Formation of Non-Metallic Inclusion and Acicular Ferrite in Ti–Zr Deoxidized Steel

Abstract

The formation of non-metallic inclusion and acicular ferrite (AF) during solidification is investigated by high temperature experiment, thermodynamic calculation and metallurgical analysis. The size distribution and composition of inclusions are carried out by optical microscope (OM), scanning electron microscope (SEM) equipped with energy-dispersive spectrometer (EDS) and image process software. The results indicate that adding Ti-Zr can modify the inclusions from Mn-Si-O-MnS to Ti-Zr-O-MnS, and the average size of inclusions can be refined obviously from 2.38 μm to 1.56 μm. The critical size of inclusion inducing AF is 0.21-0.37 μm, and the optimized size for AF nucleation induced by Ti-Zr-O-MnS inclusion is in range of 1.0-3.0 μm in this study. Moreover, for inducing AF nucleation, the inclusion larger than critical size is only necessary condition but not sufficient condition. A Mn-depletion zone resulted by MnS precipitating on Ti-Zr-O inclusion is observed adjacent to the Ti-Zr-O inclusion, which is believed to be one of the possible mechanisms to promote the nucleation of AF.

Effect of Addition ZrO₂ Nanoparticles on Inclusion Characteristics and Microstructure in Low Carbon Microalloyed Steel

“…8) Ti, Mg, Zr, and Re as the most popular deoxidizing alloying elements, which were often selected to deoxidize alone or in combination to obtain the effective deoxidation products to refine grains. 9-13) Ti 2 O 3 , 9) MgO, 10) ZrO 2 , 11) Ti-Zr-O, 12) and Ti-Re-Zr-O, 13) they were all confirmed as the effective oxides to induce AF formation and refine grains.…”

“…Among of them, the mechanism (1), inclusion as effective interface, was independent of the inclusion composition and was only related to the inclusion size. Our previous study 12) calculated that the critical diameter of inclusion inducing AF formation was 0.21-0.37 μm in low carbon steel. This meant that when the inclusion size was larger than the critical size, the inclusion could act as the effective inclusion that reduced the energy barrier of ferrite formation.…”

Generation of Acicular Ferrite in the Laser‐Welded Weld of X100 Pipeline Steel Induced by CO2 Shielding Gas

“…Thus, the Mn content around the inclusions is lower than that of the matrix, forming the MDZ. [17][18][19][20] The MDZ will greatly increase the driving force of AF nucleation and promote the formation of AF. [21][22][23] Moreover, the increase of oxygen content in the weld will increase the phase transformation temperature and further promote the formation of AF.…”

Effect of Mg on the Evolution of Inclusions and Formation of Acicular Ferrite in La–Ti‐Treated Steels

“…TiN, MgAlO 4 , and Ti–RE–Zr promote AF nucleation on account of their excellent coherency with α‐ferrite. TiN–MnS, Al 2 O 3 –TiO x –MgO–MnS, and Ti–Zr–O–MnS induce AF nucleation because of the MDZ that formed due to the precipitation of MnS. However, MDZ also formed without MnS, due to diffusion of manganese ions into Ti oxides .…”