Microstructure, Hardness and Their Relational Model of High-Temperature Aged Super304H Heat Resistant Steel

Artificial aging experiment of Super304H heat resistant steel was carried out at temperature ranging from 650 ℃ to 700 ℃ to investigate the microstructure evolution and hardness change during aging. Moreover, the relationship between the hardness of the steel and the Larson-Miller parameter (P function) was modeled mathematically. The results show that the hardness of Super304H steel decreased dramatically with the increase of aging temperature. As the aging temperature was fixed, the hardness of Super304H steel increased initially, and then decreased, but finally turned to be constant with the aging time prolonging. On condition of the same P function, a mathematical relationship model between the hardness of Super304H steel and the P parameter was obtained via a linear fitting method. The calculated and tested hardness values were coincided with each other very well. Therefore, this mathematical model could be employed to predict the service life of Super304H heat resistant steel tubes.