Characteristics of heat treatment, abrasion wear resistance, and bending strength were investigated on hyper Cr-Nb-V cast irons containing 3.2∼4.5 mass%C, 15 mass%Cr, 0∼10 mass%Nb, and 0∼10 mass%V. Each specimen (10mm×10mm×10mm) was austenitized at 1073K∼1473K for one hour and then cooled in air. The austenitizing temperature for maximizing quench-hardness (Hmax), depended on the chemical composition of the specimen. Specimens with Hmax were tempered at 473K for one hour and then air cooled. These specimens were subjected to rubber wheel abrasion test, Suga abrasion test, and bend test. Discontinuous primary MC improved abrasion wear resistance without deterioration in strength. On the other hand, coarse M₇C₃ remarkably lowered the strength. The properties of these hyper alloys were also compared with conventional high Cr cast iron.

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  Machinability of spheroidal vanadium carbide cast irons (SVI) containing spheroidal vanadium carbide (VC) in structure was investigated. SVI contains carbon of 2∼3 mass% and vanadium about 10 mass% in addition to alloy composition of SUS 304. Specimen A containing VC and considerable plate-like type Cr-carbides, specimen B little Cr-carbides and specimen C very few Cr-carbides were produced by casting. SVI was markedly inferior to SUS 304 in machinability. In the turning of SVI, tool coating TiC and TiN on Al₂O₃ showed the longest tool life, and cutting had to be performed at low speed in carbide tool P20 or K20 because of increased thermal wear, and unsuitability ceramic tool is due to large grooving wear on the side cutting edge. In both turning and drilling, specimen C showed the best machinability, and specimen A worst among the three specimens. Reduction of Cr-carbide in structure is required in order to raise the machinability of SVI.

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  In order to demonstrate the superiority of granular grain structure for thixocasting materials, semisolid samples with granular and dendrite structures were cast into a permanent mold by a punch. The test piece consisting of granular crystals revealed that the punch power was less than 1 kN until three quarters of the casting process. In contrast, the structure consisting of dendrite crystals revealed that the punch power was greater than 8 kN until one quarter of the casting process, and the power increased as the casting process proceeded. Granular grains of primary α aluminum surrounded by liquid phase could be easily moved into the die cavity, since the liquid phase acted as a lubricant. However, with test piece consisting of dendrite crystals, the liquid phase only moved at the first stage and the deformation resistance increased.

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  Multi-component white cast iron was developed for rolling mill rolls and is spreading widely. The morphology and alloy concentration of crystallized carbides were investigated by SEM, TEM and EDS analyses using three irons with typical chemical composition of Fe-2%C-5%Cr-5%V-Mo-W (mass%) system, and the influence of Mo and W on these irons was studied. The reaction of M₂C + γ-Fe → M₆C + MC + M₇C₃, which occurs by heat treatment, could be suppressed by increasing Mo content. It was found that there exists a linear relation between alloy content in each carbide and Mo ratio Mo/(Mo + W) of molten metal. In high W material, however, W contents of crystallized MC, M₂C and transformed M₆C crbides were saturated values.

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  Usually, risers used for casting are effective only at its center part to supply molten metal to prevent shrinkage cavity formation, because risers solidify from the surface toward the center. So most of the molten metal of the riser is wasted without being supplied into the casting. To realize effective use of risers, we attempted to heat a stick shaped thinner riser by high frequency heating to enable most of the molten metal of the riser to be supplied into the casting. We installed a heat resistance pipe in the mold at the location where the riser is usually located, and then we placed a coil surrounding the pipe, and heated molten metal in the pipe by high frequency heating to prevent solidification. Through many kinds of casting tests, we confirm that heating a riser by high frequency heating is very effective for reducing riser volume sharply. We also built a high frequency riser heating equipment, and proved the effectiveness of the equipment by practical use for ductile cast iron and copper alloy products.

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