Steel casting 35Cr2Ni2Mo-Mg demonstrates exceptional strength-toughness balance, wear resistance, and fatigue properties, making it indispensable for manufacturing heavy machinery components in mining and metallurgy. To optimize its non-metallic inclusion characteristics and mechanical performance, rare earth (RE) elements were introduced during alloy modification. This study systematically investigates how RE affects inclusion morphology, tensile properties, and abrasive wear behavior through advanced metallographic analysis and tribological testing.
1. Microstructural Evolution
The as-cast structure of modified steel casting reveals tempered sorbite with dispersed carbides. RE addition significantly refines both matrix structure and secondary phases:
| Sample | Spherical Carbides (nm) | Rod-like Carbides (nm) |
|---|---|---|
| 35Cr2Ni2Mo-Mg | 20-45 | 50-200 |
| 35Cr2Ni2Mo-Mg-RE | 10-45 | 30-190 |
The inclusion size distribution follows the relationship:
$$f(d) = \frac{1}{\sigma\sqrt{2\pi}}e^{-\frac{(d-\mu)^2}{2\sigma^2}}$$
where μ represents mean inclusion diameter (1.78 μm for RE-free vs 1.47 μm for RE-modified steel casting).
2. Mechanical Property Enhancement
RE modification improves strength parameters while slightly reducing ductility:
| Parameter | Base Alloy | RE-Modified | Change |
|---|---|---|---|
| Tensile Strength (MPa) | 1,254 | 1,274 | +1.59% |
| Yield Strength (MPa) | 940 | 1,198 | +27.45% |
| Elongation (%) | 5.76 | 4.97 | -13.72% |
| Hardness (HRC) | 48.67 | 52.90 | +8.69% |
The strength-ductility relationship follows:
$$\sigma_y = \sigma_0 + k_y d^{-1/2}$$
where σ0 represents lattice friction stress and d denotes effective grain size.
3. Wear Resistance Mechanism
Under 100N abrasive load, RE-modified steel casting shows superior wear performance:
| Time (min) | Weight Loss (g) | Wear Rate (g/min) |
|---|---|---|
| 10 | 0.455 vs 0.475 | 0.0455 vs 0.0475 |
| 40 | 2.503 vs 2.579 | 0.0626 vs 0.0645 |
The Archard wear equation explains the improvement:
$$W = \frac{k \cdot L \cdot s}{H}$$
where W=wear volume, k=wear coefficient, L=load, s=sliding distance, H=material hardness.
4. Inclusion Modification Mechanism
RE elements alter inclusion characteristics through:
- Oxide/sulfide modification: RExOy + MnS → RE2S3 + MnO
- Precipitation control: ΔG = -RT ln Ksp
- Morphology refinement: Aspect ratio reduction from 3.2 to 1.8
This comprehensive study demonstrates that strategic RE addition significantly enhances steel casting performance through multi-scale microstructural control, providing fundamental insights for developing advanced wear-resistant alloys.