STP955

    The Fine Scale Microstructure in Cast and Aged Duplex Stainless Steels Investigated by Small Angle Neutron Scattering

    Published: Jan 1987


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    Abstract

    Small angle neutron scattering (SANS) allows clustering phenomena to be studied in systems for which the constituent atoms do not differ greatly in atomic number. This investigation used SANS to characterize the fine scale microstructure in two cast and aged duplex stainless steels that are used in the nuclear industry; aging times extended up to eight years. The steels differed in ferrite content by about a factor of two. The intensity at the lowest scattering angle was dominated by scattering effects that were largely removed by applying a 4-kilogauss magnetic field and is, therefore, associated with the ferrite phase. In the range of momentum transfer 0.025 ⪝ q ⪝ 0.2 Å−1, additional scattering caused by a precipitate phase, assumed to be rich in nickel and silicon, was observed. This scattering was rather intense, and the volume fraction of precipitate, in the ferrite, was estimated to be 12 to 18% after long time aging. After 70 000 h at 400°C, there were about 1024 precipitate particles per m3, some 50 Å in mean diameter, and they were distributed in a nonrandom manner, that is, spatially, short-range ordered. This investigation suggests that after aging some 70 000 h at 400°C, the precipitate in the ferrite phase is undergoing ripening or coarsening. The present data are insufficient to indicate at what time this ripening process began.

    Keywords:

    fine scale microstructure, duplex stainless steels, small angle neutron scattering


    Author Information:

    Epperson, JE
    Metallurgist, Argonne National Laboratory, Argonne, IL

    Lin, J-S
    Chemical physicist and metallurgist, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN

    Spooner, SS
    Chemical physicist and metallurgist, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN


    Paper ID: STP33846S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP33846S


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