Miloš Masarik - Academia.edu (original) (raw)

Papers by Miloš Masarik

Continuously cast steel slabs, classified as flat products, find their use across the entire mach... more Continuously cast steel slabs, classified as flat products, find their use across the entire machine-engineering industry. The final products made of continuously cast steel slabs include metal sheets for shipbuilding industry, bridge structures, transport machines, pressure vessels, flame-cutting shape cuts, and pipelines. High-quality final products production requires the continuous cast steel slabs to be manufactured with accurate chemical composition, precise slab shape, high internal purity, and flawless slab outer surface. Any surface defects of continuously cast steel slabs impact the final surface of metal sheets and their mechanical properties. The surface defects initiated already in the mould may further develop by improperly set secondary cooling.

Komunikácie, Dec 31, 2012

Nomenclature a thermal diffusivity, m 2 .s Ϫ1 c specific heat capacity, J.kg Ϫ1 .K Ϫ1 i v specifi... more Nomenclature a thermal diffusivity, m 2 .s Ϫ1 c specific heat capacity, J.kg Ϫ1 .K Ϫ1 i v specific volume enthalpy, J.m Ϫ3 Q heat flow, W Q source internal heat source, W.m Ϫ3 T temperature, °C V volume, m 3 x,y,z axes in given direction w shift rate, m.s Ϫ1 λ heat conductivity, W.m Ϫ1 .K Ϫ1 τ time , s ρ density, kg.m Ϫ3 The solidification and cooling of a concasting and simultaneous heating of the crystallizer is a very complicated problem of 3D

Prace Instytutu Metalurgii Żelaza, 2009

The so called secondary cooling zone is an important part of the CCM. In this zone a breakout may... more The so called secondary cooling zone is an important part of the CCM. In this zone a breakout may occur due to an increase of the local and temperature heterogeneity of steel, due to an increase of the stress caused by bending of the slab and by high local concentration of non-metallic slag inclusions. Changes of the chemical composition of the steel during continuous casting are particularly dangerous. In the event that two melts are cast one right after another, i.e. if the melt of the steel with chemical composition A ends and it is immediately followed by the steel B, it may automatically stop the CCM and an at ypical breakout may take place. With use of dimensional analysis altogether 8 criteria of similarity were derived according to the π theorem. Important data in temperature field of the slab were calculated by the original model. Numerical values of eight criteria were determined for the steels A and B. This application of the theory of physical similarity clearly proved m...

Abstract. The paper summarizes the basic analytical and empirical findings obtained during search... more Abstract. The paper summarizes the basic analytical and empirical findings obtained during search of dependences of the influence of thermal process taking place during continuous casting of steel semi-finished products – slabs on their quality. The assessment of the quality of slabs uses the collected data and stores them for an effective evaluation of the measured qualitative quantities. The paper describes the proposal of the concept of solution and the function of software for thermal process assessment of the slab casting. Further analyses of possibilities of use of statistical methods for the assessment of the slab casting process are carried on with the possibility of slab quality prediction. The aim of the proposal of the above mentioned process is to provide to technological workers not only the possibility to analyze the process of casting, but also the long-time monitoring and optimization of the production. This approach brings at the process of slab casting important ec...

WIT transactions on engineering sciences, 2005

This paper deals with surface morphology, the mechanism of origination and causes of cross cracki... more This paper deals with surface morphology, the mechanism of origination and causes of cross cracking of a concast low alloy manganese steel slab. The cross cracking was identified in a steel slab with a sectional size of 145x1300 mm and the length of the asymmetrical cracking was approximately 600 mm. The light microscopy and the scanning electron microscopy have been applied for determination of the metallographic structure of steel and for the study of micro-morphology and the trajectory of cracking. The chemical microheterogeneity of the steel matrix and the surface of cracking have been estimated by means of an X-ray micro-analyser JEOL JXA 8600/KEVEX. The analyses of Al, Si, P, Ti, Cr, Mn and Fe on the metallograpic samples of the matrix of steel, of the neighbourhood of cracking and of the surface of cracking have been realized. It has been found that the cross cracking is characterized by high macro-heterogeneity of manganese, carbon and sulphur. The causes of cross cracking h...

The paper presents heterogeneous chemical composition of the steel slab, which was determined dur... more The paper presents heterogeneous chemical composition of the steel slab, which was determined during short-time operation of continuous casting machine after flying tundish change. Before this exchange the steel A was cast (0.41 wt.% C and 0.95 wt.% Cr), shortly after the exchange continuous casting of the steel B (0.17 wt.% C and 0.70 wt.% Cr) started. After 20 minutes the continuous casting machine automatically stopped, because in the straightening zone, between the 7 th and the 8 th segment a breakout had occurred. Part of the slab was taken from the place of breakout for more precise determination of the position of breakout. It served also for taking the test samples for analysis of local chemical composition. It was expected that basic information on chemical heterogeneity of both steels A and B will be obtained, as well as information on exchange of mass between these two steels, which occurred some 20 minutes before stopping of the continuous casting machine. The reason was...

