Zhuojin Pipe Fitting Co., LtdDevelopment of Hard Alloy Composite Overlay Welding Electrodes
Literature Overview
This 1990 paper by Zou Xumei from Zigong Hard Alloy Plant, published in "New Technology and New Process" (Issue 5, pp. 13–14), reports on the development of hard alloy composite overlay welding electrodes manufactured using recycled materials from the hard alloy production process. The paper addresses a significant quality problem in overlay welding consumables — porosity in the deposited layer — and proposes an innovative solution.
Background and Problem Statement
Hard alloy overlay welding electrodes are widely used in industrial applications requiring extreme wear resistance, such as mining equipment, cement mill components, and process equipment exposed to abrasive wear. The traditional approach uses tubular (flux-cored) welding electrodes that contain hard alloy particles in a flux coating.
Porosity Problem in Tubular Electrodes
The tubular electrode design has a well-documented problem of high porosity in the deposited overlay layer. This porosity results from:
- Flux decomposition gases — The flux coating releases gases during welding that become trapped in the molten weld pool
- Incomplete melting of hard particles — Some hard alloy particles remain unmelted, creating voids when they are pushed to the surface or rejected during solidification
- Trapped air — Air entrainment during the welding process
- Hydrogen pickup — Hydrogen from moisture in the flux or base metal contamination
The porosity problem reduces the effective wear resistance of the overlay layer, creates stress concentration points, and can lead to premature failure of the overlay.
Composite Electrode Design
The paper describes a novel approach to hard alloy overlay welding consumables that uses recycled hard alloy powder as the hard phase in a composite electrode design.
Raw Materials
The hard alloy powder is sourced from two recycled material streams:
| Material Source | Description | Processing |
|---|---|---|
| Production returns | Powder from hard alloy manufacturing | Direct use after size classification |
| Waste hard alloy | Mechanically crushed waste hard alloy | Size reduction, classification |
This approach provides several advantages:
- Reduces manufacturing costs by utilizing recycled materials
- Decreases waste from the hard alloy production process
- Provides consistent hard phase composition
- Eliminates the need for new raw material procurement
Electrode Manufacturing Process
The composite electrode manufacturing process involves:
- Powder preparation
- Size classification of recycled hard alloy powder
- Removal of fines that could cause porosity
- Mixing with appropriate bonding material
- Electrode fabrication
- Formation of composite electrode structure
- Integration of hard alloy powder into the electrode matrix
- Ensuring uniform distribution of hard particles
- Quality control
- Hardness testing of deposited layers
- Porosity evaluation through metallographic examination
- Wear testing under simulated service conditions
Comparison with Tubular Electrodes
| Characteristic | Tubular Electrode | Composite Electrode |
|---|---|---|
| Manufacturing complexity | High | Simple |
| Porosity level | High | Low |
| Hard phase distribution | Variable | Uniform |
| Cost | High | Low |
| Hardness consistency | Variable | Consistent |
| Welding performance | Good | Superior |
Technical Performance
The composite electrode demonstrated several performance advantages over traditional tubular electrodes:
- Reduced porosity — The composite design eliminates the flux decomposition gases that cause porosity in tubular electrodes, resulting in a denser, more wear-resistant overlay layer.
- Uniform hard phase distribution — The composite structure provides more uniform distribution of hard alloy particles throughout the deposited layer, improving overall wear resistance.
- Simplified manufacturing — The manufacturing process is simpler than that of tubular electrodes, reducing production costs and improving consistency.
- Improved welding characteristics — The composite electrode provides better arc stability and smoother deposition compared to tubular electrodes.
Typical Performance Parameters
| Parameter | Value | Notes |
|---|---|---|
| Hardness (as-deposited) | HV 1000–1400 | Cemented carbide-based |
| Porosity level | < 1% | Significantly reduced |
| Dilution rate | 15–25% | Depends on welding parameters |
| Wear resistance | 3–5× base steel | Relative to uncoated steel |
| Fracture toughness | Moderate | Adequate for most applications |
Engineering Practice Implications
The development of composite hard alloy overlay welding electrodes has several important implications for industrial welding practice:
- Cost reduction — The use of recycled hard alloy powder significantly reduces the cost of overlay welding consumables, making hard facing more economically viable for a wider range of applications.
- Quality improvement — The reduced porosity level results in more reliable overlay layers with better wear resistance and longer service life.
- Sustainability — The utilization of recycled materials reduces waste and environmental impact, contributing to more sustainable manufacturing practices.
- Standardization potential — The simpler manufacturing process facilitates standardization of electrode specifications and quality requirements.
- Application expansion — The improved performance and reduced cost make hard alloy overlay welding applicable to components that were previously considered uneconomical to protect.
Study Insights and Reflections
This paper represents an important contribution to the development of welding consumables technology, particularly in the area of hard facing electrodes. The innovative approach of using recycled hard alloy powder to create composite electrodes addresses a fundamental quality problem (porosity) while simultaneously reducing costs and improving sustainability.
The technical achievement is significant because it demonstrates that recycled materials can be effectively utilized in high-performance welding consumables. The recycled hard alloy powder maintains the essential properties of virgin hard alloy — high hardness, good wear resistance, and chemical stability — while providing the additional benefits of reduced cost and environmental impact.
From a practical standpoint, this development has important implications for industrial maintenance operations. The availability of lower-cost, higher-quality hard facing consumables enables more widespread application of overlay welding as a maintenance strategy, extending the service life of wear-prone components and reducing overall maintenance costs.
The paper also highlights the importance of materials recycling in the welding consumables industry. The hard alloy manufacturing process generates significant quantities of material that can be effectively reprocessed into welding consumables, creating a closed-loop material utilization system that reduces waste and improves economic efficiency.