The Elimination Mechanism of “A” Segregates of Steel Ingot

Abstract

The mobility of the interdendritic liquid metal under the solid-liquid state was measured by means of sucking out the liquid to a vacuum chamber when Si or Mo contents of materials were varied in order to discuss the elimination mechanism of “A” segregates such as by lowering Si content or adding Mo. The results obtained are summarized as follows:
1) Amounts of metal sucked decreased as solid fraction increased. An abrupt increase of the fluidity resistance of low Si material occurred in lower solid fraction side than that of high Si material, and this effect is particularly characteristic of low alloy steels with Ni, Cr, Mo and V.
2) These phenomena could not be explained only by the viscosity or density difference of the movable liquid in dendrite array. Consequently it should be explained by the difference of dendrite array when the solidification front was being formed in the solid-liquid zone.
3) These effects of Si and Mo can be explained by the following mechanism; i. e. the solidification front is formed in lower solid fraction side when Si is lowered or Mo is added, and then a driving force for floatation of the solute-enriched liquid metal will not be great enough to form the segregates as the concentration of interdendridc liquid at the solidification front does not become great.
Thus, the elimination mechanism of “A” segregates can be concluded to be caused by a shift of the solidification front to lower solid fraction side because of change in dendrite array.