RESOURCE-EFFICIENT DOUBLE-GAS-SHIELDED WELDING OF ALLOY STEELS: EFFECT OF MODES ON STRUCTURE AND MECHANICAL PROPERTIES

The study investigates the influence of welding parameters using a double-jet gas shielding technique on the microstructure and mechanical properties of welded joints made of 30KhGSA alloy steel, which is highly susceptible to hardening and cold cracking. The purpose of the work is to improve the welding process with a consumable electrode in a CO2 environment by applying a controlled dual-jet gas flow that stabilizes the weld pool, reduces thermal inhomogeneity, and eliminates the need for preheating and post-weld heat treatment. The methodology included multi-pass welding of tubular joints using traditional shielding and the proposed double-jet configuration, followed by optical microscopy, microhardness testing, and comparative analysis of structural transformations within the weld metal and heat-affected zone. The results show that the double-jet shielding mode produces a finer and more stable ferrite-pearlite structure, ensures better mixing of the weld pool, and significantly reduces structural gradients across the joint. Welded samples obtained with the proposed technique exhibit higher tensile strength and microhardness values compared with the conventional method. The originality of the research lies in demonstrating that controlled dual-jet gas flow can effectively regulate heat transfer and chemical composition in the weld without additional thermal operations. The practical value is the development of an energyefficient and resource-saving welding technology that improves the performance and reliability of welded alloy-steel structures.