PSI - Issue 36

Sergiy Kozulin et al. / Procedia Structural Integrity 36 (2022) 247–253

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Sergiy Kozulin et al. / StructuralIntegrity Procedia 00 (2021) 000 – 000

1. Introduction In the cement, mining, metallurgical and other industries, such large-sized units as rotary kilns are in operation around the clock (Fig. 1, a). Often, through cracks are formed in the support bands of the kilns (Fig. 1, b), which leads to a stop of the entire technological line, as a result of which the enterprises suffer significant losses from under-production. It is expedient to repair such large parts (with 355...500 × 900. ..1350 mm cross-sections) on the site using electroslag welding (ESW), which, as shown in the papers by Paton (1980), Paton et al. (2019), Sushchuk Slyusarenko et al. (1989), wide application in various branches of mechanical engineering for joining metal of large thicknesses in the machine parts manufacturing, as well as in repair work. However, due to the high heat input in the base metal inherent in this process, which causes grain growth in the heat-affected zone, obtaining equal-strength joints when welding carbon structural steels requires expensive high-temperature treatment (HTT) of the product. Therefore, the search for solutions to refuse or at least reduce the volume of its application is an important task. To improve the mechanical properties of welded joints obtained by different welding methods, the following works by Moltasov (2019), Dzioba and Pała (2020), Kostin et al. (2020), Knysh et al. (2020) are devoted to this problem. One of the ways to approximate the mechanical properties of the welded joint to the properties of the base metal without HTT is to perform ESW not in one but in several passes, when the heat released in the process of each adjacent pass affects the previously welded sections, producing their partial heat treatment, improving the mechanical properties, as shown in the works by Sushchuk-Slyusarenko (1977), Filchenkov et al. (1982). The same heat creates preheating of the base metal in the non-welded part of the section and reduces the cooling rate of the welded part of the joint, which is known to create favorable conditions for ESW of steels with high carbon content. However, for the repair of through cracks with a large branching and tortuosity, these methods have not found application due to the impossibility of complete removal of the defect, ensuring guaranteed fusion of welded edges and low resistance of welds against the formation of hot cracks. Yushchenko et al. (2014) proposed a method of joining metal of great thickness by multi-pass ESW with consumable nozzle (MESW CN) free from the above mentioned drawbacks. The objective of the work, developing the study by Kozulin et al. (2013), was to investigate the effect of thermal cycles of MESW CN process on the structure and mechanical properties of different areas of the weld joint (weld metal, base metal and heat affected zone – HAZ) of the cast medium carbon steels in order to assess the possibility for defects repair in large thickness structural elements under operation.

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Fig. 1. Rotary kilns ø5×185m (a) and through cracks in cement kiln banding (b, c).