CLADDING TECHNOLOGY SHANXI CO., LTDResearch on Flux and Process for Electroslag Strip Cladding Welding
Literature Overview
This study, published in 1995 by Li Yanjun from the Central Iron and Steel Research Institute under the National "8.5" Key Technology Program, addresses the development of specialized fluxes and welding processes for electroslag welding (ESW) strip cladding. The work was published in the Journal of Iron and Steel Research and represents a significant contribution to the Chinese national effort to advance heavy cladding technology during the mid-1990s. Electroslag strip cladding is a critical process for producing large-scale clad plates and thick-section overlay welds used in pressure vessels, heat exchangers, and hydrogenation reactors.
Core Technical Content and Process Parameters
The research focuses on the metallurgical behavior of the slag pool, heat input control, and microstructural evolution in ESW strip cladding. The electroslag process offers unique advantages for cladding thick sections due to its high deposition rate, deep penetration, and excellent control over the heat-affected zone. The key process parameters studied include strip feed speed, electrode voltage, slag composition, and cooling conditions.
| Parameter | Typical Range | Purpose |
|---|---|---|
| Strip feed speed | 200–500 mm/min | Control heat input and dilution |
| Electrode voltage | 30–50 V | Maintain slag pool stability |
| Slag pool temperature | 1600–1800 °C | Ensure proper fluidity and protection |
| Base metal preheat | 150–300 °C | Reduce residual stress and cracking risk |
| Interpass temperature | 250–400 °C | Control cooling rate and microstructure |
| Cooling rate | < 5 °C/s | Prevent brittle phases in overlay |
Flux Development and Metallurgical Considerations
The specialized flux developed in this study is designed to control the chemical composition of the overlay layer, minimize dilution from the base metal, and promote a stable slag pool. The flux composition typically includes MnO, SiO₂, CaF₂, Al₂O₃, and various alloying additions. The key challenge is maintaining the required corrosion-resistant composition in the overlay while achieving adequate metallurgical bond strength with the carbon steel substrate. The slag serves multiple functions: it provides thermal insulation, protects the molten pool from atmospheric contamination, modifies the solidification structure, and controls the heat flow direction.
The study emphasizes the importance of the slag-to-metal ratio in determining the final overlay composition. A higher slag-to-metal ratio increases thermal buffering but may reduce deposition efficiency. The optimal balance must be achieved through systematic experimentation considering the specific cladding alloy system, base material thickness, and desired overlay thickness.
Engineering Practice Integration
In practical applications, ESW strip cladding is commonly used for producing clad plates exceeding 200 mm in thickness, such as those specified in ASTM A263, A264, and A265. The process is particularly valuable for hydrogenation reactors and high-pressure vessels where thick stainless steel or nickel alloy overlays are required on low-alloy steel substrates. The flux development work directly supports the fabrication of clad plates conforming to NB/T 47002 and GB/T 150 requirements.
Key quality considerations include bond strength verification per ASTM A263/A263M, hardness profiling through the overlay thickness, and non-destructive examination of the overlay-to-base interface. The study's findings on process stability and slag behavior contribute directly to reducing common defects such as slag inclusion, hot cracking, and inadequate bonding at the metallurgical interface.
Study Insights and Reflections
The significance of this work lies in its systematic approach to flux optimization for a specific cladding application rather than generic flux development. The integration of slag chemistry with metallurgical outcomes demonstrates the fundamental principle that in ESW cladding, the slag is not merely a consumable but a critical process control variable. For engineers working on clad plate procurement and pressure vessel fabrication, understanding the flux development basis enables better evaluation of supplier capabilities and more informed specification writing. The 1995 publication date places this work at a critical period when China was rapidly expanding its heavy equipment manufacturing capacity, and the availability of domestically developed flux technology was essential for reducing dependence on imported materials.