1. Introduction
Ductile iron casting has become a critical material in industrial applications due to its superior mechanical properties and cost-effectiveness. However, challenges in nodularization and inoculation processes, particularly in lost foam casting, often lead to inconsistent graphite nodule counts, reduced pearlite content, and premature nodularization衰退. This study explores an optimized nodularization-inoculation process to enhance the quality of ductile iron castings.
2. Process Design and Methodology
The conventional ladle transfer method for ductile iron casting faces limitations in magnesium absorption efficiency due to high pouring temperatures (1,560–1,600°C) and rapid reaction kinetics. To address this, a partitioned ladle with multi-stage nodularization was developed.
2.1 Ladle Configuration
The partitioned ladle features a dam structure separating nodulizer compartments. The layered arrangement of nodulizers and inoculants ensures sequential reactions:
$$ t_{reaction} = \frac{\Delta H_{Mg}}{k \cdot (T – T_m)} $$
where \( t_{reaction} \) is the reaction time, \( \Delta H_{Mg} \) is the enthalpy of magnesium release, \( k \) is the rate constant, and \( T_m \) is the melting point of the cover plate.
| Layer | Component | Weight (%) |
|---|---|---|
| Base | Nodulizer (FeSiMg) | 0.7–0.9 |
| Intermediate | Covering Agent | 0.05–0.15 |
| Upper | Nodulizer + Inoculant | 0.55–0.65 |
2.2 Inoculant Strategy
A hybrid inoculation system was implemented using three distinct inoculants to combat衰退:
- Primary Inoculant (SiFe): 0.15% addition at 20s post-nodularization
- Secondary Inoculant (SiBa): 0.35–0.45% addition
- Tertiary Inoculant (SiBaCa): 0.2–0.4% addition
The total inoculant efficiency \( \eta_{inoc} \) is calculated as:
$$ \eta_{inoc} = \sum_{i=1}^{3} \alpha_i \cdot e^{-t/\tau_i} $$
where \( \alpha_i \) is the activity coefficient and \( \tau_i \) is the衰退 time constant for each inoculant.
3. Results and Analysis
The optimized ductile iron casting process demonstrated significant improvements:
| Parameter | Conventional Process | Improved Process |
|---|---|---|
| Graphite Nodules (%) | 30 | 60 |
| Pearlite Content (%) | 85 | 90 |
| Mg Absorption (%) | 35–40 | 55–60 |
4. Discussion
The dual-stage nodularization mechanism in ductile iron casting extends reaction duration by 40–60%, allowing better Mg assimilation. The cover plate (carbon steel or ductile iron) delays lower-layer nodulizer contact with molten metal until partial melting occurs, governed by:
$$ t_{melt} = \frac{\rho \cdot C_p \cdot \delta^2}{2k \cdot (T – T_m)} $$
where \( \rho \) is density, \( C_p \) is heat capacity, and \( \delta \) is plate thickness.
5. Conclusion
This study validates that optimized inoculant sequencing and partitioned ladle design significantly enhance the metallurgical quality of ductile iron castings in lost foam processes. Future work will focus on further increasing pearlite content through controlled cooling strategies.