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1

Oxygen Activity in Melts of Fe-C-Cr-Ni Based Alloys

Záděra A., Dulava M., Pernica V., Kaňa V.

Archives of Foundry Engineering

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2016

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Vol. 16, iss. 4

181--186

EN

Oxygen is an element that is first purposely brought into the steel melt to remove some unwanted elements or to reduce their concentration (oxidation). In the made cast steel there is on the contrary necessary to reduce the oxygen content with the use of deoxidation to such a level in order to avoid a reaction with carbon with the formation of CO bubbles. Concentration of oxygen in steel before casting is given, in particular, by the manner of metallurgical processing and the used deoxidation process. Oxygen is found in molten steels both as chemically bound in the form of oxides and in the form of oxygen dissolved in the solution – the melt. Chemical composition of the melt strongly influences the activity of oxygen dissolved in the melt and further on the composition of oxidic inclusions forming in the melt during the reaction with oxygen. In the Fe-C-Cr-Ni based alloys in the reaction with oxygen greatly participates also chrome, whose products are often in solid state and they are the cause of forming such defects as e.g. oxidic films.

2

Contribution to Deoxidation of Austenitic Steels in a Vacuum Induction Furnace with Carbon

Šenberger J., Pernica V.

Archives of Foundry Engineering

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2015

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Vol. 15, iss. 2

105--109

EN

Deoxidation of steel with carbon under reduced pressure is often used for increasing the steel purity. Suitable units for this purpose in foundries are vacuum induction furnaces. Possibilities of increasing the steel purity by deoxidation with carbon in the vacuum induction furnace were studied for the steel for the petrochemistry of specific composition 25Cr/35Ni. The charge composed of the return material only was melted in the air. During melting the charge oxidized and the oxidizing slag formed. Chemical composition of steel, morphology, chemical composition of inclusions in the steel and chemical composition of slag after vacuuming were studied on the basis of samples taken before and after vacuuming. Temperature and oxygen activity were measured before and after vacuuming. Globular inclusions with dominant content of silicon and manganese were observed in steel before and after vacuuming. Contents of total oxygen in steel didn’t change significantly during vacuuming. On the basis of composition of inclusions and measured oxygen activity the activity of Cr2O3 in inclusions was calculated. A slag sample was taken after vacuuming and equilibrium oxygen activity in steel with regard to the Cr2O3 content in the slag was estimated from the slag composition. Equilibrium oxygen activity in relation to the Cr2O3 content in the slag was higher than equilibrium activity measured in the steel. For this reason it is not possible, under the studied conditions, to decrease oxygen content in steel during vacuuming.

3

Kontrola stężeń aluminium i siarki w ciekłych stalach podczas procesu w piecu kadziowym

Derda W.

Prace Instytutu Metalurgii Żelaza

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2009

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T. 61, nr 5

67-70

PL

Uzyskiwanie w stalach niskich zawartości aluminium Al < 0,008% przy zachowaniu niewielkiego rozrzutu tych zawartości, wymaga ścisłej kontroli aktywności tlenu tak w objętości ciekłego metalu jak i w żużlu podczas obróbki stali w piecu kadziowym. Ustalono dla badanych warunków procesu zależności statystyczne opisujące zmiany aktywności tlenu w ciekłej stali w funkcji stężenia tlenków żelaza Fe2+ w żużlu rafi nacyjnym. Zdolność żużla w piecu kadziowym do odsiarczania ciekłej stali scharakteryzowano poprzez wartości wskaźnika Mannesmanna.

EN

Producing of steel containing the low content of aluminium, below 0,008% to obtain the narrow scatter of these contents requires exact control of the oxygen activity both in liquid metal and in slag phase during metallurgical process in the ladle furnace. The statistical relationships described changes of the oxygen activity in liquid steel as a function of iron oxide concentration in refining slag, valid for the studied conditions were established in this work. The ability of slag in ladle furnace for the sulphur removing was characterized through values of the Mannesmann index.

