Simulation of hot deformation of cast super duplex corrosion-resistant steel

Abstract

The deformation behavior of cast super duplex steel has been studied in the temperature range 1100–1250 °C and strain rates 0.1–10 s–1. Hot deformation was carried out by uniaxial compression of cylindrical samples on a Gleeble 3800 thermomechanical simulator. It is shown that the flow stresses decrease with an increase in temperature and a decrease in the strain rate in accordance with a change in the Zener‒Hollomon parameter of the temperature-speed mode of deformation. The shape of the flow curves indicates that hot deformation is accompanied by intense dy-namic softening. As a result, the flow stresses experience a drop or remain at a constant level after reaching peak values. Ferrite in all studied modes of hot deformation acquires a dynamically recrystallized structure. At the lowest deformation temperature (1100 °C) and relatively high deformation rates (1–10 s–1), the austenite softening mechanism is dynamic recovery. A decrease in the strain rate, as well as an increase in the deformation temperature, causes a partial dynamic recrystallization of austenite. Under the same deformation conditions, the level of plastic flow stresses in the steel under study is significantly higher than in standard duplex stainless steels. From the analysis of the peak stresses of the flow, the value of the effective activation energy Q = 501.31 kJ/mol of hot deformation, which is necessary for calculating the Zener‒Hollomon parameter, was determined. An expression for the peak flow stress is obtained in the form of a hyperbolic function of the Zener‒Hollomon parameter. The resulting expression describes the array of experimental data with high accuracy and can be used to estimate the required energy-power parameters of forging and rolling equipment. A comparative assessment of the hot ductility of super duplex steel is carried out by finding the amount of deformation corresponding to the appearance of the first macroscopic cracks on the sample surface. It is shown that at a strain rate of 10 s–1, which is typical for hot stamping processes, the safest temperature range of deformation of the steel under study is the temperature range of 1150–1250 °C, in which austenite undergoes partial dynamic recrystallization, and the risk of crack formation decreases.