Effect of recrystallization annealing on microstructure and tensile properties of Inconel 617B alloy cold rolled pipes

Abstract

The effects of recrystallization annealing on the microstructure evolution of Inconel 617B alloy pipes and its tensile behavior at 750 °C were investigated. As the annealing temperature increases, the grain size and grain growth rate increase dramatically due to the dissolution of the precipitated particles and the enhanced diffusion of solute atoms. Oil-quenched (OQ) samples generated evenly dispersed Cr-rich carbides with stacking faults (SFs) and Lomer-Cottrell (L-C) locks near the carbides, whereas water-quenched (WQ) samples had comparatively clean grain boundaries and matrix. The interaction of Cr-rich phases and dislocations in the oil-quenched sample resulted in the strengthening of the alloy. Besides, because the precipitation of the Cr-rich phase led to the reduction of localized stacking fault energy (SFE), the alloy could coordinate the deformation by forming nano-deformation twins, which significantly improved the tensile ductility and allowed the alloy to have a larger work hardening index (n). At 1180 °C, holding 4 min, then oil quenched annealing conditions, the sample achieved the excellent strength-elongation combination, i.e., the ultimate tensile strength (UTS) of 445 MPa and the elongation (EI) of 47.8% under tensile loading at 750 °C, since the appropriate grain size cooperated with the precipitated phase. The stress concentration caused by the Cr-rich phase in the grain leads to cavitation nucleation. However, the cavitation nucleation at the triple junction of grain boundaries caused by the precipitation phase and grain boundary slips in the samples with other annealing conditions was still the foremost responsible for the fracture.