Dynamic Migration Process and Mechanism of Phosphorus Permeating into Metallic Iron with Carburizing in Coal-based Direct Reduction

摘要

The uneven distribution of phosphorus in direct reduction iron (DRI) was found in a carbothermal reduction experiment at 1 200℃. The results showed that phosphorus creates reticular distribution in DRI, and its content is high where carbon distributes intensively. The microstructure of eroded iron at room temperature was observed, and it was found that phosphorus is distributed mainly in the ledeburite and rarely in the ferrite or cementite. Ultimately, the process of the phosphorus migration with carburization into DRI was revealed: First, the austenite grain boundary melts and absorbs significant amounts of phosphorus while carburizing; meanwhile, the internal austenite remains solid, and the process of phosphorus entering into austenite is blocked, then, the austenite melted completely, therefore, the processes of carburizing and absorption of phosphorus occurred rapidly and phosphorus was mainly absorption at this stage. Based on these studies, low phosphorus DRI can be obtained by lowering the temperature and reducing the reducing agent, which preventing melted of DRI and inhibiting the absorption of phosphorus.