OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology Answering the question why, with a standardized ratio of components, different slag separability is recorded in standard electrode brands, but produced by different manufacturers, we postulate that slag separability depends on the weld metal/slag interface and the difference in the thermophysical properties of metal and slag. As a rule [4–12], a clear metal/slag interface corresponds to good slag separation, otherwise a blurred interface undoubtedly corresponds to poor slag separation. As the basicity of the slag increased, the oxidizing ability of the slag decreased. Since SiO2, CaСO3 and CaF2 form the basis of the basic type of electrode coating, these same components are typical alkaline compounds [5], and SiO2 is a strong acid oxide, the ratios (CaO + CaF2)/SiO2 directly indicate the basicity index [5, 8]. CaСO3, CaF2 and SiO2 form the basis of the basic type of electrode coating, but the first two components are typical alkaline compounds [5], and SiO2 is a strong acid oxide, and the ratios (CaO+CaF2)/SiO2 directly indicate the basicity index [5, 8]. Therefore, with an increase in the ratio (CaO + CaF2)/SiO2, the oxidizing ability of the slag decreases, i.e. the tendency to form a chemical bond decreases (slag separation increases). Obviously, in the case of the electrodes under study, the oxidizing ability does not decrease, which affects the separability of the slag and indicates to us a violation of the component ratios (CaO + CaF2)/SiO2 in the manufacture of electrode coatings TMU-21U, TsU-5. In the course of the research, it was established that there is a difference in the chemical composition of the weld overlaid metal and the mechanical properties of TMU-21U electrodes from different manufacturers, which does not allow in practice to guarantee high quality indicators of the weld. A detailed analysis of the issue of guaranteed properties revealed a discrepancy between regulatory requirements, the characteristics of the electrodes posted on the manufacturers’website and the actual chemical and mechanical properties of the deposited metal. Manufacturers of welding electrodes indicate on the website and packaging chemical and mechanical properties taken from regulatory documents. The hardness of the weld overlaid metal is not the main indicator of electrodes, but even for one brand it differs greatly from different manufacturers. So, for example, for TMU-21U electrodes produced by “Sudislavsky Welding Materials Plant”, LLC, the hardness is 224–238 NB, for the same electrodes, but produced by CJSC “Elektrodnyi zavod”, the hardness is only 168–179 NB, for TMU-21U electrodes produced by the ESAB plant, the hardness is 202–210 NB. Failure to meet the standard indicators for the relative elongation of all electrodes under study, and the minimum permissible values of impact strength do not provide the necessary high mechanical properties, good fracture toughness at low temperatures for parts of power equipment according to the requirements [1]. An assessment of diffusion-mobile hydrogen in the weld overlaid metal showed that the manufacturers of TMU-21U, TsU-5 electrodes: CJSC “Elektrodnyi zavod” and “Sudislavsky Welding Materials Plant”, LLC, do not inform the real consumer according to the requirements [18] on the hydrogen content in the weld overlaid metal. The next question is the calcination modes of electrodes of the same brand from different manufacturers differ in the direction of increasing the calcination temperature. In the present study, the level of diffusible hydrogen varies greatly in all cases considered. Figs. 9, 10 show the content of diffusion-mobile hydrogen in the weld overlaid metal at an ambient temperature of 20 °C. No significant differences in hydrogen content were recorded; all of them fall into the group from 5 to 10 cm3/100 g. The minimum level of diffusion hydrogen was measured for electrodes TMU-21U, TSU-5 of CJSC “Elektrodnyi zavod” (Tables 4–5). During bead forming, hydrogen absorbed by the weld overlaid metal (weld zone) has a high tendency to diffuse into the HAZ. The parameters affecting the diffusion of hydrogen in the weld overlaid metal depend on temperature, residual stress, solubility, metal microstructure and trapping effect. It is important to understand that there are significant differences in strength and microstructure between different grades of pipeline steel and the behavior of hydrogen penetration into its welds is completely different. For example, for low alloy steels of strength grade X52 for pipes, it contains polygonal ferrite and some pearlite, while the weld for steels of strength grade X52 consists of polygonal ferrite, some carbide particles and acicular ferrite particles. Chaotically distributed carbide particles reduce hydrogen diffusion, resulting in welds of both low and high strength steels having lower hydrogen diffusion than base steels [4, 5]. Additionally, the weld metal when welding low alloy steel contains less acicular ferrite, resulting in the
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