Estimating the Influences of Prior Residual Stress on the Creep Rupture Mechanism for P92 Steel

Abstract

Creep damage is one of the main failure mechanisms of high Cr heat-resistant steel in power plants. Due to the complex changes of stress, strain, and damage at the tip of a creep crack with time, it is difficult to accurately evaluate the effects of residual stress on the creep rupture mechanism. In this study, two levels of residual stress were introduced in P92 high Cr alloy specimens using the local out-of-plane compression approach. The specimens were then subjected to thermal exposure at the temperature of 650 °C for accelerated creep tests. The chemical composition of P92 specimens was obtained using an FLS980-stm Edinburgh fluorescence spectrometer. Then, the constitutive coupling relation between the temperature and material intrinsic flow stress was established based on the Gibbs free energy principle. The effects of prior residual stress on the creep rupture mechanism were investigated by the finite element method (FEM) and experimental method. A comparison of the experimental and simulated results demonstrates that the effect of prior residual stress on the propagation of micro-cracks and the creep rupture time is significant. In sum, the transgranular fracture and the intergranular fracture can be observed in micrographs when the value of prior residual stress exceeds and is less than the material intrinsic flow stress, respectively.

Creep and High-Temperature Deformation of Metals and Alloys

“…Creep damage evolution can also be carefully modelled by innovative combinations of experimental investigation techniques, such as small-angle neutron scattering (SANS), scanning electron microscopy, and quantitative metallography, as reported by Jazeri et al in [4] in the case of a 304 stainless steel. The effects of prior residual stress left by welding processes on the damage at the crack tip of a 9-12% Cr steel specimen with simulated weldment was investigated experimentally by Liu et al [5], who observed residual stress-related transition of damage forms.…”

“…The paper by Wu et al [11] deals with the effect of heat treatment process parameters, and specifically the normalizing temperature, in grade 91, a 9-12% Cr steel, which is discussed on the basis of a careful microstructural analysis of crept samples. Other critical features for the industrial applications of these steels have been considered in the Issue, such as weld joint behaviour (Hu et al [5] investigated the effect of residual stresses left by these processes on creep damage) or creep-fatigue and creep relaxation phenomena (Jürgens et al [10]).…”