Evaluation of the effect of various prior creep-fatigue interaction damages on subsequent tensile and creep properties of 9%Cr steel

Abstract

The degradation of tensile and creep properties is inevitable during high temperature service operation. Hence this work aims to evaluate the effect of prior creep-fatigue interaction damages on remnant tensile and creep properties of 9%Cr steel. Prior creep-fatigue tests interrupted at different lifetime fractions and different tensile hold times are performed at 650 °C. Afterwards, subsequent tensile and creep tests are conducted at the same temperature. Results reveal that high lifetime fraction of prior creep-fatigue loading leads to obvious reduction of remnant tensile strength and creep resistance. However, the increase in tensile hold time hardly alters the remnant properties. Microstructure and fracture surface observations indicate that the deterioration of remnant tensile strength is mainly ascribed to the decline of dislocation density occurred during prior creep-fatigue process, whereas the growth of martensite lath plays the dominated role in the reduction of remnant creep resistance. Moreover, surface crack also accelerates the decline of creep resistance at high lifetime fraction. To quantify the prior creep-fatigue interaction damage, a fatigue damage 2 indicator is proposed. Determined relationships between remnant tensile, creep properties and defined fatigue damage are obtained.

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

“…Besides the loading mode, the exertion of duration period also influenced the creep‐fatigue performance. The effect of prior CFI damages and prior fatigue damage on remaining tensile and creep properties of 9%Cr steel was studied by Zhang et al 30,31 and revealed the prior performance could significantly reduce tensile strength and creep resistance. When studying the performance of alloy 709, Porter et al 32 and Amrita et al 25 also found that creep‐fatigue life was reduced in comparison with low cycle fatigue life at different temperatures, and more life reduction was observed at low temperature.…”

Microstructural damage mechanics-based model for creep fracture of 9%Cr steel under prior fatigue loading

“…Experimental results have revealed that remnant creep properties of P92 steel varied a lot with respect to lifetime fraction, strain amplitude and hold time of prior fatigue loading [13,16,20]. The higher lifetime fraction and strain amplitude the more catastrophic degradation of remnant creep strength was noticed.…”

“…Detailed experimental procedures and results have been reported in our previous works [13,16,20], therefore, to avoid a repeated description, only the main experimental procedures and results are presented in the current work. The schematic representation of the experimental procedures is presented in Fig.…”

“…and 70% lifetime fraction of 180 s hold time prior C-F loading. This is because as the lifetime fraction of prior C-F loading increases further, apart from the recovery of microstructures, the evident growth of surface cracks takes place [20]. The surface cracks will introduce additional damage on subsequent creep strength and the damage mechanism of prior C-F loading transforms to the combined effect of microstructure evolution and obvious surface cracks.…”

The Effect of Stress Ratios on the Very High Cycle Fatigue Behavior of 9%Cr Turbine Steel at 630 °C

“…Fatigue behaviors at high temperature are the major concerns for service. It is related to the creep-fatigue, low-cycle fatigue (LCF), and high-cycle fatigue (HCF) at the high temperature [2][3][4][5][6][7][8][9].…”