| The welding part of cladding and end plug play an important role in core subassemblies of SFR(Sodium-cooled Fast Reactor)in China.15Cr-15 Ni,called 15-15 Ti here after,as a kind of Ti-bearing single-phase austenitic stainless steel,possesses good high-temperature strength,high corrosion resistance to sodium,good irradiation stability.For these advantages,it has been selected for the material of cladding in SFR.However,15-15 Ti is vulnerable to the problems of hot cracking and intergranular corrosion,and at present,the end plug material matched with 15-15 Ti has not yet been localized in China.In this paper,based on the vulnerability of 15-15 Ti and existing literatures,16Cr-15 Ni modified stainless steel(16-15NbSi)was designed as the end plug material matching to 15-15 Ti.Six components of 16-15 NbSi end plug material were welded with 15-15 Ti by the method of TIG.The effects of Nb,C and Si on the microstructure and properties before and after aging were investigated systematically.In addition,hot cracking sensitivity and intergranular corrosion resistance were also examined in this paper,which may be of great significance in realizing the localization of end plugs.The main research work and results of the paper are as follows.(1)Six alloys with different composition aimed at using as end plug material are designed.The calculation results of Thermo-Calc show that with the increase of Nb content,NbC precipitates from liquid directly instead of precipitating from ? phase,and NbC can be more easily to precipitates as C concentration increases.Besides,the existence of Si can enlarge the temperature range for Laves phase precipitation.(2)Microstructures and properties of welding joints before and after aging analysis results show that the size and quantity of NbC increase with the increasing of Nb and C contents.The increasing content of Si rise the precipitate quantity.The quantity and size of NbC almost do not change after aging when concentration of Nb and C are low.However,when the concentrations of Nb and C increase to 0.9wt.% and 0.09 wt.%,the size of precipitate grow heavily.The tensile properties of welded joints before and after aging do not show too much difference,which can approach a high level of tensile and ductility properties when the contents of C are 0.03 wt.% and 0.09 wt.% while the content of Nb is 0.6wt.%.Compared with the original one,the hardness of welded joints after aging decrease slightly.In addition,only two out of these six alloys with Nb and C contents of 0.6wt.% and 0.03 wt.% can reach a higher hardness than that of base metal.(3)Hot cracking of end plug material are not found in the hot cracking sensitivity test among all six alloys.The intergranular corrosion test show that cracks only exist in one alloy with 0.6wt.% Nb and 0.09 wt.% C.While the intergranular corrosion are not found in the rest of the 5 groups.(4)According to the microstructures and properties of welded joints before and after aging,optimized alloy contents range of end plug are determined with the content range of C is 0.02 wt.%-0.04 wt.%,the content range of Nb is 0.5wt.%-0.7wt.% and the content of Si less to 0.4wt.%. |
PDF Full Text Request