Which Flux Is Used in Submerged Arc Welding?

Submerged arc welding (SAW) occupies a pivotal position in the industrial manufacturing sector, and flux, as a core component in this welding process, directly determines the quality and efficiency of welding. So, which fluxes are commonly used in submerged arc welding? Let's explore in detail.​
Main Types of Fluxes for Submerged Arc Welding​
Fused Fluxes​
Fused fluxes are manufactured by melting a mixture of raw materials such as silica, manganese oxide, and calcium fluoride at high temperatures, followed by cooling and crushing into granular forms. A typical example is HJ431, which appears as brown to light yellow glassy granules.​
This type of flux boasts excellent electrical conductivity, enabling it to maintain a stable arc during the welding process. It is widely utilized in the welding of carbon steels and some low-alloy steels. When paired with wires like H08A and H08MnA, it can enhance the mechanical properties of the weld metal through metallurgical reactions. It finds extensive applications in industries such as boiler manufacturing, shipbuilding, and pressure vessel fabrication.​
Sintered Fluxes​
Sintered fluxes are produced by mixing powdered raw materials and then sintering them at a temperature below their melting point (generally between 700 - 1000°C). SJ101 is a representative fluorine-alkaline sintered flux with an alkalinity of approximately 1.8.​
It exhibits outstanding desulfurization performance, effectively reducing the sulfur and phosphorus content in the weld metal and significantly improving the low-temperature impact toughness of the weld. Therefore, it is indispensable in large-scale engineering projects such as bridge construction and the West-East Gas Pipeline project. Another type, SJ301, a silicon-calcium neutral sintered flux, is suitable for circumferential seam welding in the pressure vessel industry due to its short slag that is not easy to flow.​
Agglomerated Fluxes​
Agglomerated fluxes are made by mixing powdered raw materials with binders (such as sodium silicate) to form granules, which are then dried and heat-treated. Raaj melt-3 is a kind of alkaline agglomerated flux.​
It has a high current-carrying capacity in both AC and DC welding, and the welds formed have good low-temperature impact properties and crack resistance, making it applicable to the welding of structural steel, pressure vessels, and boilers. Raaj melt 6, designed for high-speed welding, can achieve excellent slag removal and a smooth weld bead surface when used for welding low and medium tensile steels and pipes.​
Key Factors for Flux Selection​
Base Metal Type​
For carbon steel and low-alloy steel with low carbon content and no special alloying elements, fused fluxes like HJ431 are a good choice. For low-alloy steel requiring high strength and toughness, sintered flux SJ101 or fused flux HJ350 is more appropriate. When welding stainless steel, to prevent the loss of alloying elements, fluxes such as HJ260 (fused flux) and SJ601 (sintered flux) are often selected.​
Weld Joint Requirements​
If the weld joint needs to have high strength and good toughness, like in large bridge structures, the combination of SJ101G (an improved version of SJ101) and high-strength low-alloy steel wire can meet the requirements. In scenarios with corrosion resistance requirements, such as chemical equipment and marine engineering, SJ601 can maintain the alloy ratio of the weld, ensuring its corrosion resistance is comparable to that of the base metal.​
Welding Process Parameters​
Some fused fluxes, with their strong electrical conductivity, are suitable for high-current welding. Agglomerated flux Raaj melt-3 can be used with relatively large currents in both AC and DC welding, improving the welding efficiency of thick-section materials. Sintered flux SJ501 can support high-speed welding up to 70m/h or more, making it the first choice for spiral pipe welding and other fields that pursue high productivity.​
Significance of Flux in Industrial Production​
The correct selection of flux is crucial for industrial production. In safety-related industries such as boilers and pressure vessels, it ensures welding quality and avoids potential safety hazards. In large structural projects like ships and bridges, it enhances structural stability and service life. In high-efficiency production fields such as spiral pipe manufacturing, it can increase welding speed and production capacity.​
Industry experts emphasize that enterprises must have a comprehensive understanding of the characteristics of various fluxes and select the appropriate flux and wire combination based on the base metal type, welding requirements, and process parameters to achieve high-quality and efficient welding production.