Investigation was made on the relative reducibility of several sorts of iron ores, sintered ores and other raw materials for blast furnaces by making experiments on direct reduction and indirect reduction of them respectively by coke and CO gas. Then consideration was given on the degree of the reducing action of coke on iron ore, difference in the quantity of carbon deposit in indirect reduction of ores by CO gas and chemical reaction of CO gas on iron ore.
In case of direct reduction by coke, difference was found in reducibility of several sorts of ores within the temperature range of under about 900°C, while at higher temperature the rapid reducing reaction was recognized similarly in each ore. Reduction by coke began at low temperature both for hematite and limonite, while for magnetite it occurred at somewhat higher temperatures. In case of indirect reduction by CO gas, reducing reaction appeared at a lower temperature in hematite and limonite than in magnetite (at about 600°C). Carbon deposit was the highest in hematite and appeared within almost certain range of temperature, while in limonite it appeared at various temperatures, and in magnetite it was very little due to slight reaction. Changing process in the quantity of CO₂ in waste gas could be comparatively clearly recognized in various sorts of ore and for distinguishing the mineral and chemical properties of non-tested ores this method could be effectively applied. Further investigation in future would require on size and quantity of samples for reduction test and on the influence of the condition of flowing CO gas upon reducibility and especially the carbon deposit.

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To study thermal properties of molding sand for steel castings, the following experiments and calculations were performed. The thermal conductivities of silica sand of various grain sizes and appar nt densities were measured at various temperatures up to 1000°C. Assuming a sand grain to be a cube having a projection part, a formula was gained which represented an apparent thermal conductivity of silica sand and contains terms of grain size, temperature and apparent density as variables. This formula, also, contained the 'contact factor', that had to be assumed as to make proximate the calculated value to the measured one. The contact factor seemed to increase at a high temperature, and perhaps it was due to the partial sintering of sand. The thermal conductivities up to 1400°C were calculated by a formula.

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Using a pure Al₂O₃ crucible, authors measured the following reaction under the conditions of 3 Al₂O₃· SiO₂, Al₂O₃ or 3CaO·Al₂O₃ saturation at the temperatures of 1, 550° and 1, 600°C;
Further, the activities of SiO₂ in the molten slags of SiO₂-CaO-Al₂O₃ ternary system were calculated from the equilibrium values of Si in molten iron at a given temperature and gas ratio PH₂/PH₂O, where the pure β-cristobalite was taken as the standard state. The authors illustrated the relation of the equi ibrium among Si in molten iron, activity of SiO₂ of the SiO₂-CaO-Al₂O₃, molten slag saturated with Al₂O₃ and H₂-H₂O mixed gas.
Finally, authors determined the liquidus lines in the presence of molten iron at temperatures of 1, 500° and 1, 600°C on the Al₂O₃ side of SiO₂-CaO-Al₂O₃ ternary diagram from the equilibrium compositions of slags.

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Continued from the preceding reports, (Tetsu to Hagané 39 (1953) p. 587 & 688) the author measured potentials on the molten slag systems CaO-Al₂O₃-SiO₂, CaO-MgO-Al₂O₃-SiO₂, by means of the C (gr.)-SiC electrode pair and calculated a_CaO, a_SiO2 in these systems, utilizing the next relations:
From the behaviors of Al₂O₃, MgO upon the aCaO and aSiO₂, it was made clear that these oxides were amphoteric in these systems. The author considered this reason from the view point of the general theory of acid and base, and suggested that, in the multiple systems, all oxides excluding the most powerful acid & base behaved as arnphoteric.
Moreover, it was concluded that, as the basicity, CaO/SiO₂ was the most proper expression.

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The growth of ductile cast iron by repeated cyclic heating were measured in air and vacuum in comparison with other type cast irons and in order to observe the process of growth, some experiments were performed by a dilatometer. and micro-structure and strength of these cast irons after cyclic growth were also examined.
The results obtained were as follows:
(1) Growth of ductile cast iron both in air and vacuum were less than that of normal cast iron melted with same conditions except magnesium treatment in ladle, and the growth increased by remelting.
(2) Growth increased with elevated heating temperatures (750-950°C), but the effects were poor.
(3) Oxidation effects and decrease of strength by cyclic heating were not apparent.
(4) With the same rate of cooling and heating on the curves of length-change of ductile cast iron the Ar₁ expansion and the Ac₁ contraction apparently were not found, but with other type cast irons these changes appeared. Consequently in the microstructure of ductile cast iron more ferrite were observed.
(5) The growth of ductile cast iron were caused namely by the locational irreversibility of graphite reformation during the heating and cooling, and growth of cast iron varied with the mechanism of ferrite formation through critical range and the effects of oxidation for each cast iron.

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By actual use of the Stiefel-Mannemann piercer, the authors studied the effect of plug position upon the state of piercing phenomenon from practical points of view. The experiments were divided into two parts, namely No. A test and No. B test. In No. A test, the same plug was set back and forth in the axial direction by 60mm. In No. B test, the length of plug's upper part was made varied with in the same range of dimension.
The results obtained by No. A test were summarized as follows:
(1) O.D. and wall thickness of tubes increased, and on the other hand the elongation rate of same decreased.
(2) The power required decreased.
(3) The twist of the tube surface became larger.
(4) The piercing speed of tubes increased, while the slip diminished.
(5) The revolving speed of tubes remained unvaried.
(6) The distribution of reduction rate and speed during piercing operation became smooth, followed by the fall of peak.
(7) The cracks on inner surface of the tube somewhat decreased.
(8) The cracks on outer surface of the tube were deepened.
The results obtained by No. B test were as follows:
(1) Dimension, power, piercing speed, revolving speed, reduction rate and speed and inside defects remained unvaried.
(2) The twist of the tube surface became larger.
(3) Outside defects were deepened.
Making use of the above results obtained, the following conclusions were drawn.
(1) By moving plug position, the dimension of tubes was enabled to be made varied.
(2) The more plug was set in forward position, the more advantageous was it for us with respect to the surface twist and outside defects of tubes. But it could not be said that it was especially beneficial to inside defects of tubes.

