In order to study the behaviour of TiO₂ in molten slags, the electrical conductivity of the Na₂O-SiO₂-TiO₂ system was measured. The measured range of composition was TiO₂ 0-35 mol% at Na₂O/SiO₂=0.40, 0.50 and O.61 The conductivity decreases smoothly with temperature. At constant temperature the conductivity remains almost unchanged for the slags containing TiO₂ less than 10mol%, but with more TiO₂ the conductivity decreases with increase of TiO₂.
The conduction mechanism is ionic and the mobile ion is Na⁺. Ti ion cannot move, because the bonds Ti-O is strong owing to small ionic radius and large ionic valency.
The molar electrical conductivity, which corresponds directly to the mobility of Na⁺, was calculated. At the range of low TiO₂ contents Ti ions distort Si-O network, raising the mobility of Na⁺, while at the range of high TiO₂ contents oxygen ions impede the conduction of Na⁺, thus lowering the mobility of Na⁺. The latter behaviour of TiO₂ is different from SiO₂ or Al₂O₃, because TiO₂ lowers viscosity of sodium-silicate contrary to SiO₂ and Al₂O₃. TiO₂ is amphoteric, and it behaves as basic oxide at low contents, while it is like an acidic oxide at high contents.
For the series Na₂O/SiO₂=0.50 the conductivity of slags containing TiO₂ 40-50 mol% was measured. In the conductivity-temperature curve an anomalous point appears in the neigh-bourhood of solidifying temperature, suggesting the behaviour of TiO₂ as a semi-conductor.
It was summarized that the peculiar behaviour of TiO₂ would be ascribed to the following facts:
(1) The bonds Ti-O are strong, and Ti ion has the strong action of "network distortion"
(2) Ti is a transition metal, and TiO₂ is a typical semi-conductor.

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A study was made of vacuum heating method up to 1200°C, and vacuum fusion method up. to 1800°C in a graphite or Mo crucible for determination of hydrogen content in steelmaking slag. To analyse the gas extracted by vacuum fusion of the specimen, thermoconductivity method was applied, the accuracy of which was improved by means of new type thermocon-ductivity cells, made from thin Cu tubes dipped in ice water which was stirred by an impeller and separated from. contact with ice by a network. The followfng conclusions were reached:
1) Hydrogen in steelmaking slag could not be extracted completely by vacuum heating only up to 1200°C for complete extraction of hydrogen. It should be heated to above 1400°C or its melting Point
.2) H₂O in the specimen was quantitatively decomposed in the vacuum furnace and extracted as H₂ when it was melted in a graphite crucible. This fact was confirmed by extracting H₂ in minerals such as gypsum and actinolite.
3) Strong adsorption of H₂ caused by vaporization of reduced material of slag specimen in the vacuum furnace was found, when it was heated at high temperature in a graphite crucible. The effect was minimized, on the contrary, when a Mo crucible was used.

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The authors studied on the effect of silicon on the properties of shock-resisting steel containing 0.5%C, 1.5%Cr, 2.2%W and 0.2%V in the first report. (Tetsu-to-Hagane. Vol. 40, No. 10, p. 1001) In this report, the effect of C and V on the transformation, the hardenability, the as-quenched and tempered hardness, and the mechanical properties were investigated.
The results obtained were as follows:
(1) The critical point was lowered with the carbon content and raised with the vanadium addition. The Ms-point was lowered with the carbon content.
(2) The hardenability increased with the carbon content, and decreased with the addition of vanadium.
(3) The full hardness was obtained by the oil quenching from 860°C to 940°C, and as the carbon content decreased, a slightly higher austenitizing temperature was necessary for obtaining the full hardness.
(4) During tempering, the Charpy impact value increased by a terripering temperature up to 200°C, then decreased at higher temperatures and minimum impact value was exhibited at a temperature between 300°C and 350°C.
As the carbon content increased, the yield point and the hardness increased and the impact strength decreased.

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The authors investigated the fatigue strength of hollow drill steel rods under reversed bending, using an electromagnetic resonance type fatigue testing machine, as shown its block diagram in Fig. 1. 53 kinds of foreign and home manufactures are refered to the preparation of 10 kinds of test steels, whose chemical compositiong, physical and mechanical properties are listed in Table 1-2.
Results obtained were as follows;
1) Fatigue limits of hollow drill steel rods showed 20-30kg/mm2. Those were not affected by the kind of steel, but largely by their method or heat treatment. (Fig. 2)
2) Steels with the troostitic micro-structure, of hardness around Hv 400, couldobtain the maximum fatigue strength. (Fig. 3)
3) Surface conditions of hollow drill steel rods had a considerable influence on their fatigue strength.

