Hypoeutectic Fe-C alloys were melted in a reducing atmosphere and their cooling curves were plotted, when their specimens were quenched at a desired temperature. By the aid of the microstructures and the shapes of the cooling curves of these specimens, the solidification process was discussed. The effects of S, Mn, S, O, W, Cr, and Te were also studied.
The growth of spheroidal graphite cast iron made by calcium addition was examined during repeated heatings from 600° to 900°C and compared with the growth of some other cast irons i. e. the spheroidal cast iron made by magnesium or comparatively high nickel and the flaky graphite cast iron of normal type. If the spheroidal iron made by calcium silicide gave a nearly perfect structure of spheroidal graphite, the growth hardly occurred, while the mixed structure with flaky and quasi flaky graphite gave an appreciable growth. Because of the silicon content over 3 per cents in the spheroidal graphite iron, a ferrite-type structure was apt to be detected. For these cast irons, the transformation point existed in a few repeatings of heating, and disappeared after a several periods of repeated heating.
The purpose of this investigation was to compare, on the same basis, the mechanical and high-temperature properties of various cast irons. The irons used ranged from low-Si irons, through high-Si irons, to high-Al irons, containing small amount of alloying elements, Cr, Mo, Al, Cu. Growth and scaling characteristics of those irons were studied at 900°C for 300 hours. The strength was measured by as-cast specimens and heated specimens at 900°C for 300 hours, and observations were made on changes in the mirostructure. The results obtained were as follows: (1) Small addition of Cr was effective in resisting to growth, but not effective in resisting to scaling and in maintenance of strength at high temperature. And it merely affected the strength after long heating at high temperature. (2) Mo was merely effective in resisting to growth and scaling, but remarkably effective in maintenance of strength at high temperature. (3) Cu was merely effecttive only in resisting to scaling, but it was evil to growth and mechanical properties at high temperature. (4) Small addition of Al increased growth and scaling, but the iron containing from 4 to 7 per cent Al considerably resist to growth and scaling. (5) The 5 per cent Si iron containing 4 per cent Al and 1 per cent Cr has greater resistance to scaling and growth at 900°C. The growth of this iron was almost unmeasurable and its scaling resistance at 900°C was about equivalent to that of 20 per cent Cr cast iron. And its strength not only decreased but merely increased after long heating at high temperature.
Carburizing atmosphere was endothermically generated by conversion of the mixed gas consisting of propane gas, as a by-product of petroleum industry, and air. This atmosphere contained substantially none of the oxidizing gases, but appreciable amounts of reducing gases, carbon monoxide and hydrogen. The endothermic generator consisted of a mixing pump and an externally heated retort in which the gas-air reaction took place in the presence of a nickel catalyst. The endothermic atmosphere was successfully used for carburization of steel. It was also demonstrated in this experiment that the above endothermic atmosphere, with proper adjustment of the dew point or the water vapor content of the gas, could be used to control the surface carbon content of steel during carburizing treatment.
Following the last paper (Tetsu-to-Hagane, Vo. 39, 1953, No. 12, p. 1336), an atmosphere obtained by addition of the cyanide salt of optimum amount in a closed vessel pre-filled with air or oxygen instead of town gas was examined and found to be cheap and more powerful in the case-hardening of rimmed steel as well as of killed steel: the richer the concentration of C2N2O gas in the atmosphere, the more powerful its case-hardening ability. The concentration of C2N2O became maximum by addition of the K4Fe(CN)6 6gr per litre when air was used, and 33 gr per litre when oxygen is used. At these amount of the addition, the carbonitriding power became maximum in both cases. The mechanism of the carbonitriding on steels was also discussed.
This paper was contributed to the Journal of the Iron and Steel Institute of Japan by T.L. Joseph, Professor of Metallurgy, University of Minnesota and was translated by a member of the Institute. In the Paper, pelletizing process in U.S.A. which had developed from a pilot plant scale into a commercial scale, was described in detail. In view of the fact that details of design and construction of pelletizing piant had not been released to the public, if any of the Japanese steel companies wished to take full advantage of the experience gained in the States, the author suggested that they might write to one of the following: W.M. Kelley, President, Reserve Mining Company, Guildhall Building, Cleveland, Ohio. John C. Metcalf, The Erie Mining Company, 700 Selwood Building, Duluth 2, Minnesota. William A. Haven, President, Arthur G. McKee and Company, 2300 Chester Avenue, Cleveland, Ohio.