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Rolled 09G2S steel is used in the production of differently shaped and sized building structures. At the same time, the high mechanical strength of the material allows for the creation of thinner products compared to steels. Steam boilers, various pipes for transporting gases and liquids, oil and gas equipment as well as components of agricultural machines are also made from 09G2S steel. High heat resistance of this steel alloy allows for its usage in a wide range of temperatures. According to the standard, this steel is meant for creation of welded constructions, however, in reality the scope of its usage is very wide, being the most widely used steel alloy in Ukraine. It is from this material that most of the rolled complex shape products of increased strength are made. Also, it is the most used type of steel alloy, from which the high-strength sheets intended for pressure vessels are made. Such methods of welding 09G2C steel as: manual arc, arc under flux, arc in a protective gas environment, argon arc with a non-fusible electrode as well as contact welding are quite well researched. Meanwhile, for such innovative methods of welding such as laser welding, the need to determine the dependence of changes in the characteristics of welded joints, when the parameters of the welding modes are varied, is becoming more relevant. The aim of this study is to establish the effectiveness of changing the shielding gas on the impact toughness of 09G2S steel butt-welded joints obtained by laser welding. According to the results of the research, the effectiveness of shielding gas changes on the impact toughness of butt-welded joints of 09G2S steel obtained by laser welding was calculated. It was shown that the replacement of the 82% Ar + 18% CO 2 gas mixture with CO 2 leads to an increase in both the absolute values of the indicators as well as a decrease in the spread of values, both for the seam and for the heat-affected zone. For samples welded using CO 2 , an increase in the welding speed leads to a decrease of the absolute KCU values for both the weld metal and the heat-affected zone. The same trend is observed for samples welded using a gas mixture of 82% Ar + 18% CO 2 . To reduce the financial costs of manufacturing products containing butt-welded joints made of 09G2C steel, it is recommended to use CO 2 as a shielding gas during laser welding.

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