Modelling of hot deformation of steel 08H18N10T (AISI 321) under uniaxial compression test

The deformation behavior of 08Kh18N10T steel was studied in the temperature range 1000-1280 °C and strain rates in the range 0.01-1 s-1, which are typical for piercing of cast billets in the production of seamless pipes. Hot deformation was carried out by uniaxial compression of cylindrical specimens on a Gleeble 3800 thermomechanical simulator. It is shown that flow stresses decrease with increasing temperature and decreasing deformation rate in accordance with the change in the Zener - Hollomon parameter (Z) of the temperature-strain rate mode of deformation. The shape of the stress - strain curves indicates that at low values of the parameter Z, hot deformation of 08Kh18N10T steel is accompanied by dynamic recrystallization, and at its high values, by dynamic recovery. The conclusion about the change in the main mechanism of dynamic softening with a change in the parameter Z is confirmed by microstructural studies. From the analysis of the peak and steady-state flow stresses, the value of the effective activation energy of hot deformation required for calculating the Zener - Hollomon parameter was determined. It was found that the transition from a fully dynamically recrystallized structure to a structure containing mainly elongated unrecrystallized grains occurs in a narrow range of Z values. The critical value of the Zener - Hollomon parameter is determined, above which the dynamic recrystallization is abruptly suppressed in the steel under study. Analytical expressions are obtained that allow predicting peak or steady-state flow stresses, critical deformations required for the onset and complete completion of dynamic recrystallization, as well as the size of dynamically recrystallized grains for a given temperature-strain rate mode of hot deformation. The obtained expressions can be used as the basis for computer modeling of hot deformation processes in the steel under study.