Study of the creep cavitation behavior of P91 steel under different stress states and its effect on high-temperature creep properties

Abstract

In this study, circumferential U-notches of different depths were machined on a plain cylindrical creep specimen to simulate different stress states during steam pipe operation. The effects of stress concentration on the creep cavitation behavior and high-temperature creep properties of P91 steel were investigated through creep experiments and microstructure analysis, as well as measurement and analysis of scanning electron microscopy (SEM) micrographs using ImageJ to obtain the equivalent diameter, circularity, area and distribution of the voids after high-temperature creep of P91 steel. In the analysis of 98 notched samples of 14 bars, it was found that a large number of voids with diameters of 0.78–3.56 μm existed at the notch root, the voids were distributed in a fan shape near the notch root, the size of the distribution area was related to the stress, and the larger the stress was, the larger the area. The number, density and average area of voids increased with stress and time. The stress level at the notch root was found to be positively correlated with the area of damage caused by the voids in the region and negatively correlated with the number of voids based on the FE analysis. By analyzing the experimental data, it is found that the circularity is closely related to the void diameter, and the void coalescence occurs when the void diameter reaches a critical value, which varies with temperature, stress and time.

Keywords

• P91 steel
• Notch
• Voids
• Cracks