热处理对含Nb锆合金焊接试样显微组织和耐腐蚀性能的影响

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

用真空电子束焊接方法将Zr-1.88Sn-0.35Fe-0.52Nb合金板与Zr-4板对接焊的样品,在400C、10.3MPa过热水蒸汽中腐蚀165d后,用光学显微镜从样品横截面上测量了焊接面和其背面不同部位的氧化膜厚度,并用透射电镜观察了不同部位锆合金的显微组织。结果表明:焊接样品经过500C退火处理,耐腐蚀性能明显提高,在相同的熔区和热影响区(含Nb侧)内,经过退火和未经退火的样品表面氧化膜的厚度相差10-20倍;焊接冷却时形成的bZr在退火时分解为aZr+bNb是提高耐腐蚀性能的主要原因;焊接样品经过500C-1.5h退火处理后,熔区的耐腐蚀性能非常优良,在400C过热蒸汽中腐蚀165d后,氧化膜厚度未超过2mm,折算为腐蚀增重只有30mg·dm-2。根据电子探针的分析结果,熔区中的成分大约是Zr-1.2Sn-0.25Nb-0.25Fe-0.02Cr。

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 400°C, 10.3 MPa 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 500°C, 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 β phase after welding, into αZr+βNb after annealing at 500°C. The corrosion resistance of molten zones is excellent after annealing at 500°C-1.5 h, on which the thickness of oxide films is thinner than 2 μm after corrosion for 165 days. It is only 30 mg/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.