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The effects of the change of chemical composition and temperature on the viscosity of CaO-Al2O3-SiO2 oxide system with basicity from 0.78 to 1.63 were investigated in this paper. Experimental measurements of viscosity were performed with use of the high-temperature viscometer Anton Paar FRS 1600. Viscosity was measured in a rotational mode during heating at the rate of 2.2 K/min in the temperature interval from 1673 to 1873 K. Viscosity is often sensitive to the structural changes in molten oxide systems, which implies that the analysis of viscosity is an effective way to understand the structure of molten oxide systems. Exact clarification of the change of structure of the oxide system caused by increased content of CaO was performed by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction (XRD). Web of Science 60 4 2878 2873 more...

This paper is focused on a study of the interfacial tension between selected oxide and metal phases. The experimental research on the interfacial tension was performed in a horizontal resistive graphite Tamman furnace using an original method of measuring. This method consists of fixing both liquid phases in a horizontal position using a mandrel made of tungsten wire in a corundum cover. In this work the influence of the carbon content in the steel on the interfacial tension was studied. For this purpose a steel with 0.411 % of mass fraction of carbon and a steel with 2.64 % of carbon were used. Because of the wide variety of oxide systems used in industry, a characteristic system of casting powder was chosen for this study. This system contains dominant components, i.e., SiO2, CaO, Al2O3 and MgO, as well as a range of attendant mixtures, e.g., Fe2O3, TiO2 and Na2O. Simultaneously, the influence of SiO2 on the temperature dependence of the interfacial tension was observed. For this reason a concentration series with gradual additions of SiO2 was created. It was found that an increasing content of carbon in the steel significantly decreases the interfacial tension between the oxide system and the steel. The interfacial tension was found to decrease slightly with an increase in the content of SiO2 in the oxide system. Članek predstavlja študijo medfazne napetosti med izbranim oksidom in kovinsko fazo. Določanje medfaznih napetosti je bilo izvršeno z originalno metodo v horizontalni uporovni grafitni Tammanovi peči. Ta metoda sestoji iz zadržanja obeh talin v horizontalnem položaju s trnom iz volframove žice in korundnega pokrova. V tem delu je bil preučevan vpliv ogljika v jeklu na medfazno napetost. Uporabljeno je bilo jeklo z masnim deležem 0,411 mas. % ogljika in jeklo z 2,64 % ogljika. Zaradi velike raznolikosti oksidnih sistemov, ki se uporabljajo v industriji, je bil za študij izbran livni prašek. Ta vsebuje glavne komponente, ki so SiO2, CaO, Al2O3 in MgO, ter vrsto primesi, kot so na primer Fe2O3, TiO2 in Na2O. Hkrati je bil opažen vpliv SiO2 na temperaturno odvisnost medfazne napetosti. Zato je bila pripravljena serija z naraščajočo vsebnostjo SiO2. Ugotovljeno je, da naraščanje vsebnosti ogljika v jeklu občutno zmanjša medfazno napetost med oksidnim sistemom in jeklom. Za medfazno napetost je ugotovljeno, da se nekoliko zmanjša, če se povečuje vsebnost SiO2 v oksidnem sistemu. more...

