CLADDING TECHNOLOGY SHANXI CO., LTDHigh-Temperature Aging Properties of Self-Developed High-Temperature Resistant Overlay Electrode - Literature Study Note
Literature Overview
This 1999 study by engineers from Jiangsu Lidai Building Materials Machinery Group Company investigates the high-temperature aging behavior of a self-developed overlay welding electrode designed for high-temperature service applications. In building materials machinery—particularly cement kilns, rotary dryers, and calcination equipment—wear parts are exposed to temperatures ranging from 400 to 900 °C, where conventional overlay materials lose hardness and wear resistance due to tempering and phase transformations. This research addresses the critical challenge of maintaining overlay performance under prolonged high-temperature exposure.
High-Temperature Service Requirements
The overlay electrode was designed for the following application conditions:
| Application Component | Operating Temperature (°C) | Wear Mechanism | Required Service Life |
|---|---|---|---|
| Kiln wear plates | 600–900 | Abrasive + thermal | ≥ 12 months |
| Rotary dryer liners | 400–700 | Abrasive + erosion | ≥ 18 months |
| Calciner refractory support | 500–800 | Abrasive + thermal fatigue | ≥ 12 months |
| Fan blades (hot gas) | 300–500 | Erosion + oxidation | ≥ 24 months |
| Chute liners | 200–600 | Abrasive | ≥ 12 months |
The key requirement is that the overlay material must maintain adequate hardness and wear resistance after prolonged exposure at the maximum service temperature, not merely at room temperature.
Electrode Design Philosophy
The self-developed electrode incorporates the following design principles for high-temperature performance:
Composition Strategy
| Design Element | Purpose | Typical Range |
|---|---|---|
| High Cr content | Form stable Cr₂O₃ scale and Cr-rich carbides | 20–35 wt% |
| Mo addition | Retain solution strengthening at high temperature | 3–8 wt% |
| V or Nb addition | Form stable carbides resistant to coarsening | 1–3 wt% |
| Controlled C content | Balance carbide volume fraction with matrix strength | 1.5–3.5 wt% |
| Ni addition | Stabilize austenite, improve hot hardness | 5–15 wt% |
Microstructural Design Goals
- High volume fraction of hard carbides (M₇C₃, M₆C, or Cr₇C₃) that resist coarsening at elevated temperature
- Stable matrix that does not undergo significant softening through tempering or phase transformation
- Thermal barrier oxide (Cr₂O₃) formation capability for oxidation resistance
- Thermal fatigue crack resistance through appropriate toughness retention
High-Temperature Aging Test Results
The aging tests were conducted at various temperatures for extended durations to simulate long-term service:
| Aging Temperature (°C) | Aging Time (h) | Room Temperature Hardness Before Aging (HRC) | Hardness After Aging (HRC) | Hardness Retention (%) |
|---|---|---|---|---|
| 400 | 100 | 52–55 | 50–53 | 96–98% |
| 500 | 100 | 52–55 | 48–51 | 90–95% |
| 600 | 100 | 52–55 | 45–48 | 82–88% |
| 700 | 100 | 52–55 | 40–44 | 72–80% |
| 800 | 100 | 52–55 | 35–38 | 62–70% |
| 900 | 100 | 52–55 | 30–34 | 55–62% |
Microstructural Changes During Aging
| Aging Temperature | Primary Microstructural Change | Mechanism |
|---|---|---|
| 400 °C | Minimal change | Carbon and alloy elements remain in solution |
| 500 °C | Slight carbide coarsening | Early-stage Ostwald ripening |
| 600 °C | Noticeable carbide coarsening | Diffusion-accelerated growth |
| 700 °C | Significant coarsening + matrix softening | Carbon diffusion + carbide dissolution |
| 800 °C | Severe coarsening + phase transformation | Matrix softening + carbide reversion |
| 900 °C | Extensive phase transformation | Austenite → ferrite transformation + carbide dissolution |
Comparative Performance with Conventional Electrodes
| Electrode Type | Room Temp Hardness (HRC) | Hardness at 700°C after 100h (HRC) | Retention at 700°C (%) |
|---|---|---|---|
| Conventional CrMo hardfacing | 48–52 | 32–35 | 62–67% |
| Self-developed electrode | 52–55 | 40–44 | 72–80% |
| Ni-base alloy overlay | 35–40 | 33–36 | 83–90% |
| High-Cr cast iron overlay | 50–54 | 38–42 | 72–78% |
The self-developed electrode demonstrates superior high-temperature hardness retention compared to conventional CrMo hardfacing electrodes, approaching the performance of Ni-base alloys while maintaining significantly higher room-temperature hardness.
Engineering Application and Verification
The electrode was applied to kiln wear plates in a cement production line operating at approximately 700–800 °C. The field performance results confirmed:
- Service life extension: From 4 months (conventional electrode) to 9–11 months (self-developed electrode)
- Wear rate reduction: 55–60% reduction in material loss
- Overlay integrity: No spalling or delamination observed after 10 months of service
- Cracking resistance: No thermal fatigue cracking detected during service
Study Insights and Engineering Recommendations
This research highlights a fundamental principle in high-temperature overlay design: room-temperature hardness is not a reliable predictor of high-temperature service performance. The microstructural stability of the overlay at operating temperature is the governing factor for wear resistance retention.
Key engineering recommendations derived from this study:
- Always perform high-temperature aging qualification for overlay materials intended for elevated-temperature service. Room-temperature hardness testing alone is insufficient.
- The optimal Cr content for high-temperature applications is in the 25–35% range, providing both carbide stability and oxidation resistance.
- Mo and V additions are critical for maintaining solution strengthening at elevated temperatures, as these elements have low diffusivity and resist partitioning.
- Carbide morphology control during welding is essential—fine, uniformly distributed carbides resist coarsening better than coarse, segregated carbides.
- The service temperature threshold for this electrode class is approximately 800 °C; above this temperature, Ni-base alloy overlays become necessary.
This study represents an important contribution to the practical development of high-temperature overlay consumables for the building materials industry, where the cost-performance ratio of overlay solutions is critical for economic viability. The systematic aging test methodology employed provides a template for qualification testing of overlay materials for any high-temperature application.