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The weldability of the martensitic steel CA-6NM was investigated and the fundamental technology of its mechanized welding in a mixture of shielding gases was developed according to the requirements for the manufacture of critical parts and assemblies of the hydroturbine equipment, as well as rewelding of casting defects. According to the strength level of the steel, the welding wire thermanit 13/04 Si of a solid cross-section with a diameter of 1.2 mm and one of the variants of the shielding mixture mix 1 (82 % Ar + 18 % CO2) were selected and comprehensively investigated according to EN 12072/G 134 (Germany). It was established that in order to prevent the formation of cold cracks in welded joints, it is necessary to perform welding of this steel with preheating and concurrent heating up to 150-200 °C and a mandatory postweld tempering at the temperature of 600 °C. The developed technology provides a significant improvement in mechanical properties of welded joints and weld metal (by 30-35 % higher than that specified by the requirements to the level of values for base metal of chromium steel CA-6NM). Certification of the technology was carried out and recommendations for its use in production at JSC "Ukrainian Energy machines" were worked out. [ABSTRACT FROM AUTHOR]

Within the framework of currently urgent problem of reconstruction and restoration of equipment of thermal power units of tpp, work has been performed on development of basic technology of welding body elements of a steam turbine from low-alloyed 15Kh2m2fBS (p3) steel to branchpipes from high-chromium martensitic X10crmoVnb91 steel with 9 % cr (p91). the paper gives the results of determination of the thermal mode of welding such combined joints to prevent delayed fracture. Proceeding from study of the influence of different modes of high-temperature tempering on impact toughness of weld metal and hardness of welded joint areas hardened during welding, heat treatment modes were selected, depending on electrode material type. It is shown that the resultant mechanical properties of welded joints correspond to the requirements, specified during work performance. [ABSTRACT FROM AUTHOR]

Carbon migration from the lower-alloyed to the higher-alloyed steel takes place in welded joints of dissimilar steels, as a result of difference in carbon chemical potential after tempering and in high-temperature service. Decarburization in the HAZ nearweld zone of the lower-alloyed steel can lead to formation of service defects and subsequent failure. From mass transfer theory it is known that in polycrystalline bodies the diffusion of interstitial elements, including carbon, occurs most rapidly along the grain boundaries. Theoretically, reduction of carbon diffusion can be achieved by increasing the grain dimensions in the HAZ near-weld zone that will lead to reduction of the overall grain boundary area per a unit of volume in this zone. This work is a study of the influence of the angle of electrode inclination and welding current at deposition of austenitic metal on R91 steel on the width of the decarburized interlayer, forming at subsequent tempering at the temperatures of 700 and 760 °C. It is shown that the resultant decarburized interlayer becomes narrower with increase of the angle of electrode inclination and deposition current. [ABSTRACT FROM AUTHOR]

Welded joints of dissimilar steels are widely used in different assemblies of the steam-water mixture loop in electric power plants. Difference in alloying by chromium and other carbide-forming elements results in carbon migration from the lower alloyed to the higher alloyed steel in such joints after tempering and in high-temperature service. Decarbonization in the HAZ near-weld zone of the lower alloyed steel can lead to formation of defects and subsequent failures. In this work we studied the influence of the type of 15Kh2M2FBS steel joint (single-pass, multipass), made using electrodes with 9 % Cr, on the nature of formation and development of structural inhomogeneity in the HAZ at high-temperature annealing. It is shown that depending on joint type, development of ferrite interlayer takes place in different zones of the HAZ: in the normalized zone and in the zone of intercritical temperatures AC1-AC3 at a distance from the fusion line at single-pass welding; and in the near-weld zone through the HAZ coarse-grained region at multipass welding. Proceeding from the features of decarbonizastion on the surfaces of butt joints and near the fusion line, a scheme was proposed, that allows explaining the nature of development of structural inhomogeneity in the multipass joint of dissimilar steels. [ABSTRACT FROM AUTHOR]

