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

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. [Display omitted] • One self-designed testing system was utilized to investigate the creep behavior of the T92 steel in steam environment. • Creep stress accelerated the scale growth process and pronounced Cr enrichment stringers formed in a parallel fashion within the inner oxide scale. • The presence of water vapour accelerated the minimum creep rate and reduced the creep plasticity of T92 steel in steam at 650 °C compared to that in air. The specimen tested in steam and air showed similar stress exponents. However, the activation energy value in the steam environment was quite smaller than that obtained in the air. • The hydrogen introduced by the formation of oxidation scale in steam environment presumably promoted the diffusion of Fe atoms and then accelerated the creep rates in present research. [ABSTRACT FROM AUTHOR]