Zhuojin Pipe Fitting Co., LtdRibbon Electrode Electroslag Overlay Welding Process and Its Application Prospects
Literature Overview
The paper by Zhang Maolong and Sun Libing, published in Boiler Technology (1993, Vol. 24, No. 8, pp. 21-26), provides a comprehensive review of ribbon electrode electroslag overlay welding (RE-ESOW) technology. At the time of publication, ribbon electrode submerged arc overlay welding (RE-SAOW) was the dominant domestic technique for applying large-area corrosion-resistant stainless steel overlays to chemical pressure vessels and nuclear container internals. The authors synthesized findings from international literature to highlight the advantages of RE-ESOW over RE-SAOW and to discuss its development potential in China.
Process Characteristics Comparison
The paper presents a detailed comparison between RE-ESOW and RE-SAOW across several critical parameters:
| Parameter | Ribbon Electrode Submerged Arc Overlay (RE-SAOW) | Ribbon Electrode Electroslag Overlay (RE-ESOW) |
|---|---|---|
| Deposition rate | Lower | Significantly higher |
| Dilution rate | Higher (typically 15-25%) | Lower (typically 5-15%) |
| Weld profile | Moderate convexity | Excellent, nearly flat |
| Heat input | Moderate | Higher |
| Slag protection | Flux-cored arc | Electroslag pool |
| Surface quality | Acceptable | Superior, smooth |
| Multi-layer capability | Good | Excellent |
The higher deposition rate of RE-ESOW is attributed to the larger volume of molten metal in the electroslag pool, which allows for greater material transfer per unit time. The lower dilution rate is a direct consequence of the thicker slag layer and the distinct melting mechanism in electroslag welding, where the base metal is melted by the heat of the slag pool rather than by a direct arc.
Factors Affecting Overlay Layer Quality
The authors identified several key process variables that influence the quality of the overlay layer:
- Slag composition and viscosity: The slag must maintain sufficient fluidity to ensure uniform metal transfer while providing adequate protection against atmospheric contamination. A viscosity that is too low leads to excessive spatter and irregular metal flow, while a viscosity that is too high causes incomplete melting and poor profile.
- Electrode composition: The ribbon electrode typically contains 25-35% Cr and 18-25% Ni for austenitic stainless steel overlays. The carbon content must be carefully controlled to prevent carbide precipitation at grain boundaries.
- Travel speed and current density: Higher travel speeds reduce heat input per unit length, which can lead to incomplete fusion at the root. Lower travel speeds increase dilution and may cause excessive grain growth in the overlay.
- Preheating and interpass temperature: Preheating to 150-250°C is generally recommended to reduce thermal gradients and minimize cracking susceptibility in the HAZ, especially for high-carbon or high-strength base materials.
Application in Nuclear and Chemical Industries
The paper emphasizes that RE-ESOW has been widely adopted in Western countries for overlaying nuclear reactor pressure vessel internals, chemical reactor liners, and heat exchanger tube sheets. The process is particularly advantageous for large-diameter vessels where the total overlay area can exceed several hundred square meters. The lower dilution rate ensures that the overlay layer maintains its corrosion resistance properties even after multiple passes, which is critical for applications exposed to aggressive chemical environments.
From a metallurgical perspective, the lower dilution rate of RE-ESOW means that the overlay layer composition more closely matches the intended electrode composition. This is significant because the corrosion resistance of austenitic stainless steel overlays is highly sensitive to Cr and Ni content. A dilution rate exceeding 20% can reduce the Cr equivalent below the threshold required for full austenitic stability, leading to potential intergranular corrosion susceptibility.
Study Insights and Implications
This 1993 paper is notable for its forward-looking assessment of a process that was then considered advanced technology in China. The recommendations it makes — particularly regarding the adoption of RE-ESOW for large-scale overlay applications — have since been validated by industry practice. The process has been successfully applied to overlay welding of high-pressure reactor internals, nuclear steam generator tubesheets, and large chemical reactor shells.
One important consideration that the paper raises but does not fully develop is the effect of the higher heat input of RE-ESOW on the base material HAZ. The increased heat input can cause greater grain growth in the base metal, which may affect the mechanical properties and toughness of the HAZ. This is particularly relevant for applications where the base material is a low-alloy steel with a low Charpy V-notch transition temperature. Engineers should evaluate the HAZ microstructure and toughness after RE-ESOW overlay welding to ensure that the increased heat input does not compromise the structural integrity of the base material.
The paper also touches on the development direction of RE-ESOW, suggesting improvements in slag formulation, electrode design, and process automation. These areas have since seen significant advances, including the development of self-fluxing ribbon electrodes and robotic overlay welding systems that further enhance productivity and consistency.
In conclusion, this paper serves as a valuable historical reference and technical introduction to RE-ESOW, highlighting its superior performance characteristics over RE-SAOW and its broad applicability in demanding industrial overlay welding applications.