OBRABOTKAMETALLOV technology Vol. 25 No. 4 2023 the finer ferrite provides better coordination of deformation, effectively preventing stress concentration. At the same time, grain refining effectively restricts the movement space of dislocations inside the ferrite along the surface layer, enhancing the interaction between dislocations and increasing strength [9, 11]. However, themechanical propertiesmanifested by themicrostructure can affect the degree of deformation hardening and the behavior of plastic damage during further forming of the pipe, which, in turn, affects the final pipes’ properties [1–4]. After the pipes are formed, the outer and inner layers of the pipes in the walls experience repeated tensile and compressive deformations, respectively [1–3]. Because of these different deformation histories, the flattened segment of pipe walls often exhibits unexpectedly much lower or higher yield strength than the sheet metal from which it is made. Many studies have shown that the yield strength of the material increases and the ductility decreases during production and that the deformation behavior varies depending on the microstructure [8, 31]. Therefore, when it is necessary to obtain a strength class of steel below K60, TMT is used, and if it is required to obtain rolled products with a strength above K60, TMCT is used. Many researchers recognize that with an increase in the pipe thickness over 27 mm, there are many unresolved issues in the pipe production process to obtain a homogeneous structure across the rolled section, and in the future during the subsequent production of the pipe by wall thickness during the forming process. API class pipes can be made both seamless and welded. The seamless process is a hot-working process used to form a pipe product without a weld. Welding processes used for the manufacture of API class pipes can be divided into welding processes without the use of filler metal (contact welding, electric welding and laser welding) and with the use of filler metal (submerged-melt welding and arc welding with a metal electrode). The manufacturing technology of steel pipes and pipes by conventional electric resistance welding (ERW) is shown in fig. 2. ERW steel pipe manufacturing procedures begin with a rolled steel sheet of the appropriate thickness and a certain width to form a pipe that meets certain specifications. The steel strip is stretched through a series of rollers, which gradually form a cylindrical tube. When the edges of the cylindrical plate meet, an electric charge is applied at the right points to heat the edges so that to be welded together. However, it is difficult to get good performance when using a conventional ERW process. The reason is that ERW steel pipes are made by cold rolling steel strap, and the ductility of steel pipes is inevitably inferior to the ductility of steel strap due to deformation hardening during cold rolling. In addition, the hardening caused by rapid cooling after welding has the same effect on the mechanical properties of the steel pipe in the welded joint. The processes used to produce two levels of product specification (PSL 1 and PSL 2) for HSLA pipe steels are presented in documents [4–9]. From the information presented above, we see that the production of pipes is a complex high-tech process, which at the output gives us an innovative high-quality product, which in the future should be welded in the field into a gas or oil pipeline. The analysis of works [21–28] shows that when forming a weld in steels of strength class K60 with a predominant structure of ferrite and perlite, it is impossible to obtain high values of strength and toughness at the same time. One of the promising directions for the development of high-strength pipe steels is the production of a crystalline ordered bainite structure [1, 2, 21–25], instead of ferrite-pearlite. It is shown in [26] that two generations of low-alloy steels (ferrite/perlite, and then bainite/martensite) have been developed over the past thirty years and have been widely used in structural applications. The third generation of low-alloy steels is expected to provide high strength, improved ductility and toughness, as well as meet new requirements for weight reduction, environmental friendliness and safety. This paper examines the recent progress in the development of low-alloy steels of the third generation with M3 microstructure, namely microstructures with multiphase, metastable austenite and multiscale separations. The review summarizes alloy designs and processing methods for microstructure control, as well as the mechanical properties of alloys. Special attention is paid to the stabilization of residual austenite in lowalloy steels. Then, multiscale nanowires are added, including carbides of microalloying elements and copper-enriched precipitates obtained in low-alloy steels of the third generation. The structure-properties
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