CLADDING TECHNOLOGY SHANXI CO., LTDResearch on High-Temperature Wear-Resistant Overlay Welding Electrodes
Literature Overview
This research by Han Yongchuan (2003) from China Coal Economic Institute focuses on the development of high-temperature wear-resistant overlay welding electrodes. Published in the Yantai University Journal (Natural Science and Engineering Edition), this work addresses a significant industrial challenge in coal mining and processing equipment, where components are subjected to both abrasive wear and elevated temperatures simultaneously.
Technical Background
In coal mining and processing operations, equipment components such as crusher liners, conveyor rollers, and grinding mill liners are exposed to extreme conditions combining:
- High-impact and abrasive wear from coal and rock particles
- Elevated temperatures from friction, combustion gases, and hot material handling
- Chemical attack from sulfur compounds and moisture
Conventional hardfacing materials often lose their effectiveness at elevated temperatures due to softening, oxidation, and thermal fatigue. The development of electrodes that maintain wear resistance at temperatures up to 600-800°C represents a significant advancement in surface engineering for the coal industry.
Electrode Composition Design
The research focuses on optimizing the electrode composition to achieve the desired combination of high-temperature hardness, oxidation resistance, and weldability. The key design principles include:
| Alloying Element | Function | Typical Range (wt%) |
|---|---|---|
| Cr | Oxidation resistance, carbide formation | 8-25 |
| Mo | Solid solution strengthening, high-T hardness | 2-8 |
| W | High-temperature carbide stability | 3-10 |
| Co | Matrix strengthening, oxidation resistance | 5-20 |
| C | Carbide precipitation | 2.5-4.5 |
| Si | Deoxidation, oxidation resistance | 1-3 |
The electrode design philosophy follows a composite approach:
- Matrix phase: A high-temperature alloy matrix (often austenitic or martensitic) that provides toughness and supports the hard phases.
- Hard carbide phase: Refractory carbides (Cr₇C₃, Mo₂C, WC, Co₃W₃C) that provide wear resistance through micro-hardness.
- Oxidation-resistant phase: Chromium-rich oxide films and oxide dispersible elements that protect against high-temperature oxidation.
Performance Characteristics
The developed electrodes demonstrated the following performance characteristics:
- Hot hardness retention: Maintaining 60-70% of room-temperature hardness at 600°C, compared to 30-40% for conventional materials.
- Wear resistance: 2-3 times the wear resistance of standard high-carbon steel electrodes under high-temperature sliding conditions.
- Oxidation resistance: Significant improvement in oxidation resistance at 600-800°C due to chromium enrichment at the surface.
- Crack resistance: Adequate toughness to resist thermal fatigue cracking during cyclic heating and cooling.
Welding Process Considerations
The welding process parameters for these high-alloy electrodes require careful control:
- Preheating: 150-250°C preheating is recommended to reduce cooling rates and prevent cold cracking in the high-alloy overlay.
- Interpass temperature: Maintain between 200-300°C for multi-pass builds to prevent excessive thermal cycling.
- Arc voltage and current: Lower arc voltage (24-28V) and moderate current density to minimize dilution from the base metal.
- Layer thickness: Multiple thin passes (2-3 mm each) are preferred to achieve uniform composition and minimize defects.
- Post-weld treatment: Stress relief at 600-700°C for 1-2 hours to reduce residual stresses without affecting the hardness of the overlay.
Defect Analysis and Countermeasures
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Hot cracking | High sulfur/phosphorus in base metal | Preheating, low-dilution process |
| Cold cracking | Hydrogen embrittlement | Low-hydrogen electrode, post-heat |
| Excessive dilution | High heat input | Lower current, shorter arc length |
| Porosity | Gas absorption, poor flux coverage | Proper shielding, clean surface |
| Hardness variation | Uneven cooling rates | Controlled interpass temperature |
Engineering Application Cases
The developed electrodes have been successfully applied to:
- Coal crusher liners: Extended service life from 3-6 months to 12-18 months in medium-hard coal processing.
- Conveyor rollers: Reduced replacement frequency by 60% in high-temperature coal handling applications.
- Grinding mill liners: Improved wear life by 2-3 times in hot coal grinding operations.
- Burner components: Enhanced resistance to thermal fatigue cracking in coal-fired furnaces.
Key Reflections
This research exemplifies the engineering philosophy of tailoring overlay materials to specific service environments. The coal industry's unique combination of wear, temperature, and chemical attack demands a multi-functional approach to surface protection. The electrode development approach—balancing composition, microstructure, and process parameters—provides a template for developing specialized overlay materials for other demanding industrial applications.
A significant insight from this work is that high-temperature wear resistance cannot be achieved through a single mechanism alone. Rather, it requires the synergistic combination of solid solution strengthening, precipitation hardening, and oxidation protection. This systems-level understanding is essential for engineers designing overlay solutions for extreme service conditions. The research also highlights the importance of considering the full lifecycle of the overlay, from deposition through post-weld treatment to in-service performance, as optimizing any single stage in isolation leads to suboptimal results.