Hot deformation behaviour of Ni-30Fe-C and Ni-30Fe-Nb-C model alloys

This research investigates the effect of thermomechanical processing (TMP) parameters (temperature and strain rate) and the addition of Nb and C on the dynamic recrystallisation (DRX) of austenite and on deformation activation energy using Ni-30Fe-Nb-C and Ni-30Fe-C model alloys. Plane strain compression tests were carried out in a Gleeble TMP simulator. Critical and peak strains and stresses were determined in the temperature range of 925-1150°C at strain rates of 0.01s-1, 0.1s-1 and 1s-1. Both critical and peak strains and stresses increase with a decrease in the deformation temperature, an increase in strain rate or the addition of Nb in the model alloy. The Zener-Hollomon parameter and deformation activation energy values have also been determined using the experimental parameters of DRX and an Arrhenius type equation. The deformation activation energy of Ni-30Fe-Nb-C and Ni-30Fe-C were calculated to be 419KJ/mol and 362KJ/mol, respectively. The volume fraction of dynamically recrystallised grains determined using an Avrami type model was in good agreement with metallographic results, except for the deformation temperature near the recrystallisation stop temperature. The delayed initiation and completion of DRX due to the addition of Nb was more pronounced at lower deformation temperatures.