The equilibrium between the liquid iron-chromium alloy and the slag containing FeO, MnO, CrO and saturated silica was studied in the SiO₂ crucible at 1550°C, 1600°C, and 1650°C
The equilibrium constants for the deoxydation of silicon in the molten iron containing manganese and chromium were calculated by using the thermodynamical equation introduced by C. WAGNER, and compared with the experimental values.
Even if the calculation was uncomplete in the dilute solution, the relations between the concentrations of various components could be evaluated by using the Wagner's equation, but these thermodynamical calculations of oxides in the slag, even if the oxides were limited to a few components, could be carried out only using the Gibbs-Duhem equation and it was impossible for the multi-component systems.
In the present paper, various metallic oxides in the silica saturated slags were considered about how they react with the various elements in the molten iron. The results are summarised as follows.
1) The equilibrium constant for the deoxydation of silicon was evaluated by using the various interaction parameters, and it turned out higher than that in the liquid iron-chromium alloy with an increasing chromium concentration.
In a multi-component system, it is assumed that the deviations of the equilibrium constants occur with the errors in the experimental procedure, errors in the interaction parameters and neglect of all terms after the second in the Wagner's equation.
2) The activity of iron oxide increased with an increasing chromic oxide and a decreasing manganese oxide.The reason for this is assumed to be that the free ferrous ion in the silicate slags was increased with the ionic reaction between chromium and iron.
The activity of iron oxide was independent of temperature, and depended on the concentrations of coexistent components.It exhibited negative deviation from the Raoult's law.
3) The distribution coefficients of chromium are affected by chromic oxide and manganese oxide and do not show good agreement with those of Körber and Oelsen.The relation between the distribution coefficients of chromium and the activity of iron oxide was represented approximately by the equation.
L_cr=54·εα_Feo+0·38
4) The distribution coefficients of manganese also do not show good agreement with those of Körber and Oelsen.The relation between the distribution coefficients of manganese and the activity of iron oxide was represented approximately by the equation.
L_MN (5·37×10⁷/T-2·63×10⁴)·aα_Feo
5) The effects of chromium and manganese on the solubility of silicon were measured and by arbitrarily choosing the two elements in the molten iron, the concentrations of the other two elements and the oxides in the silicate slags can be determined.

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The author has pointed out in previous reports that the rates of transfer and diffusion of reacting elements and reacted products are important in the process of decarburization as the reaction C+O⇔CO takes place very rapidly.
The previous reports also stated that there are two regions in the process where the arriving velocities of carbon and oxygen determine the rate of decarburization, and the transi-tion point in between the two regions is 0.30% carbon in a basic open hearth furnace, and 0.15% in a small high frequency furnace.
The author clarifies here that the rate of decarburization is increased with the increase of agitation effect of metal in a high frequency furnace, especially in the low carbon range, and further that the rate of decarburization in the oxygen steel making process in a basic open hearth furnace is increased with the increase of oxygen flow rate, and the transition point where the rate-determining step changes from oxygen diffusion to carbon diffusion is also raised to a higher carbon range.

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There are earlier reports about the relations between the gas content of molten steel and the internal structure of the solidified ingot, but their mechanism was left unsolved. As an attempt to solve this problem, a series of comparative studies was made. The same heats were poured into two same ingot molds, one was solidified under high atmospheric pressure and another under ordinary pressure applied was chosen as 5, 10, 20 and 40kg/cm² based on the calculation of the gas formation during solidification. Comparison of the internal structures of the two ingots from respective heats gave the following results.
(1) The gas formation during solidification has influence on the inverse V segregation.
(2) The inverse V segregations almost disappear at pressure of 5kg/cm² in a chill mold and 40kg/cm² in a sand mold.
(3) The grain size of primary crystals is refined by high pressure.
(4) The length of columnar crystals is unchanged.

