Seznam abstraktů 2015: SEKCE A - POKROKOVÁ VÝROBA ŽELEZA, OCELI A LITINY

Many metallurgical processes in some moment needs that the specific material in form of chunks, grains, powder, dust etc. must be added. The results and benefits from it depends on the fast and uniform distribution of the introduced material inside the whole volume of the alloy being processed. That is why the method of pneumatic powder injection is widely used to introduce the powdered material of various kinds into the molten alloys. But the problem of particles penetration into the liquid metal is quite complicated and many variables and parameters influence the final result. In the paper the results of the model laboratory research on this problem were presented. The model particles of spherical shape of different dimensions, made of various materials were introduced into water. The geometrical features of the area of particle, entrapped air and water interaction was analyzed. The results were compared to those achieved by other researchers. The results can be then an initial stage to the next research to combine the obtained data with the results of real pneumatic powder injection experiments.

The high silicon cast iron is a very attractive material because of its corrosion and abrasion resistance and also the ability to work at high temperatures. The additional advantage of this material is the low cost of production. Unfortunately, the material, despite the attractive properties, makes considerable inconveniences during the manufacturing process [1, 2]. The applications, these days, are limited to corrosion resistance. It has for example a high resistance in sulphuric acid. But also as electrode for cathodic corrosion resistance, it is still very popular [3]. This material is back slowly for industrial applications but still missing detailed knowledge, for example about the influence of technological parameters on the quality of the alloy, etc. In this paper the research results of crystallization process of alloyed cast iron with high silicon content were presented. Two alloys with a silicon content at 17 and 19% were chosen to research. The results of crystallization process were based on thermal derivative analysis TDA [4, 5]. Using the recorded data a derivative of the temperature variation was calculated, wich allowed the determination of the characteristic points of the crystallization process. The results made it possible to identify the phase transitions in the studied alloys and to describe phases that were shown during the metallographic examination.

Hydrogen may cause severe degradation on some high strength alloys, and although research efforts have intensified in recent years, our understanding of such phenomena still has room for improvement.
For the metallurgical industry it would be useful to have applicable criteria able to predict the risk of hydrogen embrittlement and therefore be able to prevent embritlement damage to industrial products.
Several complex and competing mechanisms are ultimately responsible for hydrogen embrittlement (HIE, AIDE, HELP, HEDE, etc.), although it should be obvious that many embrittlement episodes originate from a localised excess in hydrogen concentration. A physical model of hydrogen diffusion that has been hitherto applied to study the manufacturing of metallic alloys is used in this work to develop and illustrate some useful criteria of embrittlement risk associated to industrial practices.
By estimating the degree of supersaturation at specific regions in the component, and considering microstructure features or mechanical properties, it is possible to anticipate defect formation and embrittlement risk, opening the possibility to prevent it.

The main problem in the production of forgings from tool steels, especially thick plates, blocks, pulleys and rods which are used for special machine components for demanding applications, it is the inhomogeneous structure with segregations, cracks in segregations or complex type of non-metallic inclusions MnS and TiCN. These forgings are actually produced from conventional forging ingots. Due to the size of forgings, it would be interesting the production of these forgings from slab ingots. It is possible that the production of forgings from slab ingots (which are distinguished by a characteristic aspect ratio A / B), it would reduce the occurrence of segregations. The paper presents the verification of the production process of slab steel ingots in particular by means of numerical modelling using finite element method. The paper describes the pre-processing, processing and post-processing phases of numerical modelling. The attention was focused on the prediction of behavior of hot metal during the mold filling, on the verification of the final porosity, of the final segregation and on the prediction of risk of cracks depending on the actual geometry of the mold.

A three-dimensional mathematical model has been developed in order to describe the electromagnetic phenomena in an Electric submerged Arc Furnace (EAF). From the electromagnetics differential equations solution, the current density, Lorentz force and Joule heating was investigated in connection with the slag’s electrical conductivity values. A first approach towards the determination of the slag’s electrical conductivity was attempted using the 3D computational model in time dependent conditions associated with electrical potential and current measurements taken from industrial installations. It was determined that the electrical conductivity of slag was 30 S/m.

