Process design for refinement and homogenization of microstructure in bar rolling

Depending on process design of the bar rolling process, the final microstructure distribution varies. In this final distribution two perspectives should be taken into account: homogenization and refinement. Most of the studies carried out so far are focused on minimization of the grain size but the uniformity of the grain size is also important because the locally coarse grain sizes significantly deteriorate the overall performance of the rolled bar. In this study two criteria are proposed as a measure of the refinement and homogenization of the austenite grain size (AGS) distribution. The effect of process parameters on these two parameters was investigated to determine the major controlling parameter for better process design of round-oval-round pass sequence in the bar rolling under the isothermal and non-isothermal conditions. The investigation revealed that the temperature was the most important controlling parameter and the decrease of initial processing temperature was effective not only in the grain refinement but also in the grain homogenization.