Strain-rate dependence of the dynamic softening in a duplex stainless steel

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The dynamic softening mechanism of a 2205 duplex stainless steel is comprehensively investigated through hot compression at the temperature of 1000 °C and the strain rates of 0.01 to 10 s−1. It is shown that an increase in the strain rate leads to a marked transition in the softening mechanism of ferrite. The ferrite is found to soften through the sub-grain coalescence at a low strain rate of 0.01 s−1 and via the continuous dynamic recrystallization (CDRX) at an intermediate strain rate of 1 s−1. While, at a high strain rate of 10 s−1, a softening mechanism akin to the discontinuous dynamic recrystallization (DDRX) is observed taking place. The applicable softening mechanism of ferrite in the duplex steel is largely associated with the formation of misoriented sub-grains and their evolution adapted to applied strain rates. By contrast, the softening within austenite is remarkably limited at all applied strain rates. At the low strain rate of 0.01 s−1, the dynamic softening may start through a mechanism analogous to the CDRX. Whereas the DRX nucleation at the high strain rate of 10 s−1 mainly occurs through the strain-induced boundary migration (SIBM). At the intermediate strain rate of 1 s−1, however, sluggish kinetics of DRX in austenite is observed since the two kinds of nucleation mechanisms both are depressed.