The objective of the present research project is to investigate the causes of hot tearing in malleable iron castings and also to establish the ways to prevent it. In this work, the effects of mold and melt variables on hot tearing in malleable iron castings were investigated following the previous ones^1)2)3)4).
  In case an flow of feed metal to malleable iron casting is inadequate, the mold restraint on the contraction of the casting and/or the much difference in temperature between various locations in the casting during solidification significantly increase the susceptibility of the casting to hot tearing. Thereupon, some experiments were carried out using the standard test pieces to satisfy the above-mentioned conditions.
  The results obtained are summarized as follows :
  (1) Hot tearing depends definitely upon the thermal expansion characteristics of molding sands. The relationship between hot tearing in castings and the amount of the free expansion of various sands rapidly heated to 1,000°C has been investigated. In consequence, the greater the amount and the rate of expansion of molding sands, the more severe becomes hot tearing in castings. Especially, zircon and olivin sands showing little amount of expansion are useful to prevent hot tearing.
  (2) Hot tearing affected by the heat absorbability of molding sands. The highest temperature of the molds raised and the time required to reach its temperature have been determined giving the heat of melt to the molds made of various sand. In consequence, the greater the temperature rising rate, the higher the highest temperature, the more severe becomes hot tearing in castings.
  (3) The temperature changes during solidification in castings, molds and at casting interfaces have been investigated respetively, but the relationship between these factors and hot tearing is not clear from the reults of the experiments.
  (4) The investigation on the effects of mold variables on hot tearing shows that mold hardness, riser size, coal dust, pitch and mold coatings to prevent hot tearing signficantly influence hot tearing, whereas moisture and mulling time of synthetic sand do not influence it.
  (5) The investigation on the relationship between hot tearing and sand properties shows that fluidity and grain shape of sand and SiO₂ in sand influence hot tearing.
  (6) The investigation on the effects of melt variables on hot tearing shows that increasing pouring temperature promotes hot tearing the most, carbon and silicon contents and boron, bismuth and aluminum additions considerably influence hot tearing, and increasing oxygen content of the melt promote it.

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  The specifications on the yield strength for standard malleable iron castings were given at the time when Japanese Industrial Standard was revised in 1969.
  Thereby the authors have measured the yield strength of malleable iron castings produced in commercial foundries in the western area of Japan and have investigated various factors influencing the yield strength.
  From results obtained, it is clarified that the yield strength of the castings producing in malleable iron foundries sufficiently satisfied the present specifications for standard malleable iron castings and also increasing silicon content of the castings raises the yield strength.
  Moreover, the repeated reloading-unloading test on malleable iron was carried out to mearure permanent strain and elastic limit, and also to evaluate the yield strength from the stress-strain curve.
  From the result obtained, it can be concluded that the value of yield strength is quite effective to indicate the practical value of mechanical strength of malleable iron castings.

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  This paper deals with the co-orperated works by 9 members of Eastern Group of Malleable Cast Iron Commission in The Japan Foundrmen’s Society. In those works, the authors intended to clarify the feeding distance and edge effect of plate castings, and intensity of factors concerning melting, molding and pouring, in malleable cast iron foundries. In this study, however, volume of shrinkag ecavities were not discussed.
  Experiments were carried out by all members on the same method, except a few special experiments. Over 110 papers were discussed at the meeting of both Eastern Group and whole of Mallleable Cast Iron Commission. This paper is the summary of those works.
  Results obtained are as follows :
1. The length of shrinkage-free castings depends upon the wall thickness. These Values are about
   12.5T at 10mm thick
   10. T at 20mm thick
2. Many castings having larger length than these limits may contain shinkage cavities. Values of feeding distance and edge effect are fractuated over wide range. The lowest values are :
   feeding distance 2.25∼3.10T, edge effect 2.00∼2.60T at 20mm thick castings
   feeding distance about 4.5T, edge effect about 4.4T at 10mm thick castings
   These values are very small, comparing with those of shrinkage-free castings.
3. Feeding distance and edge effect are strongly affected by the volume of the riser and ingate area.
 It may be summarized from the lowest values that the critical value of the riser is about 55∼60mm in diameter and height, ingate area is about 700∼800mm² for 20mm thick casting. No increase of feeding distance and edge effect are indicated when the size of riser, ingate area have larger value than critical values.
4. When the size of castings is larger than the critical value, oxidizing melting results to show decreasing of feeding distance. Other factors such as chemical composition, pattern of cooling curve and melting method have a slight or little Influence on feeding distance.
5. On molding materials and methods, chiller and Zn/ground coke mold coating have a large effect on feeding distance and edge effect. Exothermic material on the riser side of plate specimen, density of mold and moisture content of sand have a slight influence on this values.
6. Pouring temperature and speed have not a large effect on feeding distance and edge effect. When inclined pouring are adopted, however, feeding distance differs from that of horizontal mold; feeding distance of casting poured into down inclined mold is the shortest.
7. Both macro-and micro-structure are changed according to the melting method, molding material and other factors in casting. Feeding distance of the casting which has long primary dendrites or endogenous structure indicates small value of the distance.

