Submerged arc welding (including submerged arc surfacing and electroslag surfacing, etc.) is a method of welding that involves an arc burning beneath a flux layer. It boasts inherent advantages such as stable welding quality, high welding production rates, minimal arc light and smoke, making it the primary welding technique for important structural steelwork like pressure vessels, pipe sections, and box-type columns. Despite the emergence of numerous new welding methods in recent years, the application of submerged arc welding remains unaffected. In terms of the proportion of deposited metal weight among various fusion welding methods, submerged arc welding accounts for approximately 10% and has remained relatively stable over the years.
Once the welding wire is determined (usually depending on the type of steel being welded), the matching flux becomes a key material, directly affecting the mechanical properties of the weld metal (especially plasticity and low-temperature toughness), crack resistance, the incidence of welding defects, and welding productivity. The weight ratio of the welding wire to the flux is typically 1.1 to 1.6, varying according to the type of welding joint, the type of flux used, and the welding specification parameters. Compared to melted flux, sintered flux is more economical, using about 20% less.
China's welding material consumption fluctuates around 500,000 tons, with approximately 70% being melting welding agents, the remainder being non-melting welding agents. Developed industrial countries in Europe and America predominantly use non-melting welding agents, accounting for over 80% to 90%, yet there is still production and sales of melting welding agents. The sustained productivity of melting welding agents is related to some inherent characteristics.
In recent years, a new method of steel bar welding has emerged in our country, known as vertical steel bar arc-electroslag pressure welding. Compared to the previous manual arc welding method for steel bar splicing, this technique can save over 15% of steel, significantly boost productivity, and reduce the cost of welding materials. It is indeed trending to replace the latter and is being increasingly applied. This method primarily utilizes smelting flux, which serves the functions of maintaining the arc, electroslag heating, and metal solidification mold. Currently, about one-fifth of the smelting flux in our country is used for vertical steel bar welding.
China has a limited supply of manganese ore resources, particularly high-grade manganese ore with low phosphorus and iron content, which is essential for producing fluxes for smelting welding agents. Manganese ore veins are only found in Guangxi, Yunnan, and Hunan provinces, and after years of mining, the commercial manganese ore suitable for welding agent production is becoming increasingly scarce. Developing and promoting medium and low manganese fluxes to replace high manganese slag-based welding agents has become an urgent task of objective necessity. With the expansion of production and supply of welding wires containing an appropriate amount of manganese, there should be a vast market for medium and low manganese slag-based fluxes.
In regards to the technical specifications of welding flux products, the common industry practice currently is to provide the chemical composition and the mechanical properties of the molten flux, along with the filling metal properties of a specific wire, while for sintered flux, only the slag composition and the filling metal properties of a specific wire are provided. This approach seems to lack practicality. There are few users who conduct batch-by-batch chemical composition analysis of welding fluxes, as the analysis is complicated by methodological and equipment challenges, and the results are often far from meeting the users' requirements.
