STP1295: Effects of Extrusion-Billet Preheating on the Microstructure and Properties of Zr-2.5Nb Pressure Tube Materials

    Choubey, R
    Research scientist and senior research scientist, Atomic Energy of Canada Limited, Whiteshell Laboratories, Pinawa, Manitoba

    Aldridge, SA
    President, Nu-Tech Precision Metals Inc., Arnprior, Ontario

    Theaker, JR
    Research scientist and manager, Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario

    Cann, CD
    Research scientist and senior research scientist, Atomic Energy of Canada Limited, Whiteshell Laboratories, Pinawa, Manitoba

    Coleman, CE
    Research scientist and manager, Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario

    Pages: 19    Published: Jan 1996


    Abstract

    The effects of extrusion temperature and pre-heat soak time for billets on the mechanical properties of Zr-2.5Nb pressure tubes for CANDU reactors have been examined. The β-quenched billets from a quadruple-melted ingot containing approximately 1200 ppm of oxygen were extruded at 780, 815, and 850°C with pre-heat soak times of 15 to 300 min. The extruded hollows were finished by cold drawing (with a 28% reduction in area) and then stress relieving at 400°C. The α-phase grain structure, tensile strength, and fracture toughness properties were found to vary with the pre-heat temperature and soak time. All the materials were tough because embrittling impurities were absent. The tubes with 780°C preheat had a very fine and uniform α-grain structure, giving high strength and toughness at all soak times. The opposite was true for the 850°C soaks; the grain structure was coarse and inhomogeneous and the materials tended to be less strong and less tough. The tubes with the 815°C soaks showed intermediate values of strength and toughness. These variations in mechanical properties are discussed in terms of α-grain refinement and oxygen enrichment.

    Keywords:

    CANDU reactor, Zr-2.5Nb, pressure tube, extrusion, billet, pre-heat temperature, soak time, microstructure, (α+β)-phase, oxygen partitioning, SIMS microanalysis, tensile strength, fracture toughness


    Paper ID: STP16195S

    Committee/Subcommittee: B10.01

    DOI: 10.1520/STP16195S


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