CLADDING TECHNOLOGY SHANXI CO., LTDHigh-Temperature Aging Performance of Self-Developed High-Temperature-Resistant Cladding Electrodes
Literature Overview and Research Motivation
High-temperature-resistant cladding electrodes are critical consumables for the fabrication of components that must withstand elevated temperatures combined with wear, such as furnace linings, kiln refractories, cement kiln components, and metallurgical furnace parts. The literature reviewed here focuses on the development and characterization of self-developed (in-house formulated) high-temperature-resistant cladding electrodes, with particular emphasis on their performance after exposure to elevated temperatures for extended periods.
The research motivation is straightforward: standard cladding electrodes are designed for room-temperature or moderate-temperature applications and degrade rapidly when exposed to sustained high temperatures. For components operating at temperatures above 500 °C, the overlay layer must retain its wear resistance, oxidation resistance, and dimensional stability after prolonged thermal exposure. The self-developed electrodes described in the literature are formulated to meet these demanding requirements through careful control of alloy composition and microstructure.
Alloy Design and Microstructural Analysis
Alloy Composition and Design Philosophy
The self-developed high-temperature-resistant cladding electrodes are formulated based on a high-chromium, high-nickel, high-aluminum alloy system, designed to provide a combination of oxidation resistance, thermal stability, and wear resistance. The base alloy is typically a modified 21Cr-14Ni-4Al type alloy, similar to cast alloy A2 or A5 designations, with additional alloying elements to enhance high-temperature performance.
| Alloying Element | Typical Content (wt%) | Function |
|---|---|---|
| Chromium (Cr) | 20–25 | Oxidation resistance, hardness |
| Nickel (Ni) | 12–16 | Austenite stabilization, toughness |
| Aluminum (Al) | 3–5 | Oxidation resistance (Al₂O₃ scale) |
| Molybdenum (Mo) | 2–4 | High-temperature strength, corrosion resistance |
| Titanium (Ti) | 0.5–1.5 | Grain refinement, carbide formation |
| Silicon (Si) | 1–3 | Deoxidation, SiO₂ scale formation |
| Carbon (C) | 0.5–1.5 | Carbide formation, hardness |
| Iron (Fe) | Balance | Base metal |
The design philosophy emphasizes the formation of a protective oxide scale (primarily Al₂O₃ and Cr₂O₃) on the surface of the overlay layer during high-temperature exposure. This oxide scale acts as a diffusion barrier, slowing down further oxidation and maintaining the integrity of the overlay. The alloy also contains a high volume fraction of hard carbides (primarily Cr₇C₃, Cr₃C, and TiC), which provide the wear resistance and maintain hardness at elevated temperatures.
Microstructure Before and After Aging
The as-welded microstructure of the overlay layer consists of a austenite matrix with dispersed carbide particles and some delta ferrite. The carbides are primarily Cr₇C₃ and Cr₃C, with some TiC present at the interdendritic regions. The microstructure is characterized by a columnar dendritic structure typical of weld deposits, with a grain size of approximately 50–100 μm.
After exposure to elevated temperatures (typically 800–1100 °C for 100–1000 hours), the microstructure undergoes significant changes. The key observations from metallographic analysis include:
- Coarsening of carbide particles: The average carbide size increases from approximately 2–5 μm in the as-welded condition to 5–15 μm after aging at 1000 °C for 500 hours. This coarsening is driven by Ostwald ripening and reduces the wear resistance somewhat.
- Grain boundary migration: The grain boundaries migrate and recrystallize, leading to a more equiaxed grain structure. The grain size increases from 50–100 μm to 100–200 μm after prolonged aging.
- Oxide scale formation: A protective oxide scale forms on the surface, consisting primarily of Al₂O₃ and Cr₂O₃ with some Fe₂O₃ and SiO₂. The scale thickness increases with aging time, typically reaching 20–50 μm after 500 hours at 1000 °C.
- Phase stability: The austenite matrix remains stable throughout the aging exposure, with no significant precipitation of intermetallic phases such as sigma phase or Laves phase. This is a critical design achievement, as the formation of brittle intermetallic phases would severely degrade the toughness and serviceability of the overlay.
High-Temperature Performance Characterization
Hardness Retention at Elevated Temperatures
One of the most important performance indicators for high-temperature-resistant cladding electrodes is the hardness retention at elevated temperatures. The literature reports hardness measurements at room temperature, 500 °C, 800 °C, and 1000 °C for both the as-welded and aged overlay layers.
| Condition | Room Temp (HV) | 500 °C (HV) | 800 °C (HV) | 1000 °C (HV) |
|---|---|---|---|---|
| As-welded | 350–400 | 320–370 | 280–330 | 220–270 |
| After 500 h at 1000 °C | 320–370 | 300–350 | 260–310 | 200–250 |
The hardness retention at 1000 °C is approximately 55–65% of the room temperature value, which is considered acceptable for high-temperature wear applications. The slight decrease in room temperature hardness after aging is attributed to carbide coarsening and grain growth, but the overall hardness level remains sufficient for most wear applications.
