CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Sintered Flux for Strip Electroslag Cladding of Austenitic Stainless Steel
Technical Background and Significance
Electroslag welding (ESW) is a widely used process for depositing thick overlay layers on carbon and low-alloy steel substrates, particularly in the fabrication of clad-plate pressure vessels and bimetallic components. The strip electrode variant of ESW, known as strip electroslag welding (strip ESW) or electroslag cladding, uses a continuous strip of the desired cladding material as the consumable electrode. This method is advantageous for depositing thick, uniform overlay layers at high deposition rates (up to 30–50 kg/h), making it economical for large-scale production.
Austenitic stainless steels such as 304, 316, and 321 are commonly used as cladding materials for pressure vessels and heat exchangers exposed to corrosive environments. However, the development of sintered fluxes specifically designed for strip ESW cladding of austenitic stainless steels presents unique challenges. The flux must provide adequate slag fluidity for proper heat transfer and arc stability, while simultaneously preventing excessive dilution, minimizing chromium and nickel loss, and ensuring the deposited layer maintains its austenitic microstructure and corrosion resistance.
Flux Composition Design and Optimization
The sintered flux was developed through systematic experimentation, varying the proportions of key flux components. The following table presents the optimized flux composition and the role of each component:
| Component | Content (wt%) | Function |
|---|---|---|
| CaF₂ | 25–35 | Provides slag fluidity; reduces viscosity |
| CaCO₃ | 20–30 | Acts as a slag former; buffers basicity |
| SiO₂ | 10–18 | Controls slag viscosity; stabilizes arc |
| Al₂O₃ | 5–12 | Improves slag rheology; absorbs nitrogen |
| MnO | 8–15 | Deoxidizes the weld pool; replenishes Mn |
| TiO₂ | 3–8 | Stabilizes arc; improves slag fluidity |
| Ca₃(PO₄)₂ | 3–8 | Controls slag basicity; reduces spatter |
| Na₂CO₃ | 2–5 | Promotes slag fluidity at high temperatures |
| Baking soda (NaHCO₃) | 1–3 | Gas generation; slag foaming |
The sintering process was carried out at 950–1050 °C for 2–3 hours, followed by controlled cooling and crushing to a particle size of 0.5–2.0 mm (ISO 1107 size 2). The sintering temperature and time were critical parameters affecting the flux's mechanical strength, slag fluidity, and chemical stability.
Flux Performance Parameters
The following table compares the performance of the developed flux with commercially available alternatives:
| Parameter | Developed Flux | Commercial Flux A | Commercial Flux B |
|---|---|---|---|
| Slag fluidity (mm, 1500 °C) | 45–55 | 35–42 | 40–48 |
| Basicity (CaO/SiO₂) | 1.8–2.2 | 1.5–1.8 | 2.0–2.5 |
| Sintering temperature (°C) | 1000 | 1100 | 950 |
| Deposition rate (kg/h) | 35–45 | 25–35 | 30–40 |
| Dilution rate (%) | 8–12 | 12–18 | 10–15 |
| Cr loss (%) | 3–5 | 8–12 | 5–8 |
| Ni loss (%) | 2–4 | 5–8 | 3–6 |
| Nitrogen in deposit (wt%) | 0.03–0.05 | 0.05–0.08 | 0.04–0.06 |
The developed flux demonstrated superior performance in terms of lower dilution rate, reduced alloy element loss, and lower nitrogen pickup compared to commercial alternatives. These advantages translate directly into better corrosion resistance and mechanical properties of the deposited overlay layer.