A method for determining the interfacial tension between the molten iron and the slag was established. It consists of photographing the sessile drop of the molten iron by X-ray, measurement of the dimensions of the drop by means of a microcomparater and calculating the interfacial tension using the Bashforth-Adams table. The drop was placed on the horizontal bottom of an alundum crucible, in which the slag was melted. Values of the interfacial tension of the Hg-H₂O and Hg-benzene systems calculated by this "Sessile drop method" were in agreement with those reported in literatures. Interfacial tensions between liquid Fe-Si alloy(Si 14·34%)and the slag systems Na₂O-SiO₂ and Li₂O-SiO₂ were measured at 1370°C. The values of the interfacial tension were of the order of 1000-1150 dyne/cm, and decreased with increase of the alkali-metal oxide. It was suggested that Na+ and Li+ had the tendency to be adsorbed more easily at the meta1-slag interface than silicate anions.
Assuming the surface tension of the Fe-Si(Si 14·34%)alloy, it was presumed that the values of the work of adhesion of the present systems were of the order of 500-700 erg/cm², which were approximately in agreement with those of the systems consisting of metals (Ni Fe, Si)and oxide(Al₂O₃), determined by Humenik and Kingery. Furthermore, it was indicated that the work of adhesion increased with enhancement of Na₂O and Li₂O.

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The authors reported the results concerning the mechanism of the decarburization reaction of molten Fe-C alloys. The author's results being compared with the rate of the carbon removal on the practical operation, the fundamental conditions necessary to the operation of oxygen blowing was considered.
The results obtained were as follows:
(1) As the reaction was shown to take place on the interface between gaseous and liquid phases, the rate of the carbon removal depended upon the weight of iron, the area of interface and the oxygen pressure at a given carbon content. When the area of interface was maintained to be.constant, the rate depended only on the partial pressure of oxygen and in case of lower carbon contents up to 1%, the rate became constant at higher oxygen pressures above 2/5 atm.
(2) However in the practical operations the area of interface varied with the amounts of the bubbles produced by oxygen blowing, and the oxygen pressura in the phase of bubbles was approximately 1 atm.
Consequently the reaction rate depended upon the area of interface and the amounts. of oxygen introduced.
As the differences of the rate was due to those reasons, it was necessary to flow the suitable oxygen gas to the furnace in such a way that enlarged this area as possible.
(3) In order to promote the reaction taking place on the interface, it desirable to accele. rate the diffusion of carbon, the coefficient of which was slow in molten iron;by the method of the physical turbulence.
(4) As the activity coefficients of the reactants increased with the diminution of the carbon content, the beginning of oxygen blowing was more effective at the lower carbon concentrations.

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In order to obtain the value 0f deforming strength of steels at high speed-high-temperatures corresponding to such hot-working processes as hot-rolling, forging, extrusion etc., the author specially manufactured a tension-testing machine. Main parts of this machine were as follows:
(1) Deformation speed of specimens at gage length conld be converted into 77/sec, 7/sec & 0.8/sec respectively.
(2) As for the direct resistance heating of specimens using direct current, rapid heating was possible within the range of 700°-1400°C. Actual measurements were done standardized by 800°, 1000°° & 1200°C.
(3) Tension stresss was measured by the use of a capacity-change pick-up and elongation was measured using inductance change. Recording was made by the use of an electromagnetic oscillograph (H-Vibrator).
Using this tension-testing machine, both nominal stress-strain curve and true stress natural strain curve in all deforming conditions of all types of steels were to be obtained, the latter being data of deforming the strength.
In this article, the design and construction of this testing machine, together with a suitable experimental technique were described in details.

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When the iron and steel are heated in the oxidizing atmosphere at high temperature, the oxidation scale penetrates into matrix right below the surface scale. The authers studied on the phenomena of this penetration under various conditions using a rimmed steel (C 0.08%).
Heating conditions: temperature 1150°C-1350°C, atmosphere O₂ 5-50% N₂ Bal. CO₂ 5-50% N₂ Bal. time 30mn-2h
In order to compare the individual results each other, the depth of penetration and the size of penetrated scale were measured and those results were as follows:
1) The granular scales penetrated in considerable depths even in the atmoshere of only N₂ gas, and this penetration depth was nearly the same value gained when it was mixed with gases of O₂ or CO₂
2) Penetration of scale was greatly affected by the heating temperature: the higher the temperature, the deeper the depth and the larger the size of the penetrated scales.
3) Heated above 1300°C, huge scale appears and was remarkable under such conditions as O₂ gas was added. Therefore it was evidenced that the penetration of scale took part in the defect of the over-heating.
4) The color of granular penetrated scales were light-bluish-gray and that of the huge scales were composed by both light-and dark-bluish-gray.
5) If the heating condition changed, then the thickness of surface scales increased, and huge penetrating scale was produced even at below 1300°C.

