CLADDING TECHNOLOGY SHANXI CO., LTDResearch on Wear-Resistant and Heat-Resistant Overlay Welding Electrodes
Literature Overview and Research Context
This study focuses on the development and characterization of welding electrodes designed for producing overlay deposits that combine both wear resistance and heat resistance. The dual requirement of wear and heat resistance is common in applications such as cement kiln components, metallurgical equipment, power plant components, and hot-section machinery where surfaces are simultaneously exposed to abrasive materials and elevated temperatures. The challenge lies in developing an electrode composition and coating formulation that produces a deposit with a balanced combination of high-temperature hardness retention, thermal stability, and resistance to abrasive wear, while maintaining adequate weldability and crack resistance.
Core Technical Findings
The research develops and evaluates several electrode formulations based on different alloy systems, comparing their microstructure, mechanical properties, and performance under combined wear and heat exposure conditions.
Electrode Formulation Comparison
| Electrode Type | Base Composition | Filler Composition | Deposit Hardness (HV30) | Heat Treatment Temperature | Post-Treatment Hardness (HV30) |
|---|---|---|---|---|---|
| Type A (Fe-Cr-C) | Low-carbon steel | 0.8% C, 18% Cr, 3% Mo, 2% V | 580 | 600°C × 2h | 560 |
| Type B (Fe-Cr-Ni-C) | Low-carbon steel | 1.0% C, 22% Cr, 8% Ni, 1% Mo | 550 | 650°C × 2h | 540 |
| Type C (Co-Cr-W) | Low-carbon steel | 60% Co, 25% Cr, 5% W, 3% Mo | 480 | 800°C × 2h | 470 |
| Type D (Fe-Cr-C-Nb) | Low-carbon steel | 0.7% C, 20% Cr, 1% Nb, 1% Ti | 600 | 600°C × 2h | 580 |
| Type E (Ni-Cr-Mo) | Low-carbon steel | 70% Ni, 20% Cr, 5% Mo, 1% C | 450 | 700°C × 2h | 440 |
The data shows that Type D (Fe-Cr-C-Nb) achieves the highest hardness retention after heat treatment, while Type C (Co-Cr-W) provides the best overall combination of heat resistance and wear resistance despite lower absolute hardness.
Microstructure Analysis
The microstructure of the overlay deposits produced by each electrode type was characterized by optical microscopy, scanning electron microscopy, and X-ray diffraction:
| Electrode Type | Matrix Phase | Carbide Phase | Carbide Morphology | Grain Size |
|---|---|---|---|---|
| Type A | Martensite + Bainite | Cr7C3, Cr23C6 | Blocky and network | 20-40 μm |
| Type B | Martensite + Ferrite | Cr7C3, M7C3 | Chain-like and blocky | 25-50 μm |
| Type C | FCC austenite + M23C6 | Cr23C6, Cr7C3 | Fine and dispersed | 10-20 μm |
| Type D | Martensite + Bainite | Cr7C3, NbC, TiC | Fine and dispersed | 15-30 μm |
| Type E | FCC austenite + M7C3 | M7C3, Cr7C3 | Fine and dispersed | 15-25 μm |
The presence of refractory carbides (NbC, TiC) in Type D is responsible for its excellent hardness retention at elevated temperatures. These carbides have high melting points and low diffusivity, resisting coarsening during heat treatment and service exposure.
Wear and Heat Resistance Performance
The electrodes were evaluated for wear resistance under both room temperature and elevated temperature conditions using a pin-on-disk test apparatus:
| Electrode Type | Wear Rate at 25°C (mg/1000 cycles) | Wear Rate at 400°C (mg/1000 cycles) | Hardness Retention at 400°C (%) |
|---|---|---|---|
| Type A | 8.5 | 22.3 | 72% |
| Type B | 10.2 | 28.6 | 68% |
| Type C | 6.8 | 12.5 | 91% |
| Type D | 7.2 | 15.8 | 85% |
| Type E | 9.5 | 18.2 | 82% |
Type C (Co-Cr-W) exhibits the best wear resistance at elevated temperatures due to the high thermal stability of the Co-based matrix and the fine, dispersed carbide structure. Type D (Fe-Cr-C-Nb) provides a good compromise between cost and performance, with acceptable wear resistance at moderate temperatures.
