CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of High-Temperature Wear-Resistant Cladding Electrodes for Power Plant Valve Sealing Surfaces
Literature Overview
This study addresses the development of specialized welding electrodes for hardfacing overlay of power plant valve sealing surfaces that must withstand extreme temperatures and severe wear conditions. Power plant valves, particularly those used in supercritical and ultra-supercritical steam conditions, operate at temperatures exceeding 600°C and are subjected to continuous erosion from high-velocity steam flow. The sealing surface integrity is critical for valve performance and plant reliability.
Core Technical Findings
The research focuses on the design of electrode consumables that provide high-temperature hardness retention, excellent wear resistance, and compatibility with common valve base materials such as chromium-molybdenum steels. The electrode design incorporates a balanced combination of alloying elements to promote the formation of stable carbide phases that maintain hardness at elevated temperatures.
Electrode Composition Design
| Component | Content (wt%) | Function |
|---|---|---|
| Carbon | 2.5-3.5 | Carbide formation |
| Chromium | 12-18 | Carbide stability, oxidation resistance |
| Molybdenum | 3-5 | High-temperature strength |
| Vanadium | 1.5-2.5 | Fine carbide precipitation |
| Tungsten | 1-3 | High-temperature hardness retention |
| Nickel | 0.5-1.5 | Matrix toughness |
| Silicon | 0.3-0.8 | Deoxidation |
High-Temperature Hardness Performance
| Temperature (°C) | Conventional Electrode (HV) | New Electrode (HV) | Improvement |
|---|---|---|---|
| 25 | 580 | 650 | 12% |
| 400 | 520 | 580 | 12% |
| 500 | 460 | 530 | 15% |
| 600 | 380 | 460 | 21% |
| 700 | 300 | 380 | 27% |
The new electrode demonstrates significantly better high-temperature hardness retention compared to conventional hardfacing electrodes, with improvements increasing at higher temperatures. This is attributed to the formation of fine, uniformly distributed M7C3 and M23C6 carbides stabilized by molybdenum and tungsten.
Process Analysis
Electrode Design Considerations
The electrode design must balance multiple competing requirements. High carbon and chromium content promote carbide formation but can reduce weldability and increase the risk of hot cracking. The flux composition is critical for providing adequate deoxidation, slag protection, and alloy recovery. The study optimized the flux composition to include aluminum and titanium as deoxidizers, with controlled silica and alumina content for slag viscosity and alloy retention.
Welding Process Parameters
| Parameter | Recommended Range | Effect |
|---|---|---|
| Welding Current (A) | 100-180 | Heat input and dilution |
| Arc Length | 3-5 mm | Penetration and bead shape |
| Travel Speed | 2-5 mm/min | Deposition rate and dilution |
| Preheat Temperature (°C) | 200-300 | Residual stress and cracking prevention |
| Interpass Temperature (°C) | 200-350 | Microstructure control |
| Post-Weld Treatment | 600-650°C for 2h | Stress relief and carbide coarsening control |
Microstructural Analysis
The overlay microstructure consists of a martensitic matrix with dispersed primary and secondary carbides. Primary M7C3 carbides form during solidification, while secondary M23C6 and M6C carbides precipitate during cooling and post-weld heat treatment. The distribution and morphology of these carbides directly influence the wear resistance and high-temperature performance of the overlay.
Engineering Practice Integration
For power plant maintenance and valve manufacturing, this research provides a practical solution for extending valve service life in supercritical and ultra-supercritical applications. Key practical recommendations include:
- Preheating to 250-300°C is essential for thick-section valve bodies to prevent hydrogen-induced cracking.
- Multi-pass overlay with individual pass thicknesses of 1.5-2.5 mm provides optimal dilution control and microstructure refinement.
- Post-weld heat treatment at 600-650°C for 2 hours is recommended to relieve residual stresses and optimize carbide distribution.
- Hardness testing should be performed at both room temperature and elevated temperatures to verify high-temperature performance.
- Wear testing under representative service conditions is essential for qualification of new electrode consumables.
Study Insights and Implications
This research addresses a significant industrial need in the power generation sector. The development of high-temperature wear-resistant electrodes for valve sealing surfaces can extend service intervals, reduce unplanned outages, and improve overall plant availability. The key insight is that high-temperature wear resistance requires a fundamentally different approach from room-temperature hardfacing, with emphasis on carbide stability and matrix strength retention at elevated temperatures. The optimized electrode composition and process parameters provide a reliable solution for power plant valve repair and maintenance, contributing to improved operational efficiency and reduced lifecycle costs in modern power generation facilities.