Influence of asymmetric hot rolling on microstructure and rolling force with austenitic steel
(Institute of Metal Forming, University of Technology and Mining Freiberg, Freiberg 09599, Germany)
Abstract: In order to establish a new processing technique of producing steels with fine grain, asymmetric hot rolling and symmetric rolling were performed. The asymmetric condition was introduced by applying mismatched roll diameters. The diameter ratios between big and small rolls were 1.00, 1.05 and 1.11. The rolling temperatures were between 900 °C and 1100 °C. The thickness reduction of workpiece was set at 15%, 30% and 60%. The results showed that asymmetric rolling produced higher volume fraction of recrystallization grain and smaller average grain size at the center layer of rolled sample than symmetric rolling. The diameter ratio of 1.05 tended to generate the highest recrystallization level and the smallest average grain size. With high temperature and low thickness reduction value, the grain growth was obvious. The conventional dynamic recrystallization mechanism was prevailing, while accompanied by twinning. At low temperature of 900 °C, even at thickness reduction of 60%, symmetric rolling cannot initiate dynamic recrystallization as asymmetric rolling did. The asymmetric rolling force was smaller than that of symmetric rolling, except at 900 °C and thickness reduction of 60%. The rolling force also increased with descending temperature and climbing thickness reduction.
Key words: austenitic steel; asymmetric hot rolling; microstructure evolution; rolling force