CaO-Al2O3 Slag Research Articles

Activities in CaO-MgO-Al2O3 Slags and Deoxidation Equilibria of Al, Mg, and Ca.

The equilibrium experiments between CaO-Al2O3-MgO-0.06 to 0.85%MnO-0.5 to 2.1%FetO-0.07 to 0.3%S (mass content in %) slag and liquid iron were carried out at 1823 and 1873 K in order to assess the activities of Al2O3 and MgO along the spinel (MgO·Al2O3) saturation line. The activities of CaO in an entire liquid region were first determined at 1823 and 1873 K from the reported values for sulfide capacity, coupled with the activity coefficients of CaS which were estimated from those in the CaO-Al2O3 slags. On the basis of these iso-activity lines for CaO, the activities of Al2O3 and MgO were calculated by using he method of Schuhmann, in which the assessed activities of Al2O3 and MgO on the spinel saturation line were taken as the starting points. The activity coefficients of FetO and MnO along the spinel saturation line were determined and the deoxidation equilibria of Al, Mg, and Ca were discussed.

Oxidation Rate of Aluminum in Molten Iron by CaO-SiO2-Al2O3-FeO-MnO Slag.

The kinetic behavior of aluminum oxidation in molten iron by CaO-SiO2-Al2O3, CaO-Al2O3-FeO, CaO-Al2O3-MnO and CaO-SiO2-Al2O3-FeO-MnO slags was investigated at 1 600°C under an argon atmosphere. The oxidation rate of aluminum by SiO2 is slower than those by FeO and MnO in CaO-Al2O3 slag. No difference in the oxidation rate could be observed between slag containing FeO or MnO. More insoluble alumina inclusions were observed in the metal for slag containing FeO or MnO than in that containing SiO2.

Calcium deoxidation and nitrogen distribution in liquid nickel equilibrated with CaO-Al2O3 slags

The Wagner’s first-ordere o Ca and second-order (r o Ca ) interaction parameters between Ca and O in liquid nickel were determined as −1220 and 1.35 x 105, respectively, at 1873 K in the equilibrium experiments between liquid nickel and CaO-Al2O3 slags in an A12O3 or CaO crucible. The values fore Ca O , (−3060), r Ca o (8.47 × 105), r Ca O,Ca (6.76 x 105), and r Ca O,Ca (6.76 x 105) were also estimated. Nitride capacities, C(N), defined by (mass pct N)·P 2 3/4 PskN21/2 were obtained by using the present results for nitrogen distribution ratio, LN =(mass pct N)/[mass pct N], and the reported values for the activity of Al2O3.

Effect of tellurium on supersaturation in aluminum deoxidized liquid iron

The effect of tellurium addition on supersaturation observed in aluminum deoxidized liquid iron was studied at 1873 K, using CaO-Al2O3 slags in an alumina crucible. Supersaturated oxygen content for a given aluminum level decreased with the addition of tellurium as a result of lowering the interfacial energy between liquid iron and alumina and promoting the elimination of precipitated alumina by flotation. Furthermore, the degree of lowering of oxygen content was found to increase with a decrease in cooling rate. Tellurium distribution ratio between liquid iron and CaO-Al2O3 slags was determined as a function of aluminum content.

Precipitation Behavior of Fe-Al-O Inclusions under Unidirectional Solidification of Fe-30mass%Ni Alloys Saturated with CaO-Al2O3 Slags.

The inclusions composition, size, morphology and distribution in an Fe-30mass%Ni alloy were studied as a function of the initial solute contents, which were controlled by the CaO-Al2O3 slags, and of the solidification parameters. The Al2O3-rich Al2O3-CaO inclusions were observed at the initial contents of Al=300-400 and O<6, while the FeO and the FeO-rich FeO-Al2O3 inclusions were observed at the initial contents of Al=2-6 and O=20-130 on mass ppm base. The FeO-rich FeO-Al2O3 inclusions were located in later stage of solidification in the intercellular or the interdendritic region. And most of the Al2O3-rich Al2O3-CaO inclusions were located in later stage of solidification, but some distributed in the intercellular or the interdendritic region. The dependence of the composition and the size of these inclusions on the cooling rate was not observed. The precipitation of FeO and Al2O3 was discussed by using the solute segregation models.

A.C. Impedance Analysis of the Kinetics of Reactions between Molten Cu or Fe and CaO-Al2O3 Slag.

