連鋳鋳型内不均一凝固に及ぼす抜熱速度の影響

抄録

The influence of rate of heat removal on uneven solidification in a continuous casting mould has been investigated by changing thickness of a steel plate which is closely set on a surface of sand mould. The steel plate has a heat capacity corresponding to its thickness, and the rate of heat removal in initial stage of solidification decreases with the thickness decrease.
As a result, Al-killed steel containing about 0.12%C, whose shell is formed quite unevenly in water-cooled copper plate mould, has been observed to solidify evenly under some low rate of heat removal. This critical rate is about 0.8×10⁶ kcal/m²·h by heat transfer analysis.
This fact can be explained as follows. When the rate of heat removal is lowered, temperature of shell on mould side gets to drop more slowly and the difference of cooling rate between mould and liquid steel sides of shell becomes smaller, which makes the difference of shrinkage smaller. In this way, the bending force towards liquid steel, which is potentially exerted at upper part of shell by the difference of shrinkage, gets weakened. Moreover, strength of shell becomes weak due to a rise of temperature level of shell. Consequently, the bending force cannot overcome the static pressure and air gap is not formed between the shell and mould, which results in even solidification.