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The dimension change of case-hardening steels resulting from carubrizing and heat treatment was investigated. Cylindrical specimens made of low carbon Cr-Mo and Ni-Cr steels were used. They were normalized, carburized, quenched, (sub-zero treated) and then tempered in accordance with usually adopted methods, and the dimension change was measured with a precise comparator at each heat treatment step. The results wefe as follows. There was no substantial difference between Cr-Mo and Ni-Cr steels with respect to dimension change resulting from carburizing and heat treatment, but fibre structure caused by rolling had an intimate relation on the dimension change of both steels. The mechanism of this phenomenon was explained by the heating and cooling transfgrmation curves gained through a Leitz dilatometer.
In conclusion, the author proposed some recommendable methods of carburizing and heat-treatment according to his experimental results.

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The influences of solution-treament (1000°-1250°C) and of nitrogen (0.04-0.16%) on the high-temperature age-hardening phenomena (600°-950°C) of the Timken 16-25-6 heat-resisting alloy were studied.
The results were as follows;
(1) The influence of nitrogen on the hardness of solution-treatment was little. In microstructure, almost homogeneous solid solution was obtained by the solution-treatment at 1200°C for 1 hour. As the nitrogen content was higher the, temperature at which the majority of precipetated small particles were dissolved became lower.
Grain growth began at 1100°C and generally the higher the nitrogen content was, the lower became the temperature of grain growth and the more serious the degree of grain growth. The solution-treatment seemed suitable at 1170°C 1 hour.
(2) The maximum age-hardening was obtained at 700°C. Generally the higher the nitrogen content was, the slower became the rate of hardening, however at the temperature above 850°C the influence of nitrogen on it became small. As for microstructure, at 600°C precipitation arose mainly at the grain-boundaries, but at 700°C they precipitated mainly at the cleavages and "striated structure" was obtained and at the temperature above 800°C, precipitated particles globulized and at 900°C conspicuous coarsening of precinitated particles began.
(3) In order to obtain the complete high temperature age-hardening, when the nitrogen content was higher, the higher solution-treatment temperature became necessary. For the age-hardening at 700°C for 70 hours, at the solution-treatment temperature under 1100°C specimen C was minimum, but at 1200°C the influence of mitrogen was remarkable and except specimen A, the higher the nitrogen content was, the smaller became the degree of agehardening.
(4) As for age-hardening at 700°C for 500 hours, in case of 1200°C for the solution treatment temperature the higher the nitrogen content was, the smaller became the degree of hardening, while at 1250°C for the solution treatment temperature, the higher the carbon plus nitrogen content was, the more became the degree of hardening for the age-hardening at 600°C for 1000 hours, the rate of hardening was very slow and at times over 500 hours the hardeness of all specimens approached constant value independent of nitrogen content. The microstructure after the age-hardening at 600°C for 1000 hours was "striated structure" and the microstructure at 700°C for 500 hours was similar to it at 750°C for 70 hours.

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In this paper, the apparatus for determination of hydrogen contents are described. The authors succeeded in to shorten the time to determine the gaseous contents in iron and steel. It took about 15-25 minutes.
The principles of this new "Hydrogenmeter" are as follows.
In vacuum extraction method with graphite crucible, the gases to be obtained were limited to CO, N₂ and H₂. As CO and N₂ are isosteric molecules, so hydrogen contents were easily and exactly determined by measuring the difference of their thermal conductivities.
The authors found that the glass-covered thermisters with high electric resistance were enough to attain the above mentioned aim. The best method fordealing with the thermister were determined, using it as bridge arms, and the conditions to obtain a simple calibration equation were given theoretically; thus the errors of thismethod were of the order of only a few %, and necessary minimum quantities of gases were 0.006cc-0.01cc.

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The author reviews at first his prenious works on iron carbides by electron-diffraction method. Conditions of formation and decomposition of carbides are described briefly. Under 300°C, carburizing gases (CO or CO+H₂) act as oxidizing agent but this difficulty is avoided by covering the specimens with fine powder of reduced iron. Thus the author obtains the hexagonal iron carbide (ε phase). Starting from this carbide, by heating in vacuo intermittently or continuously, the author observes the transition ε→χ→θ→Fe-C and he finds no precipitation of graphite when χ phase transforms into θ phase. Namely, it appears to him that the transition is an allotropic change. This indicates that the iron carbides have approximately the same composition or they have relatively wide range of composition. The author believes that the latter view is better for interstitial alloys like iron carbides.
The author studies the tempering mechanism of quenched steel by measurement of instantaneous specific heat and he finds five principal peaks on the curve. A tentative mechanism of tempering is proposed. (1956.4.26)

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