On Various Properties of Nodular Graphite Cast Steel

This paper describes at first the outline of the theory of high grade cast iron manufacturing that has been clarified by one of the authors through a fundamental study of the relation between cast iron and its oxygen contents. In place of the relation between the oxygen content of cast iron and its qualities, the relation between tensile strength in cast state and variation of structure was examined. A little difference in the degree of deoxidation of cast iron was indistinguishable by analysed oxygen content. To grade the qualities according to the variation of structure is the most accurate and simplest method. When nodular graphite hyper-eutectoid cast steel containing less than 1.7 per cent carbon is produced the theoretical foundation for determining carbon and silicon contents is to choose the reciprocal relation between the points on the line Eγ or in the lower areas under the line Eγ in the basic projection diagram of the Fe-C-Si system. According to this theory, an investigation of the various properties of nodular graphite hyper-eutectoid cast steel was carried out. The results obtained can be summarized as follows : (1) This cast steel does not call for so careful selection of materials, and is of higher value in mechanical properties than those of DCI, malleable iron and cast steel. (2) Since this metal has far better castability than cast steel and DCI, it is possible to manufacture castings of thin section and complicated shape. (3) Compared with gray cast iron and malleable cast iron, this cast steel is very useful for electric and magnetic material. (4) Wear resistivity of the pearlitic type of this metal is far superior to any of the ordinary cast iron, pearlitic cast iron and DCI. Wear resistivity of the ferrite type is the same as that of DCI, but it is far superior to the black heart malleable cast iron. (5) This cast steel is material that has excellent property for induction surface hardening, even in the case of ferrite type, and after heat.treatment it has the about 40～50 R_c in the surface hardness. The Jominy hardness curves of nodular graphite cast steel were measured. Compared with the pearlite type, cast steel of ferrite type has low quench-hardness bccause of its carbon concentration in austenite