Zhuojin Pipe Fitting Co., LtdDevelopment of High-Temperature Wear-Resistant Surfacing Electrodes Containing Boron
Literature Overview
This paper by Meng Gongge, Lu Yunlong, and Li Dan from Harbin University of Science and Technology, published in the journal "Welding" in 2005 (Vol. 4, pp. 27-29), reports on the development of a surfacing electrode containing boron and multiple alloying elements designed for high-temperature wear resistance. The work addresses a critical industrial need: conventional surfacing electrodes lose significant hardness and wear resistance at elevated operating temperatures, which limits their applicability in hot-end equipment such as cement kilns, furnace linings, and hot metal chutes. The authors benchmarked their electrode against the well-known Castolin 6715 electrode from Switzerland, a widely used industrial standard for high-temperature wear applications.
Core Technical Content
Alloy Design Philosophy
The electrode was designed using a multi-element alloying strategy with boron as a key strengthening element. Boron plays a dual role in the weld metal: it forms hard boride phases (such as FeB and Fe₂B) that provide dispersion strengthening, and it promotes the formation of a hypereutectic microstructure. The hypereutectic organization is critical because it ensures a higher volume fraction of primary carbide or boride particles compared to hypoeutectic compositions, resulting in superior wear resistance across a broad temperature range.
Performance Results
The following table summarizes the key performance data reported in the study:
| Test Condition | Developed Electrode | Castolin 6715 | Relative Performance |
|---|---|---|---|
| Room-temperature hardness | Higher than 6715 | Baseline | Superior |
| Room-temperature wear resistance | Higher than 6715 | Baseline | Superior |
| Hardness at 600 °C | HV 613 | Lower than HV 613 | Significantly superior |
| Hardness at 800 °C | HV 297.3 | Lower than HV 297.3 | Superior |
The retention of HV 613 at 600 °C is particularly noteworthy. Many conventional martensitic surfacing alloys experience a sharp hardness drop above 500 °C due to tempering and carbide coarsening. The ability to maintain such high hardness at 600 °C suggests that the boride phases and possibly retained austenite contribute to thermal stability of the microstructure.
Microstructural Analysis
The deposited metal exhibits a hypereutectic microstructure, which typically consists of primary carbide/boride particles embedded in a eutectic matrix of austenite and martensite. At elevated temperatures, the matrix phase may partially transform or soften, but the hard boride particles remain thermally stable and continue to provide resistance to abrasive and adhesive wear. The alloying elements other than boron likely include chromium (for carbide formation and oxidation resistance), manganese (to promote austenite stability), and possibly molybdenum or vanadium (for additional precipitation hardening and thermal stability).
Engineering Practice Integration
Application Scenarios
This type of electrode is particularly suited for components subjected to combined high-temperature and wear loading. Typical applications include:
- Cement kiln wear plates and lifter bars operating at 400–700 °C
- Rotary kiln liners in metallurgical and cement industries
- Hot gas ducts and cyclone liners in waste incineration
- Coal-fired boiler components exposed to abrasive fly ash at elevated temperatures
- Slag chutes and hoppers in steelmaking plants
Welding Process Considerations
When using high-alloy hypereutectic surfacing electrodes, several process parameters must be carefully controlled:
| Parameter | Recommended Practice | Rationale |
|---|---|---|
| Welding current | Moderate to low | Excessive current causes dilution and loss of alloy content |
| Arc length | Short | Maintains alloy transfer efficiency and reduces spatter |
| Travel speed | Moderate | Too fast causes incomplete fusion; too slow increases dilution |
| Preheating | 100–200 °C | Reduces cracking susceptibility in the HAZ and deposited metal |
| Interpass temperature | ≤ 250 °C | Prevents excessive softening of previously deposited layers |
| Number of passes | 2–3 | Ensures adequate alloy content in the final surface layer |
The dilution rate is a critical factor. In the first pass, dilution from the base metal can be as high as 40–50%, which significantly reduces the alloy content and hardness of the deposited layer. A multi-pass approach is therefore recommended, with the final pass achieving a dilution rate below 20%.
Defect Analysis and Countermeasures
Common defects in high-temperature wear-resistant surfacing deposits include:
- Cracking: Hypereutectic deposits with high carbon and boron content are susceptible to hot cracking. Countermeasures include reducing welding current, using a lower carbon electrode composition, and applying a proper preheat and interpass temperature regime.
- Excessive porosity: Caused by moisture in the electrode coating or inadequate arc shielding. Countermeasures include proper electrode storage and baking, and ensuring clean base metal surfaces.
- Low hardness due to dilution: If the base metal dilution is too high, the deposited metal may not achieve the target hardness. Countermeasures include using a multi-pass technique and selecting a higher-alloy-content electrode for the final pass.
Study Insights and Reflections
The achievement of HV 613 at 600 °C represents a meaningful advance over the Castolin 6715 benchmark. In practical terms, this translates to significantly longer service life for components operating in the 500–700 °C range, where many conventional surfacing alloys fail prematurely. The boron-based alloying strategy is elegant because boride phases have high thermal stability and do not soften appreciably until temperatures exceed 900 °C.
One area for further investigation would be the toughness of the deposited metal. Hypereutectic microstructures with high volume fractions of hard boride particles can be brittle, and impact toughness data are not reported in this study. In applications where the component is subjected to impact or thermal shock loading, a balance between wear resistance and toughness is essential. A potential approach would be to develop a composite surfacing strategy: a tough, ductile underlayer followed by a hard, boron-rich topcoat.
The study also highlights the importance of high-temperature hardness testing in surfacing electrode development. Room-temperature hardness alone is insufficient to predict performance in hot-end applications. Future electrode development programs should include systematic high-temperature hardness and wear testing at representative service temperatures.
This work contributes valuable data to the growing body of knowledge on boron-containing surfacing alloys and provides a practical alternative to imported electrodes for Chinese manufacturers. The demonstrated superiority over Castolin 6715 at both room temperature and elevated temperatures validates the alloy design approach and opens opportunities for further optimization through computational thermodynamic modeling and advanced microstructural characterization.