The reduction of silica from molten slag to molten iron by H₂ gas is one of important reactions in iron and steel making process and the equation is shown as follows:
(SiO₂)+2H₂ [Si]+2H₂O……(1)
when the slag is saturated with SiO₂ equation (1) becomes,
(SiO₂)sat+2H₂ [Si]+2H₂O……(2)
As the direct measurement of the equilibrium of equation (1) is difficult we have measured the equilibrium of equation (2), using a pure silica crucible at the temperature range from 1500°G to 1600°C.
From the experimental results it is found that (a) the relation between (pp²H₂/pp²H₂O) and[Si] % at a given temperature is expressed by a straight line, and the solution of molten iron-silicon may be accepted as an ideal solution at the silicon conoentration below about 10% and (b) the temperature function of the equilibrium constant is expressed as follows;
logK^S_Si-H(=pp²H₂/pp²H₂O[Si])=12803/T-3·1673

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The author has investigated the method of sampling of hydrogen in molten iron. The results obtained are as follows; -
1) By means of sampling on the case of molten steel, the result obtained is generally high and inconstant.
2) Sample must be chilled perfectly.
3) Addition of deoxidizer is not needed
4) On the sample within the range of 2.5-4.0% C and 1.5-3.5% Si, in the diameter of sample is about 15m/m, it is chilled perfectly.
5) The surface of sample is not needed to be finished.
6) For cooling the sample after taken up from mould, mercury must be used.

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The oxidation test on steels which was reported as in the past, was proceeded below 1200°C, and the authors studied on the oxidation beyond 1200°C. By our studies the existence of the temperature of oxidation resistance limit was confirmed. The values of the limiting temperature was laying at 1350°C as armco iron, at 1300°C as Fe-Al alloys, at 1170°C as Fe-Si alloys, at about 1150°C as Fe-Al-Si alloys, at about 1250°Cas Fe-Cr-Si alloys. Beyond the limiting temperature, the part of the scale begin to melt and the oxidation resistance become wo se suddenly.

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This experiment is the continuation of former report (v). The results are summerized as follows:
(1) If the soft steel (rimmed and killed) with 0.1-0.2% C be pickled and broken immediately, we can always find the fish-eye-like defects on the fracture of tensile test pieces. And the appearance of this defects (with round or irregular round shape, bright surface and gas-pipe-like hole in the centre) is similar to fish-eye or bird-eye in the welded steel.
(2) The tensile properties and the appearance of defects hardly vary with its heat treatment or duration of pickling.
(3) This defect does not occur during the pickling.
(4) This defect vanishes, if the pickled test piece be left long time in theroom or boiled several hours in water.
(5) It is supposed that this defect also would be occured by the same cause as the normal flakelike defect of special structural steel and the difference of its appearance be caused by the difference of mechanical or plastic properties of steel against the stress.

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The ageing mechanism of various permanent magnets: namely, M.K. Steel, Cunifealloy, Kosteralloy, Fe-Al-C alloy and Fe-Mn alloy were inve tigated. From the changes of magnetic properties, hardness, Xray-and Micro-structures by tempering of quenchel samples at proper temperatures, we obtained the folowing results. (1) In Fe-Mn a loy, the hardened state is caused by the dispersion of austenite in martensite, formed by cold-working. (2) In Koster alloy, the hardening proceeds with the precipitation of the compound and in the maximum hardened state, the precipitation is already completed. (3) In Cunie alloy, the maximum hardened state is obtained after the precipitated 2 phases coagulat. (4) In Fe-Al=C alloy, the primary hardening is caused by the austenite-martensite transformation and the secondary hardenig by the precipitation of the d ub e carbide. (5) In M.K. Steel, the precipitation of the 2 phases (α.α') do not occur, and it hardens as the preliminary process of the precipitation. Then the tempering curve of M.K. steel was drawn, and the activation epergy of ageing was calculated.

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The writer carried out the experiment of mutual relation between Cr 2-6% and W 2-8% in the Cr-W tool steel for hot work containing C 0.25, Mn 0.7, V 0.45%. As the results of this investigation, tempering hardness becomes higher as tungsten content increases for constant content of chromium When it is qnenched from 1100°C, and the hardness in bigh temperature will become higher, and then the resistance for softening of tempeing increase as tungsten content increases for constant content of chromium, and decreae nearly as chromium content increases for constant content of tungsten. The resistance for softening of tempering are not direct proportional to hardness in high temperature.

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we studied the micro-structure, hardness and shock value of high Mn-Cr-V-N steels containg various amounts of N, V and C, after various heat-treatments. When we melted the samples (8kg ingot) by the laboratory high frequency electric furnace by charging the nitrogenized electrolytic manganese for the mother alloy of nitrogen, we could obtain the sound ingots if the nitrogen was added less than about 0.2%, but the bath boiled and the ingots have many blow holes if the nitrogen was added moreover. To obtain the high precipitation hardening by the heat treatment, it is better to contain the higher amount of nitrogen, but, because of the problems of melting above described, it is necessarly to keep it less than about 0.2%. For the content of nitrogen about 0.2%, it seems most adequate to keep V content at about 0.7%. It is better to be quenched from the higher temperature from the standpoint of the hardening, but, because of the grain growth and the decrease of shock value, it must be quenched, from about 1100-11500°C, and tempered at about 700°C. C content is better to be kept less than about 0.2% from the standpoint of the hardness and the shock value:

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