Numerical model for detection of microstructural events during rod hot rolling of austenitic stainless steel

A mathematical module is constructed representing the non-executable equations to determine the mean flow stress (MFS) using both Sims and Ekelund approaches. The module considers the redundant strain calculations. Solving the equations of the module develops a numerical model and consequently the MFS is then calculated. The numerical values are taken from the rod mill logs, particularly when the interpass times are short, as the laboratory equipment cannot be used. The calculated MFS values are then related to the inverse of the absolute rolling temperature (T-nr) to determine the non-recrystallization temperature, the strain accumulation and cyclic softening / dynamic-recrystallizing zones of the austenitic stainless steel. At the finishing and prefinishing stages, accumulated deformation and the adiabatic heating affect temperature raising. However, at both stages, the coefficients of friction (mu) decreases as the effect of the rolling speed becomes predominant. The. MFS values calculated by Ekelund are always higher than that calculated by Sims. The T-nr is detected as 1143 degreesC, however, between 1143 and 1081 degreesC, with 0.03 sec. interpass time, a stress accumulation zone is detected. At high strain rate, 103 s(-1), in the temperature range 1063 and 1018 degreesC, dynamic recrystallization is initiated. At higher strain rates (1200-1500 s(-1)), cyclic softening / dynamic recrystallizing is initiated.