Development of Sintered Flux for Austenitic Stainless Steel Strip-arc Electroslag Overlay Welding

Literature Overview

This paper by Xie Xiang, Bao Yefeng, Yang Ke, Jiang Yongfeng, and Li Li from Hohai University, published in Electric Welding Machine (Vol. 41, No. 2, 2011, pp. 91–93), reports the development of a novel sintered flux system for strip-arc electroslag overlay welding (SAESW) of austenitic stainless steel. The research addresses the specific requirements of electroslag welding for overlay applications, where dilution control, crack resistance, and stable slag behavior are paramount.

Core Technical Content

Flux Composition and Design Philosophy

The developed sintered flux employs a CaF2-MgO-SiO2-Al2O3 slag system with a basicity index (BIIW) of 3.5–3.8. This composition was selected based on the following design criteria:

Design Requirement	Flux Component	Function
High basicity	CaF2, MgO	Low dilution, reduced alloy burn-off
Slag fluidity	SiO2	Stable slag pool formation
Refractory lining	MgO	Corrosion resistance to lining
Deoxidation support	Al2O3	Reduced inclusion formation
Electroslag stability	CaF2	Controlled slag conductivity

Electroslag Process Characteristics

The strip-arc electroslag welding process combines the high deposition rate of electroslag welding with the precision of strip electrode feeding. Key process characteristics observed include:

Rapid slag pool establishment: The slag pool forms within 5 seconds of arc initiation, indicating excellent slag fluidity and wetting characteristics.
Stable electroslag operation: Once established, the process maintains consistent parameters throughout the weld, with minimal fluctuation in slag pool dimensions.
Minimal spatter: The flux system produces clean arc characteristics with negligible spatter, reducing material waste and improving weld surface quality.
Easy slag removal: Post-weld slag detachment is straightforward, minimizing finishing operations.

Solidification Mode and Microstructure

Metallographic analysis of the overlay weld reveals a Ferritic-Austenitic (FA) solidification mode, characterized by primary ferrite dendrites with austenite forming in interdendritic regions during solidification. This solidification sequence is beneficial because:

Ferrite dendrites provide crack resistance through their lower susceptibility to hot cracking.
Austenite forms at the solidification front, reducing the risk of solidification cracking.
The final microstructure of austenite plus a small amount of ferrite provides good mechanical properties and corrosion resistance.

Dilution and Alloy Retention

The high basicity of the flux system effectively limits substrate dilution and minimizes alloy element burn-off. This is critical for overlay applications where maintaining specific alloy compositions in the deposited layer is essential for achieving target properties such as corrosion resistance and mechanical strength.

Engineering Practice Integration

Process Parameter Windows

Parameter	Recommended Range	Effect
Basicity (BIIW)	3.5–3.8	Optimal balance of fluidity and dilution control
Slag pool establishment time	< 5 seconds	Indicates proper flux fluidity
Strip feed speed	Process-dependent	Controls heat input and dilution
Travel speed	Process-dependent	Controls weld geometry and solidification rate

Application Considerations

For austenitic stainless steel overlay welding on carbon steel or other dissimilar substrates, this flux system offers:

Corrosion-resistant cladding: The low dilution ensures the overlay maintains austenitic stainless steel corrosion properties.
Thick deposit capability: Electroslag welding enables single-pass deposition of thick layers, reducing the number of passes required.
Vertical welding capability: The process is particularly suited for vertical overlay applications on large vessels and pressure equipment.

Critical Reflections

The paper demonstrates sound engineering judgment in flux design, achieving multiple performance objectives simultaneously. However, several aspects warrant further consideration:

The long-term corrosion resistance of the overlay weld in aggressive environments (e.g., chloride-containing solutions) is not evaluated, which is critical for austenitic stainless steel applications.
The effect of interpass temperature on microstructure evolution in multi-pass electroslag overlay is not addressed.
Mechanical property data (tensile strength, impact toughness, fatigue resistance) would strengthen the case for engineering application.

Reference Value and Outlook

This work contributes a practical flux formulation for a demanding overlay welding application. The CaF2-MgO-SiO2-Al2O3 system with controlled basicity provides a template for developing fluxes for other overlay applications requiring low dilution and stable electroslag operation. For industries requiring stainless steel cladding on carbon steel substrates — such as chemical processing, food processing, and marine engineering — this flux system represents a viable process option. Future work should focus on validating the corrosion performance of the overlay welds in service-relevant environments and extending the flux design to accommodate other stainless steel grades.