After decades of development of continuous casting the process safety as well as the quality control have reached a high level. Nowadays, quality problems result frequently from singular events under unsteady conditions or on deficiencies with regard to maintenance. Only in particular cases solidification models may still contribute to the solution of quality problems. Necessary requirements are the use of time-dependant local thermal boundary conditions as well as the correct description of phase transformations during solidification and subsequent cooling and finally the coupling with advanced metallurgical models.
After a brief description of the transient 2D-solver based on the modified alternate implicit (M-ADI) method which aims mainly on short computation times and a sufficiently fine grid the presentation will mainly focus on selected peripheral tools:
- The characterization of solidification by micro-segregation models based on local partition coefficients from thermodynamic databases involving the nucleation of inclusions,
- the most accurate definition of thermal boundary conditions by a newly developed nozzle measuring stand and
- finally the quantification of shell deformation limits in order to prevent hot tear segregations or surface cracks.
The paper will illustrate the interaction of the different models, methods and experiments and illustrate the potential for a fast analysis of a continuous casting process with regard to product quality.
A monitoring system of tundish preheat process has been developed for the control of hydrogen content in molten steel at China Steel (CSC). The hydrogen gas accumulated inside the steel matrix may eventually induce pinholes or hydrogen-induced cracking. And the possibilities of hydrogen pick up during casting could be from the atmosphere, tundish lining, or casting powder. Our previous study has already proved that most of the moisture comes from tundish lining. Therefore, preheated tundish was used to avoid moisture pick-up from lining at CSC. An IR-based temperature sensor has been set up to detect tundish shell temperature in this research. The temperature of tundish shell is recorded during the preheat process. It is been noticed that the temperature profile of the preheated tundish shell has a horizontal zone at 100℃. This indicates the moisture of tundish lining is evaporating at that time. When all of the moisture is out of tundish, the temperature of tundish shell will increase with preheating time until casting starts. After compared with the amount of hydrogen pickup in tundish process, the result shows that the hydrogen content in steel will decrease with the highest preheat temperature of tundish shell. When the temperature of tundish shell is higher than 120℃, the amount of hydrogen pickup in tundish is less than 1.5 ppm. Accordingly, in this study, we have built up a quality index for the references of tundish preheat process to reduce the defects of steel product.
The surface roughness plays an important role during spray cooling of hot surfaces in a presence of the boiling. Bubbles are formed in small cavities on the surface during nucleate pool boiling. Enhanced surface roughness causes that more bubbles are formed and it causes increased cooling intensity. The surface with increased roughness has also bigger surface area, which allows higher heat flow between surface and surrounding water.
The influence of the surface roughness during pool boiling was investigated by many authors. The increased surface roughness causes shift of the Leidenfrost temperature to higher temperatures and increases critical heat flux during pool boiling. The influence of the surface roughness during spray cooling of hot surfaces was not still sufficiently investigated and it is not known if the effect of the surface roughness is similar like in a case of the pool boiling.
Experiments for describing the effect of the surface roughness on the cooling intensity were done with water nozzle with flat jet. Test samples were heated in a protective atmosphere at a temperature 730 ºC and then cooled to the room temperature. Test samples were made of the austenitic stainless steel to minimize the forming of the scales on the surface. Results shoving influence of the surface roughness on the critical heat flux and on the Leidenfrost temperature are presented.
In the continuous casting of steel, there is a variety of dynamic situations, both planned such as changing the steel grade, tundish replacement and unplanned such as breakout system interventions, equipment failure, etc. These situations cause variations of the casting parameters such as of the casting speed, casting temperature, intensity of cooling in the secondary cooling zone, etc. An improper configuration of casting parameters can negatively affect the quality of semi-finished products. A real-time tool based on a fuzzy-predictive control algorithm with the 3D dynamic solidification model was created. The real-time predictive control simulation is provided with the use of massive GPU source-code parallelization. Software implementation and integration to the Level 2 automatization system is also presented. Results are presented for the case with a casting-speed drop and for a slab caster with 17 cooling loops in the secondary cooling zone.
The article focuses on the issue of boundary conditions for the simulation of non-steady states in a continuous casting machine. Numerical model of the strand temperature field was implemented in versions of off-line and on-line and is based on the finite difference method. The correctness of the simulation results depends on the accuracy of the boundary conditions. Their determination is technically demanding and costly procedure. Experimental methods can typically obtain only approximate boundary conditions, often the average values in time or in space, rather than the detailed local and immediate values. Modelling of unsteady behaviour of the casting process is therefore loaded with uncertainty. The condition in the mould can be detected by means of measurement directly in the wall using special sensors. However, the sensors cannot be installed permanently in greater numbers. The condition in the secondary cooling area shall be based on the measurement of heat transfer coefficient on the laboratory physical model. Significant complication causes non-linearity of heat transfer coefficient in the secondary cooling area, caused by the Leidenfrost phenomenon. Two causes of the boundary conditions time variations can be distinguished. The first are deterministic, induced by the operator's changes of casting and cooling parameters, the second are random or quasiperiodic changes, caused by spontaneous fluctuations of parameters and internal quantities.