The knowledge of the solidus and liquidus temperatures of the real-steel grades is one of the most important technological factors - especially when dealing with the processes of casting and solidification. These temperatures are critical parameters for proper settings of the models (physical or numerical) or in the final stage of an applied research of a real process. A correct setting of a production technology is significantly affecting the final quality of the as-cast steel (billets or ingots). Therefore, this paper is devoted to discussing the findings obtained during a utilization of dynamicthermal-analysis methods to identify the solidus and liquidus temperatures applicable to commercially produced steels. The results obtained with a differential thermal analysis (DTA) for three steel grades and with 3D differential scanning calorimetry (3D DSC) for two steel grades are compared with the results of the selected equations commonly used for liquidus and/or solidus temperature calculations. The calculations obtained with the Computherm SW for the discussed steels were also realized. It can be stated that the equilibrium liquidus and solidus temperatures obtained with the above-mentioned methods for each steel grade differ. The differences between the calculated results, the thermodynamic calculations and thermal-analysis results are very unpredictable and vary individually for different steels. These differences are not marginal (tens of Celsius degrees). So, it is sometimes suitable to combine several methods for a proper determination of the liquidus and solidus temperatures for a correct setting of a steel-making process or its modelling. The best solution for a technological process is to obtain the liquidus and solidus temperatures for a concrete-steel grade from agiven steelmaking practice - a thermal analysis of a concrete-steel grade is a possible way. Poznavanje solidusnih in likvidusnih temperatur realnih jekel je med najpomembnejšimi tehnološkimi dejavniki - še posebno pri obravnavi procesov med ulivanjem in strjevanjem. Te temperature so kritični parametri za pravilno postavitev modela (fizikalnega ali numeričnega) ali pri končni stopnji raziskav realnega procesa. Pravilna postavitev proizvodne tehnologije pomembno vpliva na končno kvaliteto ulitega jekla (gredic in ingotov). Zato je ta članek namenjen razpravi o ugotovitvah, dobljenih med uporabo metod dinamične termične analize za ugotavljanje solidusne in likvidusne temperature pri komercialno proizvedenih jeklih. Rezultati, dobljeni z diferenčno termično analizo (DTA) za 3 jekla in s 3D diferenčno vrstično kalorimetrijo (3D DSC) za 2 vrsti jekel, so bili primerjani z rezultati iz izbranih enačb, ki se navadno uporabljajo za izračun temperature solidusa in likvidusa. Za obravnavana jekla so bili tudi izdelani izračuni s Computherm SW. Ugotovljeno je bilo, da se ravnotežne likvidusne in solidusne temperature, dobljene z omenjenimi metodami, razlikujejo. Razlike med izračunanimi rezultati, termodinamičnimi izračuni in rezultati termične analize so nepredvidljivi in se različno spreminjajo pri različnih jeklih. Te razlike niso nepomembne (desetine stopinj Celzija). Zato je včasih pomembno kombinirati več metod za pravilno določitev likvidusne in solidusne temperature pri procesu proizvodnje jekla ali njegovem modeliranju. Najboljša rešitev za tehnološki proces je ugotavljanje likvidusne in solidusne temperature pri konkretnem jeklu iz dane jeklarske prakse - mogoča pot pa je tudi s termično analizo konkretnega jekla. more...

The paper deals with the study of phase transformation temperatures of the model Fe–C–O based metallic alloys in the high temperature region (above 1,000 °C). Six model alloys with graded carbon and oxygen content were prepared and studied. Temperatures of phase transitions were obtained using DTA method (differential thermal analysis). The Setaram SETSYS 18™ (TG/DTA/DSC/TMA) modular experimental system was used for measurements. Influence of composition change (carbon and oxygen content) on shift of phase transformation temperatures is investigated in this paper. New original data (phase transformation temperatures) were obtained in this study. Controlled heating of the alloys was conducted at the rates of 2, 4, 7, 10, 15 and 20 °C min−1. Comparison of the obtained experimental data with the data presented in the literature was also carried out. It follows from comparison of the obtained results with the data accessible in the literature that a lack of experimental data exists, and these available data significantly differ. Web of Science 112 1 741 465 more...

The paper deals with a new approach to measuring and evaluating the chemical micro-heterogeneity of the elements in solidified poly-component metallic systems. The original approach is based on experimental measurements made on the samples taken from characteristic places in a casting and the subsequent application of an original mathematical model for determining the element-distribution profile, characterizing the most probable distribution of an element concentration in the frame of a dendrite, and an original mathematical model for determining the effective partition coefficients of these elements in the structure of the analyzed alloy. The paper also describes an application of this method in the research of the chemical heterogeneity on a cross-section of a CC steel slab and presents the selected results (indices of the heterogeneity and effective partition coefficients of seven analyzed elements) characterizing the chemical micro-heterogeneity on one-half of the cross-section of this CC steel slab. The following main results were obtained: (i) the dendritic heterogeneity of the accompanying elements and impurities is comparatively high; (ii) all the analyzed elements segregate during the solidification into an inter-dendritic melt, and their partition coefficient is smaller than one; (iii) the effective partition coefficients calculated in this new way inherently include both the effect of segregation in the course of an alloy solidification, and the effect of the homogenization occurring during the solidification as well as during the cooling of an alloy. Članek obravnava nov način merjenja in ocenjevanja kemijske mikroheterogenosti elementov v večkomponentnih kovinskih sistemih. Izviren način temelji na eksperimentalnih meritvah, narejenih na vzorcih, vzetih iz značilnih mest ulitka, in uporabi izvirnega matematičnega modela za določanje profila razporeditve elementov, kar omogoča oceno najbolj verjetne razporeditve koncentracije elementov v dendrite in določanje efektivnega koeficienta razporeditve teh elementov v strukturi analizirane zlitine. Članek opisuje tudi uporabo te metode pri raziskavi kemijske heterogenosti prečnega prereza kontinuirno ulitega slaba in predstavlja izbrane rezultate (indeks heterogenosti in koeficiente razporeditve sedmih analiziranih elementov) značilne kemijske mikroheterogenosti polovice prereza kontinuirno ulitega slaba. Glavni rezultati so: (i) heterogenost spremljajočih elementov in nečistoč je razmeroma velika; (ii) vsi analizirani elementi izcejajo med strjevanjem v meddendritno talino, njihov koeficient razporeditve je manjši odena; (iii) na nov način izračunani koeficienti razporeditve vključujejo v sebi oba učinka, to je učinek izcejanja med potekom strjevanja in učinek homogenizacije, ki se pojavi med strjevanjem, in nadaljnjim ohlajanjem zlitine. more...

