What role does submerged-arc welding flux play in steel processing, and what precautions should be taken when using it?

Submerged-arc welding fluxes are now widely used in industries such as boiler and pressure vessel manufacturing, pipe fabrication, cylinder production, bridge construction, architectural engineering, shipbuilding, petrochemical processing, and metal structure fabrication. The steels typically processed include carbon steel, low-alloy steel, cryogenic steel, and stainless steel. To date, submerged-arc welding fluxes have gradually replaced fused welding fluxes, delivering significant economic and social benefits.

Based on the current status of flux-cored arc welding consumables in China, the main development trends for such fluxes include the following:

1. In the area of steel pipe welding, develop high-strength, high-toughness, high-speed submerged-arc welding fluxes suitable for X80 and higher-grade steel pipes.

2. In the welding of high-strength steels, research on submerged-arc welding fluxes has primarily focused on enhancing the low-temperature impact toughness of the deposited metal, with the approach being to refine the grain structure and obtain a acicular microstructure through appropriate alloying.

3. Research on low-hydrogen fluxes. Low-hydrogen electrodes are achieved through an alkaline coating. Although the influence of alkaline slag systems on the diffusible hydrogen content in submerged-arc welding fluxes has been studied, the underlying mechanisms remain unclear. The flux industry should therefore conduct research on low-hydrogen submerged-arc welding fluxes to meet the requirements for welding high-strength steels.

4. High-efficiency iron-powder fluxes. To enhance welding and deposition efficiencies, certain industries mandate the use of iron-powder submerged-arc welding fluxes. It is essential to conduct research and discussion on the appropriate slag system, deoxidation mechanism, and requirements for the iron powder.

5. Development of a versatile, general-purpose sintered flux as a replacement for H431 flux. Given that the production of fusible fluxes is environmentally polluting and that such fluxes often suffer from quality issues, the submerged-arc welding flux industry should conduct research to develop conventional submerged-arc fluxes that can replace H431 fusible flux, thereby enhancing welding process performance, reducing flux costs, and meeting market demand.

6. With regard to surfacing, a series of surfacing fluxes suitable for various applications have been developed, including sintered fluxes for surfacing forging dies, cutting tools, high-speed wear-resistant components, rolling rolls, and continuous-casting rolls. In particular, significant progress has been made in the development and optimization of submerged-arc welding fluxes for use with solid wire, coated electrode, and flux-cored wire.

What should be noted when using it?

To ensure quality, the flux must be properly matched to the welding wire, and it must be baked for 12 hours before use to prevent defects such as porosity.

The drying temperature for flux 481 is 250°C, with a holding time of 1 to 2 hours; for alkaline fluxes such as flux 20 and flux 260, the baking temperature is 300–400°C, with a holding time of 2 hours. Flux should be used immediately after drying or stored in an oven. The selection of flux and welding wire must be based on the chemical composition and mechanical properties of the welded structure (including workpiece thickness, groove dimensions, etc.), the type of joint, as well as service conditions such as high-temperature resistance, low-temperature resistance, and corrosion resistance, and shall be determined through testing. The general principles for selecting and matching welding wire and flux are as follows:

1. The classification and brand of the welding wire shall be the same as those of the welding core. For carbon steels and common low-alloy steels, the mechanical properties of the weld joint must be ensured.

2. For alloy steels such as chromium-molybdenum steel and stainless acid-resistant steel, the chemical composition of the weld should be as similar as possible to that of the base metal.

3. For dissimilar steel welded joints between carbon steels of different strength grades and ordinary low-alloy steels, or between ordinary low-alloy steels themselves, the steel with the lower strength grade is generally selected.