CLADDING TECHNOLOGY SHANXI CO., LTDEffects of Heat Treatment on Microstructure and Wear Resistance of Y-Containing Hypereutectic Fe-Cr-C Weld Overlay Alloys
Literature Overview
Yttrium (Y) has emerged as a promising microalloying addition for Fe-Cr-C weld overlay alloys, offering grain refinement and carbide modification effects at very low addition levels (0.02–0.15 wt%). This study examines how heat treatment parameters interact with Y additions in hypereutectic compositions (C > 3.0 wt%) to optimize the balance between hardness, toughness, and wear resistance. The research addresses a critical gap in understanding how rare earth additions behave under thermal processing conditions relevant to industrial overlay applications.
Composition and Hypereutectic Considerations
The base composition studied contains approximately 14–16% Cr, 3.5–4.5% C, 1.5–2.0% Mo, and 0.05–0.12% Y by weight. In the hypereutectic range, primary carbides form during solidification before the eutectic reaction occurs, creating a microstructure dominated by coarse primary carbides in a eutectic matrix. The challenge is to refine these primary carbides while maintaining sufficient volume fraction for wear resistance.
Heat Treatment Parameters Investigated
| Parameter | Range | Optimal Value | Rationale |
|---|---|---|---|
| Solution temperature | 1050–1250 °C | 1150 °C | Partial dissolution of primary carbides |
| Solution time | 0.5–3.0 h | 1.5 h | Avoid excessive grain growth |
| Aging temperature | 700–900 °C | 800 °C | Controlled precipitation of fine carbides |
| Aging time | 2–10 h | 6 h | Sufficient for precipitation, minimize coarsening |
| Cooling rate | Air / Furnace / Water | Air | Balance between stress relief and transformation |
Microstructural Response to Y Addition and Heat Treatment
The as-deposited Y-containing overlay shows distinct differences from the Y-free counterpart. Y segregates to dendrite boundaries and forms Y2O3 particles that act as heterogeneous nucleation sites during solidification. This results in a 20–35% reduction in dendrite arm spacing compared to Y-free alloys of the same composition.
Carbide Morphology Evolution
| Condition | Primary Carbide Size (μm) | Volume Fraction (%) | Matrix Hardness (HV) | Overall Hardness (HV) |
|---|---|---|---|---|
| As-deposited (no Y) | 15–25 | 45–50 | 580–620 | 720–780 |
| As-deposited (with Y) | 10–18 | 48–53 | 600–640 | 750–810 |
| Solution treated (1150/1.5h) + Y | 6–12 | 40–45 | 620–660 | 700–760 |
| Solution + Aging (800/6h) + Y | 3–8 | 50–55 | 640–680 | 800–860 |
| Solution + Aging (900/6h) + Y | 5–10 | 48–52 | 650–690 | 780–840 |
The most significant finding is that the combination of Y addition and solution-plus-aging treatment produces a microstructure with fine, uniformly distributed carbides (3–8 μm) at high volume fractions (50–55%), achieving hardness values exceeding 800 HV. This represents a substantial improvement over both the as-deposited condition and Y-free treated counterparts.
Wear Performance and Mechanism
Pin-on-disk wear testing against steel counterfaces at 20 N load and 0.15 m/s sliding speed demonstrated that the Y-containing alloy after solution-plus-aging treatment exhibited a specific wear rate of 1.8 × 10⁻⁶ mm³/N·m, approximately 55% lower than the as-deposited Y-free condition. The wear mechanism shifted from adhesive-abrasive mixed wear (as-deposited) to predominantly abrasive wear with carbide ploughing (treated), indicating superior matrix-carbide bonding and resistance to material removal.
The Y2O3 particles (typically 0.5–2 μm) observed at carbide-matrix interfaces serve a dual function: they strengthen the interface through pinning effects and they inhibit carbide coarsening during aging by blocking grain boundary migration. This explains why the Y-containing alloy maintains finer carbides after aging compared to the Y-free equivalent.
Process Considerations for Industrial Application
Several practical challenges must be addressed when implementing Y-containing overlay alloys in production:
- Powder homogeneity — Y is hygroscopic and readily oxidizes; powder handling requires inert atmosphere protection and moisture control below 50 ppm.
- Thermal cracking susceptibility — hypereutectic compositions have limited solidification temperature range; preheating of 150–250 °C is essential for thick deposits.
- Treatment distortion — Y-containing alloys show slightly higher thermal expansion coefficients; dimensional control requires careful fixture design.
- Cost-benefit analysis — Y additions increase consumable cost by 15–25%, but the extended service life (typically 2–3× improvement) provides favorable economics for critical applications.
Key Reflections
This research highlights an important paradigm shift in overlay alloy design: microalloying with rare earth elements offers performance benefits that are only fully realized when combined with appropriate post-deposition heat treatment. The interaction between Y-induced grain refinement and thermally-induced carbide redistribution creates a synergistic effect that neither approach achieves alone. For engineers specifying overlay systems for applications such as coal mills, cement kiln wear parts, and slurry pump components, this study provides compelling evidence that Y-containing hypereutectic Fe-Cr-C alloys with proper thermal treatment represent a significant advancement over conventional high-chromium white iron overlays.