The Effect of Ingot Size and Capping Time on the Distribution, Composition and Type of Non-Metallic Inclusion in Large Rimming Ingots

Abstract

The following results have been obtained through the study made on the subject.
(1) Large non-metallic inclusions distribute mainly at the bottom part of an ingot. Whose compositions are (Fe, Mn) O, MnO-Al₂0₃ and Mn-Silicate. From the fact that larger inclusions have less value of MnO/FeO, coming closer to the composition of scum, it is estimated that large inclusionsstem partially from scum through rimming action. Since Ca is detected in the aluminate and silicate, they are considered to have origin in slag, refractory and deoxidation products.
(2) With the “ingot parameter” Y-which is defined as ingot width/ingot thickness+0.02 (ingot height-width), relations between ingot dimensions and inclusion distribution and its composition can be clearly shown: when Y becomes bigger, total amount of inclusions and amount of large inclusions (more than 100μ) increase and the inclusions have less value of MnO/Fe0.
The parameter Y is considered to have some relationship with thickness of viscous laver at the bottom part of ingot and with state of flow of rimming steel in the mold. Y therefore, is a good index to explain conditions of scum movement along rimming action, scum trap and precipitation of (Fe, Mn) O.
(3) With shorter capping time, increase in total amount of inclusion is observed, but the amount of large inclusions decreases.
This result is explained as follows:
When capping time becomes shorter, more oxygen, which would be otherwise eliminated through rimming action as CO, remains to react with iron and manganese which results in higher amount of nclusion.
Growth of inclusions is hindered as rimming action is terminated earlier, which results in less amount of large inclusions.