Abstract
This paper considers the metallurgical processes of dissociation, ionization, oxidation, deoxidation, and dissolution of oxides during underwater wet cutting. A multiphase mechanism of underwater wet cutting consisting of working and idle cycles of the electrical process in a pulsating vapor gas bubble is proposed. A model of arc penetration into metal due to metal oxidation and stabilization of the arc by the inner walls of a narrow kerf is proposed. For underwater cutting of 10 KhSND, 304L steel, CuAl5, and AlMg4.5Mn0.7 alloy, we provide a principle of modeling the phase composition of the gas mixture based on high oxygen concentration, improving ionization, enthalpy, heat capacity, and thermal conductivity of plasma through the use of a mixture of KNO3, FeCO3 and aluminum. The method of improving the thermophysical properties and ionization of plasma due to the exothermic effect when introducing Fe3O4, MoO2, WO2 oxides and Al, Mg, Ti deoxidizers is proposed. Although a negative effect of refractory slag was revealed, it could be removed by using the method of reducing surface tension through the ionic dissolution of refractory oxides in Na3AlF6 cryolite. In underwater cutting of 10 KhSND and 304L, the steel welding current was 344–402 A with a voltage of 36–39 V; in cutting of CuAl5 and AlMg4.5Mn0.7 alloy, the welding current was 360–406; 240 A, with a voltage of 35–37; 38 V, respectively, with the optimal composition of flux-cored wire: 50–60% FeCO3 and KNO3, 20–30% aluminum, 20% Na3AlF6. Application of flux-cored wires of the KNO3-FeCO3-Na3AlF6-Al system allowed stable cutting of 10KhSND, AISI 304L steels, and CuAl5 bronze with kerf width up to 2.5–4.7 mm.
Highlights
Underwater welding and cutting are used in the construction and repair of important objects, including offshore oil and gas platforms, wind farms, ports, hydraulic structures, underwater oil and gas pipelines, and the lifting and repair of ships [1]
Underwater wet welding is complicated by hydrogen-induced cold cracks, porosity, slag inclusions, and delayed hydrogen embrittlement [3,4,5]
10025-2:2004, wt.%: 0.08C; 1Si; 0.6Mn; 0.8Ni; 0.8Cr; 0.1V; 0.5Cu, AISI 304L of 16 mm according to ASTM A240/A240M-20a, wt.%: 0.01C; 0.6Si; 1.8Mn; 10 Ni; 18Cr, CuAl5 aluminum bronze of 10 mm according to ISO 428:1983, wt.%: 5Al; 0.3Fe; 0.7Ni; 0.4Mn; 0.3Zn and AlMg4.5Mn0.7 alloy of 6 and 12 mm according to EN AW-5083 were used
Summary
Underwater welding and cutting are used in the construction and repair of important objects, including offshore oil and gas platforms, wind farms, ports, hydraulic structures, underwater oil and gas pipelines, and the lifting and repair of ships [1]. Underwater welding and cutting are often performed manually by diver–welders using coated and tubular electrodes. Cutting is used to remove defective metal; after cutting, welding is performed on the cut edges of the parts. Steel is thermally affected and saturated with hydrogen. The presence of impurities, slag, and metal hydrogenation worsens the quality of welding and reduces strength, ductility, and impact toughness [2]. Underwater wet welding is complicated by hydrogen-induced cold cracks, porosity, slag inclusions, and delayed hydrogen embrittlement [3,4,5]
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