Two series of specimens were used in the present work, one was prepared from Swedish pig iron with a chemical composition of Fe-4%C-2.1%Si, the other from high purity pig iron with a chemical composition of Fe-3.6%-2%Si. These cast irons were melted in Kryptol furnace and poured into sand molds (20mmφ×70mm) kept at 500°C or into small size Y-block mold (30×60×46mm) at room temperature. Alloying elements were added in the form of ferroalloys (V, Cr, Mo, B, P, Si, etc.) or pure metals (Mg, Al, Ti, Zr, Nb, Ta, Mn, W, Co, Cu, Zn, Se, Te, Ni, Sn, Pb, As, Sb, Bi, etc.).
  The influence of alloying elements changes regularly according to their position in the periodic table and is related to the electron structure of the elements, i.e. atomic bond. Influences of alloying elements on the formation of as-cast ferritic matrix in Mg-treated spheroidal graphite cast iron seem to be in essential agreement with those of the elements on the graphitization in malleable cast iron, that is, the elements which are graphitizers in malleable cast iron such as Na and Si are also ferritizer in as-cast Mg-treated spheroidal graphite cast iron. The elements which are anti-graphitizers in malleable cast iron such as Cr, Mo, W, V, N, Sb, Te, are anti-ferritizers in as-cast Mg-treated spheroidal graphite cast iron, and the elements such as Mn, Ca, Ce accelerate or suppress the formation of as-cast ferritic matrix, depending upon the Mn/S ratio. The elements which are graphitizers in malleable cast iron such as Ni, Cu, (C) aore exceptionally anti-ferritizers in as-cast Mg-treated spheroidal cast iron. These influences of alloying elements on the formation of as-cast ferritic matrix in Mg-treated spheroidal graphite cast irons were explained based upon the irinfluences on the stability of the cementite and austenite with consideration of the nature of the atomic bonds in cementite and austenite.

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  Cast iron undergoes volume expansion during eutectic solidification by the segregation of graphite. When this expansion is restrained by mold walls, an internal pressure is generated within the casting. Since this pressure depends on the freezing manner of cast iron, it will provide a clue in predicting the quality of cast iron. This paper describes the measurement of the pressure change in castings poured into a graphite mold by an oil pressure gauge. Pressure changes in the castings were analysed from the pouring temperature up to the completion of the A₁ transformation, and the effectt of the composition of the melt and mold capacity on the pressure changes were examined.
  The pressure in the castings rises as high as 50kg/cm² under certain conditions. The behaviour of solidification of cast iron can be surmised from the features of the pressure time curves recorded. The pressure in castings increases with increasing C.E.-value in the hyper-eutectic range and decreases with increasing C.E.-value in the hyper-eutectic range, that is the pressure is highest in iron with eutectic composition.

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  Ferrite and pearlite formation manner in cast iron was examined by changing the cooling rate of the cast iron after solidification, quenching in a large ice water tank in various temperatures from eutectic temperature up to 650°C and observing the structures of the specimens obtained.
  When the cooling rate was slow, at the eutectoid temperature, ferrite precipitated on the grain boundaries of the austenite and graphite where the carbon can diffuse with ease. When the cooling rate was rapid, at the eutectoid temperature, pearlite precipitated on the grain boundaries of the ferrite and austenite or graphite. When the cooling rate was exceedindly rapid, the preeutectoid cementite in the matrix structure remained at room temperature, so at the eutectoid temperature, the pearlite also precipitated on the grain boundaries of the austenite and the preeutectoid cementite. It became known that the eutectoid temperature on stable systems and metastable systems rose with the increase of silicon and chromium contents, and fell with the increase of manganese and copper contents.

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  The authors have previously reported a series of studies on unidirectional solidification and effects of a third element on iron-carbon binary alloys. This paper deals with the solidification structure of iron-iron carbide alloys, and the crystallization of primary iron carbide(θ-type cementite) and the relation between primary cementite and eutectic(ledeburite) were particularly discussed in detail. The alloys were prepared from electrolytic iron, electrode graphite, electrolytic chromium, electrolytic manganese and iron-26.5% phosphorous alloys. Unidirectional solidification of the hypereutectic specimens with varying chromium, manganese and phosphorous contents was experimented under controlled conditions.
  The crystallization of primary cementite depended on the content of alloying cementite. The type of cementite changed with the increase of chromium and manganese content. The morphology of primary cementite also changed. Phosphorous did not dissolve in cementite. The primary cementite morphology depended on the solidification rate. Cementite grew plate-like when the rate was fast but became a peculiar transverse shape like the capital letter “L” when the rate was very slow. The Vickers hardness of unalloyed cementite obtained was about 1,000-1,100.

