PSI - Issue 40

E.E. Abashkin et al. / Procedia Structural Integrity 40 (2022) 1–6

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Abashkin E.E. / Structural Integrity Procedia 00 (2022) 000 – 000

1. Introduction Enterprises that are driven by the use of technologies with low resource intensity and automation for production of metal products, permanent joints and related structures have significant competitive advantages. An important quality assurance criterion of such products is high performance characteristics. This is particularly topical for the shipbuilding industry, since the produced volume of electric arc permanent joints is more than 90%. Productivity increase is driven by the utilization of automatic processes, where mechanized feed of the electrode wire into the welding zone is used versus manual arc welding method (Makienko et al., 2009; Arabey et al., 2011). The arc welding process is conducted in a protected environment. Therefore, manufacturers use mechanized units with steel wires utilized as a welding electrode. Despite the high performance of the process, in occasions when low-carbon and low-alloy steels welding is performed, characteristics of chemical homogeneity and structural strength are not achieved. The described challenges can mainly be resolved by increasing the energy consumption and the number of electrode passes through the weld zones of the seamed steel elements, which can decrease the quality of the joint. In certain scenarios, the required joint strength is achieved by increasing the number of electrode passes with a decrease in the input energy of the electric arc, which leads to an increase in the number of deposited metal layers in the weld structure and, as a consequence, to an increase of the recrystallized zone with a fine grain size. This, in turn, leads to increased production time of the metal structure. The search for new resource-intensive methods to obtain permanent steel joints determines the use of aluminothermic process in welding. Thermophysical conditions of a heat-affected zone formation with a use of aluminothermic processes are significantly differ from traditional methods of permanent joints production. The apparent advantages of the mentioned methods are production mobility and relatively low cost of materials (Sergejevs et al.,2008; Kargin et al.,2015; Ustinov et al., 2013). Aluminothermic welding process involves flux-cored wire with aluminothermic filler for automatic submerged arc welding (SAW) (Manakov et al., 2018; Tsurikin et al., 2006; Yang et al., 2011). The filler consists of a metal scale fractions mix and aluminum alloy with alloy component additives. This method permits to use the energies of an electric arc and aluminothermic reaction in the process of a permanent joint production. An additional heat energy of the exothermic reaction and the formed electrode metal contributes to the uniform filling of the weld pool, and the thermal insulation properties of the formed slag lead to a slower and, eventually, uniform crystallization of the weld material. This improves the quality of fabricated permanent joints in comparison with the “traditional” method of electric arc welding with a solid wire. Nevertheless, it turns to be impossible to completely avoid the negative influence of local overheating of the connection zone. Local overheating leads to a change in the structure of the permanent joint material and the appearance of residual stresses in the heat-affected zone, which deteriorates the strength properties of metal structures (Abashkin et al., 2019; Mouallif et al., 2015). The purpose of the research is to determine the effect of combined thermal exposure on the zone where weld metal contacts with a low-carbon steel plate, which is obtained by combining the electric arc and aluminothermic process during formation of structure and physical and mechanical properties of the metal in the weld and heat affected zone, when welding elements of metal structures from structural steel. 2. Materials and methods The experimental testing of the combined thermal exposure modes was carried out by welding plates with edge preparation according to type C21 GOST 8713- 79 “Submerged arc welding. Welded joints. The main types, structural elements and dimensions” 8 mm thick, 200 mm wide and 500 mm long, without preliminary surface cleaning and heating of the joint zone. Quality structural carbon steel St3sp was selected as the material of the welded elements, corresponding to GOST 1050- 2013 “Metal products from unalloyed structural quality and special steels”.