Zhuojin Pipe Fitting Co., LtdHigh-Temperature Aging Properties of Self-Developed Heat-Resistant Surfacing Electrode
Literature Overview
This paper, published in Welding in 1999 by Zhao Baojun and Wu Yunhua from Jiangsu Lida Building Materials Machinery Group Co., Ltd., reports on the development and evaluation of a self-made heat-resistant surfacing electrode for repairing the transmission shafts of cement kilns. The authors address a practical problem of high-temperature shaft wear in cement production equipment and present a cost-effective alternative to expensive cobalt and nickel-based electrodes.
Core Technical Content
Problem Statement
Cement kiln transmission shafts operate at elevated temperatures (typically 400–800 °C) and are subject to wear from mechanical loading and thermal cycling. The original repair approach used commercial electrodes such as D512, D337, or D17, but these exhibited poor processability and insufficient high-temperature strength, resulting in short service life after repair. The alternative of using cobalt and nickel alloy electrodes, while technically superior, was economically prohibitive due to the high cost of these precious metals.
Self-Developed Electrode Design
The authors developed a Cr-Mn-W alloy system electrode as a substitute for Co-Ni based electrodes. The design philosophy was to achieve comparable high-temperature strength and hardness through the use of cheaper alloying elements while maintaining good weldability.
| Alloying Element | Typical Content | Role |
|---|---|---|
| Chromium (Cr) | 10–20% | Carbide formation, oxidation resistance |
| Manganese (Mn) | 2–5% | Solid solution strengthening, grain refinement |
| Tungsten (W) | 5–15% | High-temperature strength, carbide stability |
| Carbon (C) | 1.5–3.0% | Carbide formation, hardness |
| Iron (Fe) | Balance | Base metal |
High-Temperature Aging Performance
The critical test for this application is the retention of hardness and strength after prolonged exposure at service temperature. The aging behavior of the Cr-Mn-W alloy system was evaluated through isothermal aging tests:
| Aging Temperature | Aging Time | Hardness Retention | Microstructural Stability |
|---|---|---|---|
| 400 °C | 100 h | > 90% of as-welded hardness | Minimal softening |
| 600 °C | 100 h | > 85% of as-welded hardness | Moderate carbide coarsening |
| 800 °C | 100 h | > 75% of as-welded hardness | Significant but acceptable softening |
The Cr-Mn-W system demonstrated acceptable hardness retention at all tested temperatures, validating its suitability for cement kiln shaft applications. The tungsten carbides (WC, W₂C) formed in the deposit are particularly stable at elevated temperatures, providing the primary mechanism for high-temperature hardness retention.
Comparison with Alternative Electrodes
| Electrode Type | As-Welded Hardness | 600 °C/100h Hardness | Cost Factor | Processability |
|---|---|---|---|---|
| D512 (Cr-based) | 50–55 HRC | < 40 HRC | 1.0 (baseline) | Poor |
| D337 (Cr-based) | 48–52 HRC | < 38 HRC | 1.0 | Poor |
| D17 (Cr-based) | 50–55 HRC | < 42 HRC | 1.0 | Poor |
| Co-Ni alloy | 55–60 HRC | > 50 HRC | 5–10× | Good |
| Self-made Cr-Mn-W | 50–58 HRC | > 45 HRC | 1.5–2× | Good |
The self-developed electrode achieved a favorable balance between high-temperature performance, processability, and cost, making it a practical solution for the intended application.
Engineering Practice Integration
Application to Cement Kiln Shafts
The transmission shafts of cement kilns are typically large-diameter cylindrical components made of carbon or low-alloy steel. The surfacing repair process involves:
- Machining: Remove worn material from the shaft surface to expose sound base metal.
- Surface preparation: Clean and roughen the surface to promote metallurgical bonding.
- Preheating: Apply preheat to 200–300 °C to control cooling rate and prevent cracking.
- Multi-layer surfacing: Apply 3–5 layers of the Cr-Mn-W electrode, maintaining interpass temperature below 250 °C.
- Post-weld treatment: Stress-relief annealing at 550–650 °C to reduce residual stresses.
- Inspection: VT, MT for surface cracks, and hardness profiling.
Cost-Benefit Analysis
The economic advantage of the self-developed electrode over Co-Ni alternatives is substantial. While the Cr-Mn-W electrode costs 1.5–2 times more than conventional D-series electrodes, it costs only 15–20% of the price of Co-Ni electrodes. Given that the service life achieved with the Cr-Mn-W electrode is comparable to Co-Ni electrodes, the cost-effectiveness is compelling.
Study Insights and Reflections
This paper exemplifies the ingenuity of practical engineering problem-solving. The authors identified a clear need—a cost-effective alternative to expensive Co-Ni electrodes for high-temperature applications—and systematically developed a solution based on fundamental metallurgical principles. The selection of Cr, Mn, and W as alloying elements was well-considered: chromium provides oxidation resistance and carbide formation, manganese improves solid solution strengthening and weldability, and tungsten provides the critical high-temperature strength through stable carbide precipitation.
I find the aging test data particularly valuable, as many surfacing electrode evaluations focus only on as-welded properties and neglect the long-term behavior at service temperature. The demonstration that the Cr-Mn-W system retains over 85% of its hardness after 100 hours at 600 °C is significant, as it confirms that the hard carbide phases remain stable under prolonged thermal exposure.
One limitation of the study is the relatively short aging duration tested (100 hours). In actual cement kiln service, the shaft may be exposed to elevated temperatures for thousands of hours. While the Cr-Mn-W system is expected to perform well over extended periods, long-term aging data would provide additional confidence. The coarsening of tungsten carbides at elevated temperatures is a diffusion-controlled process that progresses slowly, so the 100-hour data likely represents a conservative estimate of long-term behavior.
In conclusion, this paper presents a successful example of self-developed consumable engineering, demonstrating that cost-effective alternatives to premium alloy electrodes can be developed through careful alloy design and rigorous performance evaluation. The Cr-Mn-W system offers a practical solution for high-temperature surfacing applications where Co-Ni electrodes are economically prohibitive, and the aging performance data provides confidence in its long-term reliability.