Precipitation Upon Hot Strip Mill Conditions of a Ti-IF Steel

Abstract

<jats:p>Upon hot strip mill of titanium Interstitial Free (IF) steels, during cooling from austenite to ferrite region, the level of interstitial elements not removed by steelmaking process is dropped down by Ti that combines with N, C and S. Some authors [1-3] have reported that the traditional precipitation sequence TiN, TiS, Ti<jats:sub>4</jats:sub>C<jats:sub>2</jats:sub>S<jats:sub>2</jats:sub> and TiC occurs with freestanding particles formed by nucleation and growth processes. Other authors [4] have indicated that the transformation from TiS to Ti<jats:sub>4</jats:sub>C<jats:sub>2</jats:sub>S<jats:sub>2</jats:sub> may be considered as a hybrid of shear and diffusion, i.e., faulted Ti<jats:sub>8</jats:sub>S<jats:sub>9</jats:sub> (9R) + 10[Ti] + 9[C] → 41/2Ti<jats:sub>4</jats:sub>C<jats:sub>2</jats:sub>S<jats:sub>2</jats:sub> (or H for its hexagonal crystal structure). At low temperature (≤930°C), the stabilization process continues through epitaxial growth of carbides on H phase. to study the evolution of precipitation upon hot strip mill conditions, samples of a Ti - IF steel were subjected to double straining tests [5] by means of a computerized hot torsion machine, at 1000 °C and 920 °C, with strain rate of 1 s<jats:sup>-1</jats:sup> and interpass times ranging from 0.5 to 100 s.</jats:p>