OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 weld having a lower hydrogen penetration rate than the base steel, while a high strength steel weld typically has a higher hydrogen penetration rate than high strength steel weld and base steel. As stated earlier, hydrogen atoms from several sources can enter the molten weld pool and remain in the weld zone [8]. The microstructure of welds mainly contains ferrites, such as acicular ferrite and polygonal ferrite. Ferrite typically forms a crystallographic plane (1 0 0), where the energy barrier for hydrogen absorption is 0.38 eV, which is significantly lower than the energy barrier of 1.02 eV at a crystallographic plane (1 1 0) of bainite found in high-strength base steels. [4–8]. Moreover, non-metallic inclusions, such as Si/Al-O inclusions contained in welds, are irreversible hydrogen traps and effectively trap mobile hydrogen in the crystal lattice [4, 5]. The higher hardness of the inclusions than the base steel causes lattice distortion where the concentration of stress or strain further promotes hydrogen trapping. The accumulation of hydrogen leads to the formation of hydrogen gas molecules, which leads to an increase in local pressure (voltage). Then, hydrogen can reduce the adhesive force between iron atoms. All of it contribute to the initiation of microcracks and its propagation, and delayed brittle fracture in welds. The values of diffusion-mobile hydrogen after storage at negative temperatures are of interest (Figs. 11–14). It is generally accepted that grain boundaries and phase boundaries can serve as effective hydrogen traps, collecting and accumulating hydrogen atoms. However, it was found that the diffusion coefficient of hydrogen along solid grain boundaries is six orders of magnitude higher than inside grains [5, 8]. From our experiments it is clear that negative temperatures slow down the diffusion of hydrogen and contribute to its localization and increase in local pressure (stress), which increases the likelihood of cracking of the weld. Compared to other measures, controlling diffusible hydrogen is more effective in reducing the tendency for hydrogen to accumulate. One of the main sources of hydrogen released during welding is air moisture and hydrogen-containing welding electrodes. Mandatory calcination of the electrodes can effectively reduce the ingress of hydrogen into welds. The use of moisture-resistant coatings and optimization of arc welding parameters make it possible to control the hydrogen content. However, welding electrodes are usually prone to absorbing moisture. Reducing the cooling rate of the weldment by increasing the heat input can give hydrogen more time to diffuse out of the welds, reducing the hydrogen content. Conclusion In this work, the main objective of the study was to compare the welding engineering properties of two brands of electrodes TMU-21U and TsU-5, manufactured at different plants: “Sudislavsky Welding Materials Plant”, LLC, ESAB LLC “ESAB-SVEL”, and CJSC “Elektrodnyi zavod”. It is established that the welding engineering properties of the electrodes: TMU-21U (manufacturer: “Sudislavsky Welding Materials Plant”, LLC), TsU-5 (manufacturer: CJSC “Elektrodnyi zavod”) are outside the tolerance for such a parameter as the formation of a “fingernail”. It is established that the chemical composition of the weld overlaid metal is not stable for all brands of electrodes under study and depends on the manufacturer. It is established that the mechanical properties of the weld overlaid metal are unstable in terms of such indicators as the values of tensile strength and yield strength, and relative contraction does not meet regulatory requirements. Impact strength values are at the minimum permissible limit of values according to regulatory documents. It is established that when calcining the electrodes, the content of diffusion hydrogen in the weld overlaid metal is reduced by almost 2.5 times, which is also recommended to be done according to RD 153-34.1-003-01(RTM-1S) clause 3.10 [1]. When comparing the content of diffusion hydrogen in electrodes manufactured at different plants, the metal weld overlaid with electrodes manufactured at the CJSC “Elektrodnyi zavod”, located in St. Petersburg, has the lowest hydrogen content. And the highest hydrogen content is observed when surfacing with electrodes from ESAB LLC “ESAB-SVEL” located in St. Petersburg. A lower percentage of hydrogen leads to improved welding characteristics and a reduced risk of weld defects.
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