Currently, thick-walled pipelines made of heat-resistant chromium steels are widely used at oil refining and petrochemical enterprises. These steels are characterized by sufficiently high thermal conductivity and relaxation capacity, relatively low linear expansion coefficient, long-term thermal stability at operating temperatures and ability of changing mechanical properties within wide limits by means of heat treatment. A tendency to air quenching and martensitic phase transformations significantly complicate the technological process of welded products manufacturing. An unfavorable response to thermal deformation welding cycle, manifested in formation of quenching nonequilibrium structures in these interlayers affects the operational reliability of welded structures, reducing crack resistance, limiting deformation capacity and increasing susceptibility to brittle failures. One of the causes of failure in the area of welded joints of such pipelines may be the presence of harder and more brittle metal sections prone to defects. Heterogeneity of the structure of such welded joints causes additional residual stresses concentration, leading to a decrease in technological strength. The use of semi-automatic welding in CO2 environment provides sufficiently high quality of welded joints. During the welding process, metal drip transfer turns into jet transfer that increases welding performance and reduces metal spattering. A mixture of argon Ar and 20% carbon dioxide C02 is also used when welding low-carbon and low-alloy steels. In this paper, various modes of welding heat-resistant chromium steel 15X5M were studied in order to select the most optimal one. Metallographic analysis of the studied samples was carried out, changes in the value of welded joint microhardness in the heat-affected zone and the weld area were revealed.
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