The life of tools for hot work is influenced not only by wear but also by hot check caused due to repetition of heating and cooling. In order to investigate the hot check phenomena occurring on cast tools for hot work the authors built a testing machine which was useful to reproduce hot check on a laboratory scale. The machine has an advantage that hot check can be easily produced by such a way that a number of test pieces are simultaneously subjected to a repetition of thermal shock under the same condition. Experimental results were:
  1) Accuracy and reproducibility of the measurement was established by using a method in which a thermocouple was buried at a point of 0.5mm below the surface of specimen.
  2) The roughness of the surface of specimens had no effect upon the accuracy and reproducibility of measurement, unless the roughness was too great.
  3) As a result of experiments, it was known that cast steel was higher in the resistance to hot check than cast iron or cobalt base alloys.
  4) Experimental results thus obtained seem to be useful for developing the production of cast tools in practice.

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  For experiment, various kinds of cast irons were made by using inoculants of Ca-Si or Fe-Si, flux containing 20%TiO₂ or Ni-Mg alloy. They were cast into a metal mold preheated at temperatures ranging between 950°C and 1,120°C. Experimental results were:
  1) Supercooling was lessened by inoculation. The effect of inoculation was greater by Ca-Si than by Fe-Si.
  2) Cast iron containing titanium had a tendency to supercool at eutectic temperature more extensively than flake graphite cast iron. Herein, if the eutectic temperature was lowered to lower than 1,140°C, eutectic graphite structure developed.
  3) The degree of supercooling was the largest in the case of spheroidal cast iron treated by Mg.
  4) The eutectic temperature of ledeburite was not influenced by addition of Ti or Mg and kept a definite temperature independently of cooling rate.
  5) The length of eutectic solidifying time was made longer when the graphite structure changed from fiake to eutectic or spheroidal.

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  Quite a number of papers have been published on graphitization of white cast iron, but there were few papers concerning to the relations between the original structure of ledeburite and the graphitization of pure iron-carbon-silicon alloy. The present investigation was performed to clarify how the graphitization was influenced by the solidification process of white cast iron.
  White cast iron used had a composition of 3.0%C and 1.0%Si. It was cast into a metal or a sand mold and subsequently quenched into water during or after solidification so as to vary the cooling condition of cast products. Specimens were heated in vacuum at 1,000°C and the first stage graphitization was measured by using a displacement measuring apparatus. The experimental results are:
  1) A preparatory condition for graphitization was developed during the formation of ledeburite structure. What the preparatory condition was had signffiicant influence upon graphitization.
  2) The form, size and distribution of temper carbon were changed with changing the solidifying condition of white cast iron.
  3) The spheroidization of temper carbon was favoured when white cast iron was rapidly solidified.
  4) The preferable distribution of temper carbon was obtained by increasing the cooling rate of solidifying white cast iron.

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  The pouring volume of pressure type automatic pouring machine is influenced by gaseous pressure, pouring time and the height difference between the top level of pouring tube and the surface of liquid metal. The authors built an automatic pouring machine in which independently of the repetition of pouring, the level of liquid metal could be maintained at a definite height by moving the inner ladle up and down. Experiment was made on aluminum alloy. Experimental results are given as follows:
  1) Pouring volume was linearly increased with the extension of pouring time.
  2) Pouring volume varied in proportion to the square root of the balance of gaseous pressure and head of liquid metal.
  3) For controlling the pouring volume with ease and accuracy it needed to hold the head of liquid metal at a definite level.
  4) When the gaseous pressure was lowered and the height difference between the top of pouring tube and the surface of liquid metal was increased, the speed of pouring lowered and the accuracy of pouring rapidly changed for the worse.
  5) The accuracy of pouring obtained by the machine was in a range of 1.4% when the weight of one charge was 2 kg and the speed of pouring was 0.56 kg/s.

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  Shaking-out of castings has recently been highly mechanized. However, it is still hard to shake-out castings of a complicate form or having a long tubular core. In 1958 a German patented method applied explosion energy to remove sand from castings. The author s halikewise applied explosion to shaking out. The feature of the method is that the application of explosion is made inside water pool instead of inopen air. Experimental results were:
  1) Removal of sand could be done easily, safely and economically.
  2) Removal of CO₂ core Sand could also be easily performed.
  3) As an explosive detonating fuse was preferably employed.
  4) The amount of sand left over was dependent on the amount of explosive. The explosive needed could be roughly estimated in consideration of the thickness of sand core.
  5) This method could be applied to castings of heavy thickness more effectively than those of thin thickness.

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  The second stage graphitization of blackheart malleable iron is currently performed by slow cooling through a temperature range 760°C to 650°C, including the critical temperature range of the iron, or holding it at subcritical temperatures near 700°C. Few reports have, however, been published on the mechanism of the second stage graphitization. To investigate it, the authors have studied the graphitization phenomena in proeutectoid, critical and subcritical temperature range. For this, a differential transformer type dilatometer which is available for differential thermal analysis was used simultaneously to obtain various cooling curves of temperature, length and heat occurrence of the specimen.
  The melt was made by duplex melting of cupola-Hēroult arc furnace and cast into a green sand mold. After both first and second stage graphitization had been completed in a continuous annealing furnace, the specimen was reheated up to 900°C, held for two hours and subsequently cooled rapidly in atmosphere. For obtaining cooling curve, the specimen having pearlitic matrix was reheated to 900°C and then slowly cooled to a holding temperature of proeutectoid, critical or subcritical range. Rapid cooling was made by helium gas blowing at the temperature at which the iron showed a definite discontinuity or heat occurrence. The microstructure of specimen thus quenched showed that the matrix which was austenitic before cooling was completely changed to extremely fine pearlite, whilst the pearlitic isle which was in advance produced by Ar₁ transformation had a coarse lamellar structure.
  Experimental results are summarized as follows:
  1) Among three phases existing in the temperature range between 900°C and 760°C, ferrite was separated at grain boundries directly from austenite by holding the iron in the proeutectoid temperature range below 900°C. The longer the holding time, the more the amount of ferrite separated. Howeyer, it did not take a long time before an equilibrium was established and further separation ot ferrite ceased to take place.
  2) In the temperature range between 760°C and 730°C ferrite deposited around temper carbon nodule, and a perfect ferritization occurred. The rate of ferrite deposition depended upon the holding temperature in such a way that the lower the holding temperature, the higher the rate of the ferrite deposision.
  It is assumed that the deposition of ferrite around temper carbon nodule occurred directly from austenite because of a lack of carbon content in it which was caused by direct graphitization onto existing carbon nodule.
  3) In the temperature range just below 730°C austenite was rapidly transformed to pearlite. It is rather difficult for the pearlite to decompose at said temperatures. In this case, the deposition of pearlite can be clearly detected according to the occurrence of latent heat due to transformation. It was further well known that there was a comparatively large difference in heat occurrence detected on differential heat curve between direct graphitization and pearlite formation.
  4) As a result of experiment, it may be concluded that the time of the second stage graphitization can be minimized by holding the iron at proper temperatures in the critical range. It is, however, hard in foundry practice to maintain castings in such a narrow range of temperature. As compared wih this, in the authors' laboratory the second stage graphitization could be performed by an extremely short time holding, less than one hour, as was shown on the cooling curve of heat occurrence through Ar₁ transformation.

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