Modeling of the Hot Deformation of Cast Super Duplex Corrosion-Resistant Steel

The deformation behavior of cast super duplex steel is studied in the temperature range 1100–1250°C and the strain rate range 0.1–10 s^–1. Hot deformation is performed by uniaxial compression of cylindrical specimens on a Gleeble 3800 simulator of thermomechanical processes. The flow stresses are shown to decrease with increasing temperature and decreasing strain rate in accordance with a change in the Zener–Hollomon parameter of the temperature–rate deformation conditions. The shape of the flow curves indicates that hot deformation is accompanied by intense dynamic softening, as a result of which the flow stresses decrease or remain unchanged after reaching peak values. Under all hot deformation conditions, ferrite acquires a dynamically recrystallized structure. At the lowest deformation temperature (1100°C) and relatively high strain rates (1–10 s^–1), the mechanism of austenite softening is dynamic recovery. A decrease in the strain rate or an increase in the deformation temperature causes partial dynamic recrystallization of austenite. Under similar deformation conditions, the plastic flow stress of the steel under study is significantly higher than that in standard duplex stainless steels. When analyzing the peak flow stresses, we determined the effective hot deformation activation energy (Q = 501.31 kJ/mol) required for calculating the Zener–Hollomon parameter. An expression for describing the peak flow stress is obtained in the form of a hyperbolic function of the Zener–Hollomon parameter. This expression describes the experimental data array with a high accuracy and can be used to estimate the required energy–force parameters of forging and rolling equipment. A comparative estimation of the hot ductility of the super duplex steel is performed by finding the strain corresponding to the appearance of the first macrocracks on the specimen surface. At a strain rate of 10 s^–1 (which is characteristic of hot forging processes), the safest deformation temperature range of the steel is shown to be 1150–1250°C, in which austenite undergoes partial dynamic recrystallization reducing the risks of cracking.