Abstract
TiN precipitates in the molten steel act as effective heterogeneous nucleation sites for delta-ferrite during solidification. Some reports indicate that Si increases the activity of that of Ti. In this work, effect of Si content on the formation of TiN in the molten steel and on the solidification structure of steel ingots was investigated experimentally. And thermodynamic calculations for the formation of TiN and heat-transfer solidification analysis were conducted. Ratio of equiaxed grain structure of an ingot of 11mass%Cr-0.13mass%Ti-0.0080mass%N steel of which primary crystal was delta-ferrite increased with increase in Si content. Thermodynamic calculations suggested that Si increased the activity of that of Ti in the molten steel and increased TiN before solidification. Positive large values of eTiSi can explain the experimental results in this work, but negative small value can not. Heat-transfer solidification calculations indicate that increase in Si content can make it easy to cause columnar to equiaxed transition similar to very low superheat in the mold.
