1958 Volume 44 Issue 11 Pages 1266-1273
A study on the origin of non-metallic inclusions was carried out by the use of radio-isotope tracers. The radio-isotope 45Ca or 95Zr was impregnated in the pouring refractories which were the fertile source of inclusions. Mild steel was melted and refined in a 150KVA. Héroult furnace, tapped into the tagged ladle, and an ingot of about 90kg was obtained. Non-metallic inclusions extracted from the ingot, ingot scum, slag and all other radio-active products were collected, weighed and counted.
Thus, the behaviors of the eroded refractory materials carried along by the pouring stream were quantitatively traced with the following results:
When nozzles, stoppers and fireclay mortar were tagged (pouring temperature: 1550°C) 70.071g of the tagged parts was eroded, 6.04% of which was once transported into the ingot case. 52.3% of the transported refractories was floated as the ingot scum, and the rest (47.7%) was retained in the ingot as non-metallic inclusions. The ratio of the non-metallic inclusions of the tagged refractory origin to the total inclusions in the ingot was 2.86%.
In the case when all the refractories of the ladle were tagged (pouring temperature: 1550 °C), inclusions of refractory origin amounted to 8.74% of the total content of inclusions.
The behaviors of the eroded refractory materials were found to depend largely on pouring conditions. For instance, when pouring temperature increased, the erosion became stronger, but a larger amount of the eroded materials was floated as ingot scum than in the case of lower pouring temperature, and a cleaner ingot was obtained.