To elucidate the composition and crystal structure of spheroidal vanadium carbides precipitated in high V-Cr-Ni cast iron that have exhibited excellent performance of anti-corrosive and anti-abrasive properties, alloys of Fe-V-C, Fe-Cr-V-C, Fe-Ni-V-C and Fe-Cr-Ni-V-C systems were prepared and the compositions and structures of vanadium carbides and/or other precipitates were investigated by using SEM, EPMA and XRD. The spheroidal compound was revealed to be a vanadium carbide with an atomic ratio M/C of more or less one and a crystal structure of V₈C₇ type. The composition and crystal structure of the vanadium carbide remain unchanged even if the alloy concentration or the morphology was varied.

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  A series of cast irons was produced to determine the effect of Rare Earth additions on the graphite morphology and chilling tendency of low (0.01∼0.03%S) and high (0.03∼0.1 %S) sulfur level content flake graphite cast iron. This paper also presents solidification cooling curves and microstructures of base iron and RE-added flake graphite cast iron. In this study, various ratios of RE/S were used to find the stoichiometric balance of RE/S for the optimum condition of type A graphite forming range and maximum chill depth. To clearly identify the chilling tendencies, two types of pig iron (generally known as high quality pig iron and ordinary pig iron) were used. All experiments were conducted without post inoculation in order to clarify the effects of Rare Earth in the cast iron. The results clarified that about 2.5 RE/S ratio formed type A graphite and chill depth was of the minimum level. The recalescence of cooling curve indicates that type A graphite can be achieved at 3K or less. In the 3 to 6K range, the graphite structure tends to change from type A to type A+D graphite.

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  The effects of eutectic Si phase, Al-Fe system compounds and precipitates on the tensile properties of Al-7 mass % Si-0.5 mass % Mg 357 casting alloy produced by the thixocasting process were investigated. The tensile strength, 0.2 % proof stress and elongation of T6-treated thixocastings decrease from 360 MPa, 296 MPa and 13.6 % to 324 MPa, 274 MPa and 7.2 % with an increase in eutectic Si particle size from 2.3μm to 4.1μm, respectively. Relationships between tensile properties and eutectic Si particle size of thixocasting alloys were very similar with those of permanent mold castings. Two kinds of Al-Fe system compounds identified as β and π phases were observed at eutectic regions in both produced alloys. The needle-shaped precipitates were found lying along three [100] directions in the Al-matrix phase in thixoand permanent mold cast specimens aged at 433 K for 21.6 ks. Two types of precipitates with irregular and parallelogram network arrangement of bright dots in their cross-section were observed using high resolution transmission microscopy. These needle-shaped precipitates result in stronger Al-matrix in both alloys after T6-heat treatment. The morphology and size of precipitates of thixocast specimens were similar to those of permanent mold cast specimens. From results in this study, it was found that the tensile properties of the 357 thixocast alloy are mainly influenced by the size and shape of eutectic Si particles.

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  Penetration defects of cast iron and cast steel are caused by physical factor, chemical factors, or the interaction of these factors. In this study, a method of judging the factors of penetration defects was established by using SEM and EPMA analysis. Penetration defects were made in a casting experiment with a mold in which the refractoriness was changed first. As for penetration defects which occurred due to physical factors, the boundary of the silica sand and metal was clear in the EPMA mapping. The EPMA mapping of the silica sand and the metal overlapped for penetration defects caused by chemical factos. In the interaction of factos, the EPMA mappings of silica sand and metal did not overlap but the silica sand had melted in the SEM image. Next, the penetration defects which occurred at the casting factory were analyzed by SEM and EPMA analysis, and compared with standard analysis data. As a result, penetration factors generated at the casting factory could be clarified.

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  Using a thermal analysis system consisting of three cups (First : Inoculated, Second : Base melt, Third : Te added) , the effects of alloying elements on graphite eutectic temperature and cementite eutectic temperature of cast iron and their differences (ΔT_E)were investigated. This thermal analysis system was used to predict the chill depth and mechanical properties.
  The order of elements (graphitization elements) that expand ΔT_E is as follows : Si > Al > C_CE<3.5%> Cu > Co > P> Ni > C_CE≧3.5%. The order of elements (chilling elements) that narrow ΔT_E is as follows : B> S_≧0.45%>V> Cr> S_<0.45%> Mn> Nb> Ti> Sn> W> Mo> Sb. ΔT_E is related to the distribution coefficient of elements between cementite and austenite. When S and Mn coexist, the eutectic temperature and graphite shape are determined by soluble S and soluble Mn. The chill depth can be determined by eutectic graphitization ability (ΔT₁/ΔT_E). There is a good relationship between ΔT₁/ΔT_E and graphite type and tensile strength. We can conclude that ΔT₁/ΔT_E serves as an efficient method for predicting melt quality in cast iron.

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