The effects of nitriding treatment on rotating-bending fatigue properties were investigated on nine kinds of pearlitic ductile cast iron samples with Mo (0.1%), Cr (0.1%), V (0.1%), Al (0.1, 0.3, 0.5%), Al (0.1%) & Cr (0.1%), Al (0.1%) & V (0.1%) and without alloying element. The white layer of Fe4N nitride formed on the surfaces of all the samples was about 0.01mm in thickness. The practical nitrided depth and micro-Vickers hardness at 0.03mm below the surface in the nitride layer of the sample without alloying element were 0.148mm and 549HV, respectively. The addition of alloying elements to nitrided samples increased the practical nitrided depth and hardness in the vicinity of the surface. In the nitrided samples, fatigue existing in the higher stress range from 500 to 650MPa was found to be longer in the order of no addition, single addition, and double addition of alloying elements. However, the fatigue limit at 107 cycles in the lower stress range ranged from 410 to 450MPa and no significant difference was seen among the nitrided samples. The improvement of fatigue characteristic by the addition of the alloying element is considered to be efficient only in the higher stress range. The fatigue strength in the high stress range is considered to be related to the difference in the initiation time of the fatigue crack because the spacings of the striation formed on the fracture surfaces are more or less the same in all the samples. This suggests that the larger the nitrided depth and/or the higher the hardness in the vicinity of surface promoted by the addition of alloying elements, the more delayed will the crack initiation be.

  Surface patterns such as bamboo-leaf type, pine needle type, and hexagonal type appear at around 1350°C on molten iron. These patterns are known to be used for examining the conditions of molten cast iron in cupola. In this study, the mechanism by which these surface patterns develop was examined.

The origin of the surface patterns is a surface SiO₂ film formed by the oxidation of Si with CO. The difference in the radiation rate between SiO₂ and molten iron makes the patterns visible. The addition of 0.02mass% S reduces the surface tension remarkably. As a result, a complex Marangoni convection occurs beneath the surface and it generates complex surface patterns. The characteristics of the molten iron improve in the order of Bamboo-leaf, Pine needle, and Hexagonal pattern. The Hexagonal pattern becomes finer with inoculation.

  Surface damage caused by the impact of solid particles is called erosive wear. This phenomenon is a serious problem in the bended sections of pneumatic transportation pipes, valves, turbine blades, fan, etc. To realize efficient and low cost manufacturing of parts, it is important to develop wear-resistant materials and estimate material life span during erosion.

  Recently, many studies are being conducted on various alloys, and attempts are being made to develop wear-resistant materials.

  This study focused on multi-component cast irons, which have excellent wear-resistance because they contain strong carbides forming elements which cause precipitation of hard eutectic carbides at solidification, allowing secondary hardening of the matrix by heat treatment.

  Multi-component cast irons with about 2mass% C and Cr, Mo, W, and V (as an alternative of Nb) of about 5mass% with 0, 5 and 10mass%Co were prepared as test materials in this study. Erosive wear characteristics of the multi-component cast irons were investigated. The impact angle dependency of all the specimens decreased but differences in the erosion rates were seen. Especially, 5V-10Co showed excellent erosive wear resistance. This is because when the Co content increases, secondary carbides precipitate in the matrix and the matrix becomes tougher, thereby suppressing the plastic deformation of the material surface.

  In cast-in insertions of mild steel in cast iron, molten cast iron sometimes melts a part of the inserted steel, causing serious damage to the casting products. To clarify the mechanism of this phenomenon, the influence of the fluid flow of molten cast iron on the dissolved loss of inserted steel was quantitatively evaluated. The molten cast iron was poured into a self-curing mold with an inserted mild steel ring near the open bottom end. The height of the sprue was changed from 500mm to 50mm. The higher the head height, the larger was the fluid velocity. The change in the thickness of inserted steel ring was measured in relation with the pouring time. The experimental results showed that the thickness of steel linearly decreased with the increase in pouring time and flow velocity of the molten cast iron. Widmanstätten ferrite structures and a slightly large amount of pearlite appeared near the surface of the dissolved steel. Temperature measurement and analysis revealed that the dissolved loss of steel started at a temperature considerably lower than the melting point of cast iron. This indicates that the mild steel surface was softened by the heat of molten cast iron and eroded by the fluid flow.

  This study aimed to optimize the design of a runner for high-pressure die casting using computational fluid dynamics (CFD) simulations. A runner is a part of the flow path through which molten metal enters a product part. As a design challenge, we sought to optimize the shape of the runner to minimize air entrainment in the runner and to align the flow of molten metal after passing through the runner. The problem was solved using our proposed shape optimization method. The method is based on a genetic algorithm (GA), and can directly treat a geometric shape that is comprised of several curves as an individual of the GA in the form of a set of mathematical functions. The effectiveness of the optimized shape of the runner was eventually demonstrated with water-model experiments using a visualization device for die casting.

  The behavior of hot-tearing and solidification structures in Al-2～6mass%Mg-0～3mass%Si alloys cast in I-beam shaped mold was investigated by XRD, DSC measurements and OM, SEM-EDS observations. In the as-cast state of all alloys, solidification structures mainly consisted of primary crystallized α-Al and secondary crystallized eutectics, such as Al₈Mg₅, Mg₂Si, and Si phases. The shape of α-Al phase changed from celler to dendritic when Mg and Si contents increased. The area fraction of the hot-tearing region decreased with increasing amount of crystallized eutectic phases with increasing Mg and Si contents, due to the healing effects on cracks at the hot-tearing regions. The temperature range between the liqidus and solidus phases and the cell size of the α-Al phase had more or less no influence on the hot-tearing.

  Fluidity in micro-castings was investigated using a 0.1mm thick plate mold cavity poured through a 1.0mm diameter gate in plaster molds with phosphor bronze and Sn-11mass%Cu alloy. The influences of the pouring temperature, pouring pressure, mold temperature, and surface tension on the fluidity were discussed using a dental casting machine. The surface tension was changed by the addition of sulfur into the phosphor bronze.

  The results showed that fluidity was mainly controlled by the solidification of liquid metal except when the mold temperature exceeded the melting temperature of the metal. If the temperature was above the melting temperature of the metal, all the liquid metal flowed backwards into the gate due to the pressure difference within the plate and gate based on wettability, namely the surface tension. Therefore, the most suitable mold temperature for the micro-castings was just lower than the melting point of the metal for filling the cavity completely.

  The fracture behavior of the white layer on the cast steel brake disc in bending fatigue was evaluated using the acoustic emission (AE) method to analyze the fracture mechanical characteristics. The fatigue strength of the disc material including the white layer tended to be lower than that of the unused material. It was found that the AE signal of the unused material occurred continuously while the white layer occurred suddenly. This clarifies that the fracture of the white layer is brittle. These results indicate that heat cracking occurs easily on the white layer.