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Czochralski-silicon wafers having ring-likely distributed stacking faults (ring-SFs) were investigated by means of copper decoration. The size and density of copper precipitates were measured by X-ray transmission topography and preferential etching. In the outer region of the ring-SFs, electrical properties (recombination lifetime of minority carriers, the dielectric breakdown strength) were found to be excellent. On the other hand, in the inner region of the ring-SFs electrical properties were degraded. These phenomena may be explained by the large defects which remain in the center region of the ingot.

Synopsis:In the circum ferential part of continuously cast blooms, there is a zone of more intensive colouration in macro-etching than parts of the cross-section. This zone is called the "pattern".In order to make clear the formation mechanism of the "pattern", the casting structure and distribution of sulfide inclusions are investigated.The results obtained are as follows: (1) The "pattern" is obseved more clearly in Al-Si killed steel than in Si killed steel. (2) In the "pattern", sulfide structures are very fine and the ratio of interdendritic area is higher than other parts.In the "pattern", sulfide inclusions precipitated at the interdendritic area are very fine and numerous.(4) When the upward-streaming type immersion nozzle is used, the solidification rate in the lower part of the mold in the bloom caster is higher than that in the spray zone. It is concluded that the "pattern" of the continuously cast bloom is formed in the rapid solidification zone in the mold .(5)The reason why Al-Si killed steel exhibits the "pattern" more clearly is explained by the role of Al2O3 as nucleation sites for solidification.(6) Any difference in mechanical properties between the "pattern" and other parts is not observed.

Synopsis:The defects originated from center porosity of the continuously cast blooms have been revealed by the study on the unusual tesile fractures of the PC steel wires which contain B and Ti. The cracks initiated at the tesile fractures are caused by the nonmetallic inclusions at the center porosity of blooms during the heating in the soaking pit for the billeting.The degree of the oxidation depends upon the center porosity and heating condition. The marked oxidation of blooms containing B and Ti is caused by the development of columnar dendrites and the increase of center porosities.The oxidation of the center porosity at the ends of bloom can be prevented by controlling the casting temperature and improving the solidification structure of the bloom.