Effect of Ti Content on Grain Growth of Ultra Low-carbon Steel Sheets

Abstract

The effect of Ti content on the grain growth of Ti-added ultra low-carbon steels during annealing after cold-rolling has been investigated. The experimental result showed that the grain growth rate is slower in steels with lower Ti content than in steels with higher Ti content; the average grain size increased with 1/10th power of time in low-Ti steels and with 1/3rd power of time in high-Ti steels. This difference would be related to the change of precipitates. In low-Ti steels, the change in the average size of precipitates was small. This might be related to the disappearance of TiS and appearance of Ti4C2S2 during annealing. On the other hand, Ti precipitates in high-Ti steels ripened during annealing and this ripening of precipitates would control the grain growth; the Ostwald ripening. The grain growth is dependent on the chemical composition of steels other than Ti and the re-heating condition of slabs; the increases of Mn, the decrease of S and the decrease of re-heating temperature of slabs accelerated the grain growth rate even in low-Ti steel. This experimental result on the grain growth behavior agrees with the calculation result considering the Zener force.