Shrinkage defect in steel disk castings of 25 mm thickness, which was cast in CO
2 sand mold, was examined by X-ray and SEM. The results including the experiments by Bishop et al were discussed based on numerical analyses by the direct finite difference method developed by the authors. It was shown that the sound zone by the end chill effect can be estimated by the progress of freezing front of solid fraction of 0.7 or progress of contours of temperature gradient during freezing. Shrinkage defect near the riser, however, can not be predicted by these parameters. The pressure gradient method, proposed in this paper, could best estimate the formation of shrinkage defect. The shrinkage defect near the riser was string-like and V-shaped. It disappeared by increasing aluminum content and it could be due to macro-blowholes created by H
2, N
2 and CO gas. The shrinkage near the chill end may be microporosity formed by rapid pressure drop resulting from solidification contraction. Furthermore, the shrinkage in the riser was estimated to some extent by the analysis with Darcy's law. More accurate prediction of shrinkage defect requires the consideration of the solid phase movement, examination of the gas content in the melt and heat transfer during pouring.
抄録全体を表示