Mold filling of flat shaped aluminum die castings is examined by computer simulation technique and casting experiments. Trapped air and cold shut are observed in the die castings which are cast in the first several shots. It is shown that the mold filling pattern obtained by the experiments is quite different from the generally believed filling pattern. Injected molten metal spreads like a fan at the gate and flows along the side wall of the plate cavity.
  The accuracy of the extended quasi three dimensional model is confirmed by comparing simulated results with the experimental results.
  There are close correlations between the simulated results and die casting results.

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  The thermal conductivity of austenitic low thermal expansion cast irons with various graphite shapes was measured up to 200°C. With the measured values and the thermal expansion coefficients reported in a previous paper, computer simulation was carried out to compare the thermal deformation of a solid cylinder model under four heating conditions.
  Thermal coductivity was 11-39W/m·K, high in flake graphite and low in spheroidal graphite cast irons, about 3/4 of ordinary pearlitic irons and 1/2 of ferritic irons with the same graphite shape. The conductivity decreases with temperature and is about 90-95% of the room temperature value at 200°C.
  Computer simulation showed that the influence of low thermal conductivity in low expansion iron differs for different heating conditions. For constant heat flux conditions, the deformation is larger in lower conductivity iron, but for constant end temperature conditions, and for the transient response to the temperature change, lower conductivity iron shows smaller deformation. It must be noted that low expansion iron should be used below 100-130°C, as its advantages decrease rapidly above this temperature range.

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  White cast irons containing chromium, vanadium and/or molybdenum were sprayed by use of a thermal spraying gun and the characteristics of the very rapidly solidified coatings were investigated by means of X-ray diffraction and micro-hardness test. The sprayed coatings of the alloy having a chemical composition of 5%C, 10%Mo (Cr-Mo alloy) or 5%V (Cr-V alloy) revealed a fairly high volume fraction of ε-iron and dispersion of very fine M₃C carbides. The carbon content of the ε-iron in the Cr-Mo alloy coatings, as sprayed, was higher than that of the other alloys and the ε-phase hardly decomposed up to a tempering temperature of 500°C. The microstructure of the coating of the Cr-Mo alloy were of a mixture of fine ferrite, M₃C and M₇C₃ carbides after the tempering at 800°C, bringing about an enhanced Vickers hardness of 1000 or over. This suggested that the thermal spraying of the high-carbon Cr-Mo iron alloy could be applied to a wear-resistant coating for a high temperature service.

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  Influence of martensite on the impact characteristics of austempered spheroidal graphite cast iron was examined by shortening isothermal transformation time, subzero treatment and addition of cyclic stress. The impact characteristics was measured by instrumented Charpy impact test. As a result, the retained austenite transform to martensite because of temperature or stress induced transformation at prescribed conditions. These martensite lower the impact value. This is estimated that these martensite mainly shorten the crack generation time with lowering of excellent plastic deformation ability of the retained austenite.

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  Correlation of mechanical and magnetic properties with microstructure were studied after austempering ductile iron and steel having chemical composition of matrix of ductile iron. The tensile strength of austempered ductile iron was 60∼80% of austempered steel, but impact value and elongation of austempered ductile iron were much lower than values of steel. For the purpose of improving of impact value and elongation of austempered ductile irons and steel, austenite has need to retain from 20 to 45% in volume fraction. In the austempered ductile iron and steel, tensile strength is in direct proportion to coercivity. Similarly, relationship between hardness and coercivity is linear. The tensile strength and hardness could be estimated closely enough by measuring coercivity of austempered ductile irons and steel.

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  The influence of reduced pressure on the distribution of element, particularly of carbon, and the ocurrence of abnormal structure in the surface zone of stainless steel castings prepared by using various types of molding processes were investigated. The results obtained are as follows :
  In CO₂-process-molded vacuum assist casting, the influence of reduced pressure was not observed.
  When the vacuum-sealed mold process was used, the carbon content increased evenly through all of the castings by the reaction between the melt and the plastic film used, but the influence of reduced pressure was not observed. On the other hand, in shell-molded vacuum assist casting an abnornal structure was found in the surface zone of the casting. This abnormal structure become prominent by reducing the pressure, and the carbon content in the surface zone increased with increasing vacuum release time. It was considered that the occurrence of abnormal structure was due to the thermal decomposition of the coating resin.

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  Boronizing Treatment of spheroidal graphite cast iron has been investigated by means of electrolysis in molten salt mainly consisted of B₂O₃, K₂O and Na₂O at various temperatures and times. The microhardness and the thickness of boride layers were measured and the distributions of B, Si and C on the surface of specimens were observed by X-ray microanalyser.
  Microscopic examination and the results of X-ray microanalysis showed that the boride layer consisted of two layer and outer layer was FeB and inner was Fe₂B. The microhardness of these boride layers were about HVN 1500 1800.
  Thickness of the boride layer was increased with an increase of square root of time for treatment at constant temperature. The activation energv for diffusion of boron in the specimen obtained from the slope of Arrhenius plots was 19.5 kcal/mol.
  Si rich layer was formed at the position out of boride layer in specimens after boronizing. Moreover the graphite formation was observed in Si rich layer in the specimens boronized at austenitizing temperature on prolonged time.
  The graphite formation in Si rich layer can be consider as a consequence of the precipitation of carbon during cooling process after boronizing which diffused from spheroidal graphite to austenite matrix at boronizing temperature. Large amount of graphite formation in Si rich layer resulted in the crack passed through these graphites.

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