Our research focuses on enhancing the mechanical and thermal properties of vanadium-titanium (V-Ti) grey cast iron through systematic composition design, targeting optimized performance for automotive brake drum applications. The study reveals critical relationships between alloying elements, graphite morphology, and material characteristics through controlled casting experiments.
1. Composition Design and Experimental Methodology
Four distinct compositions of V-Ti grey cast iron were developed with controlled variations in C, Si, V, and Ti content (Table 1). The matrix composition follows:
$$CE = C + \frac{Si}{3} + \frac{V+Ti}{10}$$
where CE represents the carbon equivalent. The experimental matrix maintains:
- C: 2.99-3.28 wt%
- Si: 1.72-1.81 wt%
- Mn: 0.8 wt% (constant)
- P < 0.10%, S < 0.06%
| Sample | C (%) | Si (%) | V (%) | Ti (%) |
|---|---|---|---|---|
| 1# | 2.99 | 1.80 | 0.14 | 0.048 |
| 2# | 3.03 | 1.72 | 0.18 | 0.056 |
| 3# | 3.10 | 1.80 | 0.22 | 0.098 |
| 4# | 3.28 | 1.81 | 0.19 | 0.180 |
2. Graphite Morphology Evolution
The V-Ti grey cast iron exhibits distinct graphite structural transitions:
- Type A graphite (1#): Uniform flake distribution
- Type D graphite (3#): Fine interdendritic structure
- Hybrid morphology (4#): Coarse flakes with localized carbides
The graphite refinement mechanism follows:
$$G_s = \frac{k_v[V] + k_{ti}[Ti]}{\sqrt{C_{eq}}}$$
where:
$G_s$ = graphite size parameter
$k_v$, $k_{ti}$ = kinetic coefficients (0.85 and 1.2 respectively)
$C_{eq}$ = carbon equivalent
3. Mechanical Performance Analysis
Mechanical properties demonstrate composition-dependent behavior (Table 2):
| Sample | Tensile Strength (MPa) | Hardness (HB) | Yield Strength (MPa) |
|---|---|---|---|
| 1# | 266 ± 12 | 205 ± 8 | 185 ± 10 |
| 2# | 298 ± 15 | 225 ± 7 | 208 ± 9 |
| 3# | 366 ± 18 | 263 ± 6 | 255 ± 12 |
| 4# | 241 ± 11 | 192 ± 9 | 170 ± 8 |
The strength enhancement in 3# grey cast iron follows the dispersion strengthening model:
$$\sigma_y = \sigma_0 + k_d(\sqrt{f_v}d^{-1} + \sqrt{f_{ti}}d_{ti}^{-1})$$
where:
$\sigma_0$ = matrix strength (220 MPa)
$k_d$ = strengthening coefficient (1.8 MPa·μm)
$f_v$, $f_{ti}$ = volume fraction of V/Ti carbides
$d$, $d_{ti}$ = carbide diameters
4. Thermal Conductivity Behavior
Thermal transport properties show inverse relationship with carbide content (Table 3):
| Sample | Thermal Diffusivity (mm²/s) | Conductivity (W/m·K) | Heat Capacity (J/g·K) |
|---|---|---|---|
| 1# | 15.79 | 39.94 | 0.352 |
| 2# | 13.32 | 34.51 | 0.363 |
| 3# | 12.96 | 33.76 | 0.357 |
| 4# | 18.33 | 44.74 | 0.348 |
The thermal conductivity ($\lambda$) can be modeled as:
$$\lambda = \frac{1}{\frac{f_g}{\lambda_g} + \frac{f_c}{\lambda_c} + \frac{f_p}{\lambda_p}}$$
where:
$f_g$, $f_c$, $f_p$ = volume fractions of graphite, carbides, and pearlite
$\lambda_g$ = 400 W/m·K (graphite)
$\lambda_c$ = 25 W/m·K (carbides)
$\lambda_p$ = 50 W/m·K (pearlite)
5. Composition-Performance Relationships
Optimization models for grey cast iron components:
a) Strength maximization:
$$[V]_{opt} = 0.22 – 0.05([Ti] – 0.10)^2$$
$$[C]_{opt} = 3.10 + 0.15([Si] – 1.75)$$
b) Thermal conductivity optimization:
$$[Ti]_{max} = 0.08 + 0.02([C] – 3.00)$$
$$[V]_{max} = 0.20 – 0.15([C] – 3.15)^2$$
6. Industrial Application Considerations
For brake drum production using V-Ti grey cast iron:
- Optimal composition window: 3.10-3.20% C, 1.75-1.85% Si, 0.18-0.22% V, 0.08-0.10% Ti
- Predicted service temperature range: 150-400°C
- Wear resistance factor improvement: 35-40% vs conventional grey cast iron
This comprehensive study establishes fundamental guidelines for designing high-performance grey cast iron components through controlled V-Ti microalloying, balancing mechanical strength and thermal management requirements in automotive braking systems.