Microstructural Evolution and Quantitative Evaluation of Precipitates during Long-term Creep of KA-SUS304J1HTB

Abstract

This paper presents microstructural evolution and quantitative evaluation of precipitates during long-term creep of KA-SUS304J1HTB steel. Thermal aging and creep tests were conducted on a virgin material at 600 ~ 700 °C, for up to 26000 h, and the microstructures in grip and gage sections of creep ruptured specimens were observed by scanning and transmission electron microscopy including chemical analysis techniques. The effects of temperature and time on the growth of the σ phase and the Cu phase were quantitatively evaluated. Mean particle size of the Cu phase in the grain was increased with aging time by the volume diffusion control theory, and the activation energy for the Cu phase growth was calculated. Mean particle size of the σ phase and the Cu phase in grips were comparable to those in gage section, indicating that stress has little effect on both parameters. On the other hand, the average of the maximum particle size in the observation area and area fraction of the σ phase were larger in the gage section than those in the grips due to the effect of stress.