The operation of ultra-supercritical (USC) fossil-fired power plants places increasing demands on materials. Martensitic 9-12Cr steels have become an ideal choice for thick-walled boiler and turbine components due to their excellent properties. However, in USC power plants, the inner surface of boiler tubes is exposed to steam, and hydrogen in the steam environment can permeate into the material, potentially affecting its creep properties. Therefore, understanding the effect of hydrogen on the creep properties of heat-resistant steels is crucial.
Methods
This work investigated the effect of hydrogen, generated during steam oxidation, on the creep deformation and fracture ductility of 9Cr-0.5Mo-1.8W-V-Nb steel (Gr.92) at 650°C. The researchers compared the creep data of Gr.92 steel in steam and air, analyzing parameters such as time to minimum creep rate, strain at minimum creep rate, minimum creep rate, time to rupture, and total strain.
Highlights
Hydrogen in the steam environment reduces the creep ductility of Gr.92 steel. The total strain of Gr.92 steel in steam is significantly less than that in air, while other creep parameters, such as time to minimum creep rate, strain at minimum creep rate, minimum creep rate, and time to rupture, are essentially the same in both steam and air.
The hydrogen-enhanced deformation-induced vacancy formation model can explain the difference in creep behavior of Gr.92 steel in steam and air. Hydrogen generated by steam oxidation is uniformly distributed in the Gr.92 steel sample and promotes the formation of deformation-induced vacancies, thereby accelerating the accumulation of creep damage and ultimately leading to a decrease in total strain.
The large strain in the accelerated creep stage and the presence of hydrogen in the steam environment jointly promote the formation of micro-voids, accelerating the creep damage of Gr.92 steel.
Editor's Comment
Hydrogen in steam promotes vacancy and cavity formation, reducing creep ductility. This effect is limited to creep ductility, with no significant impact on creep life or minimum creep rate.
Welcome to the International Center for Creep Prediction ICCP! We share the latest research and insights on high-temperature materials, strength, Creep, and Fundamental Theory and experiments of Materials. We welcome you to share your research for free! Join us in advancing the field!
