The paper presents the results of the development and study of activating flux paste compositions based on traditional oxide elements for argon arc welding (A-TIG). The main attention is paid to the effect of the flux composition on the ionization of the arc and the ratio of the penetration depth to the weld width. Experiments were carried out with various compositions of flux pastes containing fluorspar (CAF₂) and welding flux AN-60, while the ratio of components in the composition of the pastes varied. During the experiments, the coating was carried out on steel plates with a thickness of 10 mm, steel grade – 09G2C. The greatest penetration depth was achieved by compositions No. 1 and No. 2, where the penetration depth was 6.5 mm and 7 mm respectively. It is found out that the optimal fluorspar content in the paste should not exceed 25%, which makes it possible to achieve the maximum penetration depth. The main ionizers of the welding arc are identified: Si, Ca, Mg and Mn, which content can be increased or changed to optimize the paste compositions. Based on the study results, it is found that the developed activating fluxes can be used to optimize argon arc welding of thick-walled structures, as well as to provide surface hardening of steels instead of traditional chemical and thermal treatment methods. The study objective: to develop and conduct experimental studies of complex activating fluxes based on widespread components to increase the penetration depth when welding thick-sheet structures with butt and lap weld joints. The study tasks: to study the effect of the developed activating fluxes on the ionization of the welding arc and the penetration depth of09G2C steel when performing surfacing by argon arc method. The research methods. Preparation of the initial components and activating flux pastes based on them; argon arc surfacing on the steel samples; sample preparation, measurement of the weld width and penetration depth by metallographic method; calculations of the ionization degree of the flux pastes components and assessment of their effect on the arc during surfacing. The novelty of the work. Application of the developed compositions of activating flux pastes for argon arc surfacing/welding (A-TIG) of thick-walled steels. An increase in the penetration depth and a narrowing of the weld width during active ionization of the arc. The use of compositions of activating fluxes as a basic component of flux pastes for surface hardening of steels. The study results. Activating flux pastes of No. 1 and No. 2 compositions showed the best penetration results, with their use the greatest penetration depth of 6.5-7 mm was achieved, which is 1.5-1.8 times higher than without the use of activating fluxes. When studying the composition of the fluxes, the optimal content of the components was determined, where the total amount of CaF2 should not exceed 25%. No defects were found in the macrostructure during surfacing. Conclusion: Compositions of activating flux pastes No. 1 and No. 2 for the argon arc surfacing/welding (A-TIG) method provide an increase in the penetration depth of steel samples, are recommended for further use in flux pastes for surface hardening of steels and further modification of chemical composition.