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Although it is important to know the deoxidation process of aluminium as strong deoxidizer and studies about deoxidation products have been done by many people, we could not clarify the process. L. S. SLOMAN and E. L. EVANS found some unknown substances formed beside aluminium deoxidation.They identified them as silica from the chemical analysis result of total isolated residues. C. E. Sims, H. A. SALLER and F. W. BOULGER reported about the deoxidation products with aluminium via the substance like AlO, but the process has remained unknown.
In ceramic division, the dehydration mechanism of aluminium hydrates has been established. But, there are many questions about their crystal structures and about the existence of many modifiers of aluminium oxide.
It is very important to know the formation mechanism of aluminium oxide in the molten iron from the viewpoint of metallurgical research and practical basis.
In this paper, the authors discussed how the variation of solidifying and cooling velocities influences the structures of deoxidation products.
The results obtained are summarized as follows:
1) Under rapid solidification, we could determine the formation of various low temperature stable modifiers besides corundum.They are chiefly θ type alumina, and supposed to be σ and κ types.
2) From their formation, we could suppose the formation of aluminium hydroxide in a moment after addition of deoxidizing agent.We must appreciate the role of hydrogen in molten steel.
3) For comparison, we used a platelet and a small lump of metallic aluminium.There was difference between their alumina modifications.Especially, in the case of small lump, they exhibited an appearance of γ type.
4) Although there are two dehydration paths in alumina modification, we could estimate from this experiment that alumina formed in steels takes both processes.

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This study was carried out to get fundamental informations on nonmetallic inclusions in order to make clear the relation betwee nonmetallic inclusions and properties of steel.To. study the behaviour of Mn oxide, Si oxide and manganese silicate in steel, electrolytic iron was melted in a high frequency induction furnace with varied addition of manganese, silicon or silicomanganese.Two kinds of rolling temperature (1250-1000°and below 1000°) and two kinds of rolling ratio (9 and 36) were selected.X-ray probe microanalyser was used to identifyinclusions and the eyepiece with micrometer was used to measure microscopically the quantity of inclusion deformation.The results were mainly as follows:
It appears that inclusions are classified into two typesaccording to course of formation, size, composition and distribution, namely: largeinclusions (5-25μ) and small inclusions (>5μ).Quantity of inclusion deformation increases as the volume of inclusion increases and rolling ratio becomes large.But the proportion of quantity of inclusion deformation to that of steel deformation decreases with increasing rolling ratio.In this experiment inclusions except sulfide, Mn silicate and silica are easier to deform at low rolling temperature than at high rolling temperature.In cases of sulfide and Mn silicate, the quantity of deformation is large at high rolling temperature.Quantity of deformation of inclusions which is produced by manganese deoxidation increases gradually with added manganese content.Quantity of deformation of inclusions in steel deoxidized with silicon increases rapidly with added silicon content, but it decreases rapidly as soon as SiO₂ begins to form and they are scarcely defo rmed by rolling. In case of inclusions in steel deoxidized with silicomanganese, the quantity of deformation increases with increasing added silicomanganese content.This deformation depends mainly on that of manganesesilicate.

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In our study on lodine methanol method and electrolytic method performed in order to isolate iron oxides in iron and steel from iron matrix, the behavior of iron oxides during isolation has been made clear.Then the change in the composition and the form of iron oxides in pure iron by heat treatment with application of the isolation technique was alsostudied.
The results are summarized as follows:
(1) In electrolytic method, generally lower values were obtained because Wustite was decomposed electrochemically during electrolysis, even if the electrolyte was neutral (pH=7); however, magnetite was not decomposed but recovered almost completely.On the other hand, in iodine methanol method, both Wustite and magnetite were recovered completely, and oxygen values calculated from iron oxides were in good agreement with those in vacuum fusion method.The oxygen values in these two different methods having been in good accord with each other, it was presumed that oxygen in solid iron exists generally as iron oxides and oxygen in the form of solid solution does not exist or is very little at 1200°C and 500°C.
(2) The composition and the form of iron oxides in iron and steel changed by heat treatment. The process of its change was almost similar to Fe-O diagram, that is, iron oxides. in iron and steel existed as Wustite at the temperature of above approx.570°C, while as magnetite below this temperature.
(3) Iron oxides in pure iron changed from Wustite to magnetite during heating at 500°C for several different hours.The velocity of change from Wustite to magnetite depended on the thermal history of specimen.In the specimen as cast this change finished in 72 hours, while in the specimen which was heat treated with 1200°C×5hr/water quench this change did not finish even in 215 hours.Then from the result of X-ray diffraction or chemical analysis of iron oxides isolated from pure iron which was heat treated at 500°C for several different hours after the heat treatment of 1200°C×5hr/water quench, it was made clear that this reaction occurred in the following order.
(i) Fe_xO→Fe₃O₄+Fe_x′O (x<x′)
(ii) Fe_xO→Fe₃O₄+a·Fe
(iii) Fe_xO→Fe_x″O+a·Fe(x>x″)
(4) Lattice parameter of Wustite having linear relation with its iron content.the iron content of Wustite could be found by applying X-ray analysis on the residue isolated from iron matrix with the aid of iodine methanol method.

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