Materials Science Forum Vol. 946

Abstract: The results of investigations of the pulsed arc welding with a cored wire with increased extension are presented. As shown, the formation of droplets varies with increasing the electrode extension. Due to the oscillography analysis, this phenomenon is reasoned from the features of the impulse control. A range of parameters is set, for which a stable impulse control of the process is ensured. The increased production capacity and high arc stability are combined in this range.

Abstract: Specific features of the formation of welded metals under the pulsed action of laser radiation are described. It is shown that the quality of the technological process of welding depends on the energy characteristics of the laser technological complex, the temperature of the surface layer. The results of experimental studies on the effect of pulsed laser radiation on steel 08YU with the possibility of obtaining a welded seam with the required quality indices are presented.

Abstract: Many product parameters are basically determined by the state of the surface layer of the material from which it is produced. Increasing the hardness of the surface layer with unique core characteristics will significantly improve the performance characteristics of products and expand field of application of 34CrNiMo6 steel. The paper presents the results of a study of the surface plasma hardening of 34CrNiMo6 steel on direct and reversed polarity current. Studies of four possible variants of plasma surface quenching, including processing with scanning and processing in closed arc mode were carried out. The results of measuring geometric characteristics and hardness of the produced hardened layers are given. The possibility of producing hardened layers with a hardness up to 52 HRC is shown. The macro-and microstructure of the produced hardened layers using light microscopy was studied. The features of structure formation in layers hardened in different variants are analyzed. It is shown that it is possible to produce hardened layers with a depth of 1.7 mm and a width of up to 24 mm in the finishing plasma treatment without significant changes in the surface roughness.

Abstract: Three brands of special electrodes for underwater welding were analyzed: LKI-1P, EPS-AN, UW-EZ-2. Experimental data on welding and processing behavior of these types of electrodes in the conditions of underwater arc welding were obtained: melting factor, metal deposit factor and losses. Experiments have been performed to determine the value of the arc breaking length of electrodes when welding under water. A comparative analysis was made with UONII-13/55 electrodes when welding in air conditions.

Abstract: The results of experimental studies of the variation of residual stresses in a frameless tubular node of the offshore stationary platform (OSP) due to technological effects on the metal are presented. It is shown in the paper that the value of the tensile residual stresses in sheet rolled products with 20-50 mm of thickness reaches 80-65 MPa. As a result of the subsequent technological redistribution, the residual stresses change in magnitude and sign, and reach 0.8-1.2 of the yield strength of the base metal. The most unfavorable from the point of view of the serviceability of OSP are the tensile residual stresses in welded joints, the maximum value of which is 350...500 MPa. High temperature tempering after welding does not always lead to the desired result: in the heat-affected zone of the corner joints of nozzles mounting to the waist tube of the node, the residual stresses amount to 120-150 MPa. Preheating temperatures in the range of 120-160⁰С do not have a significant effect on the value of residual welding stresses. For more effective reduction of σ _rs , its value should be 200-450⁰С, depending on the thickness of the joined parts and the strength class of the steel.

Abstract: The paper presents the results of metallographic studies of laser and plasma cutting methods of high-strength steel for the purpose of its application for the preparation of sample edges without subsequent machining. It is shown that as a result of the thermal and physical-chemical processes in heat affected one (HAZ), there is a change in the phase and chemical composition of the metal. The depth of the HAZ is changed from 261 μm to 337 μm. The maximum hardness at the cutting edge is 410 HV₁₀. On the surface after the laser cutting there is an oxidized layer of metal, saturated with oxygen, nitrogen and other gases as a result of contact with the oxygen jet and the surrounding air; its thickness is hundredths or even thousandths of a millimeter. A feature of the plasma cutting method is the formation of a deeper oxide layer on the surface with a thickness of 9...14 μm, in contrast to the laser cutting method. The analysis of existing research to improve the technology of repair welding of low-carbon steel is performed. The obtained results can be used in the development of high-strength steel grades welding technology in terms of preparation of edges for welding using thermal cutting methods, which are currently quite conservative.

Abstract: The weldability of high strength steel of grade 10G2FBY with a yield strength of 500 MPa is conducted in this paper according to the criterion of cold cracks formation in the seam root of plates with a thickness of 18 and 36 mm. The study was carried out in accordance with GOST 26388-84 on samples of type IX at ambient temperatures from –20 to +20 °С at heat input energy from 5.8 to 14.3 kJ/cm. After welding, the plates were cooled in the air for 24 hours. The main criterion for assessing weldability is the presence or absence of cold cracks after welding. The welding was made with a soft wire 4Y42 with a yield strength of 420 MPa. Cold cracks in high strength steel 10G2FBU for thicknesses of 18 and 36 mm are not detected in heat input over 10.3 kJ/cm by welding at the temperature of +20 °С, at the same time when welding at an ambient temperature of -20 °С cracks are not detected when running over energy of 14.7 kJ/cm. Critical cooling rate in which no cracks appeared was 55 °С/s at the temperature of welding +20 °С, and it was 44 °С/s at a temperature of welding –20 °С for both thicknesses. The criterion HV_max<300 HV is a necessary but insufficient condition for the prevention of cold cracking in steels of the type 10G2FBU. In the conditions of the experiment, cold cracks in the weld seam are absent at a hardness of no more than 250-260 HV, which is probably due to the presence of diffusive hydrogen, which is not regulated in the regulations for the supply of this steel grade

Abstract: This paper considers the results of studies of the welded joints formation in conventional friction welding of pieces with different-sized cross sections. The features of the formation of joints associated with the asymmetry of the temperature field in the pieces are defined. The results of studies of the main parameters of the welding process are given which influence on the appearance, the microstructure of the joints and the valve after the stamp. The optimum parameters of the welding mode are set; recommendations are given.

Abstract: This article offers a qualitatively new approach for production fused welding fluxes granules, based on the use of a plasma arc and the Ural region raw materials that have a particularly low content of harmful impurities. The processes of fused welding flux granules forming from the Ural region mineral raw materials under the impact of a highly concentrated energy source have been studied. A new fused welding flux for submerged arc welding is produced by plasma electric arc granulation, and has required shape and fractional, chemical and phase composition of the particles. This research presents experimental and theoretical studies of interaction processes of fine-dispersed batch from mineral raw materials with a highly concentrated energy source, aimed at obtaining new information about the basic patterns of the formation, structure and composition of resulting granules of functional materials, such as welding fused fluxes.

Abstract: A modern technology for joining materials welding is commonly used in various industries. It is a process of interaction of thermal, mechanical and metallurgical properties and behaviors. Complex phenomena, such as solidification, microstructural changes and defect formation, have a great impact on the quality of welded joints. This article presents the results of studying the features of the austenite decomposition kinetics in the application of laser-hybrid welding technology, in a combination with multi-arc automatic submerged arc welding. The cooling rates are determined, affecting the change in properties of HAZ of welded joints on pipe steel of strength class K52. Using the dilatometric method, studies were conducted and thermo-kinetic and structural diagrams were constructed. Analysis of diagrams and microstructures showed that, as a result of the impact of the laser-hybrid welding process in the area of HAZ, the decomposition of austenite occurs mainly in the martensitic zone, followed by the formation of a bainite-perlite structure, due to recrystallization from the heat generated by the facing seams.