Development of High-Temperature Wear-Resistant Overlay Electrode for Power Station Valve Sealing Surfaces

Literature Overview

This paper by Yang Genxi and colleagues from Xuzhou Institute of Technology and Shenyang University of Technology, published in the Journal of Hefei University of Technology in 2010, addresses a practical and critical problem in power station valve maintenance: the development of a cost-effective overlay welding electrode for valve sealing surfaces that must withstand severe high-temperature wear and scoring conditions. The research employs regression orthogonal experimental design to optimize the addition amounts of boron carbide, metallic chromium, and metallic manganese to an H1Cr13 steel core, with the objective function being the high-temperature anti-scoring performance of the overlay layer. The optimized formulation was then programmed in C language for computational determination, and the resulting electrode was benchmarked against the widely used D802 electrode.

Core Technical Approach and Methodology

The choice of H1Cr13 as the electrode core is noteworthy. H1Cr13 is a martensitic stainless steel with approximately 13% chromium content, which provides adequate corrosion resistance and the ability to harden through tempering. For valve sealing applications, the overlay layer must resist both abrasive wear from contact with the valve seat and scoring damage caused by high-temperature sliding friction. The researchers selected three alloying additions as optimization factors: boron carbide (B4C) for its extreme hardness and carbide-strengthening effect, metallic chromium (Cr) for solid solution strengthening and additional hard carbide formation, and metallic manganese (Mn) for its role in modifying carbide morphology and improving high-temperature stability.

The regression orthogonal design methodology represents a systematic approach to multi-factor optimization. Unlike traditional one-factor-at-a-time experiments, this method allows simultaneous evaluation of multiple variables and their interaction effects with a significantly reduced number of experimental runs. The mathematical model constructed from the experimental data was then used to predict the optimal combination of B4C, Cr, and Mn additions that would maximize high-temperature anti-scoring performance.

Key Optimization Factors and Their Roles

Performance Comparison and Engineering Significance

The experimental results demonstrate that the newly developed electrode achieves performance metrics essentially equivalent to those of the established D802 electrode across all tested parameters, including room-temperature hardness, high-temperature hardness, and high-temperature anti-scoring performance. The critical advantage lies in cost reduction, which is achieved through the optimized formulation that maintains performance while reducing the use of expensive alloying elements.

The comparison with D802 is particularly instructive. D802 is a cobalt-based hardfacing electrode (similar to Stellite-type materials) that has been the industry standard for high-temperature wear applications due to its exceptional thermal stability and wear resistance. However, cobalt-based electrodes are significantly more expensive due to the cost of cobalt and other rare alloying elements. The fact that an H1Cr13-based electrode with optimized B4C, Cr, and Mn additions can match D802 performance represents a substantial economic benefit for power station operators who must frequently repair or replace valve sealing surfaces.

Practical Considerations for Valve Sealing Applications

From an engineering practice standpoint, several factors merit attention when applying this type of overlay electrode to power station valves. The valve sealing surface operates under cyclic thermal loading, where temperatures can fluctuate between ambient and several hundred degrees Celsius depending on the steam or fluid conditions. The overlay layer must maintain its hardness and resistance to scoring throughout these thermal cycles without cracking or spalling. The H1Cr13 martensitic matrix, when properly tempered, provides good thermal fatigue resistance due to its ability to accommodate thermal strain without catastrophic failure.

The anti-scoring mechanism is particularly important in valve applications. Scoring occurs when hard particles or surface asperities from the mating surface embed into the softer sealing surface during sliding contact, creating grooves that progressively degrade sealing integrity. The optimized overlay layer combats this through multiple mechanisms: the dispersed B4C particles provide extreme local hardness to resist particle embedding, the Cr-rich carbides form a continuous network that supports the matrix under sliding loads, and the Mn-modified microstructure ensures that these hard phases remain stable at operating temperatures.

Study Insights and Engineering Implications

The methodology employed in this study offers a transferable approach to overlay material development. The combination of orthogonal experimental design with mathematical modeling provides a rigorous framework that can be adapted to other overlay welding applications, such as those encountered in pipe fitting repair, boiler tube patching, or heat exchanger tube end overlay. The regression analysis approach allows engineers to predict the effects of formulation changes without conducting exhaustive experimental campaigns, which is particularly valuable when dealing with expensive alloying elements.

One area that deserves further investigation is the long-term cyclic performance of the optimized overlay under realistic valve operating conditions. While the high-temperature anti-scoring tests demonstrate excellent performance under steady-state conditions, the actual service environment involves repeated opening and closing cycles, thermal shock, and potential corrosive fluid attack. Fatigue cracking of the overlay layer at the interface with the base metal, or spalling due to thermal mismatch, could be limiting factors in extended service life. Future work should include thermal cycling tests and, ideally, field trials under actual power station conditions.

Another consideration is the dilution effect during welding. The overlay layer composition and properties are strongly influenced by the dilution of base metal into the weld pool. For power station valves, which are typically made of carbon steel or low-alloy steel, the dilution rate must be carefully controlled to ensure the overlay layer achieves the intended composition. Multi-pass welding with proper interpass temperature control is essential to minimize dilution in subsequent passes. The H1Cr13 core material, being a martensitic stainless steel, has a relatively high carbon content that can promote dilution-related hardness variations at the overlay-base metal interface.

The economic benefit of this development should not be underestimated. Power stations typically maintain large inventories of valves, and valve repair through overlay welding is a common maintenance practice. If the new electrode can match D802 performance at a significantly lower cost, the cumulative savings across a fleet of valves can be substantial. This aligns with the broader industry trend of developing domestic alternatives to imported high-performance welding consumables, reducing dependence on expensive imported materials while maintaining or improving technical performance.

In summary, this study demonstrates a well-executed approach to overlay electrode development through systematic experimental design and mathematical optimization. The resulting H1Cr13-based electrode with optimized B4C, Cr, and Mn additions achieves D802-equivalent performance at reduced cost, offering a practical solution for power station valve sealing surface repair. The methodology and approach are directly applicable to other industrial overlay welding applications where cost-effective alternatives to cobalt-based hardfacing materials are sought.