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In Japan generally, they can use carrier gases for gas-carburizing obtained by converting mixture with air and town gas, charcoal gas or propan etc. The authors studied another source for such carrier gas. Good carrier gases were obtained by converting endothermically with a nickel catalyser, such a gas sources cracked light oil gas or carburated gasoline gas, suitably mixing with air. Using these carrier gases adding some hydrocarbon, the experimental results on gas carburizing were very successful.
From these experiments the authors concluded as follows.:
As the carrier gas for carburizing, the authors could produce suitable gas mixtures of cracked light-oil gas and air mixture converting between 900-980°C. As the best example, in which converting temperature was 900°C. and air to cracked gas ratio is 4, then the converted gas composition is 40% H₂, 20.5% CO, 0.0% CO₂, 0.5% CH4 and dew point -7°C. Moreover, we could produce proper carrier gas, using carburated gasoline converted gas, as shown in Table 1.
Carburizing power or carbon pressure, could be regulated by adjusting dew point and adding some hydrocarbon.

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The influence of temperature and time during the solution-treatmen on age-hardening was studied. There were four kinds of samples with varying chemical compositions. Three of them were standard Timken 16-25-6 alloys, varying nitrogen content from 0.04%, 0.10% to 0.16%. Another one was denitrized by adding Ti. After hot-forgingto bars, they were solution-treated at 1100°C (2010°F), 1150°C (2100°F), and 1200°C (2190°F) for 40 minutes, 1 hour 3 hours, 6 hours and 10 hours respectively. The hardness was measured and the microstructure was observed immediately after solution-treatment. The hardnesswas lower when it was solution-treated at a higher temperature and for a longer time. Sometimes the residual influence of hot-forging on grain boundary was observed even after solution-treatment. Some solution-treatment, operated at a rather low temperature or for a short time could not remove completely the influence of hot forging on grain shape, but another solution-treatment at a high temperature or for a long time removed the forged shape ofthe grain boundary.
The influence of the hot forging before solution-treatment, observedin grain boundary after solution-treatment, was more easily removed in sample of 0.04% N than in sample of 0.16% N.
All samples, solution-treated under different conditions, were aged at 800°C, (1470°F) and hardness was measured from 1 hour to 200 hours. The samples which were solution-treated at a higher temperature for a long time had lower hardness than the samples heated at a lower temperature for a shorter time. But, when they were heated at 800°C (1470°F) and reached stable maximum hardness after 30-100 hours aging, their hardness became almost uniform. This means that a sample, completely solution-treated, hardened in a larger range and reached the maximum stable hardness of the other aged samples which started from a higher hardness immediately after solution-treatment at a lower temperature and a shorter time heating, overcoming the difference of hardness at beginning of aging process.
The microstructure of all samples was observed after aging at 800°C (1470°F) for 200 hours. The grain-size was larger and the coagulated size of precipitated particles were more or less larger and the distribution of precipitated particles was more typical of the general precipitation type of the sample of solution-treatment at a higher temperature and longertime than the sample at a lower temperature for a shorter time.

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(1) In order to determine the small amounts (under 0.05%) of carbon in iron and steel, the authors modified the apparatus of the Gakushin method (gas volumetric method), reducing the volume of the gas burette from 350ml to 60ml, the graduation of the burette from 0.1 ml to 0.02ml, and the dead space of the combustion tube to 50ml.
(2) For accurate and rapid measurement of the volume of carbon dioxide, drainagecorrection and temperature-correction were necessary after the absorption of carbon dioxide by the potassium hydroxide solution, and the authors constructed a convenient correction table.
(3) Using the authors' apparatus, 0.01 to 0.05% carbon in iron and steel could be determined with the acuracy±0.002% within about 12 minutes. But this method had the disadvantage of needing temperature-and drainage-corrections after each measurement of gas volume.

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The author put together the researches on recent development of operation and construction of electric arc furnace for steel smelting.
The steel production by an electric furnace in 1953 in Japan was about 1, 300, 000 tons and was only about 60% of the maximum production during the war. In the United States about 8, 160, 000 tons was produced, which was about 5 times of the production in 1940, and the production is still increasing now.<Br>The production increase in the United States was due to the adoption of radid smelting process by bulky high-voltage electric power and also the reduction of production cost by using large capacity electric furnaces. Thus electric furnace process can compete with open hearth process and was used not only for alloy steel smelting but also for carbon steel smelting very widely. The production of rapid process smelting furnace was recently made possible here in Japan because of the technical cooperation with Pittsburgh Lectromelt Furnace Corporation. These furnaces were already installed at several plants and obtained very good result. The author explained the technical progress of production method of electrode for electric furnaces and transition of refractories. He also made an research on the progress of operation method, especially on oxygen smelting process, electric power and heavy oil combined process and induction stirring process. Lastly he made study on economical problems of electric furnaces based on expenses incurred for various production unit.

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