A previous report by the authers states that carbon and oxygen in molten iron attract each other. As the -ΔF value for the reaction C+S₂=CS₂ is larger at higher temperature, sulfur and carbon in molten iron may also attract each other. In that respect the effect of oxygen and sulfur on the spheroidal graphite formation may be similar.
  Considering the above situation, the mechanism of spheroidal graphite formation was studied tharaughly and the following results were obtained.
  (1) Spheroldal graphite was formed, when the precipitation velocity of carbon was very rapid, without the presence of any special nuclei. It was concluded that the tendency of spheroidal graphite formation was an intrinsic nature of carbon in molten iron.
  (2) The cooperative effect of silicon on the formation of spheroidal graphite was thermodynamically interpreted.
  (3) Consideratins on the activity of carbon afforded an understanding of the spheroidal graphite formation in deoxidized melt.
  (4) Calcium and magnesium exhibited a favorable effect, “filter effect”, on the formation of spheroidal graphite.
  (5) The difference between calcium and magnesium in their effects on the formation of spheroidal graphite was related to the difference in their solubility in molten iron, and hence to the difference of their “filter effects”.

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  The solidificatian process of cerium-treated cast iron which had various carbon equivalents was studied. By cerium addition, spherodization occured easily in kish graphite, but not in the graphite separated at eutectic solidification. Cerium seemed to change the eutectic graphite to quasi-flaky type with less additian and to ledeburite and then to mesh-like graphite structure with more addition. So a perfectly spherodized graphite structure was obtained in hypereutectic alloy but not in hypoeutectic alloys, especially in that of law carbon equivalent. The solidification processes of the alloys of different carbon equivalents were as follows.
  a) Hypereutectic iron : Kish graphte separates as primary from the melt in spheroidal form and is surrounded by austenite at eutectic temperature. Small austenite dendrites grow from this austenite envelope. Around the dendrites deposites spheroidal austenite in which spheroidal graphite separates in the central part. The spheroidal austenite may appear apart from the primary austenite dendrites at the later stage of the solidification. In this stage quasi-flaky graphite forms in eutectic cells, if cerium is added insufficiently or mesh-like graphite forms by the decomposition of ledeburite, if cerium is added excessively.
  b) Slightly hypoeutectic iron: A small amount of primary spheroidal graphite may form the melt due to supercooling of the eutectic liquid treated with cerium. Accordingly the same solidification processes mentioned above occur, but a structure with completely spheroidal graphite IS hardly obtained as it be accompanied by more quasi-flaky or meshlike graphite. Primary spheroidal graphite is increased and the general appearance of the structure is improved by sufficient inoculation with silicon.
  c) Hypoeutectic iron: Small addition of cerium has more pronounced effects in these alloys than in other alloys, because of the segregation of cerium in eutectic liquid owing to the separation of more primary austenite. However, the graphite precipitated in eutectic austenite is spherodized only incompletely, as the eutectic austenite is restricted by the primary austenite dendrites. On the other hand, supercooling of eutectic melt is so pronounced as to form ledeburite or mesh-like graphite structure. Complete spherodization of graphite is difficult in the alloys of this composition range.

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  Inoculation is an operation in which alloys are added to molten metal in a ladle to bring about an improvement in physical and mechanical properties of the casting, which could not be expected from the mere change in the chemical composition of the metal. The effects of inoculation are particularly complex in gray iron castings. Effects of various inoculation variables on mechanical properties, eutectic cell size, etc. were studied experimentally.
  Inoculating in high carbon and high silicon iron, as well as “Over inoculation”, decreases mechanical properties of the castings, and hence should be avoided. It has been generally accepted that inoculation decreases the difference in hardness between the center and the edge of a casting section. However, uniformity in tensile strength among test pieces of different diameters of 13, 20, 30, and 45mm was improved only slightly by inoculation. By inoculation, eutectic cell size decreased and its boundaries were obscured. The latter fact suggests a change in matrix structure, as well as in graphite shape, by inoculation.

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  Two different methods, inert gas fusion method and hot-extraction method, were used to determine hydrogen in cast iron. The hydrogen evolved from the heated or molten metal is carired away by argon gas from the extraction tube, and measured by gas-chromatography. In the inert gas fusion method cast iron sample is melted in a fused silica crucible with induction heating combustion apparatus.
  The accuracy of the method was checked against the vacuum hot-extraction method, using a palladium tube. Assuming the hydrogen distribution in the sample cast in metal mold was approximately homogeneous, routine precision of ±0.02cc/100g (mean deviation) was obtained with concentration of 0.9 to 2.3cc/100g.
  The routine conditions of the analysis were the following; (1) The dead space of the extraction apparatus was about 80cc: (2) The flow rate of argon gas was 50±2cc/mn.; (3) The samples weighed about 2 grams in the fusion method. Surface contamination of the samples was removed by rinsing them in carbon tetrachloride and then drying in hot argon gas stream (about 70C) for 5 minutes; (4) Time required for complete collection of the hydrogen gas evolved from a sample was about 6 minutes in the fusion method and 20 minutes in the hot extraction method; (5) Blank analysis was in the order of 10^-5cc/10mn.

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