The global increase in cyanobacterial blooms poses environmental and health threats. Selected cyanobacterial strains reveal toxicities despite a lack of synthesis of known toxic metabolites, and the mechanisms of these toxicities are not well understood. Here we investigated the toxicity of non-cylindrospermopsin and non-microcystin producing Aphanizomenon gracile and Raphidiopsis raciborskii of Central European origin to zebrafish exposed for 14 days to their extracts. Toxicological screening revealed the presence of anabaenopeptins and a lack of anatoxin-a, ß-methylamino-L-alanine or saxitoxins in examined extracts. The responses were compared to 20 μg L -1 of common cyanobacterial toxins cylindrospermopsin (CYN) and microcystin-LR (MC-LR). The expression of the marker genes involved in apoptosis (caspase 3a and 3b, Bcl-2, BAX, p53, MAPK, Nrf2), DNA damage detection and repair (GADD45, RAD51, JUN, XPC), detoxification (CYP1A, CYP26, EPHX1), lipid metabolism (PPARa, FABP1, PLA2), phosphorylation/dephosphorylation (PPP6C, PPM1) and cytoskeleton (actin, tubulin) were examined using targeted transcriptomics. Cellular stress and toxicity biomarkers (oxidative injury, antioxidant enzymes, thiol pool status, and lactate dehydrogenase activity) were measured in the liver, and acetylcholinesterase activity was determined as an index of neurotoxicity in the brain. The extracts of three cyanobacterial strains that produce no known cyanotoxins caused marked toxicity in D. rerio, and the biomarker profiles indicate different toxic mechanisms between the bioactive compounds extracted from these strains and the purified cyanotoxins. All studied cyanobacterial extracts and purified cyanotoxins induced oxidative stress and neurotoxicity, downregulated Nrf2 and CYP26B1, disrupted phosphorylation/dephosphorylation processes and actin/tubulin cytoskeleton and upregulated apoptotic activity in the liver. The tested strains and purified toxins displayed distinctively different effects on lipid metabolism. Unlike CYN and MC-LR, the Central European strain of A. gracile and R. raciborskii did not reveal a genotoxic potential. These findings help to further understand the ecotoxicological consequences of toxic cyanobacterial blooms in freshwater ecosystems., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Toxicity of cyanobacteria is the subject of ongoing research, and a number of toxic metabolites have been described, their biosynthesis pathways have been elucidated, and the mechanism of their action has been established. However, several knowledge gaps still exist, e.g., some strains produce hitherto unknown toxic compounds, while the exact dynamics of exerted toxicity during cyanobacterial growth still requires further exploration. Therefore, the present study investigated the toxicity of extracts of nine freshwater strains of Aphanizomenon gracile , an Aphanizomenon sp. strain isolated from the Baltic Sea, a freshwater strain of Planktothrix agardhii , and two strains of Raphidiopsis raciborskii obtained from 25- and 70-day-old cultures. An in vitro experimental model based on Cyprinus carpio hepatocytes (oxidative stress markers, DNA fragmentation, and serine/threonine protein activity) and brain homogenate (cholinesterase activity) was employed. The studied extracts demonstrated toxicity to fish cells, and in general, all examined extracts altered at least one or more of considered parameters, indicating that they possess, to some degree, toxic potency. Although the time from which the extracts were obtained had a significant importance for the response of fish cells, we observed strong variability between the different strains and species. In some strains, extracts that originated from 25-day-old cultures triggered more harmful effects on fish cells compared to those obtained from 70-day-old cultures, whereas in other strains, we observed the opposite effect or a lack of a significant change. Our study revealed that there was no clear or common pattern regarding the degree of cyanobacterial bloom toxicity at a given stage of development. This means that young cyanobacterial blooms that are just forming can pose an equally toxic threat to aquatic vertebrates and ecosystem functioning as those that are stable or old with a tendency to collapse. This might be largely due to a high variability of strains in the bloom.