Seznam abstraktů 2022: SEKCE A - POKROKOVÁ VÝROBA ŽELEZA, OCELI A LITINY

The presented research was focused on optimizing the internal equipment of the tundish with respect to residence times between the middle (No.2) and two lateral casting strands (No.1 and 3). The different values of residence times of individual strands affect the cleanliness of steel and cause thermal and chemical inhomogeneities. The specific flow given by the shape of the three-strand symmetrical T-type tundish causes the middle casting strand to have a relatively short residence time compared to the lateral strands. For this reason, the flow in the tundish was controlled by changing the angle of the outlet holes in tundish baffle separating the inlet part of the tundish from its working volume. The research was carried out using computer simulations supported by the results from the SimConT physical model.

Numerical modelling is becoming an essential part of research in the field of steel metallurgy at present. In numerical modelling, the operating equipment is replaced by a mathematical model, which consists of a system of partial differential equations. Numerical modelling is used to display processes and results that cannot be monitored under operating conditions. From numerical modelling we can obtain the results of the flow field, we can monitor the change in temperature and monitor the wear of the refractory lining, etc. This paper deals with numerical modelling of steel flow in the tundish. The tundish is a very important part of continuous casting. It supplies liquid steel during the ladle change and distributes steel between casting strands. The tundishes are made of a welded steel shell and lined with a refractory material. During casting steel, the tundish is the last reactor where it is possible to influence the quality and purity of the cast steel. It is necessary to know the processes in the tundish. This presented paper compares the results obtained by flowing steel in the tundish at different inlet temperatures. A five-strand asymmetric tundish for bloom casting was used for numerical simulations. The paper also provides an overview of the issues of numerical simulations and their applicability in practice. Fluent software, which is part of the ANSYS package, was used for numerical simulations.

The present paper is focused on the mathematical and graphical determination of temperature and thermal parameters depending on the heat dissipation from solidifying steel in the mould, respectively in the primary cooling zone of continuous casting of steel (CCS). The main task of the primary cooling is mainly to remove heat from the solidifying steel, therefore knowledge of the temperature fields in the precast and mould is important. As part of the present research to evaluate the thermal performance of the mould, the heat flux density dependencies q between the steel and the cooling water in the mould were expressed in the primary cooling region. The cooling water parameters and temperature gradients along the height and perimeter of the working surface of a copper mould insert of square cross-section of 150 x 150 mm and 1 m long were used to determine the heat removal rate from the solidifying steel. The temperature and thermal parameters were determined for the solidification and precooling tasks for two grades of steel with carbon contents of 0.18 wt.% and 0.83 wt.%. Casting speeds were chosen to range from 2.1 m·min-1 to 2.7 m·min-1 and casting temperatures from 1500 °C to 1550 °C. The obtained dependencies were used for numerical simulation in the ProCAST environment.

Three model alloys based on Fe-C-Ni were studied. The alloys containing carbon between 0.338 and 0.382 wt. % and nickel between 1.084 and 4.478 wt. %. Phase transition temperatures, coefficient of thermal expansion, and density were experimentally and theoretically determined and clarified for all specific alloys in the high-temperature area from 1000 °C to 1595 °C. Phase transition temperatures were experimentally obtained using differential thermal analysis (DTA), differential scanning calorimetry (DSC), and dilatometry. The coefficient of thermal expansion and density were determined by dilatometry. Additionally, experimental data were compared and discussed with calculation results using SW JMatPro, and Thermo-Calc. The obtained experimental results show that with increasing nickel content, the temperature of the liquidus and the coefficient of thermal expansion decrease. Conversely, the density increase with increasing nickel content. The ambiguous influence of nickel on the change in solidus temperature was observed.

Steels are commonly used metallic materials, that’s why higher requirements are imposed on their properties. Thermodynamical and thermophysical properties are one of the most important quantities of materials, which are needed for understanding behavior of materials under defined conditions. Thermal analysis has been widely used in various scientific fields, it can be used for study thermophysical and thermodynamic properties as well. The paper is dedicated to the study of six model alloys based on Fe-C-Cr-Ni, contained carbon in a range of 0.0023 - 0.0095 wt. %, chromium 0.0050 - 4.5528 wt. % and nickel 0.0020 - 4.9600 wt. %. Specific heats and phase transformations temperatures were studied in a high temperature area. Experimental data were obtained using Setaram MHTC Line 96 with a 3D DSC sensor. Theoretical data were calculated using SW Thermo Calc and JMatPro, then were compared and discussed with experimental data.