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The authors selected three kinds of 27Cr-5Ni steel, 27Cr- 5Ni-1Mo-1Cu steel, 27Cr-10Ni-1Mo-1Cu steel and made research on the influence of heat treatment at temperatures from 700° to 1100°C, the formation of sigma phase and various surface treatment upon the acid resistance. The corrosion tests were performed in the boiling 5% sulphuric acid.
27Cr-5Ni steel showed the weight loss by corrosion more than one hundred times as much that of other steels, whatever might be the treatment.
27Cr-5Ni-1Mo-1Cu steel had the best acid resistance among three kinds of these steels. This steel had the stable acid resistance when had heen water-quenched at 1000°and 1100°C. At 1100°C, this steel became nearly uniform α-structure by γ→σ transformation, and so the acid resisting property was better.
27Cr-10Ni-1Mo-1Cu steel formed sigma phase at the temperature range from 700° to 900°C and so the hardness and the weight loss by corrosion increased, but quenching at 1000° and 1100°C improved the acid resistance by resolution of the sigma phase.
When these steels were heated for 200 hours at 800°C, 27Cr-5Ni steel did not form a sigma phase but 27Cr-5Ni-1Mo-1Cu steel formed a sigma phase on account of presence of molybdenum resulting in α+γ+σ structure, then the hardness and the weight loss by corrosion increased remarkably. 27Cr-10Ni-1Mo-1Cu steel became γ+σ structure by complete performance of α→σ transformation, and the weight loss became more than that of one hour heating at 800°C.
The surface treatment, included a heating the steels in vacuum, H₂, N₂ or O₂ atmosphere at 200°C, an immersion in conc. nitric acid or sat. chromic acid solution anda cathodic treatment in KOH solution. All these treatments improve acid resistance and remove the unstability of acid resistance caused by different charge and heat treatment near 700°C on the 27Cr-5Ni-1Mo-1Cu steel which substancially has superior acid resistance. But such treatments had little effect for steels having substancially inferior acid resistance.

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To investigate the influence of vanadium and manganeae on the properties of air-hardening die steel containing 1% carbon, 5% chromium and 1% molybdenum, the authors measured Critical point, bardenability, hardness, retained austenite, specific volume and dimensional changes.
The results obtained were as follows:
(1) Critical point was raised with the vanadium content, and lowered with the manganese content. Hardenability was increased by addition of the vanadium up to 0.48%, then decreased with more vanadium addition. Manganese was very effective in increasing the hadenability.
(2) Full hardness was obtained by the oil-quenching from 900° to 940°C and by air cooling from 920° to 960°C. As the vanadium content increased, a slightly higher austenitizing temperature was necessary for obtaining the full hardness.
(3) The quantity of retained austenite increases rapidly with the quenching temperature, and the amount increaased with manganese content, and decreased with vanadium addition.
(4) A slight secondary hardness was exhibited at 550°C if the quenching temperature was 1000°C or over. On tempering, a decompoaition of the retained auatenite took place in two steps.
(5) The volume increment resulting from air-hardening was less than oil quenching. A steel containing 0.86% vanadium showed a volume increment of 0.27% by air cooling from 940°C and showed a dimentional change of +0.065% by air cooling from 940°C and +0.115% by oil quenching from 920°C.
(6) The amount of contraction measured by dilatometer due to α→β martensite during tempering of air hardening was leas than oil quenching.
(7) The absorbed energy measured by static bending test after air-hardening increased with addition of the vanadium up to 0.48% and then decreased with more vanadium content.

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Apparatus of the high voltage a. c. arc source (4400-2A; 2200V-4A) as the light source of spectrographic analysis was designed and manufactured, and the quantitative spectrographic analysis of manganse, titanium, silicon, nickel, chromium, and arsenic in steel was carried out by it. It was ascertained that the quantitative analysis which hsd been impossible for small amount of the above elements in steel in the usual spark discharge method, became possible in high sensitivity and about 3-8 percent reproducibility by the above apparatus.
As for the other characteristic, it was proved that there was practically no continuous background and few loss of testpieces on account of a lower temperature of the electrode.

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Pyrite cinders are one of the most important resources of raw mateirals in Japan. They are, however, greatly restricted in their utilization as raw materials for pig iron production, because of its higher Cu content.
The author made some experimental research, since 1950, on the elimination of the Cu content from pyrite cinders at Hirohata Works of Fuji Iron & steel Co., Ltd.
The processes were as follows:
(1) To separate pyrite cinders by a magnetic separator into magnetic pyrite cinders and nonmagnetic pyrite cinders.
(2) To roast magnetic pyrite cinders at 450°-600°C for more than one hour.
(3) To mix both cinders, roasted and unroasted.
(4) To water-leach the mixtures and eliminate much amount of the Cu content.
The first plant in Japan for this purpose was installed in 1952 and the author operated for mass production and continued to develop its application.
The author could now get such eliminating rate as 25-30% by a simple water leaching and more than 50% by a kiln roasting. (the magnetic separator not yet completed).
The author could expect, therefore, to get larger eliminating rates by some modification of the equipments.

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