CLADDING TECHNOLOGY SHANXI CO., LTD90mm Wide-Band Electrode Stainless Steel Double-Layer Electroslag Weld Overlay Process Study
Literature Overview
This 2006 study by Li Xiaoqing, Liu Zhiying, and Zhang Kun from China Second Heavy Machinery Group Corporation investigates the electroslag welding (ESW) overlay process using a 90 mm wide-band electrode to deposit a double-layer stainless steel cladding on pressure vessel components. The work is significant because it addresses a specific industrial need: the efficient and economical production of large-diameter clad pressure vessels where the traditional strip cladding or multi-wire submerged arc welding (SAW) methods are either too slow or too expensive. The 90 mm band electrode allows for a single-pass deposition width of approximately 80-90 mm, dramatically reducing the number of passes required compared to conventional wire SAW overlay.
Core Technical Points
The double-layer approach is a hathe writing systemark of electroslag overlay technology. The first layer, known as the transition or bonding layer, is deposited using a consumable with a composition intermediate between the base carbon or low-alloy steel and the final cladding alloy. Its purpose is to ensure metallurgical compatibility and to prevent excessive dilution of the final cladding layer. The second layer is the functional cladding layer, typically a stainless steel such as 304 or 316, deposited with minimal dilution to preserve corrosion resistance.
| Parameter | Layer 1 (Bonding) | Layer 2 (Cladding) |
|---|---|---|
| Electrode material | 304 or 309L stainless band | 304 or 316L stainless band |
| Electrode width | 90 mm | 90 mm |
| Flux type | ESW-specific granular flux | ESW-specific granular flux |
| Current type | DC or AC | DC or AC |
| Current density | ~200-300 A/mm | ~200-300 A/mm |
| Travel speed | 150-300 mm/min | 150-300 mm/min |
| Slag pool depth | 20-30 mm | 20-30 mm |
| Preheat temperature | 200-300°C | 150-250°C |
| Target dilution | 20-30% | <10% |
The 90 mm band width is a deliberate engineering choice. It provides sufficient heat input to maintain a stable slag pool and ensures full penetration into the previous layer, while the wide cross-section of the deposited bead minimizes the number of traverses needed for large-diameter vessels. However, the wide bead also introduces challenges: maintaining uniform slag pool depth across the full width, controlling the solidification direction to avoid centerline segregation, and ensuring complete fusion at the bead edges.
Process Analysis and Engineering Practice
The electroslag process is inherently a high-deposition-rate, low-spatter method, making it ideal for thick cladding deposits on large components. However, it requires dedicated equipment — a heavy-duty welding carriage, a flux hopper system, and a water-cooled electrode holder — which limits its application to large-scale fabrication facilities. The study from China Second Heavy Machinery Group, a major pressure vessel manufacturer, reflects the industrial context of this technology.
From a metallurgical standpoint, the ESW overlay layer exhibits a distinctive columnar grain structure growing from the fusion boundary upward. This grain structure can be detrimental to mechanical properties, particularly intergranular corrosion resistance, if not properly controlled. The authors likely discuss the importance of grain refinement through flux composition optimization or the use of a backing electrode to promote equiaxed grain formation at the root.
A critical aspect of ESW overlay is the slag pool management. The slag pool must be deep enough to fully engulf the electrode tip and prevent arc exposure, but not so deep that it causes excessive dilution or incomplete solidification. The slag pool depth is controlled by the combination of current, travel speed, and electrode feed rate. In the double-layer process, the slag pool from the first layer must be completely solidified before the second layer is deposited, or the layers will mix and compromise the composition control.
Common defects in ESW overlay include:
- Slag inclusion — entrapped slag between layers or within the overlay, caused by insufficient slag pool depth or excessive travel speed.
- Undercut — incomplete fusion at the bead edges, particularly at the transition from the base plate to the overlay layer.
- Cracking — both hot cracks in the columnar grain structure and cold cracks in the HAZ of the base steel.
- Non-uniform thickness — variation in bead height across the width due to carriage vibration or flux distribution issues.
Key Reflections and Implications
The study underscores the economic advantage of wide-band ESW overlay for large pressure vessels. In applications such as hydrogenation reactors or chemical process vessels requiring stainless steel cladding, the reduction in welding hours translates directly into cost savings. However, the technology demands rigorous process qualification under standards such as NB/T 47014 or ASME IX, including bond strength testing, intergranular corrosion testing of the cladding layer, and non-destructive examination of the overlay-to-base interface. The double-layer approach is not merely a process step — it is a metallurgical necessity that ensures the functional integrity of the final cladding. Engineers evaluating this technology should pay close attention to the flux specification, as it directly influences slag pool stability, grain structure, and inclusion content. This work remains a valuable reference for anyone planning ESW overlay operations on large-diameter pressure vessel components.