Improvement of quality and improvement of technology of production of economic alloyed steels for power engineering

Purpose. Investigate the effect of complex microalloying with nitrogen, titanium and aluminum on the structure and properties of cast steels at elevated temperatures. Methodology. Methods of optical microscopy were used for metallographic analysis of the microstructure of steels. The mechanical properties at room and elevated temperatures were determined for static tension, crease and impact bending. Results. The technology of carbonitride strengthening of silicon-manganese production steels has passed pilot testing. The results of mechanical tests indicate a favorable complex effect of nitrogen, titanium and aluminum on the properties of 20GSL steel in the entire range of operating temperatures. Scientific novelty. For the first time, the effect of nano-dispersed carbonitride phases (TiN, AlN) on the mechanical properties of low-alloy silicon-manganese steel of the GSL type at elevated temperatures (250-4500C) has been investigated. Practical value. The use of carbonitride technology for strengthening silicon-manganese heat-resistant electric steel provides an increase in operational reliability, an increase in the service life and reduce the metal consumption of equipment for power engineering. Keywords: technology, electric steel, heat resistance, carbonitride reinforcement, microalloying, steel 20GSL.

Investigation on the Chemical and Thermal Behavior of Recycling Agglomerates from EAF by-Products

In addition to the blast furnace converter route, electric steel production in the electric arc furnace (EAF) is one of the two main production routes for crude steel. In 2019, the global share of crude steel produced via the electric steel route was 28%, which in numbers is 517 million metric tons of crude steel. The production and processing of steel leads to the output of a variety of by-products, such as dusts, fines, sludges and scales. At the moment, 10–67% of these by-products are landfilled and not recycled. These by-products contain metal oxides and minerals including iron oxide, zinc oxide, magnesia or alumina. Apart from the wasted valuable materials, the restriction of landfill space and stricter environmental laws are additional motivations to avoid landfill. The aim of the Fines2EAF project, funded by the European Research Fund for Coal and Steel, is to develop a low-cost and flexible solution for the recycling of fines, dusts, slags and scales from electric steel production. During this project, an easy, on-site solution for the agglomeration of fine by-products from steel production has to be developed from lab scale to pilot production for industrial tests in steel plants. The solution is based on the stamp press as the central element of the agglomeration process. The stamp press provides the benefit of being easily adapted to different raw materials and different pressing parameters, such as pressing-force and -speed, or mold geometry. Further benefits are that the stamp press process requires less binding material than the pelletizing process, and that no drying process is required as is the case with the pelletizing process. Before advancing the agglomeration of by-products via stamp press to an industrial scale, different material recipes are produced in lab-scale experiments and the finished agglomerates are tested for their use as secondary raw materials in the EAF. Therefore, the tests focus on the chemical and thermal behavior of the agglomerates. Chemical behavior, volatilization and reduction behavior of the agglomerates were investigated by differential thermogravimetric analysis combined with mass spectroscopy (TGA-MS). In addition, two melts with different agglomerates are carried out in a technical-scale electric arc furnace to increase the sample size.

THE EFFECT OF LONG-TERM STORAGE OF ELECTRIC STEEL SMELTING SLAGS IN DUMPS ON THEIR PROPERTIES

construction, repair and reconstruction of roads require high costs of mineral raw materials in the form of sand, gravel, mineral powder. However, its reserves on the territory of our country are distributed unevenly, which causes significant transportation costs for the delivery of mineral resources to construction sites. In addition, mineral resources are inevitably reduced over time, which requires extensive involvement in the construction of roads of non-traditional types of raw materials, as well as industrial waste. The paper presents the results of studies of the properties of electric steel slag, the current output and stored in the dumps for several years. The main component of electric steel-smelting slags, both fresh and dumped, lying in dumps for about 20 years, is shannonite or γ-modification of calcium orthosilicate C2S. It has been established that the mineralogical composition of the Oskol Electrometallurgical Combine's slag is represented by hematite, wuistite, calcite, periclase, and also portlandite, formed during quenching of lime. Analysis of diffractograms of slags of different shelf life shows that in the initial periods of slag storage in the dumps there is a final quenching of lime and its carbonization with the formation of calcite. The results of the determination of the granulometric composition of the slag of different storage periods showed a decrease with time of the number of fine fractions and an increase in large fractions. It is established that when using electric steel-smelting slags in the construction and repair of highways, it is necessary to take into account changes in the physical and mechanical properties of materials. The processes that take place during the maintenance of slags in dumps determine the suitability of the use of slag mineral materials in road construction.

Biological Monitoring of Occupational Exposure to Metals in Electric Steel Foundry Workers and Its Contribution to 8-Oxo-7,8-Dihydro-2′-Deoxyguanosine Levels

In this study, the urinary concentrations of selected metals in workers from an electric steel foundry in Tunisia were assessed and compared with existing biological limit values and general population reference values. Moreover, the association between oxidative DNA damage, measured as urinary 8-oxo-7,8-dihydro-2’deoxyguanosine (8-oxodG) and co-exposure to metals and polycyclic aromatic hydrocarbons (PAHs) was evaluated. Urinary levels of 12 metals were determined by inductively coupled plasma-mass spectrometry (ICP-MS) in end-shift spot samples from 89 workers. The urinary levels of phenanthrene (U-PHE), as marker of exposure to PAHs, and 8-oxodG were also available. Median levels ranged from 0.4 µg/L (cobalt, Co, and thallium, Tl) to 895 µg/L (zinc, Zn). Only 1% of samples was above the biological limit values for Co, and up to 13.5% of samples were above limit values for Cd. From 3.4% (Co) to 72% (lead, Pb) of samples were above the reference values for the general population. Multiple linear regression models, showed that manganese (Mn), Zn, arsenic (As), barium (Ba), Tl, and Pb were significant predictors of 8-oxodG (0.012 ≤ p ≤ 0.048); U-PHE was also a significant predictor (0.003 ≤ p ≤ 0.059). The variance explained by models was low (0.11 ≤ R2 ≤ 0.17, p < 0.005), showing that metals and PAHs were minor contributors to 8-oxodG. Overall, the comparison with biological limit values showed that the study subjects were occupationally exposed to metals, with levels exceeding biological limit values only for Cd.