This study addresses the challenges in producing high-hardness steel castings for roller teeth used in roller crushers. The components require exceptional dimensional accuracy (CT12 per GB/T 6414-2017), hardness ≥400 HBW, and defect-free microstructure. Through systematic process optimization and computational modeling, our team achieved first-pass success in manufacturing these critical steel castings.
1. Technical Requirements and Metallurgical Design
The MCL400 steel casting composition was optimized for hardness and wear resistance:
| Element | C | Mn | Si | Cr | Ni | Mo |
|---|---|---|---|---|---|---|
| Target (%) | 0.25-0.29 | 1.00-1.20 | 0.20-0.40 | 1.25-2.00 | 3.20-4.00 | 0.25-0.50 |
The hardness relationship was modeled using:
$$ HBW = 120 + 150(C) + 25(Cr) + 12(Mn) + 8(Mo) $$
where element concentrations are in weight percentage.
2. Solidification Control Strategy
The casting process employed:
- Three exothermic risers (Φ200×300 mm)
- Five-tier stepped gating system
- Variable-thickness chill plates at gate junctions
ProCAST simulation confirmed directional solidification with maximum shrinkage porosity <5 mm:
$$ \frac{\partial T}{\partial t} = \alpha \nabla^2 T + \frac{L}{c_p}\frac{\partial f_s}{\partial t} $$
where \( \alpha \) = thermal diffusivity, \( L \) = latent heat, \( f_s \) = solid fraction.
3. Heat Treatment Optimization
The thermal cycle combined forced air cooling with water mist spray:
| Stage | Temperature (°C) | Time (h) | Cooling Rate (°C/min) |
|---|---|---|---|
| Normalizing | 900±10 | 4.5 | 15 (forced air) |
| Tempering | 250±10 | 6 | 5 (spray mist) |
The resulting hardness profile followed:
$$ HV = 500 – 120e^{-0.05t} $$
where t = tempering time in hours.
4. Production Validation
Fifteen steel castings were produced with consistent quality:
- Average hardness: 412±8 HBW
- Dimensional accuracy: 99.3% teeth passed gauge inspection
- Zero leakage defects in 3,200 kg pours
The successful implementation demonstrates that advanced steel casting techniques can achieve:
- Precise control of phase transformation through composition design
- Defect minimization via computational solidification analysis
- Cost-effective hardening without oil quenching
This methodology provides a framework for developing high-performance steel castings in heavy industrial applications, particularly where complex geometries and extreme wear resistance are required simultaneously.