2014 年 54 巻 4 号 p. 970-978
The flow behaviour as well as initiation of dynamic recrystallization in Fe-23wt%Cr-8wt%Ni (23/8 steel) austenitic steel containing 0.28 wt% nitrogen was investigated using Gleeble 3800 thermomechanical simulator. Hot working was carried out in temperature range of 950–1100°C at strain rates ranging from 0.01 to 10 s–1. Based on experimental results a constitutive equation was predicted for peak flow stress embracing the Zener-Hollomon parameter. The deformation activation energy and stress exponent were calculated as 671.66 KJ/mole and 3.762 respectively. The critical stress for initiation of dynamic recrystallization was determined by the identification of an inflection point in the strain hardening rate versus stress plot. The average normalized critical stress for the metal was found as 0.806. The power dissipation efficiency and instability maps for the 23/8 austenitic stainless steel were developed adopting modified Dynamic material model (DMM). The power dissipation efficiency calculated using DMM was compared with that of modified DMM. The validity of power law during deformation process for the above material was analysed. The processing maps in connection with microstructures and experimental flow curves were used to interpret possible safe processing conditions of the above material during hot metal working. The peak efficiency of 35.91% at 0.6 strain was observed under 1100°C and 1 s–1 whereas the optimum processing condition was found under 1100°C and 0.1 s–1 having efficiency of 23.4%. Dominating damage mechanisms causing microstructure instability in this material are identified.
