On the Formation of String Ghost in Killed Steel Ingot

Abstract

The first section of this paper deals with the three dimensional observation on the macrostructure of string ghosts in steel ingot. The characteristic features of string ghost were examined by applying knowledge gained from previous studies upon the gravity segregation of Al-Cu alloy. The following conclusions were obtained:
1) The string ghost was observed to be formed in the transitional solidification zone, at which stage some amounts of dendritic crystals grow. The dendritic crystals in steel ingot were found to be plate-like.
2) The solute enriched liquid located at a relatively large spacing of dendrite arms was considered possibly to move upward due to the gravitational force and to remelt dendritic crystals in process of flow. Therefore, the ghost with stringlike configuration was formed in the transitional solidification zone.
3) Direction of the flow of enriched liquid through the dendrite arms was considered to be inclined towards the center of the ingot because of smaller resistance to its movement.
In tfte second section attempts are made to reproduce the stringlike segregation line by model experiments of Al-Cu alloy.
Consequently, it was found that the stringlike segregation line could be formed artificially or naturally in the transitional solidification zone of Al-Cu alloy, and thus the above-mentioned conclusions were verified.