This paper presents optimized melting parameters for producing high-strength grey cast iron components with mechanical properties exceeding Rm ≥300 MPa and hardness ≥165 HB. Through systematic alloy design and process control, we achieved A-type graphite content >85% while eliminating casting defects.
1. Chemical Composition Design
The carbon equivalent (CE) plays a critical role in determining graphite morphology and matrix structure. For our grey cast iron formulation:
$$ CE = C + \frac{Si + P}{3} < 4.3\% $$
Key elemental ranges were established through factorial experiments:
| Element | Range (wt%) | Function |
|---|---|---|
| C | 3.05-3.25 | Graphite formation |
| Si | 1.85-2.05 | Graphitization promoter |
| Mn | 0.50-0.70 | Sulfide formation |
| Mo | 0.45-0.65 | Pearlite refinement |
| Cr | 0.25-0.35 | Carbide stabilization |
| Ni | 0.50-0.70 | Matrix strengthening |
2. Alloy Synergy Effects
The combined effect of multiple alloying elements in grey cast iron follows the relationship:
$$ \sigma_b = 100 + 15(\%\text{Ni}) + 30(\%\text{Cu}) + 10(\%\text{Mo}) + 20(\%\text{Cr}) $$
Our experimental verification showed:
| Element Combination | Rm Improvement |
|---|---|
| Mo+Cr | +42 MPa |
| Ni+Cu | +38 MPa |
| Sb+Sr | +25 MPa |
3. Melting Process Parameters
The charge composition for 3-ton medium frequency furnace:
$$ \text{Charge Ratio} = \frac{\text{Steel Scrap}}{\text{Pig Iron}} = \frac{70-80\%}{20-30\%} $$
Critical process controls include:
- Preheating temperature: 600-650°C
- Final superheating: 1,500-1,520°C
- Holding time: 8-12 minutes
4. Inoculation Strategy
The dual inoculation system combines:
$$ \text{Total Inoculant} = 0.30\% \text{ Sr-FeSi} + 0.15-0.20\% \text{ FeSi75} $$
Key parameters for inoculant selection:
| Parameter | Sr-FeSi | FeSi75 |
|---|---|---|
| Particle Size (mm) | 3-8 | 10-20 |
| Si Content (%) | 75 | 75 |
| Reaction Time (s) | 45-60 | 20-30 |
5. Quality Verification
Mechanical testing results from production samples:
| Sample | Rm (MPa) | Hardness (HB) | A-Graphite (%) |
|---|---|---|---|
| 1 | 332 | 226 | >95 |
| 2 | 315 | 232 | >95 |
The optimized grey cast iron process demonstrates excellent reproducibility with less than 5% variation in mechanical properties across multiple production batches. This methodology provides a reliable solution for manufacturing high-performance cast components requiring strict quality standards.