The paper is devoted to selected aspects of the current issues of the high-temperature interaction of the synthetic multicomponent oxidic systems and selected grades of steel. Analysing the consequences of the interaction between slag and molten steel is an integral part of modern research that can be connected with subsequent, applied research in the field of producing and refining steel. The interactions between the synthetic slag and the molten metal is realized after the processing of the liquid steel in the primary metallurgical aggregates, i.e., at the beginning of refining processes of secondary metallurgy. The addition of these synthetic systems (slag) significantly affects many technological processes and indirectly affects the final quality of the cast steel. This influence can be seen on two levels: the metallurgical and the metallographic. Both of these levels of evaluation complement each other. For the evaluation of the metallurgical aspects of refining processes a number of thermodynamic relations were used, supplemented by empirically established formulas and coefficients. Metallographic analyses utilize modern tools in the study of the structure and the chemical composition of materials, i.e., from light microscopy to sophisticated systems of microanalysis of elemental composition using a scanning electron microscope combined with an energy-dispersive X-ray micro-analyser. It is obvious that this area deserves more focused research and more attention, particularly in the context of the on-going needs for the identification and quantification of phenomena taking place in the following metallurgical innovations. Članek obravnava izbrane vidike aktualnih vprašanj o visokotemperaturni interakciji sintetičnih večkomponentnih oksidnih sistemov v izbranih vrstah jekel. Analiziranje posledic interakcije med žlindro in talino je sestavni del potekajočih raziskav in se lahko poveže z uporabnimi raziskavami na področju proizvodnje in rafinacije jekla. Do interakcije med sintetično žlindro in staljeno kovino pride po izdelavi taline jekla v primarni metalurški peči, na začetku postopka rafinacije v sekundarni metalurgiji. Dodatek sintetične žlindre močno vpliva na številne tehnološke procese in neposredno vpliva na končno kvaliteto ulitega jekla. Ta učinek se kaže na dveh nivojih: na metalurškem in metalografskem. Oba nivoja ocene sta med seboj komplementarna. Za oceno metalurških vidikov postopka rafinacije je bilo uporabljeno več termodinamskih odvisnosti, dopolnjenih z empirično določenimi enačbami in koeficienti. Metalografska analiza uporablja sodobna orodja za študij strukture in kemijske sestave materiala - od svetlobne mikroskopije do zapletenih sistemov mikroanalize, elementne sestave z uporabo vrstičnega elektronskega mikroskopa v kombinaciji z energijsko disperzijsko rentgensko spektroskopijo. Očitno to področje zahteva bolj usmerjene raziskave in večjo pozornost, posebno v kontekstu zahtev, identifikacije in kvantifikacije pojavov, ki so posledica metalurških inovacij. more...