Oxidation Resistance
The oxidation resistance of the overlay layer is evaluated by measuring the weight gain after exposure to elevated temperatures in air. The literature reports weight gain measurements for aging exposures at 800 °C, 1000 °C, and 1100 °C for durations ranging from 100 to 1000 hours.
| Temperature (°C) | 100 h Weight Gain (mg/cm²) | 500 h Weight Gain (mg/cm²) | 1000 h Weight Gain (mg/cm²) |
|---|---|---|---|
| 800 | 0.5–1.0 | 2.0–3.5 | 4.0–6.0 |
| 1000 | 1.5–2.5 | 6.0–9.0 | 12.0–18.0 |
| 1100 | 3.0–4.5 | 12.0–18.0 | 25.0–35.0 |
The oxidation kinetics follow a parabolic rate law at temperatures up to 1000 °C, indicating that the protective oxide scale is effective in limiting further oxidation. At 1100 °C, the oxidation rate increases significantly, suggesting that the protective scale begins to break down at this temperature. This sets a practical upper temperature limit of approximately 1050 °C for the application of these electrodes.
Thermal Shock Resistance
The thermal shock resistance of the overlay layer is evaluated by subjecting the overlay to repeated heating and cooling cycles between room temperature and 1000 °C. After 20 cycles, the overlay layer shows no significant cracking or spalling, indicating good thermal shock resistance. This is attributed to the ductile austenite matrix and the fine dispersion of carbides, which provide toughness and accommodate thermal strains without cracking.
Welding Process and Application
Welding Process Parameters
The self-developed electrodes are designed for use with shielded metal arc welding (SMAW) and flux-cored arc welding (FCAW) processes. The recommended welding parameters are as follows:
| Parameter | SMAW | FCAW |
|---|---|---|
| Current (A) | 100–160 | 150–250 |
| Voltage (V) | 22–28 | 24–30 |
| Travel speed (mm/min) | 150–250 | 200–350 |
| Electrode diameter (mm) | 3.2–4.0 | 1.2–1.6 |
| Preheat temperature (°C) | 150–200 | 150–200 |
| Interpass temperature (°C) | 150–250 | 150–250 |
| Post-weld treatment | 550–600 °C, 1–2 h | 550–600 °C, 1–2 h |
The preheat and interpass temperatures are set at 150–250 °C to prevent cold cracking in the high-alloy overlay and to maintain adequate ductility during welding. The post-weld stress relief at 550–600 °C is recommended to relieve residual stresses and to optimize the microstructure of the overlay layer.
Application Examples
The literature describes several application examples of the self-developed electrodes in high-temperature wear environments:
- Cement kiln wear plates: The overlay layer protects the steel wear plates in cement kilns from the combined action of high temperature (approximately 800–1000 °C), abrasive wear from cement clinker, and thermal cycling. The service life of the clad wear plates is reported to be 3–4 times longer than unclad steel plates.
- Furnace lining components: The electrodes are used to clad the steel components of industrial furnaces that operate at temperatures up to 1000 °C. The overlay provides oxidation resistance and wear resistance, extending the service life of the furnace components.
- Metallurgical hot work tools: The electrodes are used to clad hot work tools such as dies and molds that are exposed to high temperatures and wear during the metal forming process. The overlay maintains its hardness and oxidation resistance at elevated temperatures, reducing the frequency of tool replacement.
Study Insights and Engineering Implications
The development of self-developed high-temperature-resistant cladding electrodes represents a significant advancement in the field of high-temperature surface engineering. The key achievement is the formulation of an alloy that maintains acceptable hardness, oxidation resistance, and thermal shock resistance after prolonged exposure to temperatures up to 1000 °C. This is accomplished through careful alloy design that balances the competing requirements of oxidation resistance (which requires high Cr and Al content), wear resistance (which requires hard carbides), and toughness (which requires a ductile austenite matrix).
From a practical standpoint, the most important finding is that the overlay layer maintains its functional properties after extended aging at high temperatures. This means that components clad with these electrodes can be expected to perform reliably in high-temperature wear applications, with a predictable service life that can be estimated based on the aging exposure and the wear rate at the operating temperature.
The oxidation kinetics data provide a useful basis for predicting the service life of clad components in high-temperature environments. The parabolic oxidation rate at temperatures up to 1000 °C indicates that the protective oxide scale is effective in limiting further oxidation, and the weight gain data can be used to estimate the oxide scale thickness and the remaining thickness of the overlay layer after a given exposure time.
A critical engineering consideration is the selection of the appropriate overlay thickness for a given application. The overlay must be thick enough to withstand the expected wear rate over the desired service life, but not so thick as to cause excessive distortion or residual stress. A typical approach is to select an overlay thickness that provides a minimum of 2–3 mm of remaining material after the expected service life, taking into account the wear rate, the oxidation rate, and the thermal cycling effects.
The literature also highlights the importance of post-weld heat treatment in optimizing the performance of the overlay layer. The stress relief treatment at 550–600 °C not only relieves residual stresses but also promotes the formation of a fine, uniform carbide distribution that enhances the wear resistance and thermal stability of the overlay. Omitting the stress relief step can result in a coarser, less uniform microstructure with inferior high-temperature performance.
One area for further development is the extension of the service temperature range beyond 1000 °C. The current formulation of the electrodes is limited by the breakdown of the protective oxide scale at temperatures above 1050 °C. Future development efforts should focus on the addition of rare earth elements or other alloying additions that can enhance the stability of the oxide scale at higher temperatures, potentially extending the service range to 1100–1200 °C.
In summary, the self-developed high-temperature-resistant cladding electrodes described in this literature offer a reliable solution for the protection of steel components in high-temperature wear environments. The alloy design, welding process, and post-weld treatment are carefully optimized to achieve a balance of hardness, oxidation resistance, and thermal stability that meets the demanding requirements of industrial applications. Engineers implementing these electrodes should focus on careful process control, thorough quality inspection, and systematic performance monitoring to ensure reliable service life and optimal cost effectiveness.