Effect of Ti Content on the Evolution of Nonmetallic Inclusions and Grain Size in Seismic Rebar HRB400E

Modification of HRB400E rebar has considered titanium inclusions during smelting to alter the microstructure and improve corrosion resistance, as evaluated using scanning electron microscopy, electron backscatter diffraction, and high-temperature confocal laser scanning microscope analysis. The inclusion composition with Ti addition to Si–Mn-deoxidized steel follows the sequence: SiO₂–MnO → TiO₂ → SiO₂–MnO–TiO₂. At higher Ti content in the steel, the inclusions at the completion of refining were smaller in size and more numerous. The grain size of the three groups of experimental steels decreases with increasing Ti content, and the microstructural uniformity of the experimental steel with 0.2% Ti is superior to that of the experimental steel with 0.05% or 0.1% Ti. This response is attributed to the beneficial effect of Ti addition on the dispersion of nonmetallic inclusions, resulting in better dispersion of finer inclusions at a higher Ti content. During refining, the large-size inclusions are removed, and the finely dispersed TiO₂ inclusions function as nucleation points, promoting the nucleation of austenite grains. Moreover, the inclusions act as pinning points for the original austenite grain boundaries at elevated temperatures, inhibiting the growth of austenite grains and further refining the grains.