Papers by Author: Sang Min Byon

Abstract: In this paper, we present an analytic approach for the prediction of roll force to be applicable to the billet rolling process which consists of a series of horizontal stands and vertical stands. The approach is based on the deformation shape and employs the assumption that the deformation homogeneously occurs in three directions. Strain and strain rate are calculated by the geometric relationships between those components and the prescribed deformation functions. By integrating the stress components along the rolling direction, roll force is finally obtained. The prediction accuracy of the proposed model is examined through comparison experimentally mesured roll force with computed ones.

Abstract: A constitutive relation is proposed in this study by introducing a function prescrbing the volume fraction of dynamically recrystallized grains into the Voce’s equation to predict the stress-strain relations for three microalloyed medium carbon steels. We performed hot torsion test in temperature range of 900-1100 and strain rate range of 0.05-5.0s-1 to obtain the flow stress-strain curves. The calculated flow stresses are in good agreement with the measured ones. We have then applied the equations in FE analysis to predict the distribution of dynamic recrystallization volume fraction and flow stress for hot forging.

Abstract: We have investigated the static and metadynamic behaviour of the interstitial free steels and in particular the effects of the steeling elements (phosphorous and boron) on kinetics of recrystallisation. The results showed that the strain for the initiation of strain independent softening (often referred to as metadynamic recrystallisation) varies with the Zener-Hollomon parameter and steel composition. Strain rate had a strong influence on kinetics of metadynamic recrystallisation. An increase in temperature from 930oC to 1100oC led to a decrease in time for 50% softening (about one order of magnitude) in the SRX region. However, for the same temperature range, the time for 50% MDRX did not change significantly.