The quality of the working rollers used for rolling rails is determined by the chemical and structural compositions of the material of the rollers and the production technology. It is necessary to cast rollers with significantly improved utility properties, i.e., mainly a high wear resistance and optimal mechanical and structural properties. It is, therefore, necessary to find and ensure the optimal relationships between the matrix structure and the resulting values of the mechanical properties of the rollers in order to maximize their life time. The requirements introduced here cannot be ensured without a knowledge of the kinetics of the solidification. Therefore, numerical and experimental investigations of the temperature field of the solidifying roller were conducted. The kinetics of the solidification has a measurable and non-negligible influence on the chemical and structural heterogeneity of the investigated type of ductile cast-iron. Linking to the results of the model of the temperature field of the cast rollers, an original methodology was developed for the measurement of chemical micro-heterogeneity. The structure of this cast-iron is created by a large amount of the transition form of graphite and a small amount of globular graphite, and also the lamellar graphite and cementite, whereas the structure of the metal matrix is perlitic. The volume amounts of the structural components were determined using a quantitative metallographic analysis, according to which the places for the analysis of the element composition using X-ray energy-dispersive spectral micro-analysis were selected. The chemical and structural heterogeneity of the cast roller is, therefore, a significant function of the method of melting, modification and inoculation and the successive procedures of risering, casting and crystallization after cooling. Kakovost delovnih valjev za valjanje tirnic je določena s kemijsko in strukturno sestavo materiala za valje in s tehnologijo proizvodnje. Potrebno je ulivati valje z znatno povečanimi koristnimi lastnostmi, kot so obrabna odpornost in optimalne mehanske in strukturne lastnosti. Tako je treba ugotoviti in zagotoviti optimalne odnose med strukturo matrice in rezultirajočimi vrednostmi mehanskih lastnosti valjev za maksimiranje trajnostne dobe. Zahteve, ki so tu predstavljene, ne morejo biti zagotovljene brez znanja kinetike strjevanja. Zato je bila vpeljana numerična in eksperimentalna raziskava temperaturnega polja valja pri strjevanju. Kinetika strjevanja ima merljiv in ne brezpomemben vpliv na kemijsko in strukturno heterogenost raziskovanega gnetljivega litega železa. Glede na rezultate modela temperaturnega polja ulitih valjev je bila razvita originalna metodologija za merjenje kemijske mikroheterogenosti. Struktura tega ulitega železa je bila ustvarjena z veliko količino prehodnih oblik grafita in manjših količin kroglastega grafita in cementita, medtem ko je struktura kovinske osnove perlitna. Volumenska količina strukturnih komponent je bila določena s kvantitativno metalografsko analizo, po kateri so bila izbrana mesta za rentgensko analizo sestave ter spektrografsko mikroanalizo. Kemijska in strukturna heterogenost ulitih valjev je pomembna funkcija pri taljenju in modificiranju ter za uspešno ulivanje in kristalizacijo po ohlajevanju. more...

The quality of the working rollers used for rolling rails of different profiles is determined by the chemical and structural composition of the material of the rollers and the production technology The requirements for the quality cannot be ensured without a perfect knowledge of the course of the solidification, the cooling and the heat treatment of the cast rollers as well as the kinetics of the temperature field of the casting and the mould. The solidification and cooling of the ductile-cast-iron roller in metal and non-metal moulds is a very complicated problem of heat and mass transfer with the phase and structural changes described by the Fourier equation. An original application of ANSYS simulated the forming of the temperature field of the entire system, comprising the casting, the mold and the ambient. The simulation of the release of the latent heats of the phase or structural changes is carried out by introducing the thermodynamic enthalpy function. In the experimental investigation of the temperature field, an original methodology for the measurement of the distribution of temperatures and heat flows in the roller-mould system had been developed and verified in operation. In the design of the original procedure, there were a number of problems connected with the large size of the roller and the mould, the uneven dimensional changes of the solidifying roller and the mould, the installation and the insulation of the thermocouples, the wiring of the thermocouple system, etc. The findings regarding the kinetics of the temperature field of the roller and the mould, obtained from experimental research, were used to determine the boundary conditions and for the verification of the numerical simulation program. The calculation of the temperature field focused on an analysis of the effect of the mould separator on the course of the solidification of the roller. The results of the mathematical modelling indicate that the distribution of the temperatures and the solidification in the vertical direction is significantly uneven - and this has an effect on the internal quality of the casting. Kakovost delovnih valjev za valjanje železniških tirnic različnih profilov je določena s kemijsko sestavo, mikrostrukturo in s proizvodno tehnologijo. Zahteve za kakovost ni mogoče zagotoviti brez popolnega poznanja poteka strjevanja, ohlajevanja in toplotne obdelave ulitih valjev ter kinetike temperaturnega polja ulitka in forme. Strjevanje in ohlajevanje ulitega valja, ki je ulit iz sive litine s kroglastim grafitom v kovinsko in nekovinsko formo, je zelo zapleten problem z vidika prenosa toplote in mase s faznimi in strukturnimi spremembami, ki jih opisuje Fourierjeva enačba. Z uporabo programskega paketa ANSYS-a je bilo simulirano temperaturno polje celotnega sistema, ki obsega ulivanje, formo in okolje. Simulacija prenosa latentne toplote faznih in strukturnih sprememb se izpelje z uporabo termodinamične funkcije entalpije. Pri eksperimentalni raziskavi temperaturnega polja je bila razvita izvirna metodologija za merjenje temperaturnega polja in toplotnega toka v sistemu valj - forma. V konstrukciji izvirnega postopka so številni problemi vezani z velikostjo valjev in forme, neenako dilatacijo pri strjevanju valja in forme, namestitvi in izolaciji termočlenov, napeljavi sistema termočlenov itd. Ugotovitve glede na kinetiko temperaturnega polja valja in forme, dobljene z eksperimentalnimi raziskavami, so bile uporabljene za določitev mejnih pogojev ter za potrditev numeričnega programa simulacije. Izračun temperaturnega polja je bil osredinjen na analizo učinka separatorja forme na potek strjevanja valja. Rezultati matematičnega modeliranja kažejo, da je porazdelitev temperatur in strjevanja v navpični smeri neenaka, kar vpliva na notranjo kakovost ulitka. more...

