Inteiraction Mechanism Between Nano Cu-Rich Precipitate And Dislocations In RPV Model Steels

The reactor pressure vessel?RPV?is a large and irreplaceable key component in the nuclear power plant.In service,long-term neutron irradiation will lead to the precipitation of nano Cu-rich precipitates in RPV steel,which will increase the ductile-brittle transition temperature?DBTT?of steel and decrease the fracture toughness,increase the degree of material embrittlement,and affect the safety of RPV operation seriously.By studying the deformation characteristics of nano Cu-rich precipitates,the characteristics of mechanical properties of RPV steel and interaction mechanism between nano Cu-rich precipitates and dislocation can be obtained indirectly,so as to infer its deformation mechanism.Three kinds of RPV model steels were used in this study which increased the content of Cu on the basis of A508-?steel and changed the content of Ni and Mn of alloy elements.After quenching and tempering treatment,the three RPV model steels were aged at 500?for different time and the cold rolling deformation with deformation degree of5%and 10%was carried out.The crystal structure and evolution process of nano Cu-rich precipitates in the aging process were studied by HRTEM and EDS,the deformation characteristics of nano Cu-rich precipitates after deformation and its interaction mechanism with dislocation were studied by HRTEM and EDS.The Vickers hardness tester and nano-indenter were used to study the change of hardness and the influence of deformation on the hardness of the Cu-rich precipitate in the precipitation process.The change of thermal conductivity of nano Cu-rich precipitate in the precipitation process and the effect of cold rolling deformation on thermal conductivity were studied by laser thermal conductivity meter.The following results were obtained:?1?The evolution of nano Cu-rich precipitates in RPV model steel during aging at500?was observed by HRTEM.The nano Cu-rich precipitates transforms from?b.c.c?structure to 9R structure,and finally to a face-centered cubic?f.c.c?structure or face-centered orthorhombic?f.c.t?structure.The results show that there are orthogonal and monoclinic variants of 9R structure.A nano Cu-rich precipitate of the b.c.c structure having a size of 14nm was first discovered.?2?The dislocation introduced by cold rolling interacts with nano-Cu-rich precipitates and causes different deformation characteristics of nano Cu-rich precipitates.The deformation characteristics of nano Cu-rich precipitates are related to its crystal structure and matrix orientation.The deformation characteristics include dislocation of atomic plane,stacking fault and twin deformation of crystal structure.There are many different deformation characteristics in the same nano Cu-rich precipitates.?3?With the increase of deformation,the morphology and structure of nano Cu-rich precipitates change more obviously.The structure of nano Cu-rich precipitate with twinning deformation is mainly f.c.c and the twin plane is{111}_Cu plane,which is parallel to{110}?_-Fe plane.For the nano Cu-rich precipitates with twin deformation,the number of twins increases with the increase of deformation.?4?The addition of alloying elements Ni and Mn promotes the formation of nano Cu-rich precipitates.Under the same conditions,the size change of nano Cu-rich precipitates precipitated by the RPV model steels with Ni,Mn added is not obvious,and the pinning effect on dislocation during cold rolling deformation is more strong.?5?The precipitation of nano Cu-rich precipitates results in the change of sample properties.With the extension of aging time,the hardness of the sample first increases and then decreases,and the hardness reaches the peak value at 200h of aging.Cold rolling deformation increase the hardness of the samples,as the hardness increases with the increase of the deformation.The change trend of hardness under the same deformation is the same as that before deformation.With the extension of aging time,the thermal conductivity of the sample first decreases and then increases,and reaches the minimum value at 200h of aging.The thermal conductivity of the samples decreased with the cold rolling deformation,and the variation trend of the thermal conductivity was the same as before the deformation.