Mr. K. Wada, who visited the American iron and steel industry last year, pointed out to us that the life of their coke ovens were 25 to 30 years, of which one of the reasons was operation of the ovens having high collecting main pressure. The outline of the preliminary tests and the actual working with a pressure of 6mm water column made on Kukioka No. 1 coke oven was discussed.

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It is difficult to measure the heat transfer coefficient of the refractory materials. Many measuring methods have been described and some of them are as follows:-
1. Periodically repeated heat sources are used.
2. Thermal conductivity, specific gravity and specific heat capacity are separately measured. But we felt difficulties in applying these methods to actual furnaces, so the author introduced the method calculating the heat transfer coefficient approximately by a single heating cycle.
If one face of a plate which expands infinitely in both sides is heated the heat will transfer to the other face. In this case if one heats the plane not continuously but with a definite interval and then stops heating, so the temperature wave will transfer to the other as impulse wave. The temperature of the other face is written approximately such as,
By measuring the temperature change concerning time, it is possible to calculate the mean value of heat transfer coefficient of the refractoty materials.

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The author calculated the amount of active components by making use of the data given in some literatures on SiO₂, FeO (in 1600°C) in the fundamental ternary systems CaO-SiO₂-Al₂O₃ and CaO-SiO₂-FeO respectively, which are the principal parts of blast furnace slag and basic open hearth furnace or electric arc furnace slag playing an important role in making pig iron or steel. It is possible to infer, from these diagrams showing iso-activity lines, the relative functions of main slag components. But alteration of diagram into intuitive one by acquiring more accurate knowledge of the diagram of ternary phases is desired.
At the same time the more reliable data on the activities of slag components are accumulated by measuring them physico-chemically or electrochemically, the more precise iso-activity diagrams will be gained. It is assured that much useful information of its application to the practical operation will be obtained, if the method of calculation applied to the basic binary or ternary systems should be applied to the splendid results recently developed.

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Influence of Cr and W on the hardness and impact resistance of Mn-Si cast steels, containing Mn 1%, and Si 0.8%. were tested after oil quenching and tempering. The results obtained were summarized as follows:-The hardness of Mn-Si cast steel rapidly increased with about 1.6% Cr addition, but a higher Cr addition did not enhance the hardness any more.
On the contrary the impact resistance was markedly reduced with the Cr addition increase.
The first temper brittleness took place at 300°-400°C when the Cr content was small, while if Cr content was over 2%, it was very difficult to recover the impact resilience even if the tempering temperature was elevated at 600°C.
With addition of 1.5-2.0% W to Mn-Si cast steel, containing 1% Mn, and 0.6% Si, the hardness and impact resistance showed an excellent value in these steels, and the high strength and tenacity were obtained by addition of 1.5% W.
Addition of 0.8% W to Cr-Mn-Si cast steels, containing 1% Cr, 1% Mn and 0.6% Si, developed an excellent resilicnce when the W content is about 0.8%.
According to the author's conclusion from the present test, the Cr-Mn-Si-W cast steel is superior in strength and toughness as compared with the Mn-Si-W steels.

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Electrical properties of iron grid materials containing 3% C and 3-6% Si were discussed metallographically, and the following results were obtained.
1) Assuming the materials as Fe-C-Si ternary alloys, the specific electrical resistance was calculated theoretically in the case of two phase alloys consisting of both silico-ferrite and graphite or cementite, and it was clarified that the specific resistance is influenced significantly by the amount, form and distribution of graphite even in cast iron of the same chemical composition.
2) Ferrite enhances the electric resistance as the concentration of silicon in the solid solution increases. As the electric resistance of graphite is very high as compared with that of ferrite, irons high in both carbon and silicon are suitable so far as the electric resistance is concerned.
3) The higher the concentration of silicon in ferrite, the less becomes its temperature coefficient of the electric resistance. Besides, the value of the coefficient in graphite has negative sign. The temperature coefficient of irons, therefore, is less in the case of high silicon and high carbon irons having large graphite flakes.
4) While the values of specific resistance become high, their temperature coefficients become low in slowly solidified irons containing much silicon, because of the existence of flaky graphite and high silicon ferrite.
5) By the graphitization treatment of cementite-containing irons in the as-cast condition, the amount of graphite increases and the concentration of silicon in ferrite decreases. The increasing amount of graphite enhances the electric resistance, while lowers its temperature coefficient. On the contrary, the lowering of silicon concentration in ferrite causes to decrease electric resistance and to increase its temperature coefficient. As the result of the above mentioned opposite actions, the graphitization of irons generally causes both specific resistance and its temperature coefficient to increase.

