STP756: Influence of Long-Time Aging of CF8 and CF8M Cast Steel at Temperatures Between 300 and 500°C on Impact Toughness and Structural Properties

    Trautwein, A
    Chief development engineer and senior metallurgist, George Fischer, Ltd., Schaffhausen,

    Gysel, W
    Chief development engineer and senior metallurgist, George Fischer, Ltd., Schaffhausen,

    Pages: 25    Published: Jan 1982


    Abstract

    The object of this work was to investigate the influence of long-time aging at elevated temperatures between 300 and 500°C and aging times up to 65 000 h on the impact toughness and the structural properties of CF8 and CF8M cast steels. The results are derived from 18 production heats with varying chemical analysis and varying contents of ferrite.

    The observed aging effect is based on the 475°C embrittlement of the ferritic phase of these steels. In the range between 300 and 400°C the embrittlement is very uniform and can be described by a thermal activated process with the low activation energy of about 24 000 cal/mol. The activation energy permits a physically accurate description of the time-temperature relation of the aging process and a precise interpretation of the results. For the actual material performance the content of ferrite is of great importance.

    Additional investigations studied the influence of aging on the ductile-to-brittle transition of impact toughness. It shows that with increasing aging not only the transition shifts to higher temperatures, but also a lowering of the upper shelf occurs. This effect can be mathematically described by means of three parameters which are aging-dependent. Basically, it allows prediction of the influence of aging on the ductile-to-brittle transition for arbitrary aging conditions.

    Keywords:

    cast steel, long-time aging, elevated temperature, impact toughness, structure properties, α′-embrittlement, activation energy, impact transition behavior, ferrite content


    Paper ID: STP28441S

    Committee/Subcommittee: A01.18

    DOI: 10.1520/STP28441S


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