Effect of cooling method on TiN precipitation behavior of high-titanium high-strength steel during solidification

Abstract

Metallographic microscopy, scanning electron microscopy and TiN growth thermodynamic and kinetic equations were used to investigate the morphology, quantity, and size of TiN in the center of high-titanium high-strength steels under different solidification cooling rates. The results showed that TiN in the center of the experimental steels mainly existed in three forms: single, composite (Al₂O₃–TiN), and multi-particle aggregation. TiN began precipitating at around 1497 °C (solidification fraction of 0.74). From the end of melting to solidification for 180 s, the cooling rates in the center of the experimental steels for furnace cooling, air cooling, refractory mold cooling, and cast iron mold cooling tended to stabilize at 0.17, 0.93, 1.65, and 2.15 °C/s, respectively. The size of TiN in the center of the experimental steel cooled using furnace cooling was mainly concentrated in the 5–15 µm range. In contrast, the size of TiN in the center of the experimental steels cooled using air cooling, refractory mold cooling, and cast iron mold cooling were mainly concentrated in the 1–5 µm range. In addition, their density of TiN in the center of the experimental steels is significantly higher than that of the furnace-cooled experimental steel. Thermodynamic and kinetic precipitation models of TiN established predicted the growth size of TiN in a high-titanium high-strength steel when the solidification cooling rates are not below 0.93 °C/s.