The results obtained from this study are summarized as follows:
  (1) In vacuum-metled cast iron, the reticulate structure was observed with eutectic graphite. To investigate the cause of this, the author made high P content cast iron by vacuum melting and confirmed that the structure was caused by the segregation of P or impurities around the eutectic cells, since the phosphide eutectic was found concentrated in the narrow band of the reticulate structure itself.
  (2) When flake or coarse flake graphite can be observed in air-melted cast iron, or in vacuum-melted cast iron (in the case of melting in a graphite crucible), the phosphide eutectic becomes scattered uniformly along the foundaries of the primary γ·Fe dendrite and the reticulate structure did not appear. It may not be concluded, however, that if flake graphite appears, the reticulate structure can not in every case be observed with it.
  (3) There was some differenec in the size of the each reticulate structure in the case of vacuum-melted cast iron. The size of the reticulate varies proportionally with the degree of vacuum.
  (4) 8 different melts varying in carbon content from 2.14% to 4.04% was made in a vacuum by adding steel scrap or graphite carbon to Australian charcoal pig iron. They all consisted of eutectic graphite and ferrite matrix, and they had improved in tesile strength.
  (5) In air-melting. cast iron containing carbon only to the degree of 2.14 % would not graphitize easily, unless a large amount of Si was added. Moreover, the resulting silico ferrite is too hard and brittle to machine cut. On the other hand, in vacuum-melting the structure consists of eutectic graphite and ferrite matrix even in case of relatively low Si content. Thus, it seems that vacuum melting can reduce carbon content to below 2.14% with out forming white cast iron.
  (6) The appearance of eutectic graphite and ferrite matrix in vacuum-melting, may be explained as follows. The impurities, which are considered to be the nuclei of flake graphite in molten iron, are decreased remarkably or disappeared completely upon vacuum-melting, Consecuently, the molten iron is supercooled and eutectic graphite is formed. Besides, carbon in γ·Fe diffuses to and deposits easily on the eutectic graphite, and then the matrix become ferrite.
  (7) Through the vacuum-melting method, the tensile strength of cast iron was improved when the percentage of C was between 4.04% to 2.14% so that it almost obtained the tensile strength of the silico ferrite matrix itself.