The changes in some properties of cast iron treated by blowing of various gases (N₂, coke gas, H₂, air, CO₂ and O₂) into the molten state were investigated.
(1) By the blowing of reducing gases such as H₂ and coke gas, the fluidity of molten iron increased and the precipitation of flaky graphite was accelerated. The above mentioned phenomena were distinct in the B.F. iron containing of Ti, V and other impurities.
(2) By the blowing of N₂, air and CO₂ gases into the B.F. iron, the fluidity decreased, but the changes in other properties of the iron were not nearly observed. On the other hand, in a charcoal iron the structure was changed into the non-uniform fracture with fine graphite and at the same time the fluidity and tensile strength decreased.
(3) By the blowing of O₂ into B.F. irons6), impurities such as Ti, V and etc. decreased, and moreover the mechanical properties were improved so as to show the character near to that of charcoal iron.
(4) The cast iron made of charcoal iron was easily nodulized by magnesium treatment. after the blowing of H₂ or coke gas, whereas that of B.F. irons containing the amount of impurities were more easily nodulized after the blowing of O₂. Perhaps the reason of this phenomena was as follows: it had been known that oxygen and impurities such as Ti, As, V and etc. prevented the nodulizing of graphite by magnesium. By the blowing of O₂ into B.F. irons containing the amount of impurities, some of the impurities decreased but the oxygen- content did not increased. On the other hand, as charcoal iron did not contain impurities, the deoxidation by reducing gases gave the good effect for nodulizing of graphite.

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The authors studied on the effects of atmosphere and contacting time on the corrosion of chamotte brick by molten steels in sequence of report 1, and discussed the actual corrosion of runner brick by the molten steel from acid and basic open-hearth furnace. The results obtained. were as follows:
(1) The corrosion of chamotte bricks by the molten steel were influenced by the atmosphere very much, and the oxygen in the air promoted the corrosion.
(2) The oxygen oxidized the molten iron and manganese, and after these oxides diffused into the molten steel they promoted the corrosion. But corrosive ability of iron oxide was larger than that of manganese oxide, especially in case of low manganese content in the-molten steel.
(3) The longer the contacting time, the corrosion of chamotte bricks by molten steel were-the more promoted.
(4) In the actual corrosion of runner brick, by the molten steel from acid and basic open-hearth furnaces the authors demonstrated that the former corrosion was less than the latter, in consideration of the analysis of non-metallic inclusion in the molten steel just before pouring as well as seing from the analysis of floating slag in the mold.

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The author tried to describe the mechanism of formation of the segregates in the Λ segregated zone on the basis of results of the observation about the d segregated zone of 20t steel ingots. Impurity-rich drops of molten steelobeing in contact with the solidified shell tended to float upwards, interrupting growth of dendritic crystals, and some of them obstructed to float became segregated facets.
This obstacle of floating resulted in the Λ-inclination of segregated facet.
Supposing that the segregated line was nothing but the abnormally grown segregated facet, the author described the transformation of segregated facets to lines and the growth of the latter. Finally, mentioning of the solidifying speed, the casting condition, the content of hydrogen in molten steel and the alloying elements as the main factors controlling the formation of segregates, he considered about the effects of each factor.

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As a first step to study on residual stress in cold-drawn steel tubing, the author performed a preliminary test for determining the residual stress in tube-shaped test specimens. In selecting the various methods of measurement of residual stress, the author decided to adopt Sachs and Espey's splitting method, and investigated fully on this method, then obtained the following results.
(1) For determination of the diameter change, Sachs and Espey used an optical comparater and measured the length between the gauge points plotted on the outer surface both sides of the split line before and after splitting. But if, by splitting, there should take place the elastic deformation at the outer surface of the opposite arc, then the diameter change measured by this method resulted in the inclusion of this error. Therefore except for tubings with small diameter or thin wall thickness, this method was inferior, in regard to accuracy, to that which had been calculated from the mean outside diameter measured with a micrometer.
(2) But, when the author measured the diameter with a micrometer, if the wall thickness of the specimen tube be thin, the specimen was deflected by measuring pressure and this deflection resulted in an error in measurement. Then the author obtained the relationships between the specimen dimensions and the deflection amount by calculations. (Fig. 3)
(3) As the result of the above fact, the author revealed that the measurement with a micrometer within the size ranges of ordinary steel tubing was superior, in accuracy, to that with an optical comparater and he decided to perform the measurements with a micrometer thereafter.
(4) In order to determine the specimen length, the author measured the residual stress in the specimens of various lengths and revealed that the length should be 2 to 2·5 times the outside diameter. (Fig. 4)
(5) The author further obtained by accurate method the distribution diagrams of residual circumferential stress (Fig. 8 & 9) in plug-drawn and sunk steel tubing which had been drawn with two dies of different contour. (As to contours of the die and plug, see Fig. 5 (a) & (b)). As compared with those obtained by approximation method, it was made known that a general tendency was to be revealed through measurement values obtained by approximation method as far as sunk steel tubing and those which plug-drawn with (b) type die were concerned.

