Characterization of the Acicular Ferrite in Al-Deoxidized Low-Carbon Steel Combined with Zr and Mg Additions

摘要

The influences of Mg and Zr simultaneously addition on nucleation of acicular ferrite (AF) in Al-deoxidized low-carbon steel have been investigated based on four steels with different Mg and Zr contents. The typical inclusions are characterized by scanning electron microscopy (SEM) and the chemical composition of the inclusions is determined by energy dispersive spectroscopy (EDS). The microstructure characteristics are examined by means of optical microscope (OM), SEM, and transmission electron microscopy (TEM). The formation of AF is demonstrated to be enhanced by the additions of Mg and Zr in the steels, and the highest volume fraction of AF is obtained in 0.0024% Mg-0.030% Zr steel. The nuclei inclusions are identified as Al2O3-MgO-MnS and Al2O3-MgO-ZrO2-MnS multiphase particles with size in the range of 1.5-3.0 mm. Due to the number density of inclusions for 1.5-3.0 mu m is relatively low, thus the volume fraction of AF is low as 18% even in 0.0024% Mg-0.030% Zr steel. Nevertheless, it is observed that these compounds are followed by Al2O3-MgO-ZrO2, Al2O3-MgO, and Al2O3 in decreasing order of effectiveness for acicular ferrite.