The paper is devoted to verification of solidification of continuously cast round steel billets with a diameter 400 mm in the ProCAST simulation programme. The aim of numerical modelling realized under the conditions of the Department of Metallurgy and Foundry and Regional Materials Science and Technology Centre (RMSTC) at VSB-TU Ostrava is the optimization of the production of continuously cast steel in ArcelorMittal Ostrava a.s. The temperature field, the thickness of the solidified shell, the metallurgical length, the porosity and the risk of hot tearing and cracks were predicted under different boundary conditions of continuous casting. To achieve mentioned results, the different type of the geometry, computational mesh and also a definition of the numerical model was used. The paper describes the pre-processing, processing and post-processing phases of numerical modelling. The advantages and disadvantages of mentioned methods are discussed and possible future developments are outlined.
In the presented work, evaluation and further investigation of previously derived thermodynamic approach for calculation of surface tension of steel was done. Surface tension of pure iron and real steel grades was measured using the sessile drop method up to 1600 °C. Also, surface tension of iron and steels was calculated using thermodynamic approach. Furthermore, calculated and measured values of surface tension were compared and good agreement with difference ca 10 % (and better) was found. Thermodynamic quantities, which are necessary for this thermodynamic approach, were calculated using Thermo-Calc 2015b software with TCFE8 database.
The Metallurgy includes the oldest branch of technology and science of the humanity. Starting with discovering of the first metals till the actual nanostructures and special alloyed materials, the evolution of the metallurgy is fascinating. Connected to this, the evolution of the technical installation, thermal or mechanical, has followed a similar impressing path.
The iron and steel metallurgy had a fast evolution during time. The technical processes are in continuous changing, depending on humanity demands. Therefore, a study of this magnitude, embraces many aspects, including the geographic area. The present article limits only to some milestones regarding the evolution of the thermal aggregates used for iron and steel manufacturing. There are presented some processing technologies of iron ore in Europe, starting with the proto-metallurgy, when the used row material was the meteorite iron, before the human communities learned to exploit the underground storage and the final analyzed period, the 20<sup>th</sup> century. During time, there can be observed the habit and technical differences between historical periods. At the beginning, human believed that everything must remain hidden in the basement, so there were few ones in charge of mines and iron processing. Also, the entire equipment was rudimentary, constructed by wood, burned clay or iron and had specific forms, seemingly a cavity. Later, humanity began to understand the iron ore importance, getting that in 12<sup>th</sup> century to use iron for many activities. Being such a big demand, there has been an evolution of the iron ore processing instruments that has reflected in materials, shape and techniques. The main objective was to ease people’s work and to increase their productivity. The last equipment took into consideration in the present work, were the aggregates disappeared in the 20<sup>th</sup> century, as Siemens-Martin furnaces, used to obtain steel. The article has in view the primary extractive processes, but also processing methods as puddling, forging, casting, and, later, the rolling processes.
In the context of Central European ferrous metallurgy, it is interesting to have a perspective view of the processes evolution, by comparing the rudimentary techniques with the modern ones, to understand better where we come from and where we are heading.
Presence of alkaline elements such as sodium and potassium are highly detrimental for blast furnace operations. Even a trace amount of alkali affects the performance of raw materials considerably. The performance of coke in the process suffers significantly in presence of alkalis by the catalysis of Boudouard reaction during its descent through the shaft and subsequent deterioration of its strength in the lower zone of the furnace, leading to various furnace operating problems. The aim of this work is to investigate the impact of these harmful elements on the coke structure in micro as well as nano level. The Coke Reactivity Index (CRI) and Coke Strength after Reaction (CSR) values of coke are determined for original industrial coke samples as well as the same samples artificially impregnated with alkaline elements in different amounts. The original and CRI-method treated samples (with and without added alkali) are characterized using Scanning Electron Microscopy (SEM), X-Ray Diffractometry (XRD) and Transmission Electron Microscopy (TEM) to look into the lattice and crystalline structure of the constituent graphite of coke. The results demonstrate pronounced disturbance in the graphite lattice caused by alkali. An attempt has been made to explain the mechanism of the deterioration of coke properties under the influence of alkalis in terms of the difference in atomic radii of the constituent elements.
