METALLURGY OF ZIRCALOY-2. PART I. THE EFFECTS OF FABRICATION VARIABLES ON THE ANISOTROPY OF MECHANICAL PROPERTIES

The anisotropy of mechanical propertles of Zircaloy-2 was studied as a function of fabricatlon variables. The variatlon in tensile and impact properties with specimen orientation was taken as the measure of the anisotropy of mechanical properties for each material. A qualitative separatlon of the effects of the fabrication variables on the resulting anisotropy of mechanical properties is made, but it is valid only in the rolling plane of the plate. A contractile strain ratio, a ratio of the nataral contractile strain in the rolling plane to that in the direction normal to the rolling plane (measured on the round tensile specimen after testing), is introduced to aid in the interpretation of the tensile data. A Zircaloy-2 fabrication schedule (consisting of, in succession, ingot breakdown at a temperature of 1800 to 1900 gas-cooled F, major reduction at a temperature of 1800 to 1900 or 1350 to 1450 gas-cooled F, a to 1000 deg F. heat treatment of 1800 to 1850 gas- cooled F for 30 min, followed by either a water-quench or a rapid aircool to below 1200 gas-cooled F, a final reduction of 25 to 40% at l000 gas-cooled F, and an anneal at 1400 to 1425 gas-cooled F for 30 min) was found to produce a much more nearly isotropic material than any of the schedules investigated. This material is anisotropic in strain behavior and tensile properties in comparison to the common cubic materials. The elimination of the intermediate to 1000 deg F. heat treatment from the fabrication schedule resulted in the production of a material with tensile properties for all directions in the plane of rolling essentially the same, but which allowed little cortractile strain to occur in the thickness direction of the plate. This indicated that a high degree of three-dimensional anisotropy existed in the material. The effect of cross rolling on the anisotropy of mechanical properties of Zircaloy-2 was found to be a function of the temperature and stage of fabrication at which it was performed, the position of the relative to the final fabrication directions, and the type of cross rolling, whether unidirectional or rotational. It was concluded that the use of other methods of examination and interpretation was necessary to satisfactorily evaluate the effects of variation of the fabrication variables on the anisotropy of Zircaloy-2. (auth