RESUMO
Underwater wet welding is commonly used in joining pipelines and in underwater construction. Harmful and hazardous compounds are added to many flux-cored wires for underwater welding and cutting, and can have a negative impact on marine life. The specific objective of this study was to evaluate the aquatic toxicity of two suspension samples obtained using welding electrode and flux-cored wire in marine microalgae Attheya ussuriensis and Porphyridium purpureum. Growth rate inhibition, cell size, and biochemical changes in microalgae were evaluated by flow cytometry. The results of the bioassay demonstrated that the suspension obtained after welding with electrode had an acute toxic impact on diatomic microalgae A. ussuriensis, and both tested suspensions revealed chronic toxicity in this microalga with a 40% growth rate inhibition after exposure to 40-50% of prepared suspensions for 7 days. Red algae P. purpureum revealed tolerance to both suspensions caused by exopolysaccharide covering, which prevents the toxic impact of metal cations such as Al, Ti, Mn, Fe, and Zn, which are considered the main toxic components of underwater welding emissions.
RESUMO
Hydrogen is a main factor in cold cracking or hydrogen-induced cracking. The most crack susceptible region of a steel welded joint is the heat affected zone (HAZ). The formulation and functional-analytical solution of the one-dimensional problem of hydrogen diffusion in an inhomogeneous butt-welded joint considering weld and joint dimensions and initial hydrogen distribution as well as hydrogen diffusion coefficients and solubilities are presented. It is shown that the peak hydrogen concentration in the HAZ of inhomogeneous joints varies in direct proportion to the initial hydrogen concentration in the weld metal. It is inversely proportional to the ratio of hydrogen solubilities in the weld metal and the HAZ metal and is nonlinear in the diffusion coefficient ratio of these metals. The peak hydrogen concentration in the HAZ can exceed 170% of the average initial concentration in the joint if martensitic steel is welded using low-carbon low-alloy welding consumables. The utilization of austenitic consumables leads to a dramatic reduction in the hydrogen concentration in the HAZ in comparison with the non-austenitic consumables. No direct relationship was found between the hydrogen concentration in the HAZ and the hydrogen evolution from the joint surface.
RESUMO
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.
RESUMO
Development of welding consumables with fluorides and borides of rare earth metals is a promising area for improving the weldability of low alloy steels. As lanthanum fluoride and boride dissociate, lanthanum and boron dissolve in the weld pool and the welding arc plasma is saturated with fluorine. As a result of FeO, MnO, SiO2 deoxidation and FeS, MnS desulfurization, refractory lanthanum sulfides and oxides La2O3, La2S3 are formed in the weld pool, which can be the crystallization nuclei in the weld pool and the origin of acicular ferrite nucleation. The paper proposes a model of metallurgical processes in the arc and weld pool, as well as a model of electrochemical adsorption of Ni2+ cations in colloidal electrolytes during electrostatic deposition of nano-dispersed insoluble particles of LaF3 or LaB6 on the surface of wire. The paper discusses the constructional design of the welding wire and the technology for forming electrochemical composite coatings with copper and nickel matrix. The composite wires applied in the welding of low alloy steels make it possible to refine the microstructure, increase the tensile strength by 4% and the impact toughness of welds by 20%.
