Flux for electric arc surfacing providing high-temperature removal of slag coating

Abstract

It was shown as a result of analysis of mechanisms of slag crust removal from the weld metal surface that the spinels at slag-metal interface and their intergrowth have the main influence on this process. It was found on the basis of analysis of structure of spinels and slag melt that to prevent the formation of spinels at the interface and intergrowth of metal and slag, it is necessary to provide the presence in the slag melt of a structural element with configuration of a linked structure, differed from tetra-and octahedral structures, and not capable to formation of spinels. It was established that prevention of formation of spinels in providing necessary welding-technological properties of flux of SiO2-Al2O3-MgO-CaF2 system can be attained at adding of zirconium oxide in the amount of 3.5-5.5 % into flux composition. The flux has been developed, which provides a spontaneous removal of slag coating at high temperatures. The process of submerged arc surfacing is one of the widely spread methods of restoration of parts of metallurgical, mining, machine-building equipment, agricultural machines and automobile transport. Using surfacing it is possible to deposit a layer of almost any thickness, different chemical composition and physical-mechanical properties by applying optimum combination of wire-flux filler materials. In restoration of parts the general-purpose fluxes AN-348A, OSTs-45, AN-60, AN-47 and specialized fluxes AN-20, AN-28, AN-26, AN-44 found the widest application. The submerged arc surfacing is used in restoration of parts, having flat and cylindrical surfaces, including also surfaces of intricate configuration, with a sufficient wear usually (up to 3-5 mm). In this case the surfacing is usually made with a partial or complete overlapping of the deposited layer.Coming from specifics of used materials, the technology of surfacing should be realized in a multi-pass, continuous condition, and with preheating in some cases. This stipulates the strict requirements for removal of slag coating from the deposited bead surface within the range of elevated temperatures. The fluxes, produced by industry now, do not meet this requirement.Therefore, the aim of the present work was the evaluation of factors and detailed study of mechanism, defining and providing the process of high-temperature removal of slag, formation of slag system, and optimization of the flux composition.Removal of slag coating from the weld metal surface can be provided by [1][2][3]:• increase in difference of coefficients of thermal expansion (CTE), which generate shearing forces during welded joint cooling;• decrease in oxidizing ability of slag in molten state at its crystallization;• delay of processes chemisorption at the slagmetal interface by increasing the surface and interfacial tension, which retards the process of intergrowth of metal and slag.The oxidizing ability of slag in crystallization and processes of chemisorption cause the formation of chemical compounds of spinel type, which can strongly retain the slag coating on the...