Decarburization Reaction Research Articles

複合吹錬法によるステンレス鋼高炭素濃度域の脱炭反応特性

複合吹錬法によるステンレス鋼高炭素濃度域の脱炭反応特性

減圧下ステンレス脱炭反応の機構と反応に及ぼす攪拝条件の影響

減圧下ステンレス脱炭反応の機構と反応に及ぼす攪拝条件の影響

Dynamic modelling of vacuum circulation process for steel decarburization

A dynamic matbematical model of the vacuum circulation process for steel decarburization was developed. [t comprises the process parts of steel circulation decarburization reaction, adjustment of vessel pressure with its influence on the carbon equilibrium content, and the oxygen pickup from the ladle slag. The model allows to simulate the behaviour of all important process values with good accuracy and can be used for optimization of plant construction and operation as well as for improvement of process control.

Decarburization Reaction of Molten Iron of Low Carbon Concentration with Vacuum Suction Degassing Method.

A kinetic study has been made on decarburization reaction of molten iron of low carbon and oxygen concentrations with solid oxides. A new degassing method, namely Vacuum Suction Degassing (VSD) method, was applied to decarburize molten iron to an ultra-low carbon concentration. A porous oxide tube, the inside of which was evacuated, was immersed into molten iron. The initial carbon concentration was varied between 30 and 110 ppm. The initial oxygen concentration was below 50 ppm. The experiments were performed under Ar atmosphere (1.01×105 Pa). The experimental temperature was 1853 K. The VSD method can greatly increase the rate of decarburization of molten iron and the carbon concentration decreases to a very low value of a few ppm. The rate of decarburization with an Al2O3-SiO2 tube is higher than that with an Al2O3 tube. Increase in gas permeability of a porous tube enhances the decarburization reaction. The apparent rate constant of decarburization at the porous tube-molten iron interface with evacuation in the porous tube is about 10 times larger than that without evacuation.

ステンレス鋼脱炭反応におよぼすスラグの影響

ステンレス鋼脱炭反応におよぼすスラグの影響

真空排気過程におけるCO気泡発生時の溶鋼の脱炭速度

真空排気過程におけるCO気泡発生時の溶鋼の脱炭速度

Decarburization Reaction of Molten Iron of Low Carbon Concentration with Solid Oxides.

A kinetic study has been made on decarburization of molten iron of low carbon and oxygen concentrations with solid oxides. Electrolytic iron was melted in a MgO, Al2O3 or CaO crucible. The mass of iron and the initial carbon concentration were varied between 137 and 627 g and between 30 and 480 ppm. The initial oxygen concentration was below 50 ppm, and oxygen for the decarburization was supplied by the crucible oxide. Experiments were made with blowing argon gas (1000 Ncm3/min) onto the melt surface at 1580°C. The rate of decarburization decreases in the order of MgO, Al2O3 and CaO and is almost independent of the stirring condition of the bath. For the carbon concentration >100 ppm, the rate of decarburization does not change with the initial carbon concentration. From these results, it is considered that the rate is controlled by the dissociation reaction of the oxide. For the carbon concentration <100 ppm. The rate decreases with decreasing carbon concentration. In this case, the rate is presumed to be controlled by the dissociation reaction of oxide, formation reaction of CO at crucible-melt interface and CO mass transfer. A mathematical model is proposed to explain the rate of decarburization.

Decarburization Reaction in Ultra-low Carbon Iron Melt under Reduced Pressure.

