An Unified and Systematic Interpretation for the Mechanism of Formation of the Three Major Segregations

Studies on the solidification and segregation of larger steel ingots-IV

Abstract

In the 2nd and 3rd Reports (Tetsu-to-Hagane, 1958, No. 8, p. 872-880, and No. 11, p. 1259-1265) the authors made some observations and experiments with the large ingots which revealed several phenomena concerning the vertical segregation occurred in the melt of ingot core. Combining these new findings with some of the known primary causes for segregation, an unified and systematic explanation for the mechanism of formation of the three major segregations, i. e. inverse V, V and negative segregation, can be derived.
Assuming that the convection and chemical changes in the melt of solidifying, core, Soreteffect at the liquid-solid interface, dilution (diffusion) of concentrated elements into the mother-liquor, etc. have no first-order effect upon the formation of macrosegregation, then the concentrating action at the liquid-solid interface and upward transfer in the solidifying melt play a leading role in the course of forming macrosegregations, as follows:
i) Inverse-V segregation: Nearly horizontal concentration and upward movement of segregating elements give a resultant direction to the inverse-V strings. A key point of difference from the older concept lies in the manner that the enriched segregates move upwards without convection. (cf. 2nd & 3rd Reports).
ii) V and negative segregations: The forming mechanism of both segregations is essentially identical. The difference in the balance between the upward concentration and upward movement in the melt merely produces V or inverse segregation. (Figs. 3 & 4)
iii) Unified mechanism of formation for the three segregations: From i) & ii), the three segregations are formed as the liquid-solid interface advances inwards. (Fig. 5)