Domestic Development of Welding Materials for High-Speed Strip Electrode Electroslag Overlay Welding

Literature Overview

Published in China Chemical Equipment in 2017 by Song Baorui, Fan Yangyang, Wang Yingjun, Cao Jia, and Lei Li from Sichuan Xiyi New Materials Co., Ltd., Sichuan Special Welding Materials R&D Engineering Laboratory, and Erzhong Group (Deyang) Heavy Equipment Co., Ltd., this paper reports the successful domestic development of welding consumables for high-speed strip electrode electroslag overlay welding (HSESO). The study addresses a critical gap in China's welding materials supply chain, where high-performance electroslag overlay welding consumables for hydrogenation reactor applications had previously relied on imports. The work encompasses material development, process qualification, and performance verification against international benchmarks.

Technical Background and Significance

Electroslag overlay welding is the dominant method for applying corrosion-resistant stainless steel cladding to hydrogenation reactor shells. Traditional electroslag overlay welding typically operates at speeds of 15–25 cm/min, while high-speed strip electrode electroslag overlay welding achieves deposition rates exceeding 40 cm/min, dramatically reducing manufacturing cycle time for large-diameter reactor vessels. The key challenges in developing high-speed consumables include:

• Maintaining adequate slag fluidity and melt pool stability at elevated travel speeds
• Ensuring complete deoxidation and gas-free weld metal despite rapid solidification
• Achieving consistent alloy transfer efficiency with high-flux, high-consumption-rate consumables
• Controlling hydrogen absorption to prevent hydrogen blistering (hydrogen desorption cracking) in the overlay metal

Welding Material Development

The developed consumable system comprises a stainless steel strip electrode and a flux with specific compositional requirements:

The flux basicity of 4.0 or above is significant because it ensures:

1. High slag fluidity at elevated temperatures, facilitating stable slag pool formation at high travel speeds
2. Effective desulfurization and dephosphorization of the weld metal
3. Stable alloy element transfer, particularly for Ni and Cr which are critical for corrosion resistance
4. Reduced hydrogen absorption by maintaining a sufficiently alkaline slag environment

Process Qualification on 2.25Cr-1Mo Substrate

The process qualification was conducted on 2.25Cr-1Mo steel, which is the standard base material for hydrogenation reactor shells per ASME VIII Division 1 and ASME BPV Code requirements. Key qualification results include:

• Chemical composition stability: The overlay metal composition remained consistent across the full thickness of the cladding layer, with no significant compositional banding or segregation. This is critical for ensuring uniform corrosion resistance throughout the cladding.
• Hydrogen blistering resistance: The overlay metal demonstrated adequate resistance to hydrogen desorption cracking, which is the primary failure mode for hydrogenation reactor cladding layers. The test methodology likely followed API 937 or equivalent protocols.
• Mechanical properties: Tensile strength, elongation, and hardness values met the requirements specified in ASME B31.3 and relevant hydrogenation reactor design codes.
• Material consumption ratio: The consumable utilization rate was comparable to or better than imported products, indicating no disadvantage in economic terms.

Comparative Performance Against Imported Products

The head-to-head comparison with imported consumables (likely from established manufacturers such as Ewos, Voestalpine, or similar European suppliers) demonstrated that the domestic product achieved:

• Equivalent or superior welding processability at speeds up to 42 cm/min
• Comparable or better material consumption ratios
• Equivalent overlay metal quality in terms of composition, microstructure, and mechanical properties
• Satisfactory hydrogen blistering resistance

Key Technical Insights and Reflections

This work represents a significant milestone in China's welding materials industry, particularly for the nuclear-grade and high-pressure hydrogenation reactor sectors. Several technical observations merit emphasis:

• Flux design is the critical differentiator: At high welding speeds, the flux must simultaneously maintain slag pool stability, provide adequate thermal input, and ensure complete deoxidation. Achieving a basicity of 4.0+ while maintaining proper slag viscosity requires careful control of CaO, Al₂O₃, and SiO₂ ratios.
• Hydrogen control is non-negotiable: In hydrogenation service, hydrogen blistering of the cladding layer is a catastrophic failure mode. The flux composition must minimize hydrogen pickup, and the welding process must be designed to allow adequate hydrogen diffusion before subsequent welding operations.
• Process speed is not merely a productivity metric: Higher welding speeds introduce thermal cycling challenges, potential incomplete fusion risks, and altered solidification microstructures. The qualification testing must rigorously verify that these speed-related effects do not compromise overlay quality.

For engineering practice, this study validates that domestically produced consumables can meet the stringent requirements of hydrogenation reactor manufacturing, providing an important alternative to imported products and reducing supply chain dependency. The methodology employed—comprehensive material development followed by rigorous process qualification on representative substrate materials—serves as a model for similar domestic substitution efforts in other welding application areas.