Investigation of Inclusion Characteristics and Intragranular Acicular Ferrite Nucleation in Mg-Containing Low-Carbon Steel

The characteristics of the inclusions as well as their contribution to intragranular acicular ferrite (IAF) nucleation in Mg-containing low-carbon steel were investigated via electron backscatter diffraction and transmission electron microscopy. Most inclusions changed from single-phase to complex with a fine size and dispersed distribution after Mg addition, which contributed to the IAF nucleation. The complex inclusions were composed of MgAl2O4, Mn3Al2Si3O12, α-MnS, and some small particles. MgAl2O4 was present in the core, and α-MnS and some small particles were distributed on the Mn3Al2Si3O12 periphery. The observed dislocations and twinning in α-MnS and Mn3Al2Si3O12 played a vital role in the IAF nucleation by reducing the ferrite nucleation energy. Our results may enhance the fundamental understanding of the IAF nucleation mechanism, which is of importance for the practical application of oxide metallurgy technology.