| Zirconium alloys is an important nuclear structural materials in nuclear powerreactors. As nuclear fuel cladding materials. the corrosion resistance and hydrogenpickup of the zirconium alloys in reactor operation are two main issues, which greatlyrelates to the life of nuclear fuel assembles and the safety and reliability of nuclearpower reactors. With the development of the high burn-up Zircaloy, the problem howto improve the corrosion resistance of cladding materials deserves further reasearch.The Zr-Sn-Nb alloy （nominal composition is Zr-1Sn-1Nb-0.3Fe） in the hot extrusionand different cold rolling stage was mainly investigated in this paper, the effect of heatTreatment on Zr-Sn-Nb zircomium alloy recrystallization in different processes alsowas studied. Besides, the impact of the process to microstructure and the sizedistribution of the second phase were analysised. And the corrosion behaviors of thealloy was investaged in0.03mol/L LiOH aqueous solution at360℃/18.6MPa.The Zr-Sn-Nb alloy was studied by optical microscopy （OM）, scanning electronmicroscopy （SEM） and EDS. The results shows that600℃is the best suitabaleextrusion temperature for Zr-Sn-Nb-Fe alloy, and the best annealing temperature of theextrusion tube and1stcold-rolled tube.all is600℃/2h, the2nd cold rolled tube cananneal at580℃/2h or590℃/2h. So the volume fraction of recrystallization aftereach pass should be controlled strictly because of the narrow the annealing temperaturerange. There is little effect on recrystallization of Zr-Sn-Nb-Fe alloy to prolong theanneal time at600℃. The2nd cool rolling tube extruded at600℃has the smallestsize of the second phase that distribute uniformly, and the second phase which is lessthan about100nm take up55.1%; and whch has a gradual increase portion in a rollingprocess（12.7%â†'25.9%â†'55.1%）. In addition, the shape of the second phase evolved from irregular to rotundity. what is more, the second phase of these three typestubes all contain Zr, Nb, Fe elements, and the at%ratio of Nb/Fe is not significantlyaffected by the extrusion temperature, so the second phase should be Zr（Nb,Fe）2withhcp.Besides, the corrosion behaviors of this alloy was investaged by autoclavecorrosion test, the results show that the corrosion resistance of the2nd cool rolling tubeextruded at600℃is better than the tube extruded at620℃and640℃. When the2ndcool rolling tube extruded at600℃was corrosioned for210days, the weight gaincould decrease10%than the tube extruded at620℃and640℃. Compared with theZr-4alloy, Nb element can improve the corrosion resistance of the zirconium alloys in0.03mol/L LiOH aqueous solution at360℃/18.6MPa.Based on the above experiments: compared three kinds of processes about theZr-Sn-Nb alloy, the2nd cool rolling tube extruded at600℃has the best corrosionresistance. This is mainly due to the tube was extruded at600℃which is under theeutectoid temperature, the second phase β-Zr has been fully broke down, the size andthe volume fraction of the final second phase get more smaller after the two cold rolledand two intermediate annealing （600℃/2h,600℃/2h）, so the corrosion resistanceof the alloy be greatly improved. The experiment was operated under industrial-scaleconditions, which had a significant meaning for the industrial production processes ofthe Zr-Sn-Nb alloy. |
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