It is generally accepted that fayalite is formed in sinter by the reaction between partiallyreduced iron-oxide and silica. Several investigators have reported the formation of fayaliteby the reaction between ferrous oxide and silica experimentally. It is not yet established, however, whether fayalite is formed only after iron-oxide is reduced until ferrous oxide or magnetite reacts directly with silica to form fayalite during a sintering process. This. experiment intended to ascertain whether the reaction of magnetite and silica in solid state results in the formation of fayalite, and confirmed the possibility of this reaction.
In the previous reports (Tetsu-to-Hagané 45 (1959) No. 12, p. 1341 and 46 (1960) No. 7, p. 753) it was revealed that defects which were occurred on the surface and in the core of a billet were prevented by setting the primary and the secondary cooling under the suitable conditions. But the range of the suitable conditions of cooling of the billet was rather narrow and it must be operated restrictedly. Therefore it was important to find out the positive way to prevent the occurrence of the defect of a billet, besides those suitable conditions. In this report, the results of the experiments which were held in order to prevent the occurrence of the surface defects of a billet in other words, to intensify the cooling of a billet in the mold, shall be revealed. To intensify the cooling of a billet in the mold, the first experiment was carried out to remove the air gap between a billet and a mold, and the second experiment was carried out on the tubular mold with thinner wall. It was revealed that the inverse tapered solid mold and thin wall tubular mold showed a greater cooling capacity than with the normal solid mold. But in view of the availability of the mold life, the solid mold with inverse taper is only effective way to intensify the cooling of a billet.
With the chromium-molybdenum steel No. 21 containing vanadium acting as the austenite grain refiner, which had been treated with calcium-silicide as deoxidizer, the authors examined top- and bottom-teeming procedures for ingot making, which had some effects on the occurrence of the sand marks. Experimental results are as follows: 1. The occurrence tendency of the sand marks is a little more remarkable in the bottomteeming than in the top-teeming. 2. Sand marks of the complicated and the amorphous types are found in the examined steel. The rate of the occurrence of the complicated type sand marks are more remarkable than that of the amorphous type sand marks. 3. No difference are found between top- and bottom-teeming procedures in the type of the sand marks and in the nonmetallic inclusions which constitute them. 4. Oxide inclusions in the examined steel mainly consist of MnO and Si02 and, in general, the bottom-teemed ingot has a little more oxide inclusions than top-teemed one. In the topteemed ingot, oxide inclusions are rich in the top part of the ingot, while relatively poor in the middle and the bottom parts of it in quantity. In the bottom-teemed ingot, on the other hand, they are rich in the top and the bottom parts, but relatively poor in the middle part. 5. There is a correlation between the occurrence tendency of the sand marks and the quantities of oxide inclusions. Namely, forged or rolled steel containing many oxide inclusions has a greater possibility of the occurrence of the sand marks in comparison with forged or rolled steel which has less oxide inclusions.
Experiments were made on the residual stress of induction-hardened steels that affect mechanical properties, particularly fatigue limit, and quenching crack of them. Although this problem has been reported in many papers, the author studied each function of thermal and transformational stress that may be generating cause of residual stress when the steel was induction-hardened. Using pure iron, various carbon steels, carburized iron, 13Cr steel and Fe-Ni alloy, the author measured the residual stress of cylinders made by the above materials that were induction-hardened under various heating and cooling conditions, and considerd qualitatively the generating mechanism of internal stress. From the results, the author made clear the behavior of the residual stress when steel shafts had been induction-hardened.
As part of a study for the mechanical properties of spring steel, investigation was made on the effects of sorbitic microstructure, containing proeutectoid ferrite or hardness gradient, on the mechanical properties of C and Mn-Cr steels. Specimens were prepared mainly from spring steels and also from structural steels or casehardening steels for a supplementary pourpose. They were quenched & tempered, highfrequency induction-hardened & tempered, or quenched after carburizing & tempered, and divided into following two groups: A. Specimens, heat-treated to the spring hardness (Hv 400 approx.) throughout the diameter and containing 0--35% of proeutectoid ferrite. B. Specimens, heat-treated to the spring hardness at the surface but to the lower hardness (Hv 210-400) at the center. Results obtained after mechanical tests were summerized as follows. 1. The proeutectoid ferrite shows no clear effect upon the tensile strength. 2. The elongation, reduction of area, Charpy impact value, proportional limit in twisting, proportional limit in bending, and repeated impact value are lowered by the existence or increase of proeutectoid ferrite. The degree of lowering is more remarkable in C steel than in Mn-Cr steel. 3. The fatigue limit in rotary bending is also decreased by the proeutectoid ferrite, but the behaviors in each kind of steel were not revealed distinctly. 4. When the yielding shear stress curve along the radius of specimen, which is determined by the hardness gradient curve, is crossed over by the theoretical load stress line, the maximum shear stress and also the reversed twisting fatigue limit are lowered. 5. To improve the proportional limit in twisting or reversed twisting fatigue limit for the steel bar having hardness gradient, the depth of hardened layer or core hardness must be increased. The relationship between those is given in a following formula:. τmax=τrp. Ed/d-2t, Where τmax: proportional limit of bar in twisting τp: proportional limit of core in. Ntwisting d: diameter of bar t: depth of hardened layer.
The effect of various elements on properties of 19Cr-12Ni type non-magnetic steel was studied. The results obtained were as follows: (1) Yield strength was increased with the carbon content, and nitrogen addition raised the yield strength markedly. The austenitic steel containing 0. 3%C, 1. 1%Si, 1. 3% Mn, 1016% Ni, 1913% Cr and 0. 27 % N had a yield strength of 60 kg/mm2, elongation of 35% and a low magnetic permeability of 1. 003 as oil-quenched from 1050... 2) Cold working had an accelerating effect on transformation from austenite to martensite. Mngnetic permeability after cold working was increased with the carbon content and decreased with the nickel and the manganese content.
Effect of simple, or combined addition of Mo, Si and Cu, on the properties of 30Ni-20Cr stainless was investigated by hardness, tensile, microscopic and corrosion tests. The corrosion tests were carried out with specimens in boiling 5 wt %H2SO4 and 1 wt % HC1 for 6 hours. The following results were obtained. (1) Against boiling in 5 wt % H2SO4 and 1 wt % HCl, 30Ni-20Cr stainless steels containing 3% Mo showed an appreciable corrosion resistance and the same steel containing 3 % Mo+ 3% Cu showed a superior corrosion resistance. Moreover addition of 3-3. 5% Si improved mechanical properties in some degree. (2) A decrease in elongation and Charpy impact value probably may be attributed to the amount, form and distribution of a metallic compound (Fe2Mo), the amount of which has been increased mainly by addition of Mo.