In the preliminary works, the influences of various treatments of cast iron melt containing Mo and Ni on casting structure were investigated. It was comfirmed that inoculation and Mg-treatment showed a tendency to promote the formation of pearlite and to decrease the amount of bainite matrix in the Mo-Ni cast iron studied. In higher alloy irons, vacuum melting or an addition of Fe₃O₄ caused easily to form acicular matrix with a fine eutectic form of graphite, and Mg-treatment and inoculation with calciumsilicide both formed martensitic matrix of high hardness.
  In the present paper, to analyze the above experimental results, the effect of graphite structure on the S-curve (T.T.T diagram) for 0.5%Mo-1.4%Ni cast iron were investigation by microscopic examination in pearlite transformation range and by dilat-metric measurement in bainite range. The results abtained were as follows;
  1) The S-curve of Mo-Ni cast iron was divided into two C-curves; the pearlite formation occurs in a temperature range of about 720∼520°C and the bainite formation, about 520∼200°C.
  2) In the temperature range of upper pearlite, graphitization occured through both direct and indirect reaction. The letter reaction was accelerated by the presence of fine graphite in cast iron.
  3) The beginning and ending points of the upper pearlite trnsformation, which was started at austenite boundary, were almost unaffected by the graphite structure.
  4) In the case of cast iron with coarse flaky graphite, the time required for the beginning of lower pearlite reaction was remarkably shortened, and also this reaction was started around the graphite, forming troostitic structure.
  5) The distribution of fine graphite moved the S-curve of the beginning and ending for bainite formation to the left, and also produced large amounts of bainite, as interpreted from the dilation curve. The microstructure of bainite was not affected by the graphite structure, but depended upon the reaction temperature. At the relatively higher temperature, the isothermal bainite reaction remained incomplete, with large amounts of austenite untransformed.
  6) After austenizing at a high temperature, the isothermal pearlite reaction was accelerated, but the bainite reaction restrained.

抄録全体を表示

  In the study of residual stress in castings, measurements of stress during of the castings are of immediate interest to foundrymen and investigators of this subject. The author reports the results of experiments of silumin castings made by an apparatus designed on the strain-hindering principle. Stresses in the castings were measured at the strain-hindering frame work by electric resistance strain meter. The results obtained are summarized as follows:
  1. When being the ratio of cross sectional areas of the cast bars A/Ao>1, the stress in the center member at the first stage, i.e., during the solidification, is compression of less than 0.005kg/mm², and changes to tension as soon as the solidification completes. The rate of stress increase is large at first, and gradually slows off. The maximum stress at room temperature under the conditions in this experiments was less than 0.6kg/mm².
  2. When the stress-hindering is released, the strain-time curves of castings agree well with the stress-time curves.
  3. It is suggested from the results of measurements of elastic strains that plastic flow occurs throughout cooling from solidification to room temperature.

抄録全体を表示

  The object this report is to investigate the cause of the scab, rattail and veining in natural sand mold. In this report, it was investigated how the pouring rate, mold-hardness and number of gate give effects on the green and hot-properties of mold and the occuring of the scab.
  The conclusion about these are as follows:
  1) In natural sand mold, the longer the pouring lasts, the more severe the scab is.
  2) In natural sand mold, the mold-hardness influences to its green-properties severely, but not so much to hot-properties. The hot-expansion and hot-strength increase a little with increasing in mold-hardness.
  3) The higher mold-hardness is, the more severe the scab in natural sand mold becomes.
  4) The relation between the number of gate and scab in natural sand mold has to be sought after the fundamental investigation about the occuring of scab is performed.

抄録全体を表示

  In the previous report, the author reported that the height of a sand specimen is in direct proportion to the logarithm of a number of ramming, and furthermore if we take ε (=the gradient of the line/the height of a specimen which is given by first ramming=b/a)as a factor of contraction of a sand specimen by ramming, a and b are affected by the weight of a specimen but ε is not affected by that.
  In this report, the effect of bentonite content and uniform sand grain size on the values of a, b and ε are studied.
  a changes its value according to the sand grain size and bentonite content regularly.
  The curves for b or ε-water content are similar in shape. In case of same bentonite content, the band ε do not change thier values so clear as the value of a according to the sand grain size, and especially when the bentonite content is 12 or 16%, the curves for b or ε-water content in different uniform-grain sand more approach each other. On the other hand, in case of same grain size, the more the bentonite is added the heigher the b or ε bcomes.

抄録全体を表示

  To clarify the correlation between grain distribution and permeability, an analysis was made assuming that the sand grains of various size are alternately arranged by the layers of thin thickness in the specimen as shown by Fig.1. For the mixtures of coarse grains and fine grains, a calculating equation is expressed by
  [Written in non-displayable characters.]
for the mixtures of coarse, medium and fine grains
  [Written in non-displayable characters.]
where K : permeability calculated, K_a, K_b and K_c : experimental permeability of various grains respectively, H_a, H_b and H_e : heights of layers of various grains in the specimen respectively, α : ratio of a experimental value to a calculated value. In order to obtain. value α, silica sands of 70, 100, 140 and 200 mesh were used after washing with water, drying and screening by a standard sieves, and a content of binder(bentnite)and moisture were added in prorortion to specific surface of the sand grains. The combinated sample were prepared 70 kinds : The mixtures of coarse grains and fine grains were 42 kinds and the mixtures of coarse, medium and fine grains were 28 kinds. The results obtained were as follows :
      arithmetic average value ?? =1.09
      coefficient of variation ν=σ/??×100=9.4%
where σ : standard deviation.
  It may be suggested, therefore, that the permeability of the mixture of sand grian can be determined by the calculation from the above equation under the consideration of the grain distribution.

抄録全体を表示