真空电子束焊接对锆合金耐腐蚀性能的影响

Effect of Vacuum Electron Beam Welding on Corrosion Resistance of Zirconium Alloys

用真空电子束焊接方法将Zr-4板对接焊后,焊缝的耐腐蚀性能很差,在400℃过热水蒸汽中腐蚀3～14天后,焊接熔化区的表面形成了白色的氧化膜。用电子探针研究了熔区中合金成分的变化和耐腐蚀性能间的关系,结果表明:熔区中Sn、Fe和Cr合金元素的挥发损耗是造成耐腐蚀性能变差的主要原因,当采用合金成分高于Zr-4的锆合金板与Zr-4板对接焊后,可以补偿熔区中合金元素因挥发而造成的损耗,明显改善焊缝熔区的耐腐蚀性能;若在锆合金中添加0.4%～0.5%的Nb,使熔区中形成新的锆合金,将有益于改善焊缝的耐腐蚀性能,但焊接后的样品应在500～600℃进行退火处理,使添加Nb后形成的βZr分解为稳定的αZr+βNb,以进一步改善焊缝的耐腐蚀性能。

The butt joints of Zircaloy-4 plates are made by electron beam welding. The corrosion resistance of welding seams is poor to form white oxide films on the surface of molten zone after autoclave tests at 400oC 10.3MPa superheated steam for 3 to 14 days. The relationship between the variation of the contents of alloying elements in molten zone,which were analyzed by means of electron microprobe,and the corrosion resistance have been investigated. It is proved that the degradation of corrosion resistance of welding seams is mainly due to the loss of the alloying elements of Sn,Fe and Cr by the vaporization in molten zone. When the zirconium alloy plates,in which the alloying element contents are higher than that of Zircaloy-4, are employed for making butt joints with Zircaloy-4 plates, the loss of alloying elements in molten zone can be compensated,so that the degradation of corrosion resistance can also be remedied. Adding 0.4-0.5%Nb alloying element in zirconium alloy is advantage for further improvement of the corrosion resistance of welding seams,but annealing should be carried out at 500~600oC after welded in order to get the decomposition of βZr into αZr+βNb.