Materiali in Tehnologije

Electromagnetic stirring (EMS) applied on a steel caster (concasting machine) is basically a magn... more Electromagnetic stirring (EMS) applied on a steel caster (concasting machine) is basically a magneto-hydraulic process that influences the crystallisation processes and the solidification of billet steel. From the viewpoint of physics and chemistry, the course of the process is co-determined by a number of relevant parameters, the physical and thermokinetic characteristics of the contrast steel and also the electrical and magnetic quantities. EMS suppresses the growth of columnar crystals of billets and reduces, the tendency to crack during casting and at low temperatures. A caster was used for the testing of two induction stirrers one on the, actual mould and the other beneath the mould to determine the effect of EMS on the formation of the structure of non-alloyed steel. As part of these tests, certain parts of the billets had been cast without the use of stirrers, while other parts underwent alternate switching on and off of the stirrers for as many as nine combinations of modes....

Fatigue & Fracture of Engineering Materials & Structures, 2013

so-called secondary cooling zone is an important part of the continuous casting machine. In this ... more so-called secondary cooling zone is an important part of the continuous casting machine. In this zone, a breakout may occur because of an increase of the local and temperature heterogeneity of steel, resulting from an increase of the stress caused by bending of the slab and by high local concentration of nonmetallic slag inclusions. Changes of the chemical composition of steel during continuous casting are particularly dangerous. In the event that two melts are cast one after another, that is, if the melt of steel with chemical composition A ends and is immediately followed by the steel B, it may automatically stop the continuous casting machine, and an atypical breakout may take place. It has happened during continuous casting of the slab, 250 Â 1530 mm in the area of straightening, 20 min after flying change of tundish. In the present paper, by employing the dimensional analysis, eight dimensionless numbers are derived. If the values of these dimensionless numbers for two followed steels significantly differ, the atypical breakout may take place.

Surface temperatures of cast slabs at small radius segments in front of as well as at the unbendi... more Surface temperatures of cast slabs at small radius segments in front of as well as at the unbending point belong to parameters that affect the surface quality of continuously cast slabs. Older machines for continuous casting were designed with regard to the performance (to amount of cast slabs) rather than to the quality. Therefore, the adaptation of secondary cooling is required in order to accomplish the desired surface temperatures. The modification consists in the dynamic control of secondary cooling, surface temperatures monitoring by means of the numerical model of temperature field as well as in a prospective replacement of cooling nozzles. In order to optimize and control the secondary cooling, characteristics of nozzles and especially the influences of water flow rate, air pressure, casting speed and surface temperatures to the heat transfer coefficient under nozzles have to be known. Moreover, the heat transfer coefficient can be also influenced by the age of nozzles. The ...

Original numerical model was applied to the simulation of the temperature field of concast steel ... more Original numerical model was applied to the simulation of the temperature field of concast steel slab, when melt of steel of quality A finished and immediately the melt of quality B followed. In the secondary-cooling zone in the unbending point, the breakout of the steel can occur in points of increased local chemical and temperature heterogeneity of the steel. The temperature field of the slab was calculated for three variants of the chemical composition. The first variant is for the chemical composition of steel quality A, the second for the chemical composition of steel quality B and the third for the average chemical composition from quality A and quality B. The temperature model was provides the temperature history of every points of a cross-section during its movement through the whole caster from the level of the melt in the crystallizer to the cutting torch, the course of isoliquidus, isosolidus and next isotherms, further temperature isozones. Heat transfer coefficient bene...

Nowadays, continuous casting (CC) is used for providing almost one hundred percent of steel world... more Nowadays, continuous casting (CC) is used for providing almost one hundred percent of steel world production. The control of quality in CC products cannot be achieved without the knowledge of heat transfer and solidification of cast slabs. The solidifying slab passing through the caster is subjected to variable thermal conditions and mechanical stresses which can cause many serious defects in final structure of slabs. These defects might be eliminated by the optimal control of casting process. This paper describes an algorithm used to obtain time dependant casting parameters for stabilization of the casting process where high productivity is preserved. The presented algorithm can be used in two regimes. The first regime (off-line) can be used to find the control parameters such the casting speed and cooling intensities in the secondary cooling zone in order to get slab surface and core temperatures in specific ranges. The second regime allows the on-line regulation, stabilization of...

Materials and Technologies

Prejem rokopisa – received: 2012-08-31; sprejem za objavo – accepted for publication: 2012-10-23 ... more Prejem rokopisa – received: 2012-08-31; sprejem za objavo – accepted for publication: 2012-10-23 Surface temperatures of cast slabs on small-radius segments as well as on the unbent areas belong to the parameters that affect the surface quality of continuously cast slabs. Older machines for continuous casting were designed with regard to the quantity (the amount of cast slabs) rather than the quality of the production. Therefore, an adaptation of the secondary cooling is required in order to obtain the desired surface temperatures. The modification consists of a dynamic control of the secondary cooling, surface-temperature monitoring by means of a numerical model of the temperature field as well as a prospective replacement of the cooling nozzles. In order to optimize and control the secondary cooling, characteristics of the nozzles, especially the influences of the water-flow rate, air pressure, casting speed, surface temperatures and heat-transfer coefficient under the nozzles hav...