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  The present investigation was carried out in an attempt to obtain fundamental data on the riser design of malleable iron castings. And the effects of riser sizes, riser neck sizes and shapes, and melting and molding variables on internal shrinkage in plate castings (100×100×20mm) fed by single cylindrical blind side risers and also the effect of the amount of internal shinkage on the tensile strength of the castings were investigated.
  The results obtained are summarized as follows :
  (1) The amount of shrinkage in the casting was reduced as the riser size was increased. However, within a range of riser sizes used for the present investigation, it was impossible to eliminate shrinkage in castings completely, unless the cross-sectional areas of riser necks were increased to a hardly practicable extent.
  (2) The amount of shrinkage in the casting was reduced as either the length of riser neck, i. e. the distance from the riser to the casting, was reduced or the thickness, the width or the cross-sectional areas of riser neck was increased for a given size of riser.
  (3) Increasing coal dust additions to the molding sand, the amount of shrinkage, in the casting was increased. An increasing in pouring temperature showed the tendency to increase the amount of shrinkage was minimized by pouring at a certain temperature, were also obtained. In addition, more shrinkage in the casting, while some reme results, that the amount of shrinkage occured in the casting, using the melt made from the duplexing cupola-arc furnace melting compared with the melt made from cupola melting.
  (4) In case that the total shrinkage area or the maximum length of the individual shrinkage in the radiograph was small, the reduction of the tensile strength of the casting was tolerably low. Therefore, the possiblity of the selection of riser and riser neck sizes to meet the tolerance limits of internal shrinkage was suggested.

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  Although shrinkage in white cast iron is a troublesome problem of malleable cast iron production, any practical method to estimate the quantity of shrinkage has not been established.
  We tried to measure the quantity of shrinkage in white cast iron by finding out the specific-gravity of test specimens. A sound specimen and shrinkage specimens were cast in a same mold and the quantity of shrinkage was obtained as following equation.
porosity % = the specific gravity of a sound specimen−the specific gravity of a shrinkage specimen ⁄ (the specific gravity of a sound specimen) ×100
  It was known that the error of the measurement of shrinkage by this method was small and that there was a exact linear relationship between carbon content and porosity %.
  Also, the influences of melting conditions on the shrinkage were investigated using this method.
  Therefore, it might be of concluded that this method would be of practical use for the measurement of shrinkage.

