CLADDING TECHNOLOGY SHANXI CO., LTDResearch on Iron-Based High-Temperature Wear-Resistant Weld Overlay Electrodes
Literature Overview
This technical study addresses the development and characterization of iron-based weld overlay electrodes designed for high-temperature wear-resistant applications. High-temperature wear is a critical failure mode in components such as cement kiln liners, furnace burners, coal mill rollers, and power plant air preheaters, where operating temperatures exceed 400°C and abrasive or erosive media are present. The challenge lies in maintaining hardness, microstructural stability, and oxidation resistance simultaneously at elevated temperatures, which is inherently contradictory in iron-based alloy systems where softening mechanisms are thermally activated.
Core Technical Findings
The study developed a series of iron-based electrode compositions with varying alloy additions and evaluated their performance under simulated high-temperature wear conditions. The base composition contains 1.2-1.8% C, 8-12% Cr, 2-4% Mo, 0.5-1.5% V, and 0.2-0.5% Nb. The key innovation involves the addition of rare earth elements (La, Ce) in trace amounts (0.02-0.08%) to modify carbide morphology and improve high-temperature stability.
| Electrode Grade | C (%) | Cr (%) | Mo (%) | V (%) | Nb (%) | RE (%) | Hardness at 25°C (HRC) | Hardness at 600°C (HRC) | Retention Rate (%) |
|---|---|---|---|---|---|---|---|---|---|
| Baseline | 1.5 | 10 | 3.0 | 0.8 | 0.3 | 0 | 62 | 38 | 61.3 |
| Modified-1 | 1.6 | 11 | 3.5 | 1.0 | 0.4 | 0.05 | 64 | 48 | 75.0 |
| Modified-2 | 1.7 | 12 | 4.0 | 1.2 | 0.5 | 0.08 | 66 | 52 | 78.8 |
| Modified-3 | 1.8 | 11 | 3.5 | 1.0 | 0.4 | 0.03 | 63 | 45 | 71.4 |
The rare earth addition significantly improves high-temperature hardness retention, with Modified-2 achieving 78.8% hardness retention at 600°C compared to only 61.3% for the baseline composition. This represents a substantial improvement for applications where the component operates above 400°C.
Microstructural Analysis
The high-temperature wear resistance is primarily governed by three microstructural features:
- Carbide type and distribution: The modified compositions promote the formation of finer, more uniformly distributed MC-type carbides (VC, NbC) alongside M7C3 carbides, rather than the coarse M23C6 carbides that dominate in the baseline composition. MC carbides maintain their hardness at elevated temperatures due to their strong covalent bonding and high melting points.
- Matrix microstructure: The martensitic matrix in the overlay deposits undergoes tempering at elevated temperatures. The addition of Mo and V increases the temper resistance of the matrix by retarding the precipitation and coarsening of fine carbides. At 600°C, the baseline composition shows significant carbide coarsening and matrix softening, while the modified compositions maintain a tempered martensite structure with retained fine carbides.
- Oxidation resistance: The Cr content of 11-12% provides adequate oxidation resistance for temperatures up to 800°C in most industrial atmospheres. The rare earth addition further improves oxidation resistance by modifying the oxide scale morphology, reducing scale spallation tendency, and promoting the formation of a more adherent and protective Cr2O3 layer.
Electrode Manufacture and Welding Process
The electrode coating composition is critical to achieving the desired overlay microstructure. The coating typically consists of:
| Coating Component | Function | Typical Range |
|---|---|---|
| Iron powder | Base metal dilution control | 30-45% |
| Chromium oxide | Cr source | 15-25% |
| Molybdenum powder | Mo source, temper resistance | 5-10% |
| Vanadium pentoxide | V source, MC carbide formation | 3-6% |
| Niobium carbide | Nb source, carbide refinement | 2-5% |
| Rare earth oxide | Microstructure modification | 0.5-2% |
| Iron oxide | Flux, deoxidation | 10-15% |
| Silica / Alumina | Flux, slag formation | 5-10% |
| Carbon source (graphite) | Carbon control | 3-8% |
The welding process is typically shielded metal arc welding (SMAW) with a DC electrode positive polarity. Recommended parameters include an arc voltage of 24-30 V, current of 120-180 A for φ3.2 mm electrodes, and travel speed of 120-200 mm/min. Preheating to 150-250°C is recommended for thick sections or when welding to high-carbon steel base metals to prevent cracking.
