Effect of Grain Boundary Migration and Recrystallization on the Creep Strength of Inconel 617

Abstract

A study has been made of the effects of grain boundary migration and recrystallization on the creep strength of the commercial Ni-22% Cr-12% Co-9% Mo alloy (Inconel 617) at 1000°C.
Migrating grain boundaries caused a dissolution of carbides, resulting in carbide free zones behind them and in recrystallized grains. Notable grain boundary migration and recrystallization were observed preferentially on longitudinal grain boundaries in the specimens strained by more than 10% (tertiary stage) and they were considered to affect the creep strength in those specimens.
Decarburized specimens being free of grain boundary carbides exhibited significant grain boundary migration, and this fact implied a suppression of grain boundary migration by grain boundary carbides. A reduction of the creep strength by decarburization was explained in terms of a diminishing of these carbides contributing to depress the action of grain boundaries.
Partial recrystallization was observed in the specimens given a slight cold-rolling of 7.5% and subsequent annealing at 1000°C. It was shown that recrystallization not only decreased the strengthening due to cold work but also degraded the strength by the associated microstructural changes, i. e., coarsening of carbides and formation of new grains or subgrains.