The kinetics of the decarburization reaction with dissolved oxygen in a liquid iron in the ultraolow carbon concentration range under reduced pressure have been studied, using an induction furnace with a 20 kg melt. The results obtained are as follows:(1) The decarburization reaction proceeds to less than 5 ppm of carbon, and the decarburization rate constant, K, decreases as the carbon content decreases.(2) As the pressure in the chamber decreases, the decarburization rate increases with a carbon content of more than 10 ppm. On the other hand, the dependency of decarburization rate on the pressure in the chamber is small, with less than 10 ppm of carbon.(3) The influence of the sulphur content on the decarburization rate is small with a carbon content of more than 10 ppm. The decarburization rates are not affected by the mass transfer of CO in the gas phase under experimental conditions. Thus, it is concluded that the decarburization rate is controlled by the mass transfer of carbon in liquid iron.(4) The fact that the decarburization rate at a carbon content of more than 10 ppm is affected by the total pressure of the chamber has been explained by the change in interfacial area of the reaction between the gas and liquid phases resulting from CO boiling in the bulk melt.(5) The decrease in the decarburization rate in t he ultra-low carbon concentration range in RH is also caused by the decrease in interfacial area of the reaction between the gas and liquid phases.

Fluid Flow in Ladle and Its Effect on Decarburization Rate in RH Degasser.

Theoretical and experimental studies were carried out to quantitatively understand the effect of fluid flow on the decarburization reaction rate in an RH degasser. Hydrodynamic calculations on fluid flow in the ladle were proved reasonable by a cold model experiment. The decarburization model in conjunction with the fluid flow by hydrodynamic calculations in the ladle made it clear that the decarburization rate obtained from this model was faster than that for perfectly mixed flow, and slower than that for plug flow when the same parameters were used for the calculations. The decarburization model enabled us to predict the concentration distribution of carbon in the ladle during an RH treatment. The maximum carbon content, which was found in the recirculating zone in the ladle, reached about twice the minimum value obtained in the region just below the down-leg. No dead zone existed which would disturb the decarburization rate in the process, and it was also made clear that the shape of ladle had little effect on the decarburization rate.

Effect of Refining Conditions for Ultra Low Carbon Steel on Decarburization Reaction in RH Degasser.

On the basis of a mixed-control mechanism involving the mass transfer of carbon and oxygen in the molten steel in the vacuum vessel and the transport of carbon and oxygen by the circulation flow, a new reaction model for RH decarburization has been developed to clarify the effect of oxygen concentration on the decarburization rate. The model can also predict the effect of the KTB method, in which oxygen gas is blown onto the molten steel in the vacuum vessel, on the decarburization rate.A significant dependence of the decarburization rate in the RH experiments on the oxygen concentration in the ladle, OL, has been found in the range of the carbon concentration in the ladle, CL, of more than 200 ppm. In the range CL200 ppm, the decarburization rate is apparently proportional to the carbon concentration, hence its dependence on OL is small. The model analysis predicts the dependence of the decarburization rate on OL, however, there is some difference between the calculated decarburization rate and the observed rate. This is presumed to be caused by an unidentified supply of oxygen to the molten steel in the vacuum vessel, which may result from the slag being drawn into the vacuum vessel and the leakage of atmospheric air.Volumentric coefficients of the mass transfer of carbon in the vacuum vessel of the RH, akC, was also investigated in the ultra low carbon range of less than 50 ppm using recent data, and was shown to have a strong dependence on the carbon concentration and the circulating flow rate, Q..

極低炭素濃度溶鉄の減圧下における脱炭反応

The kinetics of the decarburization reaction with dissolved oxygen in a liquid iron in the ultraolow carbon concentration range under reduced pressure have been studied, using an induction furnace with a 20 kg melt. The results obtained are as follows:(1) The decarburization reaction proceeds to less than 5 ppm of carbon, and the decarburization rate constant, K, decreases as the carbon content decreases.(2) As the pressure in the chamber decreases, the decarburization rate increases with a carbon content of more than 10 ppm. On the other hand, the dependency of decarburization rate on the pressure in the chamber is small, with less than 10 ppm of carbon.(3) The influence of the sulphur content on the decarburization rate is small with a carbon content of more than 10 ppm. The decarburization rates are not affected by the mass transfer of CO in the gas phase under experimental conditions. Thus, it is concluded that the decarburization rate is controlled by the mass transfer of carbon in liquid iron.(4) The fact that the decarburization rate at a carbon content of more than 10 ppm is affected by the total pressure of the chamber has been explained by the change in interfacial area of the reaction between the gas and liquid phases resulting from CO boiling in the bulk melt.(5) The decrease in the decarburization rate in t he ultra-low carbon concentration range in RH is also caused by the decrease in interfacial area of the reaction between the gas and liquid phases.

