CLADDING TECHNOLOGY SHANXI CO., LTDAutomatic Welding Overlay of Duplex Stainless Steel 2205 Process Study Note
Literature Overview
This study originates from the 725th Research Institute of China Shipbuilding Industry Corporation (CSIC), published in 2010, and focuses on the automatic welding overlay process for duplex stainless steel 2205. The research addresses a critical industrial need in marine and offshore engineering where corrosion resistance, mechanical strength, and weldability must be simultaneously achieved. Duplex 2205 (UNS S31803/S32205) contains approximately 22% chromium and 5% nickel with a balanced ferrite-austenite microstructure, making it particularly suitable for aggressive chloride environments encountered in shipbuilding and offshore platforms. The authors—Wang Li, Gao Junsong, and Wu Daowen—investigated automated welding parameters, weld metal composition control, and microstructural evolution during multi-pass overlay operations.
Core Technical Points
The fundamental challenge in overlaying duplex 2205 lies in maintaining the target ferrite content (35-65%) throughout the weld deposit. During automatic welding, the rapid solidification rates and repeated thermal cycling can shift the phase balance toward either austenite or ferrite, compromising the duplex microstructure. The study systematically examined the effects of welding current, travel speed, wire feed rate, and interpass temperature on the resulting weld metal properties.
| Parameter | Typical Range | Effect on Microstructure |
|---|---|---|
| Welding current | 280-380 A | Higher current increases dilution and ferrite content |
| Travel speed | 400-700 mm/min | Faster speed reduces HAZ width and thermal input |
| Wire feed rate | 5.0-8.0 m/min | Must match current for arc stability |
| Interpass temperature | 50-150°C | Higher temp promotes austenite formation |
| Shielding gas | Ar + 2-5% CO₂ | CO₂ addition increases ferrite slightly |
| Heat input | 1.0-2.5 kJ/mm | Must be controlled to prevent phase imbalance |
The study emphasized the use of submerged arc welding (SAW) and flux-cored arc welding (FCAW) as the preferred automatic processes for 2205 overlay, as these methods provide the necessary deposition rates for thick overlay layers while maintaining composition control through appropriate consumable selection. The authors demonstrated that using a matched duplex 2205 wire electrode (e.g., ER2209 or ER2205 grade) with a low-dilution welding procedure is essential to achieve the target 35-65% ferrite content in the weld metal.
Microstructural Analysis and Phase Balance
The ferrite content in the weld metal was assessed using both magnetic permeability measurements and metallographic examination with standard etchants such as ASTMA or Beraha's reagent. The study found that base metal dilution from the carbon steel substrate was the primary factor affecting phase balance. In the first pass, dilution can reach 30-40%, significantly reducing the effective alloying element content. The authors recommended a multi-layer approach where the first pass uses a high-ferrite wire (such as ER2209 with 70-80% ferrite) to compensate for dilution, followed by subsequent passes with standard ER2205 wire to achieve the target balance.
The heat affected zone (HAZ) was identified as the critical region for potential embrittlement. In the HAZ of carbon steel substrates overlaid with 2205, the dilution introduces chromium and nickel into the base metal, potentially forming intermetallic compounds at higher temperatures. The study highlighted the importance of limiting interpass temperature below 150°C to minimize the formation of sigma phase and other detrimental intermetallics.
Engineering Practice Integration
In shipbuilding applications, the overlay of duplex 2205 on carbon steel hull plates, ballast tanks, and seawater piping systems is a common requirement. The automatic welding process enables consistent quality over large areas, which is essential for meeting classification society requirements (such as CCS, DNV, or ABS). The study's findings directly inform welding procedure qualification under NB/T 47014 and ASME IX, particularly regarding the parameters envelope for duplex stainless steel overlay.
Key engineering considerations include:
- Preheating carbon steel substrates to 50-100°C to reduce residual stress and prevent cold cracking
- Using low hydrogen consumables to prevent hydrogen-induced cracking
- Implementing post-weld stress relief where applicable (though duplex steels are generally not stress-relieved due to sigma phase risk)
- Performing intergranular corrosion testing (ASTM A923 Practice A) on the overlay to verify microstructural quality
- Conducting ultrasonic testing (UT) for lack of fusion and porosity defects at the overlay-base interface
Key Reflections and Study Insights
This study provides valuable guidance for the practical implementation of duplex 2205 overlay in marine environments. The emphasis on automatic welding processes reflects the industrial reality that manual welding cannot meet the throughput and consistency requirements of shipyard production. The systematic approach to managing dilution through multi-layer strategies is particularly instructive—engineers must always consider the cumulative effect of thermal cycles on phase balance, not just individual pass parameters.
The research also underscores the importance of consumable selection as a process variable. Using a single wire composition for all passes is a common simplification that leads to unacceptable phase imbalances. The multi-wire strategy demonstrated in this study represents best practice for duplex overlay and should be incorporated into all welding procedure specifications (WPS) for 2205 applications. The connection between process parameters, microstructure, and corrosion performance is clearly established, providing a solid technical foundation for quality assurance in cladding operations.