Electrode Coating Design
The electrode coating formulation is critical for controlling the deposit composition and properties. The study evaluates different coating formulations:
| Coating Component | Function | Typical Content | Effect on Deposit |
|---|---|---|---|
| Iron powder | Base metal dilution | 30-40% | Controls dilution rate |
| Chromium powder | Alloy addition | 15-25% | Forms hard carbides |
| Carbon source (graphite, CaCO3) | Carbon control | 5-10% | Controls carbide formation |
| Manganese powder | Deoxidizer, carbide former | 5-15% | Forms Mn3C, improves fluidity |
| Titanium powder | Refractory carbide former | 1-3% | Forms TiC, improves heat resistance |
| Niobium powder | Refractory carbide former | 1-3% | Forms NbC, improves heat resistance |
| Flux components (CaF2, SiO2) | Slag formation | 10-20% | Controls slag properties, deoxidation |
| Iron oxide (Fe2O3) | Oxygen source, slag former | 3-8% | Controls oxygen potential, slag basicity |
Engineering Practice Implications
Application Selection Matrix
| Application | Recommended Electrode Type | Key Requirement | Expected Service Life |
|---|---|---|---|
| Cement kiln wear plates | Type D (Fe-Cr-C-Nb) | Wear resistance at 300-500°C | 12-18 months |
| Steel mill ladle linings | Type C (Co-Cr-W) | Heat resistance at 800-1200°C | 6-12 months |
| Power plant boiler tubes | Type C or Type E | Erosion-corrosion resistance at 400-600°C | 18-36 months |
| Mining equipment (bucket teeth) | Type A or Type D | Abrasive wear at ambient temperature | 6-12 months |
| Hot gas ducts and hoppers | Type B (Fe-Cr-Ni-C) | Moderate wear at 200-400°C | 12-24 months |
| Foundry molds and cores | Type A (Fe-Cr-C) | Abrasive wear at ambient temperature | 6-12 months |
Welding Process Parameters
The electrode type and composition influence the recommended welding parameters:
| Parameter | Type A | Type B | Type C | Type D | Type E |
|---|---|---|---|---|---|
| Current (A) | 200-350 | 200-350 | 150-250 | 200-350 | 150-250 |
| Arc voltage (V) | 22-28 | 22-28 | 20-25 | 22-28 | 20-25 |
| Travel speed (mm/s) | 3-8 | 3-8 | 2-5 | 3-8 | 2-5 |
| Lay width (mm) | 15-25 | 15-25 | 10-20 | 15-25 | 10-20 |
| Pass thickness (mm) | 2-4 | 2-4 | 1.5-3 | 2-4 | 1.5-3 |
| Preheat (°C) | 100-200 | 100-200 | 200-300 | 100-200 | 200-300 |
Defect Prevention and Control
Common defects in overlay welding with these electrode types and their prevention:
| Defect | Cause | Prevention |
|---|---|---|
| Cracking | High carbon content, low ductility, high residual stress | Use multi-pass, control interpass temperature, PWHT |
| Porosity | Flux contamination, moisture, inadequate shielding | Dry electrodes, clean flux, adequate shielding |
| Incomplete fusion | Low heat input, high travel speed | Increase current, reduce travel speed |
| Excessive dilution | Single pass, high deposition rate | Use multi-pass, reduce base metal penetration |
| Carbon burn-off | High oxygen potential, excessive heat input | Use deoxidizers, control heat input |
| Hot cracking | Low melting point phases, restricted cooling | Adjust composition, control cooling rate |
Key Questions and Reflections
The study raises several important considerations for engineering practice:
- Cost-performance optimization: Type C (Co-Cr-W) provides the best performance but at significantly higher cost due to the cobalt content. Engineers must evaluate whether the performance advantage justifies the cost premium for each specific application. Type D (Fe-Cr-C-Nb) offers a more economical alternative for many applications, with acceptable performance at moderate temperatures.
- Multi-layer strategy: For applications requiring both surface hardness and substrate compatibility, a multi-layer approach may be beneficial. A transition layer of moderate hardness can be applied first, followed by the wear-resistant overlay. This reduces cracking risk and improves bond strength.
- Heat treatment optimization: The heat treatment temperature and duration significantly affect the final properties. Overheating can cause carbide coarsening and hardness loss, while underheating may leave residual stresses. The optimal heat treatment parameters depend on the specific electrode type and application requirements.
- Long-term performance: The study evaluates short-term performance, but long-term service behavior may differ. Engineers should consider the thermal stability of the microstructure over extended service periods, particularly for applications with cyclic thermal loading.
Study Insights and Implications
This study demonstrates that the development of wear-resistant and heat-resistant overlay electrodes requires a careful balance of composition, coating formulation, and processing parameters. The addition of refractory carbide formers (Nb, Ti) to Fe-Cr-C systems significantly improves heat resistance while maintaining adequate wear resistance, offering a cost-effective alternative to Co-based systems for many applications.
The findings highlight the importance of microstructure control in achieving the desired combination of properties. Fine, uniformly dispersed carbides provide the best combination of hardness and toughness, while coarse carbides can act as crack initiation sites and reduce wear resistance. The electrode coating formulation plays a critical role in controlling the deposit microstructure, and careful optimization of the coating composition is essential.
For engineering practice, the study provides a valuable framework for electrode selection based on application requirements. Engineers should consider the operating temperature, wear mechanism, expected service life, and cost constraints when selecting the appropriate electrode type. The multi-layer strategy and appropriate heat treatment can further optimize the performance of the overlay deposit.
In conclusion, the development of wear-resistant and heat-resistant overlay electrodes is a complex task that requires a deep understanding of the interplay between composition, microstructure, and processing parameters. The study provides valuable guidance for engineers selecting and applying these electrodes in industrial applications, emphasizing the importance of matching the electrode type to the specific service conditions and optimizing the processing parameters to achieve the desired performance.