Evaluation of vanadium carbide stainless cast iron (vanadium carbide cast iron), treated by plasma carburizing, was performed through the examination of wear and rotation bending fatigue. Difference in the form of the primary vanadium carbide (VC) in the matrix affected the wear and rotation bending fatigue properties. The as-cast spheroidal vanadium carbide cast iron has high wear resistance and low rotation bending fatigue resistance in comparison of the as-cast dendritic VC cast iron, The 3-10μm deep layers that were formed by plasma carburizing at various treatment times and temperatures on the vanadium carbide cast irons containing spheroidal or dendritic VC were composed of iron, chromium and vanadium carbides, and were responsible for hardening the vanadium carbide cast iron, The difference between the wear resistance of as-cast spheroidal VC cast iron and that of as-cast dendritic VC cast iron remained unaltered by plasma carburizing, and wear resistance of the plasma carburized materials increased compared with the untreated material. Plasma carburizing leads to the decrease of the rotation bending fatigue resistance of vanadium carbide cast irons, regardless of the difference in the form of the primary vanadium carbide, Fatigue crack initiated near the boundary between the plasma carburized case and core material.

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  In this study, spheroidal graphite cast iron (FCD) and austenitic stainless steel (SUS304) were bonded by friction welding method under various rotation conditions and bevel angles in friction surface of the FCD specimen. Rotational speed and friction pressure were constant. The dimensions of the test pieces were 15mm in diameter and 70mm in length respectively. After bonding, tensile test, microstructure and EPMA observation near the bonding zone of each specimen were performed. As a result, tensile strength increased with decreasing area of the deformed layer of spheroidal graphite. In particular, the FCD base metal specimen was found to break at the following welding conditions; friction time of 90s, forge pressure of 90MPa, forge time of 10s, brake timing of 1s, and bevel angle of 8 degrees. On the other hand, the length of the pearlite layer in FCD adjacent to the bonding interface increased with increasing friction time. In SUS adjacent to the bonding interface, precipitation of chromium carbides were observed which was formed, owing to the diffusion of carbon from FCD to SUS.

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  In this study, the effects of various amounts of silicon (Si) and chromium (Cr) addition on high temperature oxidation characteristics and mechanical properties of austenitic spheroidal graphite cast iron containing 30mass% nickel (Ni) and 1.0mass% molybdenum (Mo) were investigated. As a result, metal oxidation at 1073K in mixed gas of oxygen and argon decreased with increasing amounts of Si and Cr addition. As for tensile properties at 1073K, tensile strength and proof stress increased with increasing amounts of Cr addition. In particular, high ductility was obtained with 4mass% Cr addition.

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  Expendable cores with high strength and removability are required to manufacture undercut shaped products by high pressure die casting. This paper highlights bending strength of a water soluble salt core, which is one of the most attractive candidates for the expendable core. In this paper, the strength of salt cores comprised of NaCl-KCl-Na₂CO₃-K₂CO₃ multi component system were investigated by considering thermodynamics of the salt mixture and experimentally by the four point bending test. Phase diagrams and thermodynamic functions calculated from the thermodynamic data of the multi component system show that there are four composition areas where high strength is expected. A strength map of the multi component system determined by the bending test shows that high strength over 20MPa was obtained in three composition areas. This experimental result is in good agreement with theoretical prediction by thermodynamic data. Salt cores made of such high strength salt mixture should be usable for high pressure die casting. Also, the liquidus temperature of some compositions in these areas was between 873K and 973K, and was low enough to fabricate salt cores from molten salt. In another area, high strength over 15MPa was obtained but composition with high strength was very limited. SEM-EDX analysis shows that sodium content in the primary chloride phase is different among specimens. The strength of the primary phase also depends on the sodium content. Sodium content therefore plays a very important role in the control of the strength of specimens. In the decomposition region of the chloride phase, strength was found to be relatively low if the primary phase was chloride.

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