Zhuojin Pipe Fitting Co., LtdDevelopment of Sintered Flux for Austenitic Stainless Steel Strip Electrode Electroslag Surfacing
Literature Overview
This research by Xie Xiang, Bao Yefeng, Yang Ke, Jiang Yongfeng, and Li Li from Hohai University, published in Welding Machine (2011, Vol. 41, No. 2, pp. 91-93), presents the development of a novel sintered flux for strip electrode electroslag surfacing (SE-ESS) of austenitic stainless steel. Electroslag surfacing is a specialized process used for depositing thick layers of alloy material onto base metals, particularly valuable for corrosion-resistant overlay applications. The flux composition and properties are critical to process stability, metallurgical quality, and deposit properties. This study addresses the challenge of developing a flux system optimized for austenitic stainless steel deposition with minimal dilution and excellent process characteristics.
Flux Design and Composition
The developed sintered flux employs a CaF2-MgO-SiO2-Al2O3 slag system with a Basicity Index (BIW) of 3.5 to 3.8. This composition was selected to achieve:
- Adequate fluidity for stable electroslag process initiation and maintenance.
- Appropriate viscosity for controlling metal droplet transfer and slag-metal separation.
- Low deoxidation activity to minimize alloy element burn-off.
- Good slag removal characteristics after welding.
Flux Composition Parameters
| Component | Function | Target Range |
|---|---|---|
| CaF2 | Fluxing agent, reduces viscosity | Primary fluxing component |
| MgO | Viscosity control, refractoriness | Secondary component |
| SiO2 | Deoxidation, viscosity adjustment | Moderate content |
| Al2O3 | Viscosity control, slag structure | Moderate content |
| BIW | Basicity index | 3.5-3.8 |
The basicity index of 3.5-3.8 places this flux in the moderately basic range, which is appropriate for stainless steel applications where excessive basicity could promote chromium oxide formation and alloy element loss.
Process Performance and Metallurgical Quality
Process Characteristics
The welding process trials demonstrated excellent performance:
- Rapid process initiation: The electroslag pool establishes within 5 seconds of welding start, enabling efficient production cycles.
- Stable electroslag process: The process remains stable throughout the welding operation without interruption or instability events.
- Minimal spatter: The flux effectively shields the molten pool and reduces metal spatter losses.
- Easy slag removal: Post-weld slag detachment is straightforward, reducing cleaning labor and improving productivity.
- Good weld bead formation: The deposited bead exhibits uniform width and height with smooth surface characteristics.
Metallurgical Quality
The surfacing layer analysis revealed favorable metallurgical characteristics:
- Solidification mode: The FA (Fenit-Austenitic) solidification mode was confirmed, which is known for excellent resistance to hot cracking. The FA mode produces a dendritic austenitic structure with limited interdendritic solidification, minimizing the risk of solidification cracking.
- Microstructure: The surfacing layer consists of austenite with a small amount of ferrite, providing the desired corrosion resistance with adequate toughness.
- Low dilution: The base metal dilution into the surfacing layer is minimal, preserving the alloy composition integrity.
- Low alloy burn-off: Chromium and other alloying elements experience minimal oxidation losses during the electroslag process.
Engineering Applications and Process Considerations
Strip electrode electroslag surfacing is particularly suited for:
- Thick corrosion-resistant overlay on carbon steel equipment.
- Repair of worn or corroded surfaces in chemical processing equipment.
- Application of stainless steel cladding to low-alloy steel substrates.
- High-productivity surfacing operations where thick deposits are required.
The following table summarizes the key performance indicators:
| Performance Indicator | Result | Engineering Significance |
|---|---|---|
| Process initiation time | < 5 seconds | High productivity |
| Process stability | Stable throughout | Reliable production |
| Solidification mode | FA mode | Low cracking susceptibility |
| Microstructure | Austenite + minor ferrite | Good corrosion resistance |
| Dilution rate | Low | Alloy composition preservation |
| Alloy burn-off | Minimal | Cost-effective |
| Slag removal | Easy | Reduced post-processing |
Study Insights and Reflections
The development of this sintered flux represents a significant contribution to the electroslag surfacing technology for stainless steel applications. The rapid process initiation capability is particularly valuable for production environments where throughput is a critical economic factor.
The FA solidification mode achievement is a notable metallurgical success. Many austenitic stainless steel welds are susceptible to solidification cracking due to the wide solidification range and dendritic growth patterns. The FA mode, with its limited solidification interval, effectively mitigates this risk and provides a robust metallurgical foundation for the surfacing layer.
The low dilution and minimal alloy burn-off are critical economic factors. In stainless steel surfacing, the cost of alloy elements such as chromium and nickel is substantial, and minimizing losses directly impacts process economics. The flux composition's low deoxidation activity is key to achieving this result.
For practical implementation, engineers should consider the interaction between flux properties and strip electrode composition. The flux must be matched to the specific stainless steel grade being deposited, as variations in alloy content can affect slag-metal reactions and deposit properties. This study provides a validated flux system for austenitic stainless steel SE-ESS applications and demonstrates the importance of flux development in achieving high-quality electroslag surfacing.