Effect of Sulfur Content on Inclusion and Microstructure Characteristics in Steels with Ti2O3 and TiO2 Additions

Abstract

The effect of the sulfur content on the inclusion and microstructure characteristics of steels where Ti2O3 and TiO2 have been added was studied. Based on the microscopic examinations, it is found in the steel samples with Ti2O3 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 TiO2 additions, this value also decreases from 49.05% to 36.26% as the sulfur content increases. The nucleant inclusion was identified as a TiOx+MnS phase based on SEM-EDS measurements as well as on equilibrium calculations with thermodynamic calculation software, Thermo-Calc. Also, TiOx 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 TiOx+MnS inclusions for an IGF nucleation is about 0.85 μm in the present samples. Furthermore, this minimum size of TiOx inclusions is shifted to a size of about 0.5 μm by excluding the depth of a MnS layer. In addition, the effective nucleation size range of TiOx inclusions in the steels, where Ti2O3 and TiO2 had been added, is smaller than that of TiN+Mn-Al-Si-Ti-O inclusions in steel samples where TiN had been added.

On the Capability of Nonmetallic Inclusions to Act as Nuclei for Acicular Ferrite in Different Steel Grades

“…They mostly used artificially added oxide powders like Ti 2 O 3 to create the desired inclusion types because an appropriate tailoring of potent nucleation sites only by deoxidation and desulfurization reactions can be difficult. [21][22][23] However, this might be in contrast to the demands of high-quality steels, which generally require low inclusion contents. The present study investigates the acicular ferrite formation on nonmetallic inclusions on a laboratory scale, with special consideration paid to the importance of the relationship between steel composition and inclusion type.…”

“…Mu et al [21] and Xuan et al [22] investigated different steel grades with carbon contents between 0.2 and 0.3 wt pct. They mostly used artificially added oxide powders like Ti 2 O 3 to create the desired inclusion types because an appropriate tailoring of potent nucleation sites only by deoxidation and desulfurization reactions can be difficult.…”

“…Apart from weld metals, most published studies addressed High-Strength LowAlloyed (HSLA) steels. [21][22][23] Therefore, a systematic comparison of the inclusions' effects in different steel grades has been sparsely represented. Therefore, the current study compares four steel grades with significantly different compositions, and their effects on the capability of inclusions to nucleate acicular ferrite.…”

Combination of In Situ Microscopy and Calorimetry to Study Austenite Decomposition in Inclusion Engineered Steels

“…Grong et al suggested that a specially designed master alloy containing the inclusions could be added into the liquid steel directly. This possibility has been utilized to study, e.g., the formation of IGF in cast plain carbon steel inoculated by Ti‐oxide nanopowders and ferrite formation in steels where Ti 2 O 3 , TiO 2 , and TiN particles were added directly to the molten steel . The details of the decomposition of austenite are essential, and it is important to have profound knowledge of the phase transformations, including, e.g., the starting temperature of GBF and IGF formation (T GBF,s and T IGF,s ) since it can be used to control the final microstructure and thus the steel properties.…”

Modeling of Inclusion Formation during the Solidification of Steel

“…1) In contrast, fine dispersed oxides may act as inoculants for the heterogeneous nucleation of complex inclusions. These inclusions may finally be active for grain refinement during solidification 2,3) and for the control of microstructure formation in the solid state [4][5][6] just to name two examples. The adjustment of oxides to act as inoculants was recognized in the 1980s 7,8) and termed "oxide metallurgy".…”