CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of High-Temperature Wear-Resistant Slag-Free Overlay Welding Electrode
Literature Overview
This 2005 paper by Wang Zhongwei from Zhuzhou Hard Alloy Group and Zhang Qinghui from Xiangtan University, published in Welding Technology, reports on the development of a specialized overlay welding electrode designed for high-temperature wear resistance without slag formation. The work represents a significant contribution to the field of hardfacing and overlay welding for components operating in extreme temperature and abrasive environments.
Technical Background and Requirements
Conventional overlay welding electrodes for wear resistance typically rely on slag formation to protect the weld pool from atmospheric contamination. However, in certain high-temperature applications (such as furnace components, kiln parts, and high-temperature gas ducts), slag inclusion in the cladding layer can degrade wear resistance and cause premature failure. The slag, which is typically a silicate-based compound, has a lower melting point than the cladding alloy and can soften or flow at service temperatures, creating weak points in the surface layer.
The development objectives were:
- Achieve a slag-free (or near-slag-free) weld deposit that maintains wear resistance at elevated temperatures.
- Ensure adequate bonding strength between the cladding layer and the base metal.
- Maintain weldability without excessive spatter or arc instability.
- Achieve a hardfacing layer hardness of at least 45 HRC at room temperature, with retention of hardness at 600 °C.
Electrode Composition and Metallurgy
The electrode design involves a carefully balanced composition of the filler metal. The key alloying elements and their roles are:
| Element | Content (wt%) | Function |
|---|---|---|
| Carbon (C) | 2.5–4.0 | Forms hard carbides (Cr7C3, Cr3C2) for wear resistance |
| Chromium (Cr) | 25–35 | Solid solution strengthening, oxidation resistance, carbide formation |
| Molybdenum (Mo) | 3–8 | Reduces thermal cracking susceptibility, improves high-temperature strength |
| Vanadium (V) | 2–6 | Forms hard vanadium carbides (VC, V4C3) |
| Cobalt (Co) | 5–15 | Solid solution strengthening, improves red hardness |
| Nickel (Ni) | 3–8 | Improves ductility, reduces cracking tendency |
The slag-free characteristic is achieved through a combination of compositional design and flux formulation. The flux coating is formulated to be self-slagging in a minimal amount, with the slag being fully absorbed into the weld pool rather than forming a separate slag layer on the surface. This is accomplished by using a flux composition rich in iron oxide and calcium fluoride, which react with the weld pool to form a thin, reactive slag that is fully incorporated into the solidifying metal.
Performance Testing
The developed electrode was evaluated through a series of standardized tests:
| Test Method | Result |
|---|---|
| Hardness (HV30, room temperature) | 850–950 HV |
| Hardness retention at 600 °C | 720–800 HV (85% retention) |
| Bond strength (micro-indentation) | 1.8–2.5 GPa |
| Dilution rate (spectrographic) | 15–25% |
| Wear resistance (pin-on-disk, 600 °C) | 3–5 times better than 310SS |
| Thermal cracking susceptibility | No cracking with 50 °C preheat |
The wear resistance at elevated temperatures is a key differentiator. Conventional hardfacing alloys lose significant hardness above 500 °C due to carbide coarsening and matrix softening. The inclusion of cobalt and molybdenum in the developed electrode improves the thermal stability of the carbide phase and the matrix strength, resulting in superior performance at 600 °C.
Engineering Applications
The electrode is particularly suited for the following applications:
- Furnace rollers and idlers — Components in steel mill reheating furnaces that are exposed to both high temperatures and abrasive scale.
- Kiln linings and burners — Cement and ceramic kiln components that experience thermal cycling and abrasive gas flow.
- High-temperature gas ducts — Flue gas ducts in power plants and industrial boilers that are subject to fly ash erosion at temperatures above 400 °C.
- Casting molds and dies — Investment casting molds and forging dies that require both wear resistance and thermal stability.
Study Insights
This work demonstrates that the slag-free requirement, while seemingly a minor specification, has profound implications for electrode design. The challenge lies in balancing the need for slag protection during welding (to prevent oxidation and nitrogen pickup) with the requirement for a slag-free final deposit. The solution achieved through self-reactive flux design is elegant but requires precise control of the flux composition and welding parameters.
From a practical standpoint, the electrode requires careful welding technique to minimize spatter and ensure proper arc stability. The absence of a protective slag layer means that the weld pool is more susceptible to atmospheric contamination, particularly in windy or dusty environments. Shielding gas protection (e.g., argon or helium) may be necessary in some applications, which adds to the cost of the process.