STP1125: Precipitation Evolution in HT-9 Steel Under Thermal Aging and Stress Rupture Conditions

    Pai, R-N
    Graduate student and professor, Materials Engineering Program, Department of Mechanical Engineering, Auburn University, AL

    Wilcox, RC
    Graduate student and professor, Materials Engineering Program, Department of Mechanical Engineering, Auburn University, AL

    Pages: 16    Published: Jan 1992


    Abstract

    Precipitate development in two heats of HT-9 steels (84425 and 91354) during stressed and stress-free thermal aging treatments was studied. Stress-free thermal aging was conducted from 923 to 1033°K for 500 to 10 000 h while stress rupture conditions of 10.4 to 337 MPa stress at 811 to 1033°K for 60 to 17 754.8 h were utilized. Microdiffraction and energy dispersive X-ray spectroscopy techniques were used to analyze the precipitates. The carbide, M23C6, was the predominate precipitate phase in all conditions, with the exception of stressed specimens tested at 1033°K, where most of the M23C6 was replaced by chromium nitride (Cr2N). Cr2N was found only in stressed specimens at and above 977°K. The presence of Laves phase below 977°K produced a compositional variation in chromium in M23C6 and in the metal carbide phases of the MX type. Sigma phase was found only after long time testing at 811°K at a high stress level. The MX phases generally were found in both heats under all conditions. These phases were vanadium-rich in the stress rupture specimens, while titanium-rich in some of the stress-free thermally aged specimens.

    Keywords:

    stress, aging, precipitate, 12Cr-1Mo steel, HT-9 steel, ferritic steel, electron microscopy, energy dispursive X-rays


    Paper ID: STP17940S

    Committee/Subcommittee: E10.08

    DOI: 10.1520/STP17940S


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