Abstract
A semi-empirical attempt has been made to evaluate the formation of A-segregates in ingots as a function of the solute concentration in steel melts. Measurements on 22 ingots of the sum of the length of Asegregates(NA) found in unit area on the central longitudinal cross sections parallel to the narrow face of the ingots have given
NA=1.43 (H/D)-0.42Tp+12.7Φ+2.3 (cm/100cm2)
where H, D and Tp are height, width and taper of the ingot, respectively, and Φ is the difference in the density between bulk melt and solute enriched melt remaining in the mushy zone. In deriving the above empirical equation, Φ has been approximated by a linear function of the concentration, CoLn, of n-th solute in the bulk melt as
Φ=-ΣInCoLn
where theoretical consideration has enabled us to determine the value of the coefficient, In, for each solute element.
The above equation for NA indicates that the movement activated by buoyancy of the remaining melt in the mushy zone plays a dominant role on the formation of A-segregates. This is confirmed by separate experiments where plate grade carbon steel with 0.043%silicon and 0.13%molybdenum has been cast in a 26 t mold, resulting in significant decrease of NA, about 1/4, in comparison with ingot of the same grade but with 0.34%silicon and no molybdenum.
