20th International Forgemasters Meeting - IFM 2017

In vacuum ingot casting, molten steel stream is dropletized and degassed in the vacuum tank, since this process is one of the effective methods to obtain good internal quality and large ingots. There are cases that the large inclusions are observed in the vacuum casting ingots at the bottom part, which consist of SiO2, SiO2-MnO, and Al2O3-SiO2-MnO. As a result of the verification experiment with VIF, it is concluded that these inclusions are derived from the thermal insulating board which is set at the hot-top. Although this problem can be solved by replacing this board with firebrick, there is possibility of the decline in thermal insulation. Generally, macro segregation in ingot casting depends on a thermal insulation. To prevent deterioration of the macro segregation, the multiple layered refractory for the hot-top which consists of insulating brick and firebrick is developed. As a result of the application of this refractory to the hot-top, these inclusions are suppressed and center segregation is reduced. In addition, to improve the quality of vacuum casting ingots, the new vacuum tank with various sensing equipments is installed. As the operating factors, which are related to the quality of ingots, are quantified and visualized by these equipments, quality and workability are improved.