CLADDING TECHNOLOGY SHANXI CO., LTDNickel-Based High-Temperature Wear-Resistant Slag-Free Overlay Electrode and Heat Treatment
Literature Overview
Published in 2006 in the Journal of Welding (焊接学报), this research by Wang Zhongwei, Zhang Qinghui, and Xiao Yifeng from Zhuzhou Hard Alloy Group Co., Ltd. and the School of Mechanical Engineering at Xiangtan University addresses the development of a specialized slag-free overlay welding electrode designed for high-temperature wear resistance applications. The work represents a significant advancement in consumable design for severe service conditions where conventional overlay electrodes fail due to slag entrapment, inadequate heat resistance, or insufficient hardness retention at elevated temperatures.
Core Technical Content
Design Philosophy of the Slag-Free Electrode
The slag-free design is a deliberate engineering choice driven by several considerations:
- Elimination of slag inclusion defects: In high-temperature applications, slag pockets can act as initiation sites for crack formation
- Improved surface quality: Without slag coverage, the deposited bead surface is cleaner and requires less post-weld finishing
- Enhanced metallurgical control: The absence of slag allows for more predictable solidification behavior and microstructure evolution
- Suitability for automated processes: Slag-free electrodes are compatible with mechanized welding equipment
Electrode Composition Design
The nickel-based electrode composition is engineered to achieve specific microstructural features:
| Component | Content Range | Function |
|---|---|---|
| Ni | Balance (>50%) | Base matrix, corrosion resistance |
| Cr | 20–30% | Solid solution strengthening, carbide formation |
| Mo | 5–10% | High-temperature strength, carbide stabilization |
| W | 3–8% | Refractory carbide formation, red hardness |
| C | 4–8% | Primary carbide former |
| B | 0.5–2.0% | Hard boride formation |
| Si | 1–3% | Silicon carbide, oxidation resistance |
The resulting microstructure consists of hard refractory carbides (Ni3B, Cr7C3, Mo2C, WC) and borides (NiB, CrB) dispersed in a nickel-chromium austenitic or martensitic matrix.
Heat Treatment Optimization
The heat treatment regime is critical for achieving optimal properties in the deposited overlay:
Solution Treatment: Heating to 1050–1150°C for 1–2 hours, followed by water quenching, dissolves soft intermetallic phases and homogenizes the microstructure.
Aging Treatment: Subsequent aging at 700–850°C for 2–4 hours precipitates fine, coherent carbides that provide maximum hardness without excessive brittleness.
| Heat Treatment Stage | Temperature (°C) | Cooling Method | Resulting Hardness (HV) |
|---|---|---|---|
| As-deposited | — | Air cooling | 800–1100 |
| Solution + Water Quench | 1100 | Water | 900–1200 |
| Solution + Aging (800°C/4h) | 800 | Air cooling | 1300–1600 |
| Solution + Aging (850°C/4h) | 850 | Air cooling | 1200–1500 |
High-Temperature Performance
The key differentiator of this electrode is its performance at elevated temperatures:
- At 200°C: Hardness retention of 90–95% of room temperature value
- At 400°C: Hardness retention of 80–85%
- At 600°C: Hardness retention of 60–70%
- At 800°C: Hardness retention of 40–50% (still exceeding 500 HV)
This performance is achieved through the combination of:
- Refractory carbides that maintain hardness at elevated temperatures
- Solid solution strengthening from Mo and W in the nickel matrix
- Thermal barrier properties of chromium-rich phases
Process Parameters and Welding Characteristics
The slag-free electrode exhibits specific welding characteristics that require attention:
- Current range: 180–350 A (depending on electrode diameter)
- Voltage: 22–32 V
- Deposition efficiency: 65–75% (higher than slag-forming electrodes)
- Dilution rate: 15–25% with carbon steel base metals
- Deposition rate: 1.5–3.0 kg/h
The absence of slag means that the weld pool is exposed to atmospheric contamination, making the use of shielding gas (typically argon or argon-helium mixtures) or welding in a controlled atmosphere essential for high-quality deposits.
Engineering Applications
This type of electrode finds application in:
- Hot work tooling: Dies, punches, and molds operating at 400–600°C
- Power plant components: Boiler tubes, turbine blades, and furnace parts
- Mining equipment: Crusher jaws and hammers in hot environments
- Oil and gas: Downhole tools and wellhead components
FMEA Analysis of Potential Failure Modes
| Failure Mode | Cause | Effect | Mitigation |
|---|---|---|---|
| Overlay spalling | Excessive residual stress | Component failure | Stress relief at 600–700°C |
| Cracking at fusion line | High dilution, carbon segregation | Loss of overlay integrity | Preheat control, transition layer |
| Soft spots | Localized dilution variation | Premature wear | Multi-layer deposition with grinding |
| Porosity | Gas entrapment without slag protection | Reduced load-bearing area | Strict shielding gas flow control |
| Hardness non-uniformity | Inconsistent heat input | Variable wear performance | Process parameter optimization |
Study Reflections
This research demonstrates a sophisticated approach to consumable design, where the decision to eliminate slag is not merely a process simplification but a fundamental metallurgical strategy. The slag-free design enables more precise control over the solidification microstructure, which is particularly important for achieving the fine, uniformly distributed carbide morphology required for high-temperature wear resistance. The integration of heat treatment with the electrode composition design represents the mature approach of considering the entire process chain—from melting through deposition to post-weld treatment—as a unified system for achieving target properties. The practical significance of this work is amplified by its application in the hard alloy industry, where the demand for high-temperature wear-resistant components continues to grow with advancing industrial processes.