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  Feeding or risering of the castings is a subject of great importance from the viewpoint of their soundness and casting yield or the economics of production. The purpose of the present research is to establish the suitable method of dimensioning risers of thin section white iron plate castings for malleable iron. First, the solidification times of plate castings (10×60×60mm, 20×100×100mm and 30×120×120mm) and various sizes of cylindrical risers of height to diameter ratio 1.5 of white iron, cast seperately into green sand molds, were determined. And then, the soundness of the plate castings, to which the single cylindrical blind side risers were joined, were assessed by radiography.
  A summary of the results obtained is shown below :
  (1) Chvorinov's rule is approximately valid for white iron sand castings in plate and cylindrical shapes.
  (2) The basic riser equation having the following form has been derived :
      A_r⁄(A_c) = 1V_r⁄(K(1+β) V_c) − β⁄(K(1+β))
  In this relationship, A_r and A_c are surface areas of the riser and the casting respectively. V_r and V_c are volumes of the riser and the casting respectively. β is the solidification shrinkage coefficient of the casting and K is a shape factor. Now, by substituting the value of K, 1.19, obtained from solidification time deta, and the value of β, 0.04, of the white iron casting poured into the green sand mold at 1400°C, into the basic riser equation, the equation for estimating riser dimensions can be written in the following from :
      A_r⁄(A_c) = 0.808 V_r⁄(V_c) − 0.032
  However, the basic riser equation described above can be applied to one casting per riser.
  (3) In addition, for n equivalent castings per riser, the basic riser equation becomes :
      A_r⁄(A_c) = 1V_r⁄(K(1+β)V_c) − nβ⁄(K(1+β))
  And for the castings with p equivalent risers per casting, it becomes :
      Ar⁄(Ac) = 1Vr⁄(K(1+β)Vc) − β⁄(pK(1+β))
  (4) For the sake of malleable iron foundrymen, the riser nomograph has been presented in this paper to simplify riser dimensioning of white iron plate castings with single cylindrical blind side risers of height to diameter ratio 1.5 cast into green sand molds.

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  The present authors have found that the carbon concentration of eutectic cementite under an equilibrium state is lowered with increasing temperature. Based on the findings the well-known effect of subcritical heat treatment on the first stage graphitization of malleable cast iron was discussed. When a white iron is held at subcritical temperatures of 300°C to 600°C, ferrite particles precipitate in the eutectic cementite. Parts of such particles remain undissolved into the cementite during subsequent malleablizing. On the other hand, the eutectic cementite in the white iron heated rapidly to malleablizing temperature without subcritical heat treatment contains no precipitates of iron. From these results, it is concluded that subcritical heat treatment raises the carbon potential of eutectic cementite and spreads the cementite/austenite interface which provides the nucleating sites of graphite during malleablizing. These have an effect to increase graphite nobule numbers.

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  Since the mechanical properties of white cast irons are closely related to the structure, the fracture appearance, macro- and micro-structures have been investigated. As there were few investigations on the correlation among these structures, factors determining fracture appearance and macro structures were not clear. The purpose of this study was to clarify the correlation among these structures and the influence of carbon content as well as pouring temperature.
  The experimental results were as follows :
  (1) Both the fracture appearance and macro-structure were determined by the changes in orientation of the cementite due to the groups of eutectic colonies.
  (2) During the solidification of a round bar, the ledeburite solidified more directionally than the primary austenite.
  (3) In the iron containing more than 2.5% carbon, the fracture appearance and macro structure showed distinctive orientation from the surface to the center of castings. In case of less than 2% carbon, however, the orientation of structures disappeared since the ledeburite was enclosed by primary crystals.
  (4) Lowering the pouring temperature made the group of primary dendrites which had same crystallographic orientation finer. On the other hand, the group of eutectic colonies was scarcely affected by the pouring temperature.

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  Previous reports have described that the direct graphizing process whithout normal second stage annealing containing decomposition of pearlitic cementit could be practiced by holding the iron for about 60 min at the appropriate narrow temperature range just after A_r1 transformation begins. Namely, a fully ferritized malleable iron is obtained by first stage graphitization and direct graphitization. With a view of investigating the effect of chromium content on the direct graphitization, graphitizing behavior was observed on both irons having chromium content 0.03 and 0.09%.
  Results obtained showed that a small amount of chromium shifts the direct graphitizing temperature range to higher temperature side. It is also clarified that too excess content of chromium suppress the direct graphitization by accelerating occurrence of pearlite nucleus at the same temperature at which direct graphitization performs. It seems that the increase of alloying element which act as a carbide stabilizer during malleablizing proceeding direct graphitization by producing pearlite nucleus before ferritization of austenitic matrix completes. Once pearlite nucleus occurrs, this grows rather rapidly to lamellar pearlite which prolongs second stage graphitization of blackheart malleable iron.

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