OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 be diff erent for each case [2]. In fact, for those applications where the strength of the weld metal consisting of acicular ferrite is insuffi cient, it is necessary to add special strengthening elements for solid solution and other alloying elements to retard the austenite/ferrite transformation and produce martensitic welds with the required high strength. In work [4], specimens obtained by the SMAW (Submerged Metal Arc Welding) method were studied; automatic submerged metal arc welding and GMAW (Gas Metal Arc Welding) is a designation used to indicate the use of the MIG/MAG method in automatic (robotic) welding. The authors wanted to evaluate (fi gure 3) whether the use of the GMAW process could improve the weld performance of high-strength steels while maintaining good quality even at lower levels of reheat. It was found that a good relationship between mechanical strength and toughness could be obtained. Multi-pass welding is widely used in pipe manufacturing, circular welding of pipe butt joints, and in-service welding. For automatic welding of large diameter pipes, the root welding method by an internal welding machine and the cap welding of external welding machine are usually used [18]. The pipe neck group is fi rst welded to the inner root of the pipeline using a welding robot, and then the weld root is welded (hot pass), then the fi ller and lining layers of the joint are welded, as shown in fi gure 4, where layer 0 is a root weld, layers 1–6 are fi lling ones, and layers 7–8 are cap ones. The fi rst layer completes the fusion of the root weld. Due to the large number of fi lling layers, the likelihood of defects greatly increases. Thermal cycles encountered during welding are characterized by a range of peak temperatures that can alter the microstructure and properties of the HAZ compared to the base metal. It was found that the supercritical (reheated above Ac3) and subcritical (reheated below Ac1) regions resulting from the second thermal cycle retain toughness properties comparable to the original ones. Among all the sub-zones of the HAZ in multi-pass welding, the IC-CGHAZ (i.e., the pre-existing CGHAZ reheated to the temperature range between Ac1 and Ac3 in a subsequent weld) is considered to be subject to the most signifi cant degradation in toughness [11–18]. This is confi rmed by the work of the authors [29, Fig. 3. The relationship between the mechanical strength and impact toughness of the weld deposit of high strength steels in comparison with several works by SMAW (Submerged Metal Arc Welding) and GMAW (Gas Metal Arc Welding) method [4] Fig. 4. Transverse microsection of an annular welded joint of pipes with narrow edge cutting [18]
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