As metal fiber (Fe-Cr-Si fiber) fabricated by melt extraction method (NHK spring Co., Ltd.) has superior high temperature strength, and magnesium alloys are lightweight, Fe-Cr-Si fiber reinforced magnesium alloy composites are expected to be lightweight as well as have superior high temperature strength. However, to date, there have bean no reports on the fabrication of Fe-Cr-Si reinforced magnesium alloy composites, and mechanical properties of these composites are not known. In this study, tensile strength of Fe-Cr-Si reinforced magnesium alloy composites was measured from room temperature to 573 K. Moreover, the relationship between experimental and theoretical strength was examined. At all tested temperatures, the composites had higher strength than matrix metal. Compared to JIS-AC8A aluminum alloy (Al-12Si-Cu-Ni-Mg alloy), the composites showed superior high temperature strength at more than 523 K. By means of Baxter's equation which takes into account interfacial bonding strength, the tensile strength of the composites at room temperature was approximately close to the theoretical strength of weak bonding models. At elevated temperatures, the experimental strength approached the theoretical strength of rigid bonding models. This suggests that the interfacial bonding strength increased at elevated temperatures.

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  Multi-component white cast irons containing Cr, Mo, W and V are widely popular as roll materials for hot strip finishing mills because of their excellent wear resistance. Work rolls of multiple rolling mills applied usually to hot strip finish rolling are required to endure the contact pressure generated by rolling force between work roll and back-up roll or intermediate roll. In this research, effects of alloy and C contents on compressive properties were investigated. 0.2% compressive proof strength was found to increase with increase in hardness. It was also found that the relation is σ_0.2 (MPa)＝3.52・HV30－588 for irons with martensitic and fine pearlitic matrices. The equation P_max=1.65・σ_0.2% was obtained between Hertzian contact pressure and compressive proof strength. In order for rolls to endure contact pressure of 2.6GPa, compressive proof strength over 1.6GPa is necessary and multi-component white cast irons with macro-hardness over 600HV30 can be said to be appropriate roll materials for recent hot strip finishing mills applied by heavy load.

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  Several factors affecting eddy current hardness of spheroidal graphite cast iron were examined. Sensitivity of the eddy current hardness measurement was influenced by the coil turn number and measured frequency. In case of a 22mm diameter 400-turn coil, the applied frequency of 6kHz showed highest correlation with hardness, and 30kHz showed lowest correlation. Applying this result, we fabricated a prototype eddy current hardness tester, by which we evaluated the effects of heat treatment and surface machining methods, milling and grinding. At first, the eddy current hardness tester was calibrated on a grinding surface of ten specimens with different hardness. Each side of the same cast iron block specimens was machined by either milling or grinding. On a grinding surface, measured eddy current hardness well agreed with Brinell hardness. On the other hand, measurement on a milled surface clearly showed higher eddy current hardness than on a grinding surface. Vacuum heat treatment at 973K for one hour followed by furnace cooling clearly reduced eddy current hardness. Heating temperatures ranging from 673 to 873K for one hour had little effect on eddy current hardness, but additional heating at 733 to 833K for one hour clearly reduced eddy current hardness. Finally, the effect of heat treatment on cold rolled low carbon steel was examined. Heat treatment of the steel at 673 to 973K for one hour reduced eddy current hardness, which showed good correlation with Vickers hardness.

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  Pores in pressure die castings are generated by entrapped gases or solidification shrinkage. To determine the pore formation mechanism and prevent the formation of pores, the morphology of pores, such as their shape and spatial distribution, should be quantitatively evaluated, and the cause of pores, such as gas or shrinkage, must be quantitatively specified. The accurate identification of pores requires a huge amount of knowledge about the die casting process, the lack of which may lead to misjudgment. We previously introduced a fractal dimension to quantitatively identify the cause of pores and verified the validity of using the fractal dimension D_a^M, calculated by the spatial distribution of the areas of pores from optical micrograph images. This fractal dimension can also be calculated from an X-ray CT image, which allows nondestructive inspection. However, X-ray CT images generally have lower resolution than optical micrographs. In this study, we examined the validity of identifying the cause of pore formation using the fractal dimension D_a^X, calculated from X-ray CT images, by comparison with D_a^M. In aluminum alloy die castings, D_a^X was found to have a lower value inside the samples than on the surface. This result showed that the effect of shrinkage increases in the inner area, which is consistent with the behavior of D_a^M Therefore, the evaluation of D_a^X is also expected to provide sufficient information to identify the cause of pore formation.

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