A chemical reaction at the interface between slag and metal can be analyzed as a kind of electrode reaction because of the ionic nature of liquid slag.In the present work, application of an A.C. impedance method to slag-metal reaction in iron- and steel-making process was tried to clarify the individual kinetic factors concerning the electrode reactions at the interface between slag and metal. The total impedance between CaO-Al2O3 slag and Cu-S or Fe-C-S melts was measured in this paper.The results obtained were successfully used to determine the individual factors on kinetics of the electrode reaction between slag and metal, such as solution resistance of slag, interfacial capacitance in electric double-layer, overvoltage of charge transfer, rate constant and so on.

溶銅または溶鉄とCaO-Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt;系スラグ間反応速度の電極インピーダンス法による解析

A chemical reaction at the interface between slag and metal can be analyzed as a kind of electrode reaction because of the ionic nature of liquid slag.In the present work, application of an A.C. impedance method to slag-metal reaction in iron- and steel-making process was tried to clarify the individual kinetic factors concerning the electrode reactions at the interface between slag and metal. The total impedance between CaO-Al2O3 slag and Cu-S or Fe-C-S melts was measured in this paper.The results obtained were successfully used to determine the individual factors on kinetics of the electrode reaction between slag and metal, such as solution resistance of slag, interfacial capacitance in electric double-layer, overvoltage of charge transfer, rate constant and so on.

CaO-Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt;系融体-溶鉄間の窒素,硫黄分配

Nitrogen and sulfur distribution ratios between CaO-Al2O3 slags and Fe-0.0001-33mass%Al alloys were measured in the temperature range of 1823 to 1923 K, using an Al2O3 and CaO crucibles. The distribution ratios under a CaO crucible were higher than those under an Al2O3 crucible, and increased with an increase of Al content. Nitride and sulfide capacities defined by CN3-=(mass%N)·PO23/4/PN21/2 and CS2-=(mass%S)·PO21/2/PS21/2, respectively, which were obtained by using the reported values for activity of Al2O3, agreed well with those directly measured in a gas-slag experiment under an Al2O3 crucible, but disagreed with those under a CaO crucible. Activities of Al2O3 in the CaO-Al2O3 melts saturated with CaO were evaluated based on the results in the gas-slag experiments.

Partitions of Nitrogen and Sulfur between CaO-Al2O3 Melts and Liquid Iron.

Nitrogen and sulfur distribution ratios between CaO-Al2O3 slags and Fe-0.0001-33mass%Al alloys were measured in the temperature range of 1823 to 1923 K, using an Al2O3 and CaO crucibles. The distribution ratios under a CaO crucible were higher than those under an Al2O3 crucible, and increased with an increase of Al content. Nitride and sulfide capacities defined by CN3-=(mass%N)·PO23/4/PN21/2 and CS2-=(mass%S)·PO21/2/PS21/2, respectively, which were obtained by using the reported values for activity of Al2O3, agreed well with those directly measured in a gas-slag experiment under an Al2O3 crucible, but disagreed with those under a CaO crucible. Activities of Al2O3 in the CaO-Al2O3 melts saturated with CaO were evaluated based on the results in the gas-slag experiments.

ＧＲＡＦ精錬による実用鋼の品質改善

Gas Refining Arc Furnace (GRAF) is an arc heating converter which is exclusively applied for reduction refining. It makes possible to realize an effective simultaneous refining (i.e. degassing, slag refining and powder injection etc. in a same period) by a strong Ar injection through the bottom tuyere.This paper provides some examples of quality improvement as shown below, which were obtained from operation results of the 3 ton furnace.(1) Clean carbon and low alloy steels of 10-15ppm [O] and 5-10ppm [S] can be produced by simultaneous reduction of [O], [N], [H] and [S] with the strong gas stirring. CaO-CaF2 slag decreases oxygen and sulfur in molten steel to lower level than CaO-Al2O3 slag. MgO content in CaO-Al2O3 slag must be kept low in order to promote desulfurization reaction.(2) Ultra low (C+N) stainless steels, such as 26% Cr-1% Mo steels of 180ppm (C+N), can be produced by high flow rate of argon gas injection which causes decarburization and nitrogen removal.(3) In making clean molten steel by GRAF treatment, it is possible to reduce casting defects and to increase Charpy impact energy in stainless steel castings. This results in reduction of repair time, compared with electric arc furnace melting.

