Analysis on stress‐strain behavior and life prediction of P92 steel under creep‐fatigue interaction conditions

Abstract

Considering the flexible operation conditions, the creep‐fatigue performance of P92 steel plays a crucial role in manufacturing structural components of ultra‐supercritical fossil power plants at 620°C–630°C. The creep‐fatigue interaction tests of P92 steel were conducted at 630°C in air with different duration periods, where the duration periods were simultaneously added on the peak tensile strain and valley compressive strain. The addition of hold time resulted in a rapid decrease of fatigue life, where the reduction amplitude increasing with the hold time. There was more than five times reduction as the hold time increased to 300 s. Moreover, the stress relaxation behavior during hold time exhibited a saturation behavior at long dwell time, where the limited relaxed stress gradually approached to the creep threshold stress. Furthermore, a modified strain energy density exhaustion model involving creep threshold stress was proposed and provided more accurate predictions in comparison with the conventional model, reducing the conservatism.

Relationship between the microstructure and the heat treatment and creep behavior of Fe–33Ni–19Cr alloy

“…2 A large number of triple junctions in fine-grained specimens can limit crack propagation. [36][37][38][39][40][41][42] These results agreed with the critical length criterion for intergranular creep rupture 43 and are found to be applicable in Ni-based alloy 32,[44][45][46][47] and 316 stainless steel. 12,44 The percentage elongation results, which are the ductility, were slightly affected by the testing temperature.…”

Probing strain rate effect on the creep–fatigue fracture mechanism of 9%Cr steel‐welded joint via nanoindentation characterization

“…The accumulated fatigue damage was widely characterized by using plastic strain range (inelastic strain range), 9,26 which can be estimated from stress-strain hysteresis loop. On the other hand, the stress-strain hysteresis loop of 50% life was widely reported to be an important state to characterize the CF damage.…”

“…On the other hand, the stress-strain hysteresis loop of 50% life was widely reported to be an important state to characterize the CF damage. [26][27][28] Figure 6 therefore shows the hysteresis loops measured in CF tests for the first loading cycle and for the load cycle equivalent to 50% life (502th cycle for 0.0001 s À1 , 868th cycle for 0.001 s À1 , 1005th cycle for 0.002 s À1 , and 895th cycle for 0.005 s À1 ) with strain rates of 0.0001 (Figure 6A), 0.001 (Figure 6B), 0.002 (Figure 6C), and 0.005 s À1 (Figure 6D). From the stress-strain hysteresis loops, two phenomena that the vertical drop of stress at the maximum peak and vertical rise of stress at the minimum peak were observed.…”

The Investigation of the Fracture Behavior of a Chinese 9% Cr Steel Welded Joint under Creep-Fatigue Interactive Loading

“…Figure 6 shows the typical strainstress hysteresis loop of the welded specimen with a holding time of 300 s. It schematically indicates that the inelastic strain amplitude can be directly obtained from the strain-stress hysteresis loop. The creepfatigue behaviors at the first cycle and the cycle equivalent to 50% of the lifetime fraction are widely reported to be important to the investigation of the damage mechanisms [4,19,20,23]. Figure 7 shows the variations in measured inelastic amplitude during the creep-fatigue test for all of the BM and welded specimens.…”

“…Based on the linear damage rules, the nonlinear damage curve and twostage linearization approaches, the life-curve modification methods, the approaches based on crack-growth concepts, the continuum-damage mechanics models and energy-based theories, the fatigue life-prediction methods have been widely used for metals and their alloys [18]. As for the life prediction of creep-fatigue fracture, Zhao and Wang have each proposed a modified strain energy density exhaustion model for creep-fatigue life prediction, which can accurately predict the cyclic life of CF-tested high-Cr steels [19,20]. However, if the fatigue life-prediction method is selected to predict the cyclic life of the creep-fatigue-ruptured welds, the accuracy of life prediction can be significantly reduced.…”