Model for Prediction of Microstructural Events During Rod Hot Rolling of Austenitic Stainless Steel

Abstract

A mathematical model is constructed representing the non-executable equations to determine the mean flow stress (MFS) using both Sims and Ekelund approaches. The model considers the redundant strain calculations. Solving the equations of the model develops a numerical solution and consequently the MFS is then calculated. The numerical values are taken from the rod mill logs, particularly when the interpass times are short, since the laboratory equipment cannot be used. The calculated MFS values are then related to the inverse of the absolute rolling temperature to determine the non-recrystallization temperature (Tnr), the strain accumulation and the cyclic softening / dynamic recrystallizing zones of the austenitic stainless steel.At the finishing and prefinishing stages, the accumulated deformation and the deformation heating affect temperature raising. However, at both stages, the coefficients of friction (μ) decrease as the effect of the rolling velocity becomes predominant. The MFS values calculated by Ekelund are always higher than those calculated by Sims. The Tnr is detected as 1143 °C. However, between 1143 and 1081 °C, with 0.03 seconds interpass time, a stress accumulation zone is detected. At the high strain rate, 103 s−1, in the temperature range 1063 and 1018 °C, dynamic recrystallization is initiated. At higher strain rates (1200-1500 s−1), cyclic softening/dynamic recrystallizing is initiated. The finishing temperature is found to be the most attributable to the grain size, whereas, the sub-grain structure is mainly due to multi-passes deformation.