On-line dynamic solidification models are widely used for monitoring and control of continuous steel casting. In recent years, there has been an increasing effort for utilization of solidification models. Coupling of models with control algorithms is one of actual trends. The paper presents the use of a solidification model coupled with control algorithms for optimization of secondary cooling. The solidification model provides data to control algorithms, which evaluate an actual thermal state of a strand and control casting parameters such as cooling intensity in secondary cooling zone. Currently, a number of casters and their control systems use so-called cooling curve regulation, which considers cooling intensity as a function of the casting speed. This approach is unfortunately convenient rather for steady-state casting situations. In case of dynamic changes with an altering casting speed, such regulation is very often inappropriate. Another often implemented approach is the usage of PID control. However, PID controllers have many limitations, mainly due to nonlinearity of a controlled system, which is also the case of continuous casting. The paper aims at our recent development of advanced control methods for secondary cooling. A fuzzy logic and model predictive control approaches are tested and compared to traditional PID regulation and cooling curve control. A study case with a dynamic change of the casting speed, which may occur in production, is used to assess control capabilities of developed algorithms. Simulation results show the developed control and regulation tools are robust and effective for control of secondary cooling in continuous casting.

Traditionally, scrap has been the raw materials feed to the electric arc furnace, but increasingly direct reduced iron (DRI), pre reduced pellets and hot briquetted iron (HBI) are being focused as potential alternative charge materials for the electric arc furnace. The partial substitution of scrap by these charge materials directly affecting on the quality of steel and process consumptions in electric arc furnace.
Whereas DRI/HBI products have low contents of copper, nickel, nitrogen, sulfur, etc., they can contain large amounts of phosphorus. Depending upon the quality of ore used to produce the DRI/HBI; these products can contain five to ten times as much phosphorus as scrap. Most commercially available DRI/HBI materials commonly contain between 0.03 to 0.09% phosphorus as compared with 0.015 to 0.02 % for scrap.
The goals of this research are to contribute to a more complete understanding of the behavior of Phosphorus with melting of direct reduced iron (DRI and HBI) having phosphorous content 0.061 wt %, and thermodynamics of phosphorus transfer in metal - slag (or DRI/HBI gangue) systems. The experiments have been conducted at EZZ Flat Steel Company in Egypt, with annual production 1.2 mln. t of hot-rolled flat steel with thickness 1.0–12.0 mm. The thermodynamic and statistical analysis showed that, the dephosphorization reactions sufficiently far from equilibrium, and the continuous feeding of metalized materials (DRI and HBI) hinders the phosphorous removal process and decreases the distribution of phosphorous between slag and metal. For optimum dephosphorization with using the metalized materials having high phosphorus content 0.061 wt %, the slag should have 25-30 % FeO, 4% MgO, slag basicity preferable being between 2.5-3 and temperature – 1625-1635o C.

The paper deals with the study of thermo-physical properties of selected real steel grade. The work is focused mainly on phase transition temperatures and heat capacities, particularly liquidus and solidus temperatures, eutectoid transition, alfa-gamma and magnetic transition. Different thermal analysis methods were used for obtaining of experimental data: Differential Thermal Analysis (DTA), “direct” thermal analysis (TA) and Differential Scanning Calorimetry (DSC). Theoretical study of analysed steel grades was performed using IDS SW (Solidification Analysis Package) and thermodynamic SW Thermo-Calc with database TCFE7. Experimental and theoretical data were compared and discussed.

The article describes an approach to decreasing the rejection rate of the steel plates due to the surface defects in the rolling mill done by optimization of air-water secondary cooling on the continuous casting machine (CCM) of steel. In context with the occurrence of the surface cracks on the steel plates a complex analysis of possible reasons causing the creation of monitored cracks was made. Control of all technological procedures, including setting parameters of the CCM, was introduced. On the basis of statistic evaluation of selected technological parameters and according to the occurrence of specific cracks on the steel plates, of which their character signalize the possibility to create the cracks due to effect of the secondary cooling, the calibration, nozzles replacement and adjustment of the casting parameters in this cooling area was performed. Optimization of secondary cooling adjustment was made for the steel quality S355.

In the presented work, new thermodynamic approach based on fundamental thermodynamics was used for calculation of the surface tension of steel. Surface tension was computed for three steel grades and computed values were compared with experimental values at 1550 °C. Thermodynamic properties, which are necessary for this thermodynamic approach of surface tension, were calculated using Thermo-Calc software with TCFE7 database.

