Temperature and time effects of post-weld heat treatments on tensile properties and microstructure of Zircaloy-4

Opportunities exist to expand the application of Zircaloy-4 (Zry-4) into lower-temperature (<100 degrees C) applications. Welded areas within these structures are potential failure points and post-weld heat treatments (PWHTs) are not yet standardized for application in this temperature range. Zry-4 tungsten inert gas (TIG) welds were given PWHTs from 450-900 degrees C with hold times from 0.5-48 hours to investigate changes to tensile properties and microstructure. Treatment of 800 degrees C for 1 hour was found to produce the most ductile material, measured by total elongation of the tensile bar (16.5%). Both PWHT time and temperature were observed to increase total elongation, except in extreme (>800 degrees C or >18hours) cases, but the effect of temperature was stronger. The second order cumulative annealing parameter shows a trend with tensile properties. Average grain sizes in the fusion zone and heat affected zone did not change under any of the PWHTs until the development of an undesirable blocky-alpha phase, which was only observed to form in the heat affected zones for hold times greater than 18hr at 800 degrees C. (C) 2021 Elsevier B.V. All rights reserved.