鋳鉄の凝固時に生成される黒鉛形態と黒鉛化に及ぼすビスマスの影響

抄録

  Retardation of graphitization with bismuth causes the change of structure of synthetic gray cast iron having 1%Si and 3%C to be mottled or white cast iron. Morphological change of graphite in the process was analyzed by scanning electron microscope and quantitative television microscope. It became clear that total area of graphite as well as mottling ratio decreases with the amount of bismuth in cast iron. The graphite carbon content also decreases in the same way. The retardation effect of bismuth on the graphitization of gray cast iron during solidification in stable eutectic system is approximately one sixths of the effect in mottled cast iron. Consequently, it can be assumed that the number of bismuth atom necessary to retard the precipitation of approximately four thousand carbon atom as graphite during solidification is only one. On the other hand, it has been recognized from the experiment of measuring various items, such as area, size, axial ratio, excursion rate of graphite in eutectic cell while increasing bismuth that the form of graphite is always constant but the size of graphite becomes much finer compared with that of normal cast iron.