4

Dynamic control of slag foaming at Sidenor Basauri Meltshop

Landa S., Rodriguez T., Munoz J. L., Laraudogoitia J. J.

Archives of Metallurgy and Materials

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2008

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Vol. 53, iss. 2

419-424

EN

The melting process in the EAF is normally controlled via fixed operating patterns; the aim of this practice is to achieve the optimum conditions at the tapping. Industrial practice indicates that sometimes deviations appear, so it is not uncommon to obtain very high or low C contents at melt-down promoting bad slag foaming conditions, rising electrical consumption and tap-to-tap times. As a consequence the productivity decreases and the running cost increases. The slag foaming process in the EAF has been studied analyzing process data, such as: EAF electrical consumption, steel oxygen activity, steel and slag composition, temperature, acoustic noise signal, Total Harmonics Distortion (THD) of arc voltage and current. A dynamic model has been developed, with the aim of controlling the oxygen and carbon injection process in order to achieve the target of composition, O activity and temperature at tapping while maintaining a good foaming quality during the process leading to a lower electrical consumption and tap to tap time. The model starts working after the first C sampling measurement takes places, and from that time it controls the oxygen and carbon injection. This model has been integrated in the plant as part of the EAF automatic control system.

PL

Wytapianie w piecu łukowym zwykle sterowane jest przy użyciu wyznaczonych modeli; celem tej praktyki jest osiągnięcie optymalnych warunków przy spuście. Praktyka przemysłowa wskazuje, że mogą wystąpić odchylenia w zawartości węgla przy złych warunkach spieniania żużla podczas wytopu, wzrastającym zużyciu energii elektrycznej i czasie wytopu. Konsekwencją jest spadek wydajności i wzrost kosztów. Proces pienienia się żużla w piecu łukowym zbadany został przez analizę danych takich jak, zużycie energii, aktywność tlenu w stali, skład chemiczny żużla i stali, temperatura, poziom sygnału dźwiękowego, całkowite zniekształcenie harmonicznych (THD) napięcia i prądu łuku elektrycznego. Model dynamiczny został stworzony, celem sterowania procesem wdmuchiwania tlenu i węgla, aby uzyskać odpowiedni skład chemiczny, aktywność tlenu i temperaturę przy spuście przez utrzymanie dobrego spieniania w trakcie procesu, przy niższym zużyciu energii i czasie wytopu. Model zaczyna funkcjonować po pierwszym pomiarze zawartości C i od tego momentu steruje wdmuchiwaniem węgla i tlenu. Model ten został zintegrowany z system automatycznego sterowania piecem łukowym.

5

Sledování aktivity kyslíku při výrobě litiny s kuličkovým grafitem

Nová I., Bradáč J., Vrba M., Šmrha J.

Archiwum Odlewnictwa

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2006

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R. 6, nr 18/2

15--20

CS

Článek se zabývá měřením aktivity kyslíku litiny s kuličkovitým grafitem. Pro měření aktivity kyslíku byly použity kombinované termosondy (TERMOSONDY Kladno TSO-FS), které byly vyvinuty pro měření nízkého obsahu aktivity kyslíku. V rámci experimentů byla sledována aktivita kyslíku před a po modifikaci taveniny litiny. K výpočtu aktivity kyslíku byla použita rovnice ČSAV Ostrava a rovnice uváděná firmou ELECTRO-NITE.

EN

The article deals with measurements of oxygen activity ductile iron. The methodology of the oxygen activity measurement using TERMOSONDY Kladno TSO-FS (combined) sensors was developed at the Department of Engineering Technology of the Technical University of Liberec. The sensors were originally assigned for very low oxygen activity measured in molted steel. The EMF and the temperature are sensor’s output parameters used for oxygen activity calculation. Measured data are processed by the computer and results are displayed on the screen. All the results are saved in computer’s memory together with the time of measurement. Oxygen activity is calculated using two formulas (ČSAV Ostrava and Electro Nite c.o.) at the time. The oxygen activity measurement proved, that oxygen activity in molted iron depends on technology of melting, chemical composition and temperature of the melt.