Effect of Sulfur on the TTT Diagram of CaO–Al₂O₃ Slag at Eutectic Composition

Abstract

It is important to know the behavior of inclusion in a CaO–Al₂O₃-(SiO₂ and/or MgO) system for controlling the properties of steel. The crystallization of inclusion has a large effect on the rolling process. However, there is little study of the effect of sulfur on the crystallization of inclusion. In the previous paper, the authors were investigated the sulfur behavior in the CaO–Al₂O₃ slag at the eutectic composition (CA_EU) under controlled atmosphere. In the present study, the effects of sulfur on the TTT diagrams were measured by the hot thermocouple method under controlled atmosphere. 1 mass%, 5 mass% and 10 mass% CaS were added to the eutectic composition of calcium aluminate (CA_EU).
The crystal region in TTT diagrams was expanded by the addition of CaS from 1 mass% to 10 mass% under Ar atmosphere. And the start of crystallization became faster with the increase of CaS addition. The crystal phases were monocalcium aluminate (CA) and tricalcium aluminate (C₃A) regardless to the CaS content. However, primary crystal was changed from the content of CaS. When 1 mass%CaS was added to CA_EU, the primary crystal was CA. On the other hand, the primary crystal was C₃A in the cases of 5 mass% and 10 mass%CaS.