The relation of additional Al with combined nitrogen in Fe-C alloy, and influence of combined nitrogen upon the graphitizing ability of aluminum were investigated. The mechanism of graphitization of aluminum in Fe-C alloy depends upon both aluminum neutralizing the effect of combined nitrogen which has a chilling tendency and the graphitizing ability of aluminum itself. As the amount of Al increases, the quantity of N as AlN increases as much as over 80% of the combined nitrogen. The N as AlN is contained more in 6N-HCI insoluble nitrogen than in 6N-HCl soluble nitrogen. Insoluble Al in 6N-HCl is composed of both Al as Al₂O₃ and Al as AlN. Also, Al₂O₃ and AlN influence separation from melt.

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  The possibility of the flaw inspection of gray iron castings by ultrasonic testing with 2 M Hz normal probe was investigated. Tests were carried out on specimens in which artificial flaws were made, consisting of flat bottom holes of 2.8 mm in diameter and 25 mm in depth. The intensity of the echo from the artificial flaw and grass echo were measured on specimens with different tensile strength. When the tensile strength of the gray iron castings was above 25 kgf/mm², the intensity of the grass echo became low in comparison with the flaw echo, and flaws could be inspected.
  Ultrasonic testing with 1,2 M Hz and 5 M Hz normal probe was performed to find out how mechanical properties, and attenuation and velocity of longitudinal ultrasonic wave are related to one another. Material testing and ultrasonic testing were carried out on the same specimens of 27 mm in diameter and 200 mm in length, and gray iron cast products. It was recognized that there was a linear relationship between mechanical properties and attenuation and the velocity of ultrasonic waves, and mechanical properties can therefore be estimated by ultrasonic testing.

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  When white cast iron is molten at given temperatures between cementite eutectic and graphite eutectic temperatures and is held at the same temperatures, the amount of graphite eutectic formed increases with lowering holding temperature (increasing the degree of undercooling) and with increasing holding time. Though the solidification of graphite eutectic in the melt of hypo-eutectic iron does not start by holding the melt as long as 90 min at 1,152°C which is below graphite eutectic temperature, that in eutectic iron starts within 5 min of holding at the same temperature. The nucleation in the melt of hypo-eutectic iron is more difficult than in that of eutectic iron, at any degree of undercooling. This phenomenon is essentially different from the fact that when iron melt is conventionally solidified by cooling from above the liquidus temperature, the melt of about 3.9%C hypo-eutectic iron is most favorable for the nucleation of graphite eutectic. The difference might result from the different nucleation ability of carbon-microgroups existing in the melt produced under different experimental conditions. The ability could be dependent on the carbon content of cast iron reflecting the liquid structure and on the effect of austenite rejecting or robbing carbon in the neighboring part of the austenite existing in the eutectic melt.

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  Machinability of spheroidal graphite cast iron was studied as a function of its pearlite content varied by heat treatment. The shape of specimens was cylindrical; 200 mm in outer diameter, 160 mm in inner diameter and 250 mm in length. The chemical composition of the cast iron was as follows: 3.7%C, 2.4%Si, 0.4%Mn, 0.03%P, 0.01%S and 0.06%Mg. The machining operation for estimating the tool life was carried out on a lathe using a WC-Co sintered tool without coolant under the following conditions: depth of cut 2.0 mm, feed rate 0.4 mm/rev, and speed of cutting 100 to 280 m/min. Increasing the pearlite quantity decreases the tool life because it increases hardness. The tool life for 5% and 95% pearlitic spheroidal graphite cast iron can be expressed in terms of the cutting speed V (m/min) and tool life T (min): log V_5%=−0.148 log T+2.398; log V_95%=−0.290 log T+2.222.

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  Two- and three-dimentional solidification analyses of stainless steel castings with L-junction were compared with experiments. The solidification process and the validity of the numerical analyses are discussed. In the analyses, the inner nodal point method has been employed, a report of which has already been made in an earlier paper by the authors. The three-dimensional analysis agreed well with the experimental results and showed that the three-dimensional effect can not be ignored even when the ratio of the flange length to the plate thickness L/T is 10. This result may be an indication that a three-dimensional analysis is necessary for ordinary castings. The interesting numerical result was confirmed by the temperature measurement which indicated that the hot spot in a cross-section is located near the casting surface apart from the plane of symmetry when the inner fillet radius at the junction is very small. It was also shown that the line where the columnar structure meets each other in a macrostructure corresponds to the liquidus temperature contour line but that the hot spot is not always situated there. The burning tendency at the junction was explained from the calculated mold temperature. The shrinkage defect could not be sufficiently estimated from the temperature-gradient and flow conductance methods and a severe shrinkage defect was observed in the region surrounded by the 0.7 solid fraction contour line. For a more exact prediction of the shrinkage defect, it may be necessary to take account at least of fluid flow induced by solidification contraction.

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