An original three-dimensional (3D) model of solidification is used to describe the process of solidification and cooling of massive (500 * 1000 * 500) mm cast-iron sand moulds castings. The calculated mode of the kinetics of the temperature field of the casting was verified during casting with temperature measurements in selected points. The sizes and positions (xsubi, ysubi, zsubi, where i = 1, 2, 3 is the number of samples taken) of the experimental samples are exactly defined and corresponding with the decreasing rate of solidification. The experimental samples - 15 mm in diameter and 12 mm high - were metallographically analysed and also in terms of heterogeneity of chemical composition. The coordinates xsubi, ysubi, zsubi characterise approximately - within an accuracy of 5 mm - the centres of the samples. Successively, the local solidification time Q (i.e. the time the specified position of the casting, defined by the coordinates xsubi, ysubi, zsubi, remained within the temperature range between the liquid and solid curves) is also calculated using the 3 D model. The following dependences are later determined according to experimental and calculated data: the average size of graphite spheroids rsubg and of graphite cells Rsubb as well as the average distances among the particles of graphite Lsubg - always as function of the local solidification time Q xsubi, ysubi, zsubi. Furthermore, it was founded that the given characteristics of the structure of the cast iron rsubg, Rsubb and Lsubg are directly proportional to the logarithm of the local solidification time. The original spatial model of solidification can therefore be used therefore as first approximation for the ironparts. This paper creates the starting point for the estimation of the assessment of the casting structure of massive cast iron parts. This paper creates the starting point for the estimation of the local mechanical properties and fracture behaviour of massive ductile cast iron castings. Za opis procesa strjevanja in ohlajanja masivnih železovih ulitkov velikosti (500 * 1000 * 500) mm smo uporabili osnovni tridimenzionalni (3 D) model strjevanja. Ulitki so bili uliti v peščene forme. Izračunan kinetični model temperaturnega polja ulitka je bil preverjen med ulivanjem z meritvami temperature v izbranih točkah. Velikosti in lege (xspodaji, yspodaji, zspodaji, kjer je i = 1, 2, 3 število vzetih vzorcev) poskusnih vzorcev so bile točno določene in so v skladu s padajočo hitrostjo strjevanja. Poskusni vzorci premera 15 mm in višine 12 mm so bili metalografsko analizirani in preverjena je bila tudi heterogenost kemijske sestave. Koordinate xspodaji, yspodaji, zspodaji označujejo sredino vzorcev s približno z natančnostjo 5 mm. Lokalni čas strjevanja Q (t. j. čas določenega položaja v vzorcu, definiranega s koordinatami xspodaji, yspodaji, zspodaji ostaja v temperaturnem območju med likvidusno in solidusno krivuljo) je bil tudi izračunan z uporabo 3D-modela. Kasneje so bile določene naslednje odvisnosti glede na eksperimentalne in izračunane podatke: srednja velikost kroglastega grafita rspodajg, grafitnih celic Rspodajb in srednje razdalje med delci grafita Lspodajg - vedno kot funkcije lokalnega časa strjevanja Q xspodaji, yspodaji, zspodaji. Nadalje je bilo ugotovljeno, da so dane značilnosti strukture litega železa rspodajg, Rspodajb in Lspodajg direktno sorazmerne z logaritmom lokalnega časa strjevanja. Osnovni prostorski model strjevanja lahko tako uporabimo v prvem približku za ugotovitev lite strukture masivnih železovih ulitkov. Ta članek omogoča začetno stopnjo ocene lokalnih mehanskih lastnosti in vedenja pri zlomih masivnih duktilnih železovih ulitkov. more...