Slag from iron and steel metallurgy can be divided into the blast furnace slag and ladle slag (ladle slag are divided into furnace slag and ladle slag). Slag is a by product of the metallurgical industry and it is the subject of several research. Slag can not be considered as waste material. Slag is a valuable resource because it has a suitable raw material composition. Most of the produced slag is currently utilized material. However a significant proportion of slag is still landfilled. Currently, there are several ways of utilization blast furnace slag and steel slag. Utilization of granulated blast furnace slag is satisfactory. Blast furnace slag is used in the production of cement or concrete. Use of steel slag is difficult and its applications bring a lower value. Slags from steel furnaces are usually processed in less valuable stones. For a specific application slag is besides her origin critical chemical and phase composition, method of processing but also other factors such as its time of landfiling. This article focuses causes of instability slag volume. Next article wil be also paid attention blast furnace slag, ladle slag and used periklas.

Cooling by water sprays is widely used in heat treatment and other metallurgical processes to control the process temperature. Water spray cooling is used statically (without movement of the spray nozzles relative to the cooled object) or dynamically (with the movement). The static regime is typical for quenching systems intended for heat treatment of fixed steel plates. The dynamic regime is used in steel treatment processes such as rolling and finishing in mills. The movement of the steel plate relative to the fixed cooling section causes non-homogeneous distribution of water on the surface of the steel plate. The variability of the cooling section length, position of water nozzles and non-homogeneity of water distribution lead to non-uniform and distorted cooling conditions. Thus it is an important issue to define the impact of these parameters on cooling intensity and the heat transfer coefficient during the cooling process of steel plates. Heat treatment of high-temperature steel is held without protective atmosphere and is accompanied by growth of different oxides on the steel plate surface as well. The layer of oxides significantly affects the cooling regime and intensity. The influence of the oxide scales on the cooling intensity was studied experimentally and by numerical modeling for different cooling regimes. Experiments were conducted for static and dynamic regimes on surfaces with different rate of oxides layer. Prepared numerical analysis simulates the process with different conditions of the cooling section and samples with different oxide scale layers. Results obtained by numerical simulation approved the impact of the oxide layer on the cooling intensity and shown different character in the static and the dynamic regime.

This work studies the influence of precipitation on branched crack formation in the surface skin of continuously-cast slabs of Ti-Nb HSLA steel. Two slabs were analysed, cast at pulling rates of 0.43 m.min-1 and 1.03 m.min-1. The results show that branched cracks are located on the slab with pulling rate 0.43 m.min-1, extending to a depth of 10 mm below the slab surface and occurring mostly below oscillation marks. In the case of the slab cast at pulling rate 1.03 m.min-1 branched cracks did not occur. Evaluation of precipitates obtained by the method of carbon extraction replicas on selected samples confirmed the presence of predominantly spherical or elliptical particles. Square particles were observed in small amounts. Application of selection electron diffraction showed the presence of TiC and NbC carbides. Formation of cracks is influenced by the size of precipitate particles, but also by morphology and distribution of precipitates. It is known that elliptical precipitates have significantly worse effects than spherical precipitates, even when significantly smaller and fewer in number. Globular particles also influence formation of surface cracking, but only when they occur in steel at high volumes or very large size. It is also known that precipitates arranged in rows on grain boundaries cause surface cracking. In this work the slab cast at the lower pulling rate 0.43 m.min-1 showed the presence of adverse precipitates and also rows of excluded precipitates on grain boundaries, which are considered responsible for the observed branched cracks. The formation of branched cracks is conditioned not only by segregation of impurities, but possibly also by the presence of undesirable brittle cementite networks. The presence of cementite was confirmed not only through microstructural analysis, but also diffraction of hard X-ray radiation. This diffraction revealed a branched crack in the sample část at pulling rate 0.43 m.min-1 including the presence TiC and Fe3O4, the amounts of which were comparable to the amount of Fe3C in the analyzed area. On a sample without occurrence of branched cracks at pulling rate 0.43 m.min-1, there was only Fe3C in detectable amounts. It is known that precipitation of microalloying elements in connection with cementite can lead to higher probability of surface crack formation, as also confirmed in this study.