In general the mechanical properties of grey cast iron are represented by tensile strength and elongation. However, they are not always sufficient to represent some particular qualities of grey cast iron. This may be specially emphasized with respect to the toughness of grey cast iron. For this reason the authors endeavoured to represent the toughness by the stress-strain curve obtained in a tension test instead of by tensile strength and elongation. Grey cast iron is characterized by the fact that it hardly deforms elastically but produces strain plastically, and that it shows a stress-strain curve of simple form. Hence the curve can be represented by a formula as follows:
      ,i>δ=Σb(a+Σ)………………………(4)
where b depends on tensile strength and the ratio of b : a represents the tangent of the stress-strain curve at the start of tensile loading.
  Any kind of stress-strain curve can be given by the equation (4) by changing the constants a and b. The constant b may be increased by increasing the tensile strength of grey cast iron while the constant a is dependent neither on tensile strength nor on elongation. The ratio b : a tends to be enlarged with changing matrix pahse from pearlite to ferrite of graphite structure from DE type to A type.
  The toughness of grey cast iron can be given by the work to be done under tensile load till fracture is caused. The work is given by the area which is enclosed by the curve in the stress-strain diagram, or by integrating the formula (4). From the integra it is known that to increase the toughness it is necessary to increase b or tensile strength, the ratio b : a, and the elongation of grey cast rion. Hence, for producing grey cast iron of high toughness the graphite structure must be of A-type and the matrix phase has to be partly ferritic. Further, with respect to mechanical properties it is neccessary that the tensile strength and elongation are well balanced. Grey cast iron which satisfied such requirements showed a better experimental result when it was subjected to repeated thermal impact test.

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    In using cold-setting moulds and cores for heavy steel castings, carburization which occurs on moulds bonded by organic material becomes a problem. In this experiment, carburizing phenomena were investigated on samples taken from steel castings, and influence of mould conditions on carburization was also investigated on a laboratory scale.
    The results obtained are summarised as follows:
  (1) Usually, the heavier the steel castings are, the more severe the carburization becomes.
  (2) Carburization is severe at the core side of castings, but is slight at the mould side of castings.
  (3) The depth of the carburizing layer is not more than 20mm.
  (4) The degree of carburization is not related to the amount of resin when it is within the range of 2-4wt.%.
  (5) Carburization becomes more severe when the quantity of sand flower is increased.
  (6) If Fe₂O₃ is mixed with silica sand, carburization decreases. More than 10% of Fe₂O₃ must be added to sand in order to prevent carburization completely.
  (7) Carburization can be prevented completely by using chromite sand.

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    Pure copper castings are used for water jacket at high temperatures because of their excellent heat conductivity, and so these castings are required to have high strength at elevated temperatures.
    A study was carried out the effects of alloying elements on the high temperature strength of pure copper castings. Alloying elements were classified into two groups according to their solubility in copper; silver and cadmium have relatively large solubility in copper, while chromium and zirconium have small solubility. By an addition of elements of the former group, we expected an increase in strength of copper as a result of solid-solution formation. In the case of the latter group, increase in strength was expected as a result of of precipitation hardening.
    Measurement of tensile properties and hardness was made in the range from room temperature to 600°C and that for creep rupture tests in the range from 400°C to 600°C. The experimental results were :
  1) the high temperature tensile strength and hardness of pure copper castings were more improved by the addition of chromium and zisconium than by the addition of silver and cadmium,
  2) creep rupture strength of copper castings was raised by addition of chromium and zirconium especially,
  3) the largest difference in high temperature strength was found with respect to creep rupture strength at 400°C.
  4) the type of fracture surfaces of test pieces of creep rupture tests were closely related to degrees of creep rupture strength.

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    For the investigation of influence of gas atmosphere and alloy elements on burning reaction at cast steel-mold inteiace, mixed CO and CO₂ gases were used for atmosphere, and carbon steel, high manganese steel, high chromium steel and nickel-chromium steel were used for alloy steels.
    The following are the results.
  (1) In mixed CO and CO₂ gases, the metal-mold interface reaction increases with incresing CO₂ gas ratio. The rection is more remakable at 1,400°C than below 1,350°C. When CO₂/ (CO₂+CO) ratio is 0∼10%, steel does not react with SiO₂ at all because of stronger reducing atmosphere.
  (2) As for the influence of alloy elements on FeO-SiO₂ reaction, manganese promotes the reaction and chromium restrains it, but the influence of nickel is not clear.
  (3) From the observation of microstructure, results of X-ray diffraction and X-ray microanalysis, it is considered that the reaction products are mostly composed of fayalite, and that manganese forms manganese silicates in the reaction products, while chromium is present as chromium oxide in the oxide layer of the surface of steel and restrains the emergence of FeO.

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  For a quick estimation of tensile strength of cast iron, the wedge penetration test which makes measurements by breaking a disc shaped specimen with a steel wedge has come to be adopted these few years.
  We have already completed basic experiments on this method, and in a previous report defined wedge penetration breaking strength as the value of maximum breaking load divided by cross sectional area of specimen, and proved the method to be reliable in the foundry provided that the relationship between wedge penetration breaking strength and tensile strength is known.
  We have, this time, studied the mechanism of fracture from the results of wedge penetration tests under various conditions and microscopic observations of the breaking process.
  The results obtained were as follows :
  (1) Relationship between loading speed and breaking strength.
  No variation on breaking strength was recognized on increasing the loading speed so it was found that there was no relationship between loading speed and breaking strength.
  (2) The influence of edge angle and tip radius of wedge on wedge penetration breaking strength.
  The relationship between wedge penetration breaking strength and tensile strength were examined on various edgle angles and tip radius of wedge.
  When the edge angle was kept at 90°, the wedge penetration breaking strength increased as the tip radius of wedge increased. The coefficient of correlation showing the rlationship between wedge penetration breaking strength and tensile strength became larger. However, the constant of regression equation decreased. No influence of edge angle on wedge penetration breaking strength could be found.
  (3) Observation of breaking process by microscope.
  On increasing the breaking load, shearing stress works at the contact points of fixed and removable wedges and cracks the graphite around these points. The compression stress also begins to work on the inner portion of the specimen remote from the contact points of wedges. On increasing the load still more, the compression stress increases at the center of the specimen and cracks the graphites around the center and finally the crack joins with those cracks growing downward upward from both surfaces of the specimen. The propagation of these cracks finally results in breakage of the specimen.
  (4) On observing the breaking process and broken specimen, it was found that the combination of shearing and compression stress acted on breaking. When the tip radius is small the shearing stress is greater than the compression stress, but as the radius becomes large the compression stress becomes greater than the shearing stress.
  Because, in general the compression stress is proportional to tensile strength in cast iron the wedge penetration breaking strength and tensile strength was considered to be correlated.

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