真空吸引脱ガス法による溶鉄の低炭素濃度域における脱炭反応

真空吸引脱ガス法による溶鉄の低炭素濃度域における脱炭反応

固体酸化物による溶鉄の低炭素濃度域における脱炭反応

固体酸化物による溶鉄の低炭素濃度域における脱炭反応

RH真空脱ガス装置の取鍋内溶鋼流動と脱炭反応

Theoretical and experimental studies were carried out to quantitatively understand the effect of fluid flow on the decarburization reaction rate in an RH degasser. Hydrodynamic calculations on fluid flow in the ladle were proved reasonable by a cold model experiment. The decarburization model in conjunction with the fluid flow by hydrodynamic calculations in the ladle made it clear that the decarburization rate obtained from this model was faster than that for perfectly mixed flow, and slower than that for plug flow when the same parameters were used for the calculations. The decarburization model enabled us to predict the concentration distribution of carbon in the ladle during an RH treatment. The maximum carbon content, which was found in the recirculating zone in the ladle, reached about twice the minimum value obtained in the region just below the down-leg. No dead zone existed which would disturb the decarburization rate in the process, and it was also made clear that the shape of ladle had little effect on the decarburization rate.

Effect of carbon on surface crystallization of amorphous FeBSi alloy induced by selective oxidation

The relationship between the annealing atmosphere and the magnetic properties of amorphous Fe 78.5B 13Si 8.5 and Fe 80.5B 14Si 3.5C 2 alloys has been studied, showing that annealing in dry H 2 significantly improves core loss in amorphous ribbons, giving much better results than annealing in an H 2H 2O atmosphere. A boron depletion zone containing 0–3 mol.% B and 9–11 mol.% Si or containing 5–7 mol.% B, 3–4 mol.% Si and 0–2 mol.% C in the surface layer of amorphous FeBSi and FeBSiC ribbons respectively was detected by Auger electron spectroscopy under the oxide film formed during annealing in H 2H 2O. When the amorphous ribbons are annealed in H 2H 2O, the H 2O in the annealing atmosphere selectively oxidezes boron in the alloy to form a B 2O 3 film and a boron depletion zone; the alloy in this zone is then crystallized into α-Fe. The thickness of the surface crystalline layer induced by selective oxidation is more significant in FeBSi than in FeBSiC, possibly because the apparent dew point in the annealing atmosphere near the amorphous ribbon surface decreases with decarburization reaction in the FeBSiC system.

Decarburization kinetics of liquid Fe−Csat alloys by CO2

The kinetics of the decarburization reaction of Fe−Csat liquid alloys by CO2 were investigated at 1600°C under conditions where the rate is not significantly affected by liquid- or gas-phase mass transfer. Rates of decarburization were measured by monitoring the change in gas composition with an in-line mass spectrometer. Small amounts of S, P, Sn, and Pb were alloyed with the Fe−Csat melt to determine their effect on the interfacial rate constant. The rate constant measured for the Fe−Csat−S alloys is in agreement with previous results for Fe−S alloys and was found to be inversely proportional to sulfur concentration at low sulfur levels. For high S-containing alloys where the surface is saturated with sulfur, a residual rate was observed. The effects of phosphorus and lead on the rate constant are negligible. Tin decreases the rate constant, but the effect is small, even when the tin content is as high as 2.6 wt pct.

