CLADDING TECHNOLOGY SHANXI CO., LTDDomestication of Consumables for High-Speed Strip Electrode Electroslag Overlay Welding
Literature Overview
This 2017 study by Song Baorui, Fan Yangyang, Wang Yingjun, Cao Jia, and Lei Li, conducted by Sichuan Xiyi New Materials Co., Ltd., Sichuan Provincial Special Welding Materials Research and Development Engineering Laboratory, and ERPC Group (Deyang) Heavy Equipment Co., Ltd., published in China Chemical Equipment, addresses the critical challenge of domesticating welding consumables for high-speed strip electrode electroslag welding (ESW) overlay processes. Electroslag welding is widely used for the fabrication of thick-section clad plates and pressure vessel components in the chemical and petrochemical industries, but high-quality strip electrode consumables have historically been imported, creating supply chain vulnerabilities and cost pressures for Chinese manufacturers.
Electroslag Overlay Process Characteristics
High-speed strip electrode electroslag welding combines the advantages of electroslag welding (high deposition rate, deep penetration, low dilution) with the flexibility of strip electrode feeding (consistent composition, low moisture content, stable arc). The process is particularly well-suited for overlaying corrosion-resistant or high-alloy layers on thick carbon steel or low-alloy steel substrates, with typical applications including hydrogenation reactor shells, heat exchanger tubesheets, and storage tank bottoms.
The key process parameters for high-speed strip ESW overlay include:
| Parameter | Typical Range | Effect on Overlay Quality |
|---|---|---|
| Welding current (A) | 800–1500 | Higher current increases deposition rate and penetration |
| Travel speed (mm/min) | 200–600 | Higher speed reduces heat input and dilution |
| Strip electrode thickness (mm) | 1.5–3.0 | Thicker strips provide more stable arc |
| Flux composition | Rutile or basic type | Affects slag viscosity, wetting, and deoxidation |
| Shielding gas flow (L/min) | 15–30 | Protects molten pool from atmospheric contamination |
| Interpass temperature (°C) | 100–200 | Controls cooling rate and microstructure |
| Number of passes | 2–6 | More passes reduce dilution and improve microstructure |
The high-speed nature of the process (travel speeds up to 600 mm/min) imposes stringent requirements on consumable performance: the strip electrode must maintain consistent composition and mechanical properties along its entire length, the flux must provide adequate slag protection at high travel speeds, and the overall process must be stable under high production rate conditions.
Consumable Development and Characterization
The study focused on developing strip electrode consumables for overlaying austenitic stainless steel (304, 316, 321) and nickel-based alloy (Inconel 625, Monel 400) layers on carbon steel substrates. The development process involved systematic optimization of strip electrode composition, flux formulation, and welding process parameters, followed by comprehensive characterization of the resulting overlay welds.
The domesticated strip electrode consumables were characterized through the following tests:
- Chemical composition analysis: Verification of carbon, chromium, nickel, molybdenum, and trace element content against specification requirements (ASTM A263, EN 10028-7).
- Mechanical properties: Tensile strength, yield strength, elongation, and hardness measurements at room temperature and elevated temperatures.
- Metallographic examination: Microstructure characterization including grain size, phase distribution, and inclusion content.
- Corrosion resistance: Intergranular corrosion testing (ASTM A262 Practice E), pitting resistance (PREN calculation), and immersion testing in simulated service environments.
- Bond strength testing: Peel test and bend test to verify overlay-to-base metal bond integrity.
- Hydrogen-induced cracking resistance: HIC and SSC testing per NACE MR0175/ISO 15156 for sour service applications.
The results demonstrated that the domestically developed consumables met or exceeded the performance of imported equivalents, with particular advantages in terms of cost reduction (approximately 40–50% lower than imported consumables), supply reliability, and the ability to tailor compositions for specific service requirements.
Process Optimization and Quality Assurance
The study also addressed the process optimization required to achieve consistent overlay quality with the domesticated consumables. Key findings include:
- Flux-electrode matching: The flux composition must be carefully matched to the strip electrode alloy composition to ensure adequate deoxidation, slag wetting, and gas protection. Mismatched flux-electrode combinations can result in porosity, inclusions, or inadequate slag coverage at high travel speeds.
- Arc stability: At high travel speeds, arc stability becomes critical. The study found that maintaining a consistent electrode stickout (8–12 mm) and proper current distribution between the strip electrode and the flux-cored backing wire is essential for stable welding.
- Dilution control: The high deposition rate of strip ESW can lead to higher dilution of the base metal into the overlay layer. The study recommended using 3–4 overlay passes with decreasing heat input per pass to achieve dilution levels below 5% for the final overlay layer.
- Residual stress management: The high heat input of ESW creates significant residual stresses in the overlay layer. The study recommended post-weld stress relief at 600–650°C for carbon steel substrates and 1050–1100°C solution treatment for austenitic overlay layers where required.
Engineering Practice and Supply Chain Implications
The successful domestication of high-speed strip ESW consumables has significant implications for the Chinese pressure vessel and chemical equipment manufacturing industry. By reducing dependence on imported consumables, manufacturers can achieve greater supply chain resilience, faster procurement cycles, and lower material costs. This is particularly important for large-scale projects such as hydrogenation reactor fabrication, where the consumption of overlay consumables can be substantial (several tons per reactor).
The study also demonstrates the importance of integrated consumable-process development: simply replicating the composition of imported consumables is insufficient; the entire consumable system (strip electrode, flux, backing wire, shielding gas) must be optimized as a package for the specific welding process and application. This systems engineering approach is essential for achieving reliable, repeatable overlay quality in production environments.
Key Reflections
The domestication effort documented in this study exemplifies the broader trend of indigenous development of critical welding consumables in China. The technical challenge lies not only in matching the chemical composition of imported consumables but in achieving equivalent or superior metallurgical performance across the full range of quality criteria — mechanical properties, corrosion resistance, weldability, and process stability. The study's success demonstrates that with systematic research and development, domestic manufacturers can achieve world-class consumable performance, provided they invest in comprehensive characterization and process optimization programs alongside consumable development.