Seznam abstraktů 2018: SEKCE A - POKROKOVÁ VÝROBA ŽELEZA, OCELI A LITINY

Mathematical modeling is a useful tool for predicting material properties even in case of complex technological processes. One of the most complicated processes in the mass production of steels is continuous casting. Defect free casting requires an excellent accordance between steel properties being cast and the technological parameters, especially from the aspect of inner quality and homogeneity of cast products. As an example, one of the most unpredictable defects of cast slabs is the centerline segregation can be mentioned. Complex mathematical model was developed for predicting the expected centerline segregation level in the mid region of continuously cast slabs.
The centerline inhomogeneity frozen in the slab structure can have a detrimental effect on the properties of semi or final hot rolled products, i.e. some remaining forms of this casting defect can be identified even in hot rolled strips. During hot rolling the centerline segregation pattern will become thinner and will be stretched, but it can also be detected in the middle part of heavy plates and coils. It is a common experience that decreasing the centerline segregation of heavy plates by post heat treatment is not easy. The modification of centerline segregation pattern was physically and mathematically modeled. Diffusional calculations proved the governing role of carbon activity, which is influenced by the distribution of alloying elements.

The campaign length of a blast furnace is limited by the hearth inner lining lifetime. In order to maximize the campaign length and ensure a good draining of hot metal and slag, a good understanding of the flow in the hearth is essential. Challenges in modeling the flow involve several continuous phases (hot metal, slag and hot blast) as well as the presence of the deadman, a dense bed of coke particles. The shape and position of the deadman is highly dynamic and depend on several conditions, e.g. the weight of the burden, the deadman porosity as well as the liquid iron and slag levels in the hearth.
We present a numerical coupled CFD (Computational Fluid Dynamics) – DEM (Discrete Element Method) model to account for the transient behavior of the deadman. A VOF (Volume of Fluid) method is used to model the multiple continuous phases and the DEM method to model the discrete particles. The VOF and DEM models are coupled together in a 2-way manner, resulting in a complete 4-way coupled CFD-DEM model. Experimental validation was performed on a lab-scale particle filled tank and a demonstration of a small-scale blast furnace hearth is shown.
Finally, we present our latest advancements towards modeling industrial scale blast furnaces. Due to the big dimensions, difficulties with extreme computational times arise as the particle number becomes infeasible. Commonly a parcel approach (coarse graining) is used to handle this problem, where several particles are treated as one large particle. However, in combination with VOF, the amount of coarse graining is limited as the increased particle size impairs the resolution of the fluid interfaces. Additionally, the wide range of time scales (ranging from particle collisions of fractions of a second to several hours of operational times) present in the blast furnace remains a major challenge. With information gathered from several short-term coarse grained DEM simulations for various liquid levels, we performed a long-term fully Eulerian simulation that used the data to create a dynamic porosity field. By not resolving any particle collisions in the long term simulation, we could simulate a longer process time while still accounting for the dynamic behavior of the deadman.

A stable & productive blast furnace operation greatly depends not only on its design, operator skill or input material but on the profile & shape of its refractory lining also. The blast furnace inner wall profile exerts a large influence on the descent velocity distribution of the burden, the layer structure of the burden and the gas flow across the furnace. Furnace wall brick erosion and the scaffolding make the solid and gas flow unstable in the upper part of the shaft; it also changes the shape of cohesive zone greatly in the lower part of the furnace, thus affecting the heat transfer and melting rates. Conditions within the blast furnace vary widely by region and the refractories used in BF lining, particularly in the stack, belly & bosh are highly susceptible to a variety of wear mechanisms. Due to the very nature of its geometry and the pyro metallurgical process occurring at different stages there are diverse physical and chemical wear mechanisms in play at the different regions of the blast furnace and they are complex in nature but ultimately alter the blast furnace’s inner profile by means of eroding / damaging the refractory lining.