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The method for measuring the internal stress of the ring-type test pieces such as ball bearing was not established firmly, and so the calculating formula for measuring two demensional stresses of it was obtained.
By using this formula, the effect of tempering temperature on the internal stress of the ring-type ball bearing steels was studied and the results were obtained as follows.
(1) In case of oil quenching of the ring-type test pieces, the radial internal stress was very small in comparison with the circlumferential interna1 stress. The latter was tensionstress near the inner face. In quenching, the circumferential stress was about +76.9kg per mm2 (tenson) at about 1.4mm, and then about-28.3kg per mm2 (eompression) at about 5.5 mm from the inner face.
(2) In case of the 130°C×1hr tempering, the internal stress increased about twice by the ε carbide precipitation. The circumferential stress was about +139.5kg per mm2 at about 1.4 mm from the inner face.
(3) When the 180°C tempering ring-type test piece was compared with the 130°C tempering one, the former increased a little in the circumferential stress distribution. If the tempering temperature raised such as the above, the internal stress should be reduced by the stress relief. But the internal stress increased a little in fact. This cause was considered to be the expansion phenomenon that the retained austenite decomposed to martensite at 180°C×1hr tempering. It was necessary for the 180°C tempering to be avoided in the pratical heat-treatment.
(4) In case of the 200°C×1hr tempering, the internal stress decreased in comparison with the 180°C and 150°C tempering.
The circumferential stress was about +25.1kg per mm2 (tension) at about 1.4mm from the inner face.

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The distortion of the standard specimens, A and B type, made of ball-bearing steel was measured after various heat-treatments, such as conventional heat-treatment and interrupted quenching the so-called martempering or marquenching, and subzero-treatment.
The most of distortions on quenching were due to the thermal stress during the rapid cooling. By martempering, the thermal strains were eliminated excepting the unavoidable strains directly caused by austenite-martensite transformation. The distortion produced on quenching was reduced by subsequent tempering but increased by subzero-treatment, and in A type specimen whose shape was so complicated its tendency was less than in B type.
From these experimental results, it was indicated that hot-oil quenching and martempering were suitable for the heat-treatment of ball-bearing steel, and that the distortion after quench-temper-subzero-treatment was generally less than that after quench-subzero-treatment-temper.

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In the previous report, ("Hitachi Hyoron" No. 11, 1955) the authors described the effects of Nb, V, Ti and N on the properties of Ni-Cr (20-15%) series heat-resisting steel for gas turbines. In this report, the authors examined the effects of Nb, V, Ti and N on the forgeability, solution-treatment, hardness, aging hardness, microstructure, mechapical properties at high temperaturb, oxidatkon, resistnce and creep limits of Ni-Cr-Co (20-15-15%) series heatresisting steel for gas turbineis.
The results obtained were summarized as follows:
1) In respect to forgeability, Nb was superior, while the specimen A (which contained no special element) Ti and V were comparatively good next to Nb, and then N had worse effect on it.
2) When the solution temperature was 1200°C, the specimen. "A" showed highest aging hardness. Next to the specimen "A", those with N, V, Ti and Nb were good in the term.
3) N conferred the best Property in the tensile strength at high temperature, however when the temperature rose above 700°C, the differences. between the properties pf steels with different elements became very small.
4) In respect to oxidation resistance, Nb was most effective and v had worse effect on it.
5) As for the creep limit, the specimen "A" Was superior, and then, next to "A". speci mens containing Ti, N, V and Nb were good in the term.

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The authors studied the influence of the time of solution-treatment on the mechanical properties at 650°C with Timken alloys. Test pieces of Timken alloys were solution-treated for 1 hour and 10 hours before "hot-cold working" or age-hardening. The results were as follows.
(1) Creep resistance and yield strength at 650°C increased by the long-time solution- treatment before "hot-cold working" or age-hardening, because the precipitate were finelv distributed and the precipitation-hardening during testing at 650°C became prominent.
(2) In the case of the long-time solution-treatment, ductility of creep rupture testing decreased than the case of short-time solution-treatment, because the precipitation during the testilng was more prominent in the former case than in the latter case. On the contrary, the ductility of the short-time tensile test, in which precipitation during testing was slighter than creep rupture test, was smaller in the case of short-time solution. treatment than long-time solution-treatment. It was because of advanced diffusion and homogenizing by the long.time solution-treatment.
(3) Effect of long-time solution-treatment became prominent by precipitation-hardening during-esting, so that its effect was more prominent in "hot-cold-worked" condition than in age-hardened condition, and in the long-time and high-temperature testing than in the shorttime or room-temperature testing.

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Recently, the determination of oxygen in cast iron has been required and it is important to determine not only the total oxygen but the oxygen as each oxide. The non-metallic inclusion method such as the chlorine method, the electrolytic method, the hot nitric acid method etc. is the usual method for determining each oxide in cast iron but this method is tedious and not reliable. The authors studied on the fractional vacuum-fusion method and it was found that by using a tin-bath, FeO could be extracted at 1050°C, MnO at 1150°C, SiO₂ at 1450°C and Al₂O₃ at 1750°C by this simple method. The same cast iron samples were analyzed bv the fractional vacuum-fusion method, the hot nitric acid method, the chlorine method and the electrolytic method. Successful results were obtained by the fractional vacuuni-fusion method in comnarison with the case of the non-metallic inclusion method.

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