Interactive Relationship between the Superheat, Interfacial Heat Transfer, Deposited Film and Microstructure in Strip Casting of Duplex Stainless Steel

摘要

In this study, a new droplet solidification test has been developed to simulate the process of sub-rapid solidification of 2205 duplex stainless steel (DSS) strip casting process. The results suggest that the maximum heat flux and amount of heat removed increase with the repeat of dropping tests. Furthermore, the final wetting angle between the solidified droplet and substrate decreases, and the bottom area of the droplet increases with the successive addition of solidifying material on prior film. The major composition of the films is detected mainly as oxides containing O, Fe, Si, Mn, Cr and Cu, which precipitate from DSS samples and substrate. The microstructure of the sub-rapid solidified DSS samples consists of δ -ferrite (60–65%) and Widmanst?tten-like austenite (35–40%) phases. The element N mainly segregates in austenite phase and elements Si, Mo tend to stabilize ferrite phase. The finer microstructure in HS4 (the 12th droplet experiment with high superheat) sample implies that a higher interfacial heat flux (10.4360 MW m~(?2)) brings a higher cooling rate, and the nucleation rate can be increased markedly, causing a less space for each grain to grow and further refine the as-cast grain size.