Metallurgical Interpretation on Grain Refinement and Synergistic Effect of Mn and Ti in Ti-microalloyed Strip Produced by TSCR

The grain refinement mechanism and synergistic effect of Mn and Ti involved in the Ti-microalloying technology of thin slab casting and direct rolling (TSCR) were elucidated. Because the inevitable precipitation of TiN in high Ti-containing liquid steel decreases the volume fraction of TiN precipitated from austenite and the rapid coarsening rate leads to a large size of TiN particles, a relatively weak inhibition effect on the recrystallized grain growth was obtained compared with that in the low Ti-containing steel. However, the ferrite grain size in high Ti-containing steel can be refined by the so-called non-recrystallization rolling. The complex addition of Mn and Ti can improve the strength and toughness of strip remarkably, and the mechanisms are that Mn decreases the transformation temperature, refines the ferrite grains, and enhances the formation of bainite and TiC precipitation in ferrite.