Synopsis: The mechanism of formation of the "inverted V" segregation in killed steel ingots was investigated by means of the autoradiographic technique. The results obtained can be summarized as follows: 1) An inverted V segregation occurs in the transitional solidification zone, when liquid enriched with solute in the interdendritic region which commonly forms microsegregation begins to move upwards owing to the gravitational force. Then it grows gradually to a larger segregation. 2) The

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... ed V segregation occurs in the transitional solidification zone, but grows mainly in the boundary region between the transitional zone and the liquid bulk. 3) The solute concentration inside the interted V segregation diminishes gradually as it grows larger, but this concentration appear again at the final stage of the solidification. 4) The process of the growth of the inverted V segregation is rather the confluence and spread of the liquid which is already enriched with the solute than the enrichment or accumulation of the solute at the socalled solidification front or interface. 5) Thus the inverted V segregation is not formed as a result of the solute enrichment at the solidification front, but rather the solute is ejected and enriched at the solidification front through the formation of the inverted V segregation.