STP499

    Temper Embrittlement Study of Ni-Cr-Mo-V Rotor Steels: Part I—Effects of Residual Elements

    Published: Jan 1972


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    Abstract

    Variations in temper embrittlement of vacuum carbon deoxidized Ni-Cr-Mo-V rotor steels, produced by step cooling through the temperature range of susceptibility, are related primarily to variations in P and Sn content. The embrittlement produced by isothermal exposure at 750 F (399 C) for 1 year is about doubleth at produced by step cooling. The effects of P, As, and a P-Sn interaction are significant, while the significance of the effect of Sn alone is considerably less. Increased Mo is associated with reduced isothermal embrittlement.

    Relationships are found between deembrittled Charpy 50 percent fibrous fracture appearance transition temperature (FATT) and P and Sn content. A P-Sn interaction is also observed. Variations in the Charpy 15-mil lateral expansion transition temperature (LETT) in the deembrittled condition are related to P, Mo, a P-Sb interaction, and a Mo-Sb interaction.

    Based on previous investigations, the effect of P on temper embrittlement is about as expected while that of Sn is somewhat greater. Sb displays no significant effect in this study; contrary to definite effects which had been reported previously.

    Keywords:

    sembrittlement, tempering, cooling, heat treatment, isothermal, impact tests, transition temperature, steels, steam turbines, turbogenerators, arsenic, antimony, molybdenum, phosphorus, tin, statistical analysis, correlation, evaluation


    Paper ID: STP38783S

    Committee/Subcommittee: A01.06

    DOI: 10.1520/STP38783S


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