抄録
Recently many reports have been given on the graphitization of white cast iron. When the process fo graphitization of white cast iron is considered, we must have a sufficient knowledge on the some basic factors in the solidification process of white cast iron and the relation between additional elements and microstructures. In the preceeding paper, we have reported that the white cast iron solidified unidirectionally in the mold composed from an exothermic material and water-cooled copper chill plate as shown in Fig. 1. The microstructures of these white cast iron are very simplified form more than the ordinary specimens solidified in the sand mold. We also mentioned the merit of this method in the investigation of the solidification process of white cast iron because we could defined the eutectic cells of ledeburite in these specimens. In this paper, more detailed discussion on the relations between the microstructure of white cast iron and the contents of manganese and chromium and solidification velocity was given on the eutectic iron-carbon, hypereutectic iron-carbon-manganese and iron-carbon-chromium alloy solidified in the mold-mentioned above. The alloys were prepared from high purity iron-carbon mother alloy shown in Table 1, electrolytic iron, electrolytic manganese and chromium. The results obtained are as follows: (1) The solid-liquid interface of specimen moved according to the well-known equation: D=K√t−C (2) As the contents of manganese and chromiun increased or as the solidification velocity decreased, the ledeburite structure of pure iron-carbon alloy, which was almost lamellar, became coarse in structure and turnd to rod-like structure. Tne contents of chromium were more effective factors in these structural change than that of manganese. (3) In the case of iron-carbon and iron-carbon-chromium alloy, the width of ledeburite eutectic cell was in inverse proportion to the square root of solidificatication velocity, while, in the case of iron-carbon-manganese alloy, the same relation might not be observed depending on the contents of manganese. (4) In the hypereutectic alloy, the primary graphites influenced the continuity of columnar structure of ledeburite eutectic cell, but its reverse case rarely observed.
Table 1 Chemical Analysis of Iron-Carbon Mother Alloy
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