The paper deals with the study of thermo-physical properties of real tool steel grade. The work is focused mainly on phase transition temperatures, particularly liquidus and solidus temperatures determination. These key phase transition temperatures were studied using two thermal analysis methods: “direct” thermal analysis (TA) and Differential Thermal Analysis (DTA). Temperatures of solidus and liquidus are discussed with values used for real casting process and with theoretically calculated temperatures using selected polynomial equations and by SWs, such as Thermo-Calc 2015b version with database TCFE8 and IDS (solidification analysis package). Differences between solidus and liquidus temperatures were encountered between theoretical and experimental values and values used for real casting process. Temperatures of solidus and liquidus were specified with use of thermal analysis methods. Discussion of obtained temperatures is performed with possible impact to the real casting process.
The solidification of liquid steel generally accompanies with different phenomena, like solidification shrinkage and a change of the solubility limit of alloying elements. These phenomena are the base for negative side effects like micro- and macrosegregation as well as the formation of shrinkage cavity and gas porosity. This paper focuses on the formation of shrinkage cavity during solidification of steel through the numerical simulation and experimental validation at ingot casting.
The first part of the paper deals with the performed lab experiments at the Chair of Ferrous Metallurgy. Four different ingots were cast with varying cooling conditions and hot topping configurations. The metallographic examination shows substantial differences between the cast ingots regarding the cavity formation at the ingot center.
Further the used method to predict the formation of shrinkage cavity is briefly described. Thereby the needed solidification parameter for the criterion and the determination of those are discussed. The method is implemented at the numerical model of the lab experiments whereby the solidification software ProCAST was used. The extent of experimentally determined pores is in good agreement with the numerical calculation. Especially the cooling conditions have an influence on the extent of cavity formation which was well reflected from the numerical model. Finally this criterion can be used for other casting process to predict the formation of shrinkage porosities.
To achieve a sound casting of at least acceptable quality many production process parameters must be concerned. One of the most important is a casting design with the particular focus on the gating system. The better the gating system the better casting quality and this is a well known statement. But in many cases it is very difficult and sometimes even impossible to design and make the gating system according to all theoretical and practical rules. So the issue of the gating system optimization is still interesting both from the scientific and practical point of view. In the paper the authors approach to the problem of gating system optimization was presented. The experimental casting was equipped with the typical gating system and with the optimized gating system based on professor John Campbell considerations and theories. Then a computer modeling was performed and the research stand was created and the real mold pouring process was captured by high speed camera. All results were analyzed and compared and some preliminary conclusions were formulated.
In this work there is presented the way how to improve the utility properties of steel cast by alloy layers application (on the base of alloy FeCrC) directly during the process of casting. The way how to forecast the thickness of the surface alloy layer on the cast with the use of simulation program Fluent was described.
Computer simulation was conducted to forecast the distribution of particular elements on cross section of the cast. Thanks to it, it was possible to determine the thickness of obtained layer. The aim of the researches was also the analysis of conducted simulations of alloy layer forming process. There was the attempt to determine the influence of the geometry of the connection surface metal/pad and the grain size (of the pad from FeCrC) on their runs.
Thanks to the analysis of obtained results, it was said that it was possible to forecast initially the distribution of the particular elements on the section cast- surface alloy layer and determine the virtual thickness of the layer with the use of Fluent program.
Nowadays efficient reclamation of used molding sand is a vital part of foundries policies from both economical, technological and environmental-friendly points of view. The ability to use reclaimed sand of proper quality not only allows to save money that would have to be spent on new sand, it also allows the foundry to have smaller storage area and to reduce the negative impact on the environment caused by worn out moulding sand. The purpose of the study was to identify the impact of increased temperature fluidized bed drying of alphaset and floster moulding sand in their reclamation process on the quality of the reclaimed sand. Moulding sand reclamation plant taken into examination used in cast steel and cast iron foundry Odlewnia Staliwa Łabędy utilizes mechanical reclamation process. Part of this process is fluidized bed drying of the sand in 120°C. This article presents the comparison of two obtained reclaims: first with the drying temperature of 120°C, second with room drying temperature. Preliminary research revealed that humidity of the reclaim is not affected whether the temperature is increased or not. To determine and compare the quality of both obtained reclaims their screen analysis and ignition loss was executed alongside with bending and tensile strength tests of moulding sand prepared with the use of two examined reclaims.
Work presents the design, implementation and subsequent analysis of experiments based on theoretical calculation and comparing it with actually achieved degree of reduction in chromium slag. The goal is the reduction of chromium from the slag with a high content of Cr2O3 by using reducing agents in the form of anthracite carbon and silicon in the form of ferroalloys of FeSi. Experimental melting were made in an atmospheric induction melting furnace were performed by using an oxygen fuel burner which was designed a made for those experiments. Average contents of elements in the melt during the reduction amounted to 16% Cr, 5% Ni and 1% Mo. Reduction Technology of chromium from slag was proposed and experimentally realizace for transmission to a big metallurgical unit electric arc furnace.