Austempered Ductile Cast Iron (ADI) has outstanding strength and elongation balance because the retained austenite enhances ductility by strain induced transformation. The effects of fine pearlite as the prior structure for heat treatment on the formation of fine ferrite, bainitic ferrite, and retained austenite and its mechanical properties were investigated in our previous research. However, the effects of chemical composition on strain induced transformation have yet to be sufficiently studied. Thus in this study, fine ferrite, bainitic ferrite and retained austenite structures were formed by combining different types and addition amounts of austenite stabilizing elements. The influence of strain induced transformation of retained austenite in these fine structures for strength and ductility was also investigated. The dynamic change of retained austenite volume fraction during tensile deformation was measured with synchrotron radiation in SPring-8. The behaviors of strain induced transformation after initiation of plastic deformation were varied from the chemical composition. High strength and low ductility was obtained when the strain induced transformation occurred rapidly after the initiation of plastic deformation, and low strength and high ductility were obtained when the strain induced transformation hardly occurred. On the other hand, high strength and high ductility were obtained when the strain induced transformation gradually occurred. The stability of retained austenite, which affects strain induced transformation behavior in the specimen with various chemical compositions, was considered in terms of Md₃₀. Md₃₀ indicates austenite stability during deformation in metastable austenite. The strain induced transformation behaviors of the specimens were in good agreement with the tendency of Md₃₀. Since the effect of the solute carbon content is the largest in the equation of Md₃₀, the concentration of solute carbon into austenite with proceeding bainite transformation was considered. Mn is also thought to have influenced bainite transformation.

  The authors have been investigating a fabrication method to obtain high performance SiC ceramics by two-step reaction sintering using a Fe-Si alloy that is well known as an inoculation agent. In this study, compositions of C as a constituent of first-sintered body and the Fe-Si alloy as a constituent of molten infiltration alloy for the second sintering were changed for SiC ceramics fabrication. The second-sintered body was fabricated by infiltrating the Fe-Si molten alloy into the porous first-sintered body at 1723 K for 6 h under a pressure lower than 10^-2 Pa. The C content for the first sintered body was changed from 0 to 28 mass%, whereas the Fe concentration of the alloy for infiltration was changed from 0 to 66 mass%. Microstructure observation, elemental distribution measurements of Fe and Si, and phase identification for obtained second-sintered specimens were conducted using a laser microscope, EPMA, and XRD, respectively. Hardness and fracture toughness were evaluated by results of micro Vickers hardness testing. The electrical resistivity was measured using the four-terminal method.

  The microstructure of sintered SiC changed with the Fe content of the infiltration alloy, whereas the generated amount of SiC changed only slightly irrespective of the Fe content. No Fe carbide formation was observed, but FeSi₂ and FeSi phases were formed at high Fe contents. The fracture toughness of sintered bodies improved to 5.9 MPa·m^0.5 at maximum by the increase in the C content of the first sintered body and the Fe content of the infiltration alloy, although the electrical resistivity was reduced to 1.5 × 10^-5 Ωm at the minimum by the increase in Fe contents. Consequently, the fracture toughness of the Fe-Si alloy infiltrated SiC improved by two times compared to the conventionally sintered SiC ceramics. Furthermore, the electrical resistivity of the SiC sample largely decreased by one digit or more. It is considered that the superior characteristics are brought about by the extensive formation of finely distributed FeSi₂ and FeSi phases.

  For the purpose of improving crack resistances of roll materials in steel rolling mill, the effects of carbon content (C) and heat treatment on fracture toughness and fatigue crack propagation were studied using 17mass%Cr cast iron. The main results obtained from this study are summarized as follows ; Fracture toughness (K_IC) decreases with increasing C content, but it rises to the maximum value in the eutectic composition, and drops conspicuously when the C content exceeds the eutectic value. The range of threshold stress intensity factor for fatigue crack propagation (ΔK_Ith) decreases with rising C content in the same manner as the variation of K_IC. It was found that Paris-Erdogan equation, da/dN=C (ΔK_I)^m held well between the crack propagation rate and range of stress intensity factor, and that there was a constant relation of C=A/B^m. Hardening treatment deteriorates ΔK_Ith because of martensite formation in the matrix. In as-cast specimens with high ΔK_Ith values, constant m decreases with increasing ΔK_Ith except for eutectic alloy, and in hardened specimens with low ΔK_Ith value, m increases with an increase in the ΔK_Ith value.

  A design supporting tool for a flexible cast iron feeding system based on modulus expressed by the ratio of volume to surface area was developed for casting engineers to design efficient cast iron feeding system quickly and accurately. The main features of this tool are that (1) design of feeding system can be completed on general-purpose spreadsheet software, (2) the overall modulus of a casting product or effective partial modulus of the area affected by a feeder is accurately calculated using the 3D CAD data of the product, (3) the modulus and dimension of the feeder are calculated using the modulus of the product, and (4) users can set calculation formulas and material data. In addition, the effectiveness of this tool was confirmed by using it for designing a feeding system based on actual cast iron products.

  In hypoeutectic Al-Si alloys, modification treatment is performed to improve mechanical properties and improve shrinkage. However, the Sr / P ratio at the time of improvement has not been clarified. Therefore, in this report, thermal analysis was performed while varying P and Sr to clarify the influence of the Sr / P ratio on the modification treatment while observing the microstructures of the allys. As a result, it was revealed that the Sr/P ratio of modified alloy structures more or less agrees with the stoichiometric ratio of Sr₃P₂.