Cyclic deformation behavior of an Fe-Ni-Cr alloy at 700 °C: microstructural evolution and cyclic hardening model

Abstract

The cyclic deformation behavior of an Fe-Ni-Cr alloy was studied based on low-cycle fatigue (LCF) experiments at 700 °C with various total strain amplitudes Δεt/2 A cyclic hardening behavior was found for Sanicro 25 alloy. The increasing rate of stress amplitude increased first, and subsequently decreased with prolonged cycles. The cyclic hardening ratio increased when Δεt/2 increased. Microstructure observations revealed that the Cr23C6 in the grain interiors were mainly distributed around the NbCrN precipitate. Additionally, the Cr23C6 precipitate aggregated and coarsened with an increasing Δεt/2 The shape of Cr23C6 precipitate also changed from rectangular to circular. The fracture surface observation showed the precipitates can be observed at the crack initiation site and in the microcavities and dimples. It indicates that the precipitates affect the fatigue fracture. In addition, the fraction of deformed grains increases as Δεt/2 increases. Furthermore, based on the modified Fisher-Hart-Pry (FHP) back-stress influenced by precipitates with different radii, the influences of the glide strain, half spacing of precipitates, and radius of precipitates on FHP back-stress were investigated. The applied stress increases with increasing glide strain and radius of precipitates. When the half spacing of precipitates increases, the applied stress decreases.