Effect of Heat Treatment on the Microstructure and Corrosion Resistance of Zirconium Alloys with Nb Welding Samples

The butt joints of Zr-1.88Sn-0.35Fe-0.52Nb and Zircaloy-4 plates were made by electron beam welding. The corrosion tests of welding samples were carried out in autoclave at 400C, 10.3MPa superheated steam for 165 days. The thickness of oxide films of these corrosion samples in different zones on welding surface and the opposite side of welding surface was measured by means of optical microscopy. The microstructures of different zones were also examined by transmission electron microscopy （TEM）. The results show that the corrosion resistance of welding samples is obviously improved by annealing at 500C, and the thickness of oxide films is 10-20 times different between the annealed sample and non-annealed sample on the same molten and heat-affected zones. This is mainly due to the decomposition of βZr, which was formed because of the containing of Nb and the cooling from b phase after welding, into αZr+βNb after annealing at 500C. The corrosion resistance of molten zones is excellent after annealing at 500C-1.5h, on which the thickness of oxide films is thinner than 2μm after corrosion for 165 days. It is only 30mg/dm² if converted into the weight gain. The composition of molten zones is about Zr-1.2Sn-0.25Nb-0.25Fe-0.02Cr according to the analysis of electron microprobe.