Influence of Inclusions on the Nucleation of Acicular Ferrites in a Ti-Zr-Bearing Steel

Laboratory experiments are conducted to study the influence of inclusions on the nucleation of acicular ferrite in Ti-Zr-bearing steels. The ferrite transformation in steels with different Ti-Zr contents is observed using a high-temperature confocal laser scanning microscope (HT-CLSM). The average composition and size of inclusions and the information about the nucleation of acicular ferrite (AF) are analyzed using a scanning electron microscope. When the content of titanium in the steel increased from 70 to 370 ppm, the main composition in the inclusion transformed from Al2O3 to Ti2O3, the volume fraction of AF increased from 24.4% to 52.5%. The average content of ZrO2 in inclusions is 0%, 18.51%, and 90.39%, when the Zr content of steel is 0 80, and 140 ppm, the volume fraction of AF is 52.5%, 76.9%, and 56.8%. The relationship between the cosine of the contact angle at the inclusions-ferrite interface and the diameter of inclusions is established based on experimental results, which is consistent with the results calculated based on the classic nucleation theory.