Thermal Processing Map and Deformation Behavior of Zr-2.5Nb Alloy in Nuclear Power AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY23090011

Chinese Library Classification Number:TG304

Citation Information:

Zr-2.5Nb pressure tube is the core structural components of the heavy water reactor nuclear reactor cores，which needs to be replaced every 20 years to ensure the safety，and it's time for Qinshan heavy water reactor power plant to change. Meanwhile，the manufacturing process of Zr-2.5Nb pressure pipe is complicated and the control parameters are numerous，e.g.，hot extrusion，cold draw etc.，it's difficult to control the final microstructure and the corresponding properties. As a components of nuclear reactor cores，Zr-2.5Nb pressure tube are subjected to harsh service environments and stringent performance requirements，e.g.，high strength，plastic toughness，good high temperature performance，and corrosion resistance to irradiation，etc. Thermal deformation involving hot forging and hot extrusion，is not only a necessary process for Zr-2.5Nb pressure tube to obtain the designed shape，but also an effective method to change the microstructure （phase composition，grain size/topography/orientation，substructure，etc.） of materials. Hot deformation plays a crucial role in the engineering applications and scientific research，due to the controlling microstructure and expected performance of the alloy by the process of work-hardening and dynamic softening with the core transformations of phase change，recrystallization and grain growth. Therefore，analyze the various types of phenomena that may occur during hot deformation and elucidating the corresponding microscopic mechanism of the phenomena can lay a theoretical foundation for the design of the process and the regulation of the organization in the actual production. The thermal processing diagrams take into account the effect of thermal deformation parameters，i.e.，deformation temperature T，strain rate $\dot{\epsilon }$ and strain ε，on the thermal deformation behavior of the material and provide a preferred processing range for engineering applications. Combine with the microstructure of the typical peak energy consumption region，the thermal deformation behavior of the alloy and its mechanism are analyzed，finally achieve the purpose of controlling the microstructure，avoiding defects and optimizing the process parameters. In this paper，the thermal deformation behavior of Zr-2.5Nb alloy was analyzed by using Gleeble 3500 to conduct thermal compression tests under different conditions （i.e.，750~960 ℃，0.01~10 s⁻¹） ，constructing the thermal processing map of the alloy，and characterizing the typical microstructure by electron scanning electron microscope （SEM） and electron backscatter diffraction （EBSD） . The results showed that the alloy mainly underwent α-phase basal slip at lower temperatures （T<810 ℃） ，which led to strong grain selective orientation due to grain rotation and a large number of defects resulting in deformation instability. In addition，the alloy existed in two preferred processing zones with high energy consumption values and stable deformation： the medium-temperature preferential processing zone （810 ℃<T<840 ℃，$\dot{\epsilon }$<0.1 s⁻¹，ε>0.5） ，where deformation and dynamic recrystallization occurred simultaneously of α-phase and β-phase in the alloy，the room-temperature organization consists of polygonal/long-stripe α-phase and martensite α'；high temperature preferred processing zone （850 ℃<T<900 ℃，ε>0.5）， the work hardening and dynamic softening balance in this zone，due to the simultaneous occurrence of deformation and dynamic recrystallization of β-phase，resulting in the complete formation of α' martensite in the room temperature. In summary，Zr-2.5Nb alloy was unstable in deformation at low temperature （T<810 ℃），and at high temperature （T>850 ℃） the organization was β-phase with large grain size resulting in α' martensite after quenching，in order to achieve the purpose of regulating the microstructure of the alloy，the temperature and the strain rate could be controlled in the medium-temperature preferred machining zone （810 ℃<T<840 ℃，$\dot{\epsilon }$<0.1 s⁻¹，ε>0.5） .