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    STP1543

    Identification of Safe Hot-Working Conditions in Cast Zr-2.5Nb

    Published: 25 September 2014


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    Abstract

    Cast Zr–2.5Nb was hot-deformed in the temperature range of 700°C to 1100°C and in the strain-rate range of 10−3 to 10 s−1 using compression tests. The stress-versus-strain data generated at different rates and temperatures were used to compute the strain rate sensitivity and generate processing maps. The map showed a single domain that spanned the temperature range from 800°C to 1100°C and strain rates less than 0.1 s−1 with a peak strain rate sensitivity of 0.3 at 1000°C and 10−3 s−1. Regimes of flow instability were identified using different criteria based on work-hardening rate and strain rate sensitivity, as well as on parameters based on thermodynamics and extremum principles. Optical metallography of the deformed samples revealed that the domain of high strain rate sensitivity showed equiaxed grains. This, along with the high strain rate sensitivity domain, suggested the occurrence of dynamic recrystallization in this regime. At low temperatures (700°C and 750°C) and high strain rates of 1 and 10 s−1, some macroscopic flow localization was observed. This was predicted by one thermodynamics-based instability criterion that also represents regions of low strain rate sensitivity. On the basis of the processing map generated and metallographic observations, it was found that the cast structure could be safely broken in both the α + β and β phases when deformed at strain rates less than 0.1 s−1.

    Keywords:

    hot deformation, Zr alloys, ingot breakdown


    Author Information:

    Chakravartty, J. K.
    Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai

    Kapoor, R.
    Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai

    Sarkar, A.
    Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai

    Kumar, V.
    RDCIS, Steel Authority of India Limited, Ranchi, Jharkhand

    Jha, S. K.
    Nuclear Fuel Complex, Hyderabad

    Saibaba, N.
    Nuclear Fuel Complex, Hyderabad

    Banerjee, S.
    Dept. of Atomic Energy, Mumbai


    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP154320120197