In recent years, semi-solid casting technologies are becoming increasingly practical. In the semi-solid casting process, the granulation of the primary α-Al phase is carried out to improve fluidity. However, the mechanism of the granulation has not been fully clarified so far. Therefore, this paper aimed to clarify the mechanism by pouring molten Al-7%Si alloy just above the liquidus temperature and then super-heating it at 100℃. The molten Al-7%Si alloy was also poured from a high position. The granulation mechanism of the primary α-Al phase was then discussed based on the results obtained.

  By pouring the molten Al-7%Si alloy just above the liquidus temperature, large amounts of the granulated primary α-Al phase were obtained. The reason for this may be because the growth velocity of each crystal decreased as the nucleation number density increased, causing the interfacial stability to increase because of the decrease of the solute quantity which accumulated on the solid/liquid interface. In addition, the results were related more to the enforced diffusion of the solute accumulated on the solid/liquid interface by the molten metal flow at the time of crystal growth, than to the pouring of the molten alloy at the super heat of 100℃.

  A cellular automaton model with a triple-grid method was developed to simulate dendritic growth with less computational cost. As a new approach of the multi-grid method, temperature, solute concentration and solid fraction fields are described by three kinds of grids in the proposed model, respectively. In order to evaluate the validity of the proposed model, simulations of secondary dendrite arm growth of Al-Si and Al-Cu alloys were carried out, and the simulated results were compared with phase-field simulations and experimental data. According to comparison of secondary dendrite arm spacing, simulation results were in good agreement with phase-field simulations and experimental results during dendritic growth. Additionally, in order to investigate the capabilities of the model, the proposed model was applied to simulate the formation of multi-equiaxed dendrites of Al-7%Si alloy under practical solidification conditions. In the early stage of solidification, primary dendrite arms developed along their crystallographic orientations. As solidification proceeded, the growth and coarsening of secondary dendrite arms occurred. From this result of multi-equiaxed dendrites, it was confirmed that the proposed model can perform quantitative simulation of dendritic growth under practical solidification conditions.

  Four types of alloys were prepared, in which C and Cr contents were about 2 and 8%, respectively, while Ni contents were changed in the range of 0 to 2%, and Mo contents were 1 or 2%. The previous paper showed that there exists a window between pearlite and bainite transformation at around 773K in the TTT diagrams for these cast irons. The specimens were heat treated at 1273K for 7.2 × 10³s, cooled down to the temperature of 773K with a cooling rate of 0.3K/s, and then isothermally tempered various times. The hardness of the specimens increased with increasing holding time and then decreased after peaking at 24.5 × 10⁴s. The increase in hardness was mainly attributed to the formation of martensite.

  Although the amount of retained austenite decreased with the holding time, the increase in the area fraction of pearlite was observed in the prolonged treatment specimens. The addition of Ni and Mo led to increased hardness with suppression of pearlite transformation during treatment, while the amount of retained austenite also increased.

  Porcelain enamel processing is performed on the inner surface of iron kettle and tea pot for export. The biggest problem of the porcelain enamel processing on cast iron is the occurrence of bubble defect. Many studies have been reported on the causes of the bubble defect, but there remain many unclear points. In this work, five kinds of annealed cast iron samples, namely flake graphite cast iron with A-type, C-type and D-type graphite structure, spheroidal graphite cast iron with ferritic and pearlitic matrix and white cast iron without and with annealing, were used. Porcelain enamel processing was performed and the relation between surface microstructure of cast iron and bubble defect was examined. The surface microstructure differed from the center microstructure in the sample used. It became clear that graphite morphogy in the surface have a relation close to bubble defect formation in the porcelain enameled sample. The flak graphite cast iron sample, having a center microstructure of D type graphite in ferrite matrix, and the so-called non-graphite phase in the surface microstructure, has the smallest amount of bubble defect. Considerable bubble defect was observed in the samples with chill or with graphite fiakes protruding to the surface. Abnormal graphite formed in the surface texture of spheroidal graphite cast iron, and considerable bubble defect was observed, irrespective of the matrix microstructure.