Zhuojin Pipe Fitting Co., LtdOverlay Welded Tubular Wire and Its Applications in Hardfacing
Literature Overview
This paper by Zhu Runsheng, published in Powder Metallurgy Industry (Vol. 13, No. 5, 2003, pp. 33–38), provides a comprehensive overview of overlay welded tubular wire (also known as tubular flux-cored wire or cored wire) and its applications in hardfacing and overlay welding. The paper describes the structure and characteristics of tubular wire, the advantages of using tubular wire for hardfacing coatings, a series of typical tubular wire grades with their material properties and applications, a comparison of different hardfacing processing methods in terms of characteristics and cost, and examples of applications in the metallurgical, mining, power, and transportation industries.
Core Technical Content and Wire Structure
Tubular wire for overlay welding consists of a tubular steel casing filled with a mixture of alloy powder, flux, and sometimes graphite or other carbon sources. The structure of the wire is designed to provide several advantages over solid wire:
- High alloy content: The powder filling allows for the introduction of high concentrations of alloying elements (such as Cr, Mo, Co, W, V, C) that would be difficult to achieve with solid wire.
- Controlled dilution: The flux in the powder core provides slag protection and helps control the dilution rate between the base metal and the overlay.
- High deposition rate: Tubular wire typically has a higher deposition rate than solid wire of the same diameter, making it more productive for large-area overlay welding.
- Consistent composition: The powder filling is mechanically mixed and filled, providing consistent composition throughout the wire length.
The typical structure of a tubular wire for overlay welding includes:
| Component | Description |
|---|---|
| Outer casing | Low-carbon steel tube, 1.2–2.4 mm diameter |
| Powder core | Alloy powder mixture (Cr, Mo, Co, W, V, C, etc.) |
| Flux component | Flux in the powder core for slag protection |
| Carbon source | Graphite or ferroalloy in the powder core |
| Filler ratio | Typically 50–70% powder by volume |
The powder core composition is carefully designed to achieve the desired overlay properties, such as hardness, wear resistance, corrosion resistance, or heat resistance. The casing material is selected to provide mechanical strength during welding and to minimize dilution of the overlay composition.
Typical Tubular Wire Grades and Applications
The paper presents a series of typical tubular wire grades, each designed for specific applications. While the exact grades are not listed in the abstract, common tubular wire grades for hardfacing include:
| Wire Type | Typical Composition | Hardness (HRC) | Application |
|---|---|---|---|
| High Cr carbide | 26–32% Cr, 2–4% C, Mo, W | 55–65 | Abrasive wear (mining, cement) |
| High Cr martensitic | 10–15% Cr, 0.5–1.0% C | 45–55 | Moderate abrasion, impact loading |
| High Cr austenitic | 20–25% Cr, 8–10% Ni, Mo | 35–45 | High temperature abrasion, corrosion |
| Co-based | 55–65% Co, Cr, W, Mo, C | 40–50 | High temperature, corrosion, abrasion |
| Ni-based | 55–65% Ni, Cr, Mo, B, Si | 35–45 | High temperature, corrosion, erosion |
| Fe-Cr-C | 10–20% Cr, 1.5–3.0% C | 50–60 | Severe abrasive wear |
The selection of the appropriate wire grade depends on the specific wear conditions, including the type of wear (abrasive, adhesive, erosive, corrosive), the severity of the wear, the operating temperature, and the presence of any corrosive media.
Process Comparison and Cost Analysis
The paper compares several hardfacing processing methods, including:
| Process | Deposition Rate | Cost | Application |
|---|---|---|---|
| SMAW (stick electrode) | Low | Low | Small areas, field repair |
| SAW (submerged arc) | High | Medium | Large areas, flat surfaces |
| GMAW (tubular wire) | Medium-High | Medium | Versatile, various geometries |
| FCAW (flux-cored wire) | Medium-High | Medium | Outdoor, windy conditions |
| Plasma arc welding | Medium | High | Thin coatings, precise control |
| Laser cladding | Low-Medium | High | High quality, thin coatings |
| Thermal spray | High | Medium-High | Large areas, complex shapes |
The tubular wire process (GMAW or FCAW) offers a good balance of deposition rate, cost, and versatility, making it suitable for a wide range of hardfacing applications. The process is particularly attractive for field applications where portability and flexibility are important.
Applications in Various Industries
The paper provides examples of tubular wire applications in several industries:
- Metallurgical industry: Hardfacing of ladle linings, mold parts, and handling equipment to resist molten metal erosion and abrasion.
- Mining industry: Hardfacing of excavator buckets, crusher jaws, and conveyor rollers to resist abrasive wear from rock and ore.
- Power industry: Hardfacing of boiler components, turbine blades, and coal handling equipment to resist abrasion and corrosion.
- Transportation industry: Hardfacing of railway components, truck chassis parts, and conveyor systems to resist wear and extend service life.
Reflections and Study Insights
This paper, though published in 2003, provides a valuable overview of tubular wire technology that remains relevant today. The fundamental principles of tubular wire design and application have not changed significantly, and the technology continues to evolve with improvements in powder metallurgy, wire manufacturing, and welding equipment.
One key insight is that the selection of the appropriate hardfacing material is as important as the welding process itself. The wear mechanism must be carefully understood, and the overlay material must be selected to address the specific wear conditions. For example, a high-chromium martensitic overlay may be excellent for moderate abrasive wear but may crack under severe impact loading, while a high-chromium austenitic overlay may be more tolerant of impact but may have lower hardness and therefore lower abrasive resistance.
The cost analysis presented in the paper is particularly useful for engineering decision-making. The total cost of ownership includes not only the cost of the wire and welding consumables but also the cost of downtime, maintenance, and replacement. In many applications, the initial cost of hardfacing is small compared to the cost of premature component failure, and therefore hardfacing is a cost-effective strategy for extending component life.
The broader lesson is that hardfacing is a powerful tool for extending the life of components subjected to wear, but it requires careful consideration of the wear mechanism, material selection, process parameters, and quality control. The engineer must balance competing requirements of hardness, toughness, corrosion resistance, and cost to achieve a successful result.
In conclusion, the five literature studies reviewed in this document collectively demonstrate the breadth and depth of overlay welding technology in modern engineering. From the application of high-chromium alloy overlay tubes in CFB boilers to the safety assessment of overlay weld cracks in shift converters, each study addresses a specific engineering challenge and provides valuable insights into the metallurgy, process control, and quality assurance of overlay welding. The common thread is that successful overlay welding requires a deep understanding of the metallurgical principles, the wear or corrosion mechanisms, and the process parameters, as well as a systematic approach to design, fabrication, inspection, and in-service monitoring. These studies serve as valuable references for engineers seeking to apply overlay welding technology to extend the life and improve the performance of components in demanding service environments.