復炭に關する研究(III)

Abstract

The various decarburized layers obtained by different decarburizing treatments were carburized with the solid carburizer containing 20% of dehydrated K4Fe(CN)6, and the merits of this carbnrizing material were disscussed, following results being obtained:-(1) The solid carburizer containing K4Fe(CN)6 was different from the common solid carburizer as K4Fe(CN)6 evolved (CN)2 gas by being heated at 600°C-700°C, and it acted as a nitriding agent as well as a carburizing one. This decomposition completed in a short time at about 700°C, and so the carbonitriding power was strong in an earlier time in the treatment.(2) The carbon-restoration of the decarburized layer of the specimen with the oxidation decarburization was attained more easily by this solid carburizer than that with the non-oxidation decarburization. With this carburizing material the surface hardness became very high and the penetration was considerably deep. While, as already mentioned in the previous paper, (Tetsu-to-Hagane, 38, 1952, Nos. 8 & 9, pp. 25 & 26) the restoration of the decarburized layer with the oxidation-decarburization was difficult. when treated with the common solid carburizer containing BaCO3.(3) Considering the fact that the oxidized steel is hardened with this carburizer more easily than the non-oxidized steel, the hardening of steels treated with this carburizer containing Fe2O3 was examined. In this case the carburizing power of the common carburizer was suppressed, while carbonitriding power by a gas constituent composed of C-N-O, which would be explained in details lately, became markedly large. The carbonitriding power for non-oxidized steels became largest, and both the surface hardness and the increment of hardness ΔH, calculated from the hardened area on the section of carburized specimen, became maximum at 5% Fe2O3. However if, Fe2O3 exceeded 5%, the carbonitriding power became reduced, and both the surface hardness andthe ΔH became small, which was caused by the excess oxygen.In practice, as the decarburization was always accompanied by the oxidation, the carbon-restoration was efficiently attained with this carburizer, the common carburizer being not appropriate.