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Already described in the Report (I) of the previous issue.

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For the purpose of ascertaining the properties of sintered iron ore, the authors synthesized fayalite and other specimens from ferric oxide and quartz sand by reduction method with solid carbon and CO-gas, and investigated their microstructure, reducibility and some other properties. The outline of the results obtained were as follows:-
Fayalite could be synthesized by the reduction method, and crystalized thoroughly to form a lathlike shape, a pillar shape or an irregular polyhedral tabular shape. But, when the heating temperature was above the liquidus line of FeO-SiO₂ diagram, fayalite and its eutectic matters were liable to present glassy state.
In the other sintering test at 1000-1105°C of small briquettes which were made from the raw materials of coke powders and two kinds of ores, a peculiarly characteristic structure, which indicated the formation of Wüstit phase and metallic iron during sintering process, was recognized.

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In the foregoing papers it was reported that, with addition of ferro-chromium in the last period of refining, how the non-metallic inclusion in molten steel varied, when chromium steel was melted in a basic arc furnace, basic and acid open-hearth furnaces. (Tetsu-to-Hagane, Vol. 36, 1950, No. 11, p. 15; Vol. 37, 1951, No. 3, p. 19) Further, the effect of chromium contained in the charging materials upon the non-metallic inclusion was investigated.
Summarizing the relation between chromium and non-metallic inclusion, the following table was obtained.
Namely, the effect of chromium on the non-metallic inclusion in every case had a quite similar tendency at the same furnace, but, comparing the case of basic arc furnace with that of acid open-bearth furnace, an entirely opposite phenomenon was observed. In the case of basic openhearth furnace an intermediate effect of the above two was shown.

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The author investigated the rapid method of measuring slag basicity and decided the method with a reflex microscope in which the slag basicity could be measured in 5-15 minutes. But this method was not yet applicable in some points to an electric furnace melting practice. Therefore, the author continued to investigate the method which was more applicable to the actual operation than the above-mentioned one.
The results obtained were as follows:-
The slag basicity could be measured with conditions of surface, fracture of slag pancake and colour of slag powder. The relations between lustre and crease of surface, porosity of fracture, colour of powder, basicity (CaO/SiO₂) and ΣFeO were decided. As the result of these experiments, basicity and ΣFeO could be measured in only 3 minutes after the slag pancake was taken. But this method was a little inferior to the method by reflex microscope in accuracy.

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The conditions, necessary for the production of the cast iron having all eutectic graphites, were determined having the cast iron of common grade brought into contact with the slag of CaO-SiO₂-Al₂O₃ system containing TiO₂.
It was found that about 0.2-0.3% titanium was contained in the cast iron having all eutectic graphites, produced by the method above mentioned. This increase of titanium did not reduce the nitrogen content of the cast iron.
The authors explained the reason why the graphites in the cast iron were refined under the slag treatment as follows:
A great part of titanium contained in the molten cast iron presumably exist in the form of TiC. When the cast iron containing about 0.2-0.3% titanium solidifies, a great number of minute TiC crystals disperse into the eutectic form containing cementite or graphite, barring the development of graphite crystals.

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Picking up a kind of samples which contained 1.16% C, 0.23% Si, 0.4% Mn and 0.47% Cr, the authors studied on the effect of cold rolling reduction and annealing on the hardness and size of cementite of the safty razor blade steel.
As the results of this investigation, it was ascertained that the hardness became lower as the annealing temperature was raised to 725°C. In the case of cold rolling reduction of 35-18%, the hardness showed minimum value at range of annealing temperature of 500-725°C.
When the annealing time was 3 and 6 hours, the hardness became scarcely different. The size of cementite was not influenced by the annealing temperature under the A₁ point, and then grobulizing of cementite became more remarkable as annealing temperature was raised to the A₁ point.

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