Study of the Ti-Mn-Al-Si-O-S Complex Inclusions Inducing Intragranular Acicular Ferrite

摘要

High temperature confocal laser microscope, FE-SEM-EDS and EPMA were utilized to study the Ti-Mn-Al-Si-O-S complex inclusion inducing IAF in Ti deoxidized steel. FactSage was also used to calculate the thermodynamics of inclusion formation. It was demonstrated that when the cooling rate is fixed to 5K/s, IAF can be induced by complex inclusions which act as the core of IAF at 609℃. Microstructure of the complex inclusions is complicated. These inclusions are consisted of the TiOx-MnO core which is surrounded by MnO-Al_2O_3-SiO_2 complex inclusions and small amount of MnS. The reason that Ti-Mn-Al-Si-O-S complex inclusions can induce IAF is that a Mn-depleted zone is formed by the core TiOx-MnO and the MnS around it. Meanwhile, the difference between MnO-Al_2O_3-SiO_2 and austenite thermal expansion coefficients is tremendous is another principle element for the IAF formation.