Effect of steam on the creep behavior of T92 steel at 650°C

Abstract

One self-designed testing system was utilized to investigate the creep behavior of the T92 steel in steam environment. The creep tests were conducted at 650 °C with a certain stress range from 100 MPa to 160 MPa in the steam environment and air respectively. The specimens tested in steam environment shows typical multi-layered oxide scale consists of an outer scale of magnetite and an inner scale of Cr-rich spinel. Compared to the specimens in air, the steam specimens possessed larger minimum creep rate and reduced plasticity. The stress dependence of minimum creep rates exhibited a power law with similar exponents of 12.0 and 12.6 in steam environment and air respectively, indicating similar operating mechanism of creep. However, the activation energy in steam environment was smaller than that in air. Microstructural observation demonstrated that the degradation of tempered martensite lath structure and coarsening of the precipitations were mainly responsible for creep damage both in steam environment and air. The results concentrating on the possible interaction between the oxidation scale growth process and creep were discussed on the basis of oxidation process, a potential effect of hydrogen on creep and potential hydrogen embrittlement.