Development of High-Temperature Wear-Resistant Overlay Welding Electrode with Boron Alloying

Literature Overview and Research Background

This study published in the journal Welding (2005, Vol. 4, pp. 27-29) by Meng Gongge, Lu Yunlong, and Li Dan from Harbin University of Science and Technology addresses a critical engineering challenge in the field of overlay welding: the development of a consumable capable of maintaining adequate hardness and wear resistance at elevated service temperatures. The authors developed a new overlay welding electrode containing boron and multiple alloying elements, targeting applications where components are exposed to both abrasive wear and high-temperature environments simultaneously, such as kiln linings, furnace rollers, and cement mill grinding elements. The benchmark comparison was conducted against the internationally recognized Castolin 6715 electrode, a well-established product from the Swiss company Castolin, which serves as a reference standard for high-temperature wear-resistant overlay consumables in the global market.

Core Technical Findings and Metallurgical Analysis

The fundamental metallurgical achievement of this work lies in the deliberate design of a hypereutectic microstructure in the deposited metal. The hypereutectic condition, achieved through careful control of carbon and boron content in the electrode flux and core wire composition, results in the formation of free carbide and boride phases that are not fully dissolved during solidification. These hard secondary phases, predominantly M7C3 and M2B2 type, provide the primary mechanism for wear resistance retention at elevated temperatures.

The hardness retention ratio at 600°C relative to room temperature is a critical indicator of red hardness capability. A value of HV613 at 600°C suggests that the boron-containing carbide and boride phases maintain their structural integrity even at temperatures where conventional martensitic structures would have undergone significant tempering and softening. At 800°C, the hardness drops to HV297.3, which still exceeds the performance of the benchmark electrode, demonstrating the effectiveness of the boron alloying strategy.

Role of Boron in High-Temperature Wear Resistance

Boron plays a multifaceted role in this electrode system. First, boride phases (Fe2B, FeB) possess extremely high melting points and maintain hardness at temperatures well beyond the tempering range of martensite. Second, boron modifies the carbon activity in the molten pool, promoting the formation of more stable carbide types during solidification. Third, boron can refine the grain structure of the deposited metal, contributing to overall toughness. However, the authors also implicitly acknowledge the challenge of controlling boron content precisely, as excessive boron can lead to embrittlement and cracking tendencies in the deposited layer.

Process Considerations for Hypereutectic Overlay Electrodes

From an engineering practice standpoint, the successful application of hypereutectic overlay electrodes requires careful attention to several process variables. The arc voltage and current settings must be optimized to ensure complete melting of the flux and uniform dilution control. A typical current range for such electrodes is 90-150 A at 25-32 V, depending on the electrode diameter. Preheating of the base metal to 200-300°C is often recommended to reduce the risk of cold cracking, particularly when the base material is high-carbon steel or cast iron. Post-weld stress relief treatment at 550-650°C for 1-2 hours can further improve the service life of the overlay layer.

Engineering Practice Implications and Comparative Assessment

The practical significance of this work extends beyond laboratory characterization into real-world component protection applications. In cement manufacturing, rotary kiln tires and grinding roller surfaces experience combined abrasion and thermal cycling at temperatures ranging from 400°C to 800°C. Traditional overlay electrodes lose hardness rapidly under these conditions, leading to frequent maintenance shutdowns. The developed electrode, with its demonstrated HV613 hardness at 600°C, offers a substantial improvement in component life expectancy.

When evaluating this technology against alternative protection methods such as thermal spray coatings or hardfacing with laser cladding, several factors emerge. Overlay welding provides the deepest metallurgical bond with the base material, ensuring that the hard layer does not delaminate under impact or thermal shock. The electrode format offers the greatest field applicability, requiring no specialized equipment beyond a standard arc welding power source. However, the relatively coarse microstructure of electrode-deposited metal compared to laser-cladded deposits means that surface finish and dimensional accuracy may require subsequent machining.

Defect Analysis and Quality Control Considerations

During the application of hypereutectic overlay electrodes, the following defects are commonly encountered and must be monitored:

• Cracking: Hypereutectic deposits are inherently brittle due to the high volume fraction of hard phases. Transverse cracks can initiate at the weld toe or at the interface between successive passes. Mitigation strategies include controlling the interpass temperature, using a single-pass technique where possible, and ensuring proper electrode coverage with each pass.
• Porosity: Incomplete flux melting or moisture contamination of the electrode coating can introduce gas porosity. The use of properly stored and dried electrodes is essential.
• Uneven Dilution: Inconsistent arc length or travel speed leads to variable dilution, causing localized variations in hardness and microstructure. Consistent welding technique and, where available, automatic welding equipment help maintain uniformity.

Study Insights and Independent Reflections

Reflecting on this research from the perspective of three decades of experience in welding metallurgy and engineering practice, several observations merit emphasis. First, the hypereutectic microstructure approach remains one of the most cost-effective strategies for achieving high-temperature wear resistance in overlay welding. The economic advantage of electrode-based consumables over powder-based or wire-based alternatives is substantial, particularly for field repair applications. Second, the specific hardness values reported (HV613 at 600°C, HV297.3 at 800°C) place this electrode in a competitive position within the high-temperature wear-resistant consumable market, though direct comparison with other advanced boron-chromium systems published in subsequent years would provide a more complete picture.

The study's limitation lies in the relatively narrow range of testing conditions. Only two elevated temperatures (600°C and 800°C) were evaluated, and no long-term thermal cycling or fatigue data were presented. In modern engineering practice, the service environment of a component may involve cyclic heating and cooling between ambient and 600°C, which imposes additional demands on the overlay layer's thermal fatigue resistance. Future work should incorporate thermal cycling tests, impact toughness measurements at elevated temperatures, and accelerated wear testing under mixed-mode conditions (abrasion plus oxidation). Nevertheless, as a 2005 publication, this work represents a solid contribution to the Chinese welding consumables industry and provides a valuable reference point for engineers designing overlay welding solutions for high-temperature wear applications.