-20% price increments)
Special Considerations
QT600 requires Cu/Mo alloying (0.5-1.0%) during casting
Maintain Si ≤2.8% during welding to avoid brittleness
All grades require ≥90% nodularity (metallurgical inspection)
QT400-18L (low-temperature grade) achieves >12J at -40°C
Note: Through Austempered Ductile Iron (ADI) treatment, QT600 can be upgraded to:
- Tensile strength: 1400MPa
- Elongation: 10%
- Fatigue limit: +100% improvement
This comparison highlights the progressive trade-off between ductility and strength across the QT series, with QT400 favoring impact resistance and QT600 providing near-steel mechanical performance while maintaining castability advantages.
Great, Together
