Recrystallisation-assisted creep of an austenitic Fe-Ni alloy under low stresses after hot deformation

Abstract

Static and meta-dynamic recrystallisation are known to take place in some steels under low tensile stresses during thermo-mechanical processes, e.g. between rolling stands in a hot strip finishing mill. The main objective of the present work is to understand the mechanisms responsible for the recrystallisation-assisted visco-plastic deformation in a hot worked iron-nickel austenitic alloy subjected to low stress levels at high temperatures. To that purpose, the recrystallisation kinetics of the alloy was first quantified from stress relaxation, interrupted creep and double-hit compression tests, followed by a microstructural study. The evolutions of strain both in the recrystallising and in the fully recrystallised microstructures were quantified. One of the most original aspects of this work is the experimental verification that the acceleration of the viscoplastic deformation of a recrystallising material is unequivocally and intrinsically associated with the ongoing recrystallisation phenomenon itself. For the austenitic alloy of interest, the most important contribution to this deformation enhancement was found to arise from the deformation of newly recrystallised grains in the primary creep regime. Finally, it is also shown that this recrystallisation-assisted deformation can be qualitatively predicted with acceptable accuracy using a relatively simple, physics-inspired constitutive model.