During the production of plain carbon steel from hot metal and/or scrap considerable amounts of dust-laden off-gases are produced. In de-dusting of these off-gases considerable amounts of fine grained residues are produced, which have to be stored, transported and handled. Thereby, the flow-related properties of the dusts are of great importance. In this study the mechanical properties of dusts from dry off-gas de-dusting in steelmaking plants were investigated. The mass median diameters of electric arc furnace (EAF) dust, basic oxygen furnace (BOF) primary de-dusting dust and vacuum degassing dust (VD) were in the range of a few micrometer, while it was up to more than 100 µm for the residues from the pre-separators in EAF and BOF de-dusting. The values for the particle density were quite similar for all dusts (approximately 3,800-4,800 kg/m³), but the bulk density of the dusts varied in a wide range (approximately 190-1,900 kg/m³). With respect to the flow relevant parameters - flowability, angle of internal friction, wall friction angle and angle of repose – the investigated dusts can be split into two groups: the coarse residues from the pre-separators, which are characterized by low values for the angles and a good flowability, and all other dusts with higher values for the angles and a flowability in the range of very cohesive to cohesive.

The paper deals with the study of phase transition temperatures of pseudoquaternary Fe-C-Cr-O based alloys between RT up to 1600 °C. The knowledge of phase transition temperatures is crucial for application purpose and also for basic research related always closely to the applications. The deeper insight in to the knowledge of behavior of simple systems can lead to enhancement of production of more complex alloys with enhanced properties by simultaneous lower cost production. The paper deals with phase transition temperatures such as: temperature of eutectoid transformation, magnetic transition, alfa-gama transition, solidus and liquidus temperature and peritectic transformation temperature. Phase transition temperatures were obtained by Differential Thermal Analysis (DTA). The comparison and discussion with calculated phase transition temperatures (IDS – Solidification Analysis Package, TE – Thermo - Calc) was done. In some cases substantial differences between experimental and calculated phase transition temperatures were encountered.

Presented works investigates a possibility of using modeling based on artificial neural network for prediction of liquidus temperatures of low-alloyed steels. Paper describes the methodology of creating such model by tools incorporated in commercial software MATLAB. Neural network is trained, validated and tested and previously unseen data measured by DTA method are used as new input data. Results are then compared to those measured and calculated by commonly used software for such applications like IDS and Thermo-Calc. Performance of these three modeling approaches is discussed.

Three model alloys based on Fe-C-Cr were studied. Alloys contained carbon of 0.34 wt. % and chromium in a range of 0.92 – 4.76 wt. %. Heat capacities were studied in a low and high-temperature region. The experimentally heat capacities (“apparent heat capacities”) were obtained using Differential Scanning Calorimetry (DSC) with use of a continuous method. The Setaram MHTC (Multi High-Temperature Calorimeter) 96 with a 3D DSC sensor was used for experiments with the use of DSC method. Measurements were done in inert atmosphere of pure argon by a heating rate of 5°C/min. The experimental data were compared and discussed with the calculation results using SW Thermo Calc with the use of the TCFE8.1 (Thermo-Calc Fe-based alloys) database. There is not an unequivocal trend in increase or decrease of experimental heat capacities with increasing content of chromium in the temperature range of 457.15 – 1370.15 K. Experimentally obtained heat capacities decrease with increasing content of chromium except for phase transformations in the temperature range of 1371.15 – 1853.15 K.

Formation of oxide layers on the surface is inherent part of steel production. The presence of the oxide layer primarily influences the surface quality and material losses during steel processing. The influence of the oxide layer on the cooling intensity and homogeneity is not frequently reported but even thin layers of oxides can significantly modify the cooling intensity. Although the cooling intensity is primarily affected by spray parameters as pressure and coolant impingement density, the influence of the oxide layer should be also considered for optimal setting and regulation of the secondary cooling zone. The influence of the oxide layer on the heat transfer coefficient and Leidenfrost temperature is investigated in this paper. Laboratory measurement compares the spray cooling of oxide-free steel surface and oxidized steel surface. Results of measurement also show the impact on the spray cooling homogeneity due to local breaking up of the oxide layer.

