Sub-rapid Solidification Study of Silicon Steel by Using Dip Test Technique

Abstract

Dip test technique has been used for the study of sub-rapid solidification (cooling rate ranges from 100 ℃/s up to 1000 ℃/s) of molten steel to effectively simulate the thermophysical phenomena during strip casting process due to its convenient and online observation advantages. In this study, a 6.5 wt% Si electric steel strip was produced by an improved dip test apparatus, which has been developed for the research of interfacial heat transfer and microstructure of strip casting steels. The heat transfer rates were calculated by the inverse heat conduction program (IHCP). The analysis of solidification microstructure and second phase precipitation was also carried out by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the maximum heat flux could be up to 8.2 MW/m2, and only a very small amount of MnS (0.5 μm) and AlN (2 μm) precipitates were found in the as-cast strip while nano-size MnS (~50 nm) and TiN (50–200 nm) precipitates were observed with subsequent heat treatment, after which the magnetic properties were also significantly improved.