Abstract:
The influence of heat input on the as-welded microstructure and hardness of autogenous bead-on-plate gas tungsten arc welds on nuclear grade Zircaloy-2 was investigated. In addition, the β-α transformation behaviour was examined using dilatometry. In particular, the transformation start and transformation end temperatures at various cooling rates were determined.
The microstructure of the welded joints (heat input 10 to 90 J/mm) and of the dilatometry samples (at cooling rates of 600 to1.1°C/s) was predominately basket-weave. In the range of cooling rates used, the hardness did not change with the fraction basket-weave structure or the prior beta grain size. The hardness of the weld metal and heat affected zone was not sensitive to heat input or the use of a pulsed power supply for the range of heat input and welding speed investigated. There was no difference in hardness between contaminated welds and non-contaminated welds. Second phase particles found in the base material did not seem to be present in the weld metal or HAZ .
The transformation start and transformation finish temperatures, on heating, for all the samples were 807°C to 1071°C. On cooling, transformation start and transformation end range was 801°C to 647°C. The cooling time from 900⁰C to 600⁰C, Δt 9-6, calculated for weld metal and HAZ was therefore considered an appropriate parameter.
The findings show that Zircaloy- 2 has good weldability over wide range parameters and that practical welding problems such as shielding did not compromise the integrity of the welds.