Compacted graphite iron (CGI) is an important engineering material, studied first in 1948, with special morphology of graphite particles often resulting in a good combination of thermal and mechanical properties [1, 2]. So, CGI is considered as an important potential material in modern industries, with many investigations dedicated to its thermomechanical behaviour, especially under extreme working conditions [3]. However, few studies of its fracture and strengthening mechanisms were implemented for CGI. Therefore, more systematic and comprehensive analysis should be carried out to gain a better understanding of underpinning deformation processes.
The aim of this research is to establish relationships between the manufacturing (casting) process, resulting local microstructures and thermo-mechanical properties employing advanced thermomechanical tests. In this study, the influence of thermal conditions on microstructure evolution and thermo-mechanical properties including tension, compression was investigated. Additionally, micro-mechanisms of deformation and failure in CGIs were studied at various temperatures and loading conditions by using scanning electron microscopy.
REFERENCES: [1] M. Gorny, M. Kawalec, J. Mater. Effect of titanium addition on microstructure and mechanical properties of thin-walled compacted graphite iron castings, J. Mater. Eng. Perform. 22 (2013), 1519-1524.; [2] V.D. Cocco, F. Locoviello, M. Cavallini, Damaging micromechanisms characterization of a ferritic ductile cast iron. Eng. Fract. Mech. 77 (2010), 2016-2023.; [3] M. Konig, M. Wessen. Influence of alloying elements on microstructure and mechanical properties of CGI. Int. J. Cast Met. Res. 18, 2005, 321-330.

This article deals with the secondary cooling in a continuous caster. In particular, it deals with homogeneity / inhomogeneity in places where surface of slab is partial shielded by rollers and bearing pocket between rollers. Influence of gap between rollers was also considered.
Homogeneity of cooling intensity distribution was experimentally studied in two stages (cold and hot tests).
In the first stage (cold tests) water flow and water distribution was observed optically using a transparent board with studied surface structures (rollers and bearing pockets).
In the second stage (hot tests) the cooling tests with steel plate (fitted with studied structures) were performed. Cooling homogeneity were studied based on temperature distribution of the non-cooled side of sample, which was recorded by infrared camera.

This paper presents intensively cooled ingot during casting and solidification and comparison of obtained results with numerical simulation in Magma 5 software. The technology of intensive cooled ingot has been developed and physically verified in MATERIAL AND METALLURGICAL RESEARCH Ltd. The results of the numerical casting simulation of the cast ingot were obtained in the Magma 5 software, which includes a new module, including the heat transfer through the flowing medium. The 1.3520Mo steel melt was cast in both cases into a V2A ingot mould set, the forging ingot weighing 1,690 kg. Intense heat removal was provided by a cooler placed on a casting plate, which became an integral part of the ingot after melt casting.

A modification to the Metropolis algorithm, which drives Monte Carlo (MC) simulation of grain growth, is suggested here. Though MC simulation allows for study of effects of variables on growth kinetics and growth inhibition in ways not possible by experimentation, the method has been largely limited to the understanding of these phenomena with a generic metal in mind rather than a specific one. During MC simulation, variables such as time, temperature and grain size have only their simulation equivalents considered and are assumed the same for all materials. The present work manipulates the Metropolis algorithm in such a way that it mimics growth kinetics of known metals, as observed through experimentation. We propose Kalale-Bhat-Mukherjee-Kashyap (KBMK) factors, which help yield precise grain growth exponents. This, along with other results relating length and time scales between real and simulated microstructures, can pave the way for an effective Material-Specific MC simulation of grain growth in future.

This paper deals with results of plant experiments aiming achievement of low oxygen concentrations and high micro-cleanness during steel treatment for energetic industry on units of secondary metallurgy. Plants heats were aimed at analysis of influence of slag-making agents, wear of the lining, modification of inclusions, choice of mode of their out-stirring by the help of EMS and Ar blowing. Study of rules of formation, origin and conditions of elimination of non-metallic inclusions during steel treatment in ladle furnace ASEA-SKF was the aim of the experiments. Proper evaluation was made at determination of oxygen concentration together with evaluation of micro-cleanness according by DIN 50 602:1985K4 and ISO 4967 Method A, namely on samples taken from the base and underhead part of the ingot forging. Results present the oxygen concentration, number, ratio and analysis of chemical composition of non-metallic inclusions. Evaluation given in this paper presents the basic information on the achieved micro-cleanness at chosen refining technology. Results in this paper enable to point to the necessity of knowledge of the whole process of refining without that it is not possible to achieve low oxygen concentrations and thus also the high micro-cleanness of steel.