Investigation of the reaction UO2+ x + PuO2 + C + N2 by thermogravimetry

The kinetics of formation of uranium-plutonium nitride pellets by carbothermic reduction of uranium- and plutonium oxides under flowing nitrogen has been investigated using thermogravimetric techniques in the temperature range 1650–1870 K. The starting blends were prepared from powder material with different characteristics, and contained about 1% carbon in excess of the amount to obtain the stoichiometric composition. The reactions investigated were: (a) the carbothermic synthesis under nitrogen of a low-carbon carbonitride containing free carbon and small amount of oxygen impurity and (b) the decarburization of the carbonitride under a N 2-8% H 2 gas mixture. The carbothermic synthesis follows a first-order rate equation and the value of the activation energy is 307 kJ/mol. The rate constants of the decarburization reaction could not be determined by gravimetric procedures because the hydrogenation of free and chemically bound carbon caused at the same time opposing weight changes. This work was carried out within the frame work of the study for the fabrication of (U, Pu)N fuel using the direct pressing method.

The kinetics of decarburization of iron melts by argon-hydrogen plasma jets.

A plasma-torch and refractory-lined furnace with a 20kg capacity were used to study the kinetics of decarburization of iron melts. Molten iron with an initial carbon content of either 1.1 or 2.6wt% was decarburized using an argon-hydrogen plasma jet. The rate of decarburization was found to be limited by mass transfer in the melt; a mass transfer coefficient of 2.76×10-3cm/s was obtained. Additionally, it was determined that the decarburization reaction occurred only in the region of plasma jet impingement.

Application of CO as bottom stirring gas in combined blown converter.

At Kakogawa Works, steels of low to high carbon contents are produced by the use of LD converter of top and bottom blowing type. Argon and nitrogen has been used for the bottom stirring gas. In response to the recent increase in argon consumption, carbon monoxide (CO) recovered from LD exhaust gas is now being used to replace argon for bottom stirring.By the COSORB® process using a large scale CO gas generating equipment introduced from Kinetics Technology International Corporation, highly purified CO can inexpensively be produced from LD exhaust gas. The COSORB® process is a gas-liquid absorption method using the COSORB® solution, which is a toluen solution of Cu-AlCl4. By the COSORB® method, the gas having the chemical composition suited for bottom blown gas in the BOF can be produced in large enough quantity.The use CO as the bottom blown gas, particular attention should be paid to the CO concentration in the bulb station room where the possibility of CO leakage is present and to clean the pipe line during the non-blowing period.The characteristics of metallurgical reactions in the converter, for examples [O]F and slag (T.Fe) at turn down, are almost the same as those of argon and nitrogen bottom stirring. However, the carbon content in the molten steel is increased by CO rinsing after the oxygen top blowing; in contrast the carbon content is reduced in the case of argon rinsing.This is attributable to the fact that the decarburization reaction does not occur during CO rinsing due to the presence of CO bubble; otherwise the CO decomposition reaction (CO (gas) in CO bubble→C+O) occurs.At Kakogawa Works, the erosion rate of refractory has been reduced by the development and installation of S.A. tuyere (Single Annular tuyere). By the use of CO as the bottom blown gas, mushroom is formed in a similar manner as in the case of argon blowing. The life of the tuyere can be prolonged 20% as compared with the case of argon blowing due to the cooling effect of CO.By the installation of safety devices, it is possible to substitute CO for argon in order to reduce the gas cost.

ＬＦプロセスにおける極低炭素鋼の溶製改善

Some improvements for making ultra low carbon steel have been obtained since AF-LF duplex refining process coupled with vacuum degassing was induced in Hoshizaki plant, Daido Steel Co., Ltd.Main points of the improvements are as follow;(1) Carbon pick-ups during LF processings are eliminated by the choice of low carbon bricks, the application of long arc heating and the usage of low carbon alloys.(2) Decarburization reaction is controlled by the αFeO. In order to reach the minimum carbon level, αFeO must be kept as higher as possible.