High-Temperature Wear Testing Methodology
The study employed a pin-on-disk wear tester with the overlay deposit as the disk and a SiC pin as the counterface. Testing was conducted at temperatures of 25°C, 300°C, 500°C, and 600°C under a normal load of 10 N and a sliding distance of 1000 m. The results showed a consistent trend where the modified electrodes maintained significantly lower wear rates at elevated temperatures compared to the baseline.
| Test Temperature | Baseline Wear Rate (10^-3 mm³/N·m) | Modified-2 Wear Rate (10^-3 mm³/N·m) | Improvement (%) |
|---|---|---|---|
| 25°C | 2.1 | 1.4 | 33.3 |
| 300°C | 3.8 | 2.5 | 34.2 |
| 500°C | 8.5 | 4.8 | 43.5 |
| 600°C | 15.2 | 7.6 | 50.0 |
The improvement in wear resistance at elevated temperatures is more pronounced than at room temperature, which is the most desirable outcome for high-temperature applications. This indicates that the microstructural modifications are specifically effective against thermally activated wear mechanisms.
Common Defects and Quality Control
| Defect | Root Cause | Prevention / Correction |
|---|---|---|
| Cracking | High carbon equivalent, hydrogen embrittlement,拘束 stress | Preheat 200°C, post-weld heat treatment, low-hydrogen coating |
| Poor fusion | Excessive travel speed, low current | Optimize welding parameters, ensure proper base metal preparation |
| Excessive porosity | Moist coating, contamination | Store electrodes in drying oven at 150°C, clean base surface |
| Hardness variation | Inconsistent coating application | Quality control of electrode manufacture, regular hardness testing |
| Spalling of overlay | Thermal mismatch, poor bond strength | Control dilution, ensure proper heat input, consider multi-pass strategy |
Engineering Application Cases
The developed electrodes have been applied in several industrial settings:
- Cement kiln burners: Overlay on burner throat sections operating at 800-1000°C with abrasive coal dust. Service life improved from 6 months to 14 months with Modified-2 electrode.
- Coal mill rollers: Hardfacing of roller surface operating at 350-450°C with abrasive coal. Grinding efficiency increased by 18% due to maintained surface hardness.
- Furnace tuyeres: Overlay on tuyere nozzles exposed to hot blast air at 1200°C with entrained particles. Life extension of 2.5x achieved.
Key Questions and Reflections
The study raises important considerations regarding the long-term performance of these electrodes in actual service conditions. Laboratory wear testing, while providing valuable comparative data, cannot fully replicate the complex loading, thermal cycling, and environmental conditions of industrial applications. Engineers should validate the laboratory findings through pilot-scale testing before committing to full-scale production applications.
Another critical question is the cost-effectiveness of the rare earth addition. While the performance improvement is significant, the rare earth content, though small in percentage terms, adds to the electrode cost. A thorough life-cycle cost analysis should be conducted to determine the economic viability of the modified electrodes compared to conventional alternatives.
The weldability of the modified electrodes also deserves attention. The higher carbon content and alloy additions increase the susceptibility to cracking, particularly in thick sections or when welding to high-carbon steel base metals. Process qualification in accordance with NB/T 47014 or ASME IX is essential before deployment on pressure vessel components.
Study Insights and Implications
The most valuable contribution of this study is the demonstration that trace rare earth addition can significantly enhance the high-temperature performance of iron-based weld overlay materials without requiring exotic alloying elements or complex manufacturing processes. This represents a practical and cost-effective approach to developing next-generation wear-resistant consumables for high-temperature industrial applications.
For engineers involved in material selection and process development, the key takeaway is that the traditional trade-off between room-temperature hardness and high-temperature stability can be partially overcome through careful microstructural engineering. The rare earth modification approach offers a pathway to extend the service life of critical components in cement, power generation, and metallurgical industries where high-temperature wear is a major degradation mechanism.