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  The mold produced by vacuum sealed molding process differs from those produced by other molding processes in the following three points; 1) There is no binder or moisture in the molding sand. 2) The mold surface is covered by a plastic film until the pouring of metal. 3) The pressure is reduced from 300 to 500 Torr inside the mold. It was discovered in our laboratory that the structure of the surface layer of gray iron castings made by this molding process differs from those made by other processes. Taking notice of various characteristics of the vacuum sealed moldiug process, the variations in the structure of the surface layers by the various mold factors were examined and analyzed utilizing statistics.
  It became clear that the surface layer of the cast iron by vacuum sealed molding process was different from those of the CO₂ process molds or green sand molds. Moreover, there was very thin graphite-free layer in the surface layer of those made by the vacuum sealed process, and the microstructure of matrix in this iron differed from the others. The factors contributing to the formation of the surface layers with the vacuum sealed molding process are film thickness and the stripping temperature, in light sections, the constituent of the surface layer is strongly affected by the film thickness, and in heavy castings, it is affected by the stripping temperature. The factor contributing to the total graphite area on the surface of the castings with vacuum sealed mold is the interaction with film thickness, pressure in the mold and stripping temperature.
  The macrostructure of pure aluminum castings made by vacuum sealed molding process differs remarkably from those of CO₂ process mold or green sand mold. It can be assumed that this resulted from the differences in the thickness of the plastic films used, that is, the ratio of the volume of film to the mold cavity.

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  Specimens (30mmφ×70mm) were solidified unidirectionally in exothermic molds on a watercooled copper chill plate. The chemical composition of the specimens varied : 1.8-3.8%C, 1-5%Cr, 1-3%Mn, 0.25-1%Mo and 0.5-1%V.
  The size of a group of primary dendrite cells, having a constant crystallographic orientation, became finer with increase of the content of alloying elements, while the dendrite cell size was not affected by any alloying elements. The secondary dendrite arm spacing became finer with increase of the chromium content because it reduced the amount of primary austenite. In each specimen, ledeburite solidified with a cellular morphology and presented a colony structure. The size of the colony became larger with increase in the chromium and molybdenum content probably because they extended the freezing range of the eutectic. In low carbon specimens, less than 3.0%C, the eutectic cementite was inclined to become more massive by the addition of molybdenum.

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  White cast irons containing 2.7%C and 1-3%Si were nitrided by the Tufftride Process at 570°C for 4 hr. The first and second-stage graphitization were carried out at 900°C for 5 hr. and 700°C for 20 hr. in nitrogen and argon atmospheres.
  A compound layer and diffusion zone were obtained by nitriding. The compound layer consisted of ε(Fe_2-3N base carbonitride), γ' (Fe₄N) and Si₃N₄. ε nitride was easily decomposed at first-stage graphitization temperature. This decomposed nitrogen escapes into the outer atmosphere and a part diffuses into γ solid solution and primary cementite at the outer layer in the nitrided sample. Si₃N₄ diffuses into γ at A_C1 temperature on heating. Therefore. at first-stage graphitization temperature, the nitrogen content of γ and cementite at the outer layer were increased. First-stage graphitization was retarded by this increase in nitrogen content. At the A_C1 temperature. γ was tran a formed into pearlite and nitrogen was dissolved in Fe₃C and α solution. Si₃N₄ was reproduced at second-stage graphitization.
  Low silicon (1%) iron was not graphitized in the outer layer of the sample owing to the increase in nitrogen, but high silicon (3%) iron was easily graphitized by the strong graphitizer of Si. The highest hardness in the surface layer of low silicon iron was due to the presence of primary Fe₃C, pearlite and Si₃N₄. The slightly high hardness of the inner zone was due to undecomposed pearlite. If the hardening of the surface of malleable cast iron is to be obtained by nitrided white cast iron, white cast iron with low silicon content should be used.

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