Assessment of the possibility of resistance butt welding of pipes made of heat-resistant steel 0.15C-5Cr-Mo

OBRABOTKAMETALLOV Vol. 26 No. 3 2024 technology This is due to the fact that the microstructure adjacent to the fusion zone is transformed into hard phases such as martensite and bainite during rapid cooling. These hard phases result in low impact toughness and high hardness values of the material due to the content of a significant amount of residual stresses. Thus, pipe welds require an additional cycle of post-weld heat treatment to restore mechanical properties and reduce the likelihood of brittle failure in the joint area. The most widely used post-weld treatment mode is the normalization cycle. Normalizing treatment can significantly improve weld alignment characteristics; however, process parameters include maximum heating temperature, heating rate, holding time, and initial cooling water temperature. In addition to normalizing treatment, secondary normalization, quenching, quenching and tempering, and other thermomechanical treatments are carried out to increase the impact toughness of the pipeline [4, 12–19]. Although welding of high chromium steels has become a well-known method that is widely used in the conventional power industry, the weld characteristics of high Cr and Cr-Mo steels are still often considered a life-limiting factor at high temperatures. In fact, a high percentage of failures in the power generation industry have been reported to be welding-related [4–9]. Moreover, despite extensive experience in welding high chromium steels, many certified welding procedures have been developed for specific applications, and the environmental conditions of new applications can greatly affect the weld. In [19], an analysis was carried out based on world experience of failures due to incorrect heat treatment of heat-resistant steels after welding. It is concluded that the creep damage and observed cracking mechanisms resulted from the high degree of mechanical stress experienced by the failed pipe in the heat affected zone (HAZ) immediately adjacent to the pipe weld [20]. One solution to this problem is to develop a new material whose microstructure in the HAZ would be similar to the microstructure of the base metal. This was achieved, for example, by adding boron [5–7]. Several effects are used to achieve good quality welded joints: optimization of the welding procedure and parameters, development of a suitable filler metal and the use of post-weld heat treatment. Currently, research is being conducted to develop new welding processes (laser, electron beam, friction welding) to improve the characteristics of 0.15C-5Cr-Mo and its modifications 0.15C-5Cr-Mo-V and 0.15C-5Cr-V-W steels is a promising direction [6–9, 12–33]. For example [22], Magnetically Impelled Arc Butt (MIAB) welding is a joining method that replaces traditional welding methods such as resistance welding, friction welding, flash welding and butt welding. This is a solid-state process in which a rotating arc heats the ends of the tubes, followed by a forging process to complete the joining of the workpieces. Magnetic-flux density and current interact to create a Lorentz force that causes the arc to move along the adjoining surfaces. This process has been found to provide high tensile strength and defect-free welds in ferrous materials, and for this reason it is predominantly used in the automotive industry for joining metal pipes. Additionally, this joining procedure can be used in the manufacture of boilers, heat exchangers, furnace piping in the petrochemical industry, and in the manufacture of other safety-critical high-pressure machine parts. Using Magnetically Impelled Arc Butt welding (MIAB), it is possible to connect pipes with an outer diameter from 75 mm to 450 mm and a wall thickness of up to 10–35 mm in 10–15 s [22]. However, as many researchers believe [1, 5, 8, 9, 15], power plant workers may be slow to adopt new materials and new welding methods for a number of reasons, including the development of new industry sector codes and standards [11], as well as confidence in long-term work of already assembled welded units in machines and mechanisms. At the same time, the well-known method of resistance butt welding of pipes is widely used in boiler making, pipeline construction, and the production of oil equipment. Depending on the cross-section and material of the pipe, continuous or flash welding with preheating is selected. This paper presents the results of research on resistance butt welding of pipes made of 0.15C-5Cr-Mo steel. The purpose of the work is to assess the possibility of the resistance butt welding method of welding pipes made of 0.15C-5Cr-Mo steel, to select technological parameters for resistance butt welding of pipes to obtain high mechanical properties.

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