酸化性雰囲気下における溶融スラグの気化脱硫

The rates of desulphurization from liquid slag to the gas phase have been studied under an oxidizing atmosphere. A series of experiments was carried out by introducing Ar-O2 gas mixtures on to the surfaces of those liquid slags containing sulphur, such as CaO-SiO2, CaO-Al2O3 and some CaO-SiO2-MO ternary slags as well as CaF2 bearing slags.The results are as follows:(1) The desulphurization reaction of those slags by oxidizing gases is divided into a rapid rate reaction at the initial stage and a slow rate reaction at the later stage. The former should be controlled by the chemical reaction at the surface of the slags and the latter by the diffusion of sulphur in slags.(2) The rates of desulphurization of slag are proportional to the square root of partial pressure of oxygen and the rates of desuliphurization of the binary CaO-Al2O3 are higher than those of the CaO-SiO2 system. However, the rates of desulphurization for ESR slags are higher than those for CaO-Al2O3 slag. The rate constants for CaO-SiO2-MO ternary slags can be estimated from the sulphide capacity of the slags.(3) It was found that the rates of desulphurization increase in proportion to the concentration of basic oxides (CaO, MgO, MnO, FeO) but decrease as acid oxides (SiO2, Al2O3) contents are increased. Particularly, the effects of MnO and FeO are significant.

CaO-Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt; 2元系溶滓中の炭素の形態について

The state of carbon dissolved in molten binary CaO-Al2O3 slag has been studied. The sample of this slag was melted in a graphite crucible with or without carbon saturated iron, and the amount of CO evolved was measured by means of the thermo-balance. Then, the amounts of carbon dissolved in slag and aluminium transferred from slag to metal were determined by chemical analysis, and the amount of CO was calculated on the basis of stoichiometry. From a comparison between the measured and calculated amounts of CO evolution, it is supposed that carbon dissolved in slag as C2− is given by the following reaction; 2C+O2−=C2−+CO(g).

Solubility of nitrogen and carbon in CaO-Al2O3 melts in the presence of graphite

CaO-Al2O3 slags were melted in graphite crucibles under N2-CO-Ar gas mixtures at 1600°C. The contents of total nitrogen, cyanide and total carbon of the slags were determined by chemical analyses of quenched samples taken by suction from the melt. The nitrogen is present in the melt as nitride N3- ion and cyanide CN-1 ion, and carbon as cyanide and carbide C2- ion. The equilibrium constants for the respective reactions were evaluated. It is found that the nitride capacity of the melt decreases whereas the cyanide and carbide capacities increase with increasing CaO/Al2O3 ratio.

溶融鉄合金とCaO-Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt;スラグとの間の界面張力の測定について

An improved method for measurement of interfacial tension between liquid iron alloy and liquid slag has been developed. The method is based on simultaneous determination both surface tension of liquid iron alloy σmg, which is measured by use of large drop method, and contact angle of liquid slag droplet on the liquid iron alloy. The interfacial tension ‘σms°’ between CaO-Al2O3 slag and liquid iron alloy was determined at 1 570°C by the method within 0.5 second after contacting the two liquids. Results obtained are as follows:(1) Oxygen dissolved in liquid iron brings about drastic decrement of a σms°, while both carbon and chromium in liquid iron lowers slightly σms°.(2) Both decrement of am; and that of crag by addition of one of the elements mentioned above into liquid iron are nearly equal to one another, and also both decrement of σms° and that of surface tension of CaO-Al2O3-SiO2 slag asg by addition of SiO2 component into the slag are nearly equal to one another.(3) Main cause of the interfacial tension character will be induced by independent contributions both of σmg and σsg respectively, while interaction between the slag and the iron alloy may play a minor role in the interfacial tension character.(4) Work of adhesion Wa between the slag and the iron alloy within 0.5 second after contacting the two liquids keeps constant value even when only one of the two liquids makes change in composition.

黒鉛ルツボ中で溶融したCaO-Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt; 2元系溶滓の窒素溶解度について

Solubilities of nitrogen and carbon in molten CaO-Al2O3 slags were measured to discuss the form of nitrogen. Samples were melted in graphite crucibles and N2-CO gas mixtures were equilibrated with nitrogen and carbon in molten slags. The results obtained are summarized as follows:(1) It is considered that in the presence of graphite, nitrogen and carbon dissolve in molten slag electrochemically.(2) The solubilities of nitrogen and carbon decrease with decreasing PN2.(3) The temperature dependences of solubilities of nitrogen and carbon are represented as follows: log(wt%N)=−23300⁄T+12.9, log(wt%C)=−14000⁄T+0.17(50 wt%CaO-50 wt%Al2O3, PN2=0.92).(4) The carbon content increases in proportion to the CaO content in the CaO-Al2O3 binary system, while the maximum content of nitrogen was obtained at the composition with nearly 50 wt%CaO.(5) The correlation was observed between nitrogen and carbon contents in molten slags.(6) Nitrogen in the CaO-Al2O3 melt exists as CN− and N3− annions, although it remains unclear whether CN22− annion exists in the melt or not.

Reducing Action of CaO-Al2O3 Slag upon the Molten Steel and its Effect on the Steel Quality

Reducing Action of CaO-Al2O3 Slag upon the Molten Steel and its Effect on the Steel Quality