Considerable amounts of Fe-containing fine dusts are generated in an integrated steel mill, mainly at the blast furnace (BF) and the basic oxygen furnace (BOF). Limitations in dust recycling via the sinter plant arise especially from the limit for Zn in the BF feed. Therefore, dust with an elevated Zn content is usually discharged to landfill, resulting in considerable losses of Zn. In this study the possibilities for increased internal dust recycling in integrated steel mills by implementing air classification of dusts are discussed. The aim of this concept is to avoid landfill of steel mill dust by recycling of the Fe in the steelmaking process while producing a Zn-enriched by-product that can be utilized in secondary Zn production. Since the distribution of Zn in the dusts is not even but depends on the size of the particles, air classification can be applied to separate dusts into a coarse Zn-depleted size fraction and a Zn-enriched fine fraction. Low-Zn content coarse fractions of the dusts can be recycled in ironmaking, medium Zn content dust fractions could be recycled in steelmaking, where the Zn input is not as limited as in ironmaking and Zn-rich fine dust fractions with a Zn concentration high enough for use in secondary Zn production could be recycled there.

The refining process in steel making involves multiple reactions occurring simultaneously in a short span of 15-20 minutes, which limits detailed understanding of the process behavior. The major challenge faced in producing high quality steel in larger volumes, dynamic control of compositions and temperature throughout the process. Hence, we developed a dynamic model to predict the behavior of the process in terms of transient composition, temperature and volumes of liquid steel, slag and top gases involving multi-reactor model based upon thermodynamics of chemical reactions and their mass/heat transfer governed kinetic limitations. The three reaction zones (i) jet impact zone, (ii) slag-bulk metal-gas emulsion zone (iii) slag-solid -gas zone were considered for the computing of overall process. In this work we have used six adabatic/equalibrium reactors which are interconnected with each other to described the overall basic oxygen steel making process. We used the macro programming facility of FactSage™ software to understand the thermochemical model of basic oxygen steel making process. The model predicts the bath as well as reactors composition and temperature for every minute of blowing time. In this present work, correlation between〖dO〗_slag/dt and wt.% FeO, decarburization and post combustion ratio are investigated. The resulting profile can be used as a guiding tool for optimizing the lining life and thermal efficiency of basic oxygen steel making process in industry in a better way. The results from the model were consistent with the plant data and other researchers. Our model can be scaled up to industrial basic oxygen steel making process, and can be potentially used as a guiding tool to optimize the operation conditions.

Lead and chromium removal from water solutions using the basic oxygen furnace slag was investigated. Calcium, iron, and silica were the main components of the slag. The samples were characterized by means of the thermal, surface, and mineralogical analysis and infrared spectroscopy. The experiments were performed at the ambient temperature. Chromium adsorption proceeded according to the Langmuir isotherm and lead adsorption proceeded according to the Freundlich isotherm. The sorption capacity over 150 mg/g was reached for chromium and the value was higher than 250 mg/g for lead. Kinetic data were analysed using the pseudo-first, pseudo-second and intra-particle diffusion models. Adsorption data of chromium were correlated with the pseudo-second-order kinetic model and lead sorption was very quick and the models could not be applied.

Bentonite is widely used in various branches of industry due to its special properties like low hydraulic conductivity, high sorption capacity, low permeability. Knowledge about thermal stability of bentonite and, precisely speaking, all its components, is important for industrial applications. From this reason, the purpose of this study is to investigate the mineralogy and high temperature transformations of bentonite under oxidative (in air) conditions. For these studies the 57Fe Mössbauer spectroscopy will be use. It is well known that the Mössbauer spectroscopy method as a local probe technique is very sensitive to the local atomic structure, its local deformation, and atomic or lattice defects when treating the Fe nucleus as a probe of its local surrounding. The thermal stability testing has been carried out by heating the sample for three hours at various temperatures between 100C and 800C. Raw bentonite sample contained montmorillonite (47%), magnesioferrite (30%), orthoclaste (11%) and goethite (8%). The changes in the Mössbauer spectra well reflected various phases decomposition and transformation, because Fe-bearing minerals make up majority (89%) in all present phases of investigated bentonite. High temperature studies show that all of Fe bearing phases remained unchanged up to temperature about 300C. It can be important note for the potential use of this material as bentonite buffer and for its waste repositories function. Dehydroxylation process of montmorillonite starts at a relatively low temperature, namely above 400C, and the breakdown of the clay structure takes place at about 700C. Such knowledge about high temperature stability of clay-mineral fraction is important in the making of foundry sand, ceramic or in civil engineering. Mössbauer spectrum obtained after heating at 800C showed hematite as the main iron oxide phase with approximately the same relative ratio of iron oxides and hydroxides as in the starting material.