Surface Effects and Contact Mechanics X, 2011

The solidification and cooling of a continuously cast slab and the simultaneous heating of the mo... more The solidification and cooling of a continuously cast slab and the simultaneous heating of the mold is a very complicated problem of three-dimensional transient heat and mass transfer. The solving of such a problem is impossible without numerical models of the temperature field. Experimental research and measurements must be carried out simultaneously with numerical computation. An important area of the caster is the so-called secondary cooling zone, which is subdivided into thirteen sections. In the secondary cooling zone, where the slab begins to straighten, a breakout of the steel can occur at the points of increased local chemical and temperature heterogeneity of the steel, due to increased tension resulting from the bending of the slab, and also due to high local concentration of non-metallic, slag inclusions. The changes in the chemical composition of the steel, during the actual continuous casting, are especially dangerous. In the case of two immediate consequent melts this could lead to immediate interruption of the continuous casting and to a breakout. The temperature field of a slab was calculated by means of original numerical model before, as well as after the breakout and the calculated parameters were collected. If the dimensionless analysis is applied for assessing and reducing the number of these parameters, then it is possible to express the level of a risk of breakout as the function of five dimensionless criteria.

AIP Conference Proceedings, 2010

ABSTRACT The paper describes the original proposal of ways of solution and function of the progra... more ABSTRACT The paper describes the original proposal of ways of solution and function of the program equipment for assessment of the process of casting slabs. The program system LITIOS was developed and implemented in EVRAZ Vitkovice Steel Ostrava on the equipment of continuous casting of steel (further only ECC). This program system works on the data warehouse of technological parameters of casting and quality parameters of slabs. It enables an ECC technologist to analyze the course of casting melt and with using statistics methods to set the influence of single technological parameters on the duality of final slabs. The system also enables long term monitoring and optimization of the production.

Key Engineering Materials, 2011

ABSTRACT In the secondary-cooling zone, where the slab is beginning to straighten out the breakou... more ABSTRACT In the secondary-cooling zone, where the slab is beginning to straighten out the breakout of the steel can occur in points of increased local chemical and temperature heterogeneity of the steel, from increased tension as a result of the bending of the slab and also from a high local concentration of non-metal, slag inclusions. Especially dangerous are the changes in the chemical composition of the steel during the actual concasting. In the case of two melts one immediately after the other, this could lead to immediate interruption in the concasting and a breakout. The material, physical, chemical and technological parameters, which both melts differed in were determined. If the dimensionless analysis is applied for assessing and reducing the number of these parameters, then it is possible to express the level of risk of breakout as a function of five dimensionless criteria.

Materials Science Forum, 2005

Solidification and cooling of a continuously cast steel slab and the heating of the mould is a ve... more Solidification and cooling of a continuously cast steel slab and the heating of the mould is a very complicated problem of transient heat and mass transfer. This original three-dimensional (3D) numerical model is capable of simulating the temperature field of a caster. The numerical computation has to take place simultaneously with the data acquisition—not only to confront it with the actual numerical model, but also to make it more accurate throughout the process. The utilization of the numerical model of solidification and cooling plays an indispensable role in practice. An important step in this analysis is to determine the necessary quantities in the course of concasting. The software enables data acquisition in real time, which is necessary for optimization. This is ensured by the correct process procedure: real process → input data → numerical analysis → optimization → correction of process. This procedure is necessary for optimization (i.e. maximization of the quality of the ...

The surface temperature on the small radius surface in positions of straightening is an important... more The surface temperature on the small radius surface in positions of straightening is an important parameter that can influence the surface quality of continuously cast steel slabs. Based on the detailed analysis the replacement of cooling nozzles pertaining to the small radius surface in the secondary cooling was performed on the caster in Evraz Vitkovice Steel due to the requirement on the increase of surface temperatures on the small radius surface of cast slabs. The results and experiences obtained after the replacement of cooling nozzles are compared to long-time operational data for the preceding setup of cooling nozzles that are used on the caster since 1995. The comparison is performed with the use of data acquired from the dynamic solidification model and with the use of the statistical operational data. The optimization of cooling nozzles setup is also discussed in the paper.

Production quality control of slabs continuously cast on the continuous casting machine (CCM) for... more Production quality control of slabs continuously cast on the continuous casting machine (CCM) forms an integral part of the metallurgical plant information system. The main premise for this process is data collection and archiving of the necessary data for an effective assessment of production and determination of dependencies between the measured and qualitative data. The article describes the proposal of the concept of solution and gives an overview of functions of the software for evaluation of thermal processes at slab casting. The example of such solution is the original software system LITIOS, which together with temperature model provides comfort of services for optimisation of parameters for casting of slabs above standard. The system makes it possible to technologists to analyse the course of casting of heats with use of mathematical and statistical methods. Moreover this software analytical tool gives to CCM operators a possibility not only to evaluate in a complex manner ...