Effect of Sulfur Content on Inclusion and Microstructure Characteristics in Steels with Ti_2O_3 and TiO_2 Additions

摘要

The effect of the sulfur content on the inclusion and microstructure characteristics of steels where and TiO_2 have been added was studied. Based on the microscopic examinations, it is found in the steel samples with Ti_2O_3 additions that the area fraction of intragranular ferrite decreases from 52.68% to 39.09% as the sulfur content increases from 0.009 mass.% to 0.030 mass.%. In the steel samples with TiO_2 additions, this value also decreases from 49.05% to 36.26% as the sulfur content increases. The nucleant inclusion was identified as a TiO_x+MnS phase based on SEM-EDS measurements as well as on equilibrium calculations with thermodynamic calculation software, Thermo-Calc. Also, TiO_x was found to be the nucleation site for an intragranular ferrite formation. Moreover, the nucleation probability increases with an increased inclusion size. It is also noted that the nucleation probability decreases slightly with an increased sulfur content. The minimum size of TiO_x+MnS inclusions for an IGF nucleation is about 0.85 μm in the present samples. Furthermore, this minimum size of TiO_x inclusions is shifted to a size of about 0.5μm by excluding the depth of a MnS layer. In addition, the effective nucleation size range of TiO_x inclusions in the steels, where Ti_2O_3 and TiO_2 had been added, is smaller than that of TiN + Mn-Al-Si-Ti-O inclusions in steel samples where TiN had been added.