A stable equilibrium diagram of the system Fe-C-Si was drawn standing on the stable equilibrium diagram of the system Fe-C proposed by the author in 1937^*. Following the ternary equilibrium diagram by H. Jass the present author arrived at a somewhat different one.
  The space model and its projections on the basal plane were drawn. The vertical sections of the space model parallel to Fe-C system keeping the content of Si constant at 1.0, 2.0, 2.6, 6.0, 7.0, 9.0, and 12.0%, and the horizontal sections at 700°C, 800°C and 1100°C were also drawn. Various figures were moreover given to illustrate the complex relations in the space model.

抄録全体を表示

  The decomposition rate of the carbides in Fe-C-Si alloy treated with calcium-silicon was measured at 600°, 700° and 800°C to learn the effects of calcium on the stability of the carbides.
  It was observed that the decomposition rate of carbides in the alloys treated with calcium-silicon was considerably faster than that of the carbides in the alloys treated with silicon, in an equivalent amount of silicon. Namely, calcium lowered the stability of the carbide. However, in comparison with the stabilities of various carbides in the case of treated alloy, the decomposition rate of the primary cementite (crystalized along the Acm line) was the largest, that of pearlite cementite next to it, and that of ledebulite cementite the smallest. The decomposition rate of the carbides varied with the composition of the alloys, and was the largest at a little higher carbon content than the carbon saturated solubility of austenite. Treating with calcium-silicon, the decomposition rate of the carbides in steel was, moreover, in the same order as that of the carbides of low carbon cast iron, at a temperature between 700°C and A₁.

抄録全体を表示

  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.

抄録全体を表示

  The authors investigated various conditions which produced such foundry defects as scab or rattail; these defects occurred when molten cast iron was poured into a natural sand mould.
  The conclusions from this study were as follows :
  1. The scab which occurred in the natural sand mould was caused by two factors : the expansion of the foundry sand on the mould surface and the physical load which broke up the mould surface.
  2. The scab and rattail were apt to occur as long as the internal stress, which was caused by the thermal expansion of sand, was concentrated on the surface of the sand mould.
  3. The more the moisture in mould and the higher the pouring temperature become, the more easily the scab in the natural sand mould forms.
  4. It seems that moisture in the sand mould has an influence upon the permiability and the evaporating speed of the moisture upon pouring the molten metal into the mould, and then it has an important effect on the formation of scab.

抄録全体を表示

  In this paper, the fundamental experiments on the castability of molten iron and on the mechanical properties and microstructures of the castings are included, when gray iron was cast into natural sand moulds which varied in the moisture content from 0 to 17%. The results were as follows :
  (1) Castability
    i) The fluidity of the molten iron is extremely high when the metal was cast into dry sand moulds, and is slightly lower than before when the metal was cast into moulds with moisture content from 4 to 8%.
    ii) The surface of the casting is at its most beautiful stage when the moisture content in the moulds is from 8 to 9%.
    iii) The shrinkage cavities grow in number with the increasing of the moisture content. The total shrinkage also becomes larger with the increasing of the moisture content up to 8.5%, but over that it does not develop any more.
    iv) When cores, with moisture content of less than 8.5%, are used, the blow scarcely occured in the casting with the dimensions by which we carried out the experiment.
  (2) Mechanical properties
  In general, the mould with a moisture content from 2 to 4% yields a casting that has good mechanical properties.
  (3) Chill test
  The depth of clear chill varies slightly with the moisture content in mould, while the total chill does not.
  (4) Microscopic test
  There are little differences in graphite structure between the inner and outer surfaces of the casting, and the chilling effect is very little.
  Summarily, the castability of the molten iron is found to be good when the metal is poured into the mould with a moisture content of 4%. However, the surface of the casting is not so good at that time. The mechanical properties are also good when the moulds have moisture content from 2 to 4%, when natural sand is used for the mould, the moisture content in the mould must be increased to the greatest extent, unless there are difficulties in making moulds. Even in this case, it should not go beyond 9%.

抄録全体を表示