原子能科学技术2023，Vol.57Issue(12)：2409-2416,8.DOI:10.7538/yzk.2023.youxian.0047
Zr-2.5Nb压力管制造过程中的组织结构演变(Ⅰ)
Microstructure Evolution during Fabrication of Zr-2.5Nb Pressure Tube(Ⅰ)
摘要
Abstract
Zr-2.5Nb pressure tube is one of the most important components of the fuel channel in the CANDU reactors.The α/β phase transformation of Zr-2.5Nb during pressure tube fabrication is much more complex than that in single α phase zirconium alloys for fuel cladding tube,since Zr-2.5Nb is a α+β dual-phase alloy.In consideration of the α/β phase transformation effect on the microstructure evolution of Zr-2.5Nb pres-sure tube,microstructure characterization of Zr-2.5Nb alloy in VAR ingot,forged bil-let,hot-extruded tube was carried out.In addition,heat treatments of β quenched billet at 950-1 070 ℃ for 5-120 min and at 780 ℃ for 3 h were performed as well for a better understanding on the microstructure evolution of the Zr-2.5Nb pressure tube during fabrication.Microstructures were mainly characterized by OM,SEM/ECC,and EBSD.Microstructures of Zr-2.5Nb alloy are various with fabrication processes,such as α+βWidmanstatten structure in ingot and forged billet,α'martensite and α laths in βquenched billet,α+β lamellar structure in hot-extruded tube.Those differences are cor-responding to different α/β phase transformation types,α/α'nucleation and growth mechanisms.It is demonstrated that the cooling rate plays an important role on the α/βphase transformation types as well as microstructure characteristics of Zr-2.5Nb alloy.The microstructure of β quenched billet is linked to the depth in the radius direction.Owing to the fast-cooling rate,the outer surface of β-quenched billets undergoes β→α'transformation and consists of α'lath.The internal location of β-quenched billets suffers a slower cooling rate and performs β→α'+α transformation,leading to a microstructure of α'+α lath.Compare to the quenched billet,ingot and forged billet suffer a much slo-wer cooling rate and have α+β Widmanstatten structure resulting from β→α+β phase transformation.The relatively slow cooling rate of hot-extruded tube makes β→α+βtransition happened,where transformed α grows on the basis of primary α.The width of transformed α lath increases with the decrease of the cooling rate,which leads α lath with about 1 μm width exists in the ingot while that in β-quenched is less than 300 nm.Based upon the interaction of dynamic recrystallization,α/β phase ratio,strain,and cooling rates,forged billet exhibits different microstructures in the radius direction.In addition to the β→α+β and β→α/α'transformations during cooling,α/α'→α+β andα+β→β appeare in the heating process.Metastable and supersaturated α/α'laths in βquenched billet would be decomposed into α+β lamellae under heating treatment at 780 ℃ for 3 h.And those α+β lamellae will transform equiaxial β phase when the tem-perature increases to above α+β/β transition line.关键词
Zr-2.5Nb/压力管/组织结构/相变Key words
Zr-2.5Nb/pressure tube/microstructure/phase transformation分类
能源科技引用本文复制引用
周宣,李科元,李新意,李宇力,周军,惠泊宁,赵冠楠,郁光廷..Zr-2.5Nb压力管制造过程中的组织结构演变(Ⅰ)[J].原子能科学技术,2023,57(12):2409-2416,8.基金项目
中核集团"青年英才"项目 （）
陕西省秦创原"科学家+工程师"队伍建设项目(2022KXJ-145) （2022KXJ-145）
