The physico-chemical principles involved in iron and steel making process were discussed. Presence of silicon reduced solubility of the carbon in iron. From this experimental data, it was concluded that the activity coefficient of the carbon diminished with the silicon. Since the diffusion constant of the silicon in iron is about one hundredth of that of the carbon, it is considered that carbon diffuses from a high-silicon steel to a low-silicon steel, even though the carbon content of the lower silicon is the greater. In steel making practice, it was found that 15min after the addition of ferrosilicon, the concentration of the silicon in the surface layer of molten bath was several times greater than that in the bottom layer, whereas, the carbon content of the surface was less than that of the bottom layer of the bath. According to J. Chipman, the reduction of silica in blast furnace slag by the carbon in molten pig iron did not reach eguilibrium even after a long period of holding at 1525°C. This results may be interpreted so that the reduction of silica forms the high-silicon layer which interrupts contact of the slag and the carbon in molten pig iron and prevent further reduction of silica. This high-silicon layer also affected upon the rate of desulphurisation of molten pig iron. Desulphurising power of the manganese increased as temperature went down. However, at 1200°C, 1% Mn in liguid iron could not lower the sulphur content to 0.47%. On the other hand, activity coefficient of the sulphur in pig iron was about five times greater than that in pure liguid iron. Therefore, it was expected that the pig iron contained about 0.09% S might be obtained by presence of 1% Mn.

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Viscosity of Synthetic CaO-SiO₂-Al₂O₃ slags was measured by rotating an innercylinder viscosimeter. Iso-viscosity lines at 1, 500 and 1, 600°C were plotted on the diagram. Viscosity of CaO-SiO₂ slags at 1, 600°C increased with SiO₂ content; and anomaly was not found at the composition corresponding to CaO-SiO₂. By a small amount of Al₂O₃ added to CaO-SiO₂ slag the viscosity was almost unaffected, but at more than 20% Al₂O₃ increase of the viscosity became remarkable. Viscosity of the CaO-Al₂O₃ side slags which had never been determined were found rather low and comparable to the low viscosity region in the CaO-SiO₂ side slags. And some considerations on structures of these molten slags were given from the experimental results.

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Influence of Mn on the hardness and impact resistance of Cr-Mo cast steels containing Cr 1.2%, Mo 0.25%, and Ni-Cr-Mo cast steels containing Ni 2%, Cr 1.5%, Mo, 0.4% were investigated. The results obtained were summarized as follows:
(A) Cr-Mo-Mn cast steel: The hardness increased with addition of the Mn increase, and with 1.8% Mn addition the hardness reached to the maximum value. The impact resistance showed the maximum value at Mn content 1.0-1.4%. The first temper-brittleness, which took place at 300-400°C, was marked as the Mn content increased.
(B) Ni-Cr-Mo-Mn cast steel: The hardness increased with increase of the Mn content.
The impact resistance increared slightly with the addition of Mn up to 1%, but with higher Mn addition it decreased rapidly. The first temper-brittleness took place at about 400°C, and it showed a large sensibility as the Mn content increased.
In general the Ni-Cr-Mo cast steel was somewhat lower in strength, but addition of Mn to these cast steel, the strength and toughness was markedly increased due to the quenching properties and uniformity of heat-treatment.

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The author investigated the repeated impact value of 0.25-1.09% plain carbon, Ni-Cr, Cr-Mo, Ni-Cr-Mo, Mn-Cr-Mo. Mn-Cr-Mo-V, high C-Cr and high C-high Cr-Mo steels, by the Charpy impact and the Matsumura repeated impact testing machines. Because, although these steels have been utilized for hollow-shank-steel in America as well as in European countries, we have had no suitable shank steel in Japan until now.
The results, are summarized as follows:-
(1) The results of the repeated impact test were shown in Figures 2, 5 and 6, which were plotted to logarithmic scales. There was a certain amount of scattering of results, but in each case a mean straight line could be drawn through the points to include the single blow test.
(2) Accordingly, these lines were represented by the equation Y=dX+β. In this case it was intended to enlarge β.
(3) 0.55%C steel was presumably the most excellent among all plain carbon steels, and Ni-Cr-Mo steel the most suitable for shank steel.

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The following heat-resisting steels for gas turbine blades were made and several properties were studied:
(i) High C-Cr-Ni austenitic steel (C 0.5, Cr 15, Ni 20, W 3, Mo 3) (ii) Tinidur of Krupp (C 0.1, Cr 15, Ni 30, Ti 2) (iii) High Cr-Ni-V steel (C 0.3, Cr 19, Ni 9, W 1.2, Mo 1.3, V 1, (N 0.15)) (iv) Timken 16-25-6 type (C 0.1, Cr 16, Ni 25, Mo 6, (N 0.15)) (v) LCN-155 (C 0.1, Cr 20, Ni 25, W 2, Mo 3, Co 20, (N 0.15)) (vi) WH42B (Cr 18, Ni 45, Co 25, Ti 2).
Also influences of about 0.15% nitrogen added in the samples (iii)-(v) by using nitrogenized ferro-Cr were tested.
(a) These samples were generally difficult to forge, especially in (v) & (vi). The difficulty was, however, overcome after several trials in melting and forging processes, and success obtained in making the test piece. (b) At first the hardness and microstructure of specimens were studied, with samples heated at 1000-1200°C for 30min-10hr, and tempered at 600-900°C for 30 min-10 hr after quenched at 1100-1200°C. (c) Next the tension and impact tests at high temperatures up to 800°C were made, with specimens quenched from 1100°C and tempered at 800°C.
And also, the high temperature creep tests at 600 and 725°C were made. (d) From these results obtained, WH42B and N-added LCN-155 seem to be the most suitable for gas turbine blades among these samples studied, and non-N LCN-155 or N-added Timken 16-25-6 type was also recommended. For this purpose, besides, there was N-added high Cr-Ni-V steel, being of considerably inferior quality. Problems in practice were the scarcity of Ni & Co, the trouble in N-adding procedure and the difficulties in ingot forging. If, however, the series of the authors 301 (C 0.4, Cr 14, Ni 15, W 3) was used for this purpose, could not expect a higher thermal efficiency in gas turbines.

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