Effect of variation in microstructures on high temperature creep of Fe-Ni-Cr superalloy

Abstract

Fe-Ni-Cr or known as Incoloy 800H is a solid solution strengthened iron-nickel based superalloy which is extensively used in high temperature environment. Based on its advantages such as high strength and corrosion resistant at high temperatures, this alloy was selected as one of the potential candidate alloy for Generation IV supercritical water-cooled nuclear plant design and for nuclear reactor systems. The effect of grain size in creep strength and creep rate comes through the grain boundary sliding mechanism. This paper describes the effect of microstructural variation of Fe-Ni-Cr on the high temperature creep properties. The material was heat treated at temperature 1050°C and 1200°C followed by water quenching process. The grain size of the samples is 95.47µm for as-received, 122.81µm for solution treated at 1050°C and 380.95µm for solution treated at 1200°C. The creep damage investigation was carried out in the three different grain sizes of Fe-Ni-Cr superalloy at 900°C with stress at 90MPa and 100MPa. Rectangular section forms of specimens are used in the research. In all the tests conducted, the creep curves show primary, secondary and tertiary stages. The creep fracture mode was characterised by using optical and scanning electron microscope. It was found that larger grain size results in higher creep rate.