Zhuojin Pipe Fitting Co., LtdHigh-Temperature Aging Performance of Self-Developed Heat-Resistant Hardfacing Electrode for Cement Kiln Drive Shafts
Literature Overview
This 1999 technical paper by Zhao Baojun and Wu Yunhua from Jiangsu Lidajian Building Materials Machinery Group addresses a specific and challenging industrial problem: the hardfacing repair of drive shafts in cement rotary kilns that operate continuously at elevated temperatures. The authors developed a Cr-Mn-W alloy electrode system as a cost-effective alternative to expensive cobalt and nickel-based electrodes, and demonstrated through high-temperature aging tests that the self-developed consumable provides adequate performance at service temperatures while significantly reducing repair costs.
Problem Statement and Technical Challenge
Cement rotary kiln drive shafts operate in an exceptionally demanding environment:
- Temperature: Shaft surfaces in contact with kiln linings or in proximity to hot gas flow can reach 400–700°C continuously.
- Mechanical loading: The shaft transmits the entire driving torque required to rotate the kiln, subjecting the surface to cyclic shear and contact stresses.
- Thermal cycling: Startup and shutdown cycles create thermal gradients that induce additional fatigue stresses.
- Abrasive contact: Kiln lining material and dust deposits act as abrasives against the shaft surface.
The previous consumable selections (D512, D337, D17 electrodes) exhibited poor processability and insufficient thermal strength, resulting in short repair intervals. Cobalt and nickel alloy electrodes provided adequate performance but at prohibitive cost, making them economically unviable for routine maintenance.
Alloy Design Philosophy
The Cr-Mn-W alloy system represents a deliberate metallurgical strategy:
| Alloying Element | Primary Function | Effect on Microstructure |
|---|---|---|
| Chromium (Cr) | Hardenability, oxidation resistance | Forms Cr₇C₃, Cr₂₃C₆ carbides; promotes martensitic transformation |
| Manganese (Mn) | Hardenability, hot strength | Stabilizes austenite; forms Mn₃C carbides |
| Tungsten (W) | Hot hardness, retained strength | Forms WC, W₂C carbides; retards softening at elevated temperature |
The combination of these elements produces a tempered martensitic matrix with a high density of hard carbide particles. The key advantage over Co-Ni systems is that the Cr-Mn-W system achieves comparable hot hardness through carbide strengthening rather than solid solution strengthening, which is inherently more cost-effective.
High-Temperature Aging Test Results
The critical validation of this electrode system was the high-temperature aging test, which simulates the long-term thermal exposure experienced during service:
| Aging Temperature | Aging Time | Hardness Before Aging | Hardness After Aging | Hardness Retention |
|---|---|---|---|---|
| Room temperature | — | 55–58 HRC | 55–58 HRC | 100% |
| 400°C | 10 h | 55–58 HRC | 52–55 HRC | ~95% |
| 500°C | 10 h | 55–58 HRC | 48–51 HRC | ~88% |
| 600°C | 10 h | 55–58 HRC | 42–45 HRC | ~78% |
| 700°C | 10 h | 55–58 HRC | 35–38 HRC | ~65% |
These results demonstrate that the Cr-Mn-W deposit maintains acceptable hardness (above 40 HRC) up to 600°C, covering the typical operating temperature range of cement kiln drive shafts. The tungsten carbides are responsible for the retained hardness at elevated temperatures, as WC has a high melting point (2870°C) and maintains its structural integrity well beyond the softening temperature of iron-based martensite.
Process Parameters and Application Guidelines
For successful application of this electrode on cement kiln drive shafts:
- Preheat: 200–300°C to prevent cold cracking in the HAZ of the carbon steel shaft
- Interpass temperature: Maintain below 250°C to control cooling rate and prevent excessive HAZ hardness
- Welding current: 140–200 A (depending on electrode diameter) with DCEN polarity
- Travel speed: 40–60 mm/min for consistent bead geometry
- Post-weld treatment: Stress relief at 550–600°C for 2 hours per 25 mm thickness
- Surface finish: Grind to achieve Ra ≤ 3.2 μm for smooth operation in bearings
Comparative Cost Analysis
The economic advantage of the Cr-Mn-W system over Co-Ni alternatives is substantial:
| Cost Factor | Co-Ni Electrode | Cr-Mn-W Electrode | Savings |
|---|---|---|---|
| Electrode cost (relative) | 100% | 30–40% | 60–70% |
| Repair labor cost | 100% | 100% | 0% |
| Service life (relative) | 100% | 85–95% | — |
| Cost per month of service | 100% | 32–47% | 53–68% |
The Cr-Mn-W electrode delivers approximately 85–95% of the service life of Co-Ni electrodes at only 30–40% of the material cost, resulting in a 50–70% reduction in cost per unit of service life.
Study Insights and Implications
This paper exemplifies the engineering principle of fitness-for-purpose: the optimal solution is not always the highest-performance solution but rather the one that meets requirements at acceptable cost. The self-developed Cr-Mn-W electrode demonstrates that careful alloy design, informed by metallurgical understanding, can produce consumables that outperform established solutions on a cost-effectiveness basis.
The high-temperature aging testing methodology employed in this study is particularly valuable, as it provides predictive data on long-term performance that would otherwise require years of field service to establish. Engineers evaluating hardfacing solutions for high-temperature applications should insist on aging test data as part of the qualification process.
One important limitation to note is that the study focuses on hardness retention as the primary performance metric. In practice, other properties such as thermal fatigue resistance, oxidation resistance, and dimensional stability under thermal cycling also influence service life. A comprehensive qualification program should include thermal shock testing and oxidation exposure testing in addition to aging hardness measurements.