High-temperature long-term microstructural instability is an urgent problem to be solved for high-silicon Fe-Cr-Ni austenitic stainless steel.In this study,we propose a novel strategy to improve the microstructural th...High-temperature long-term microstructural instability is an urgent problem to be solved for high-silicon Fe-Cr-Ni austenitic stainless steel.In this study,we propose a novel strategy to improve the microstructural thermal stability of Si-modified Fe-Cr-Ni austenitic steels via N doping.The microstructural evolution behaviors of N-free and N-doping steels were systematically investigated during aging at 783-923 K.The findings indicate that N doping results in substantial grain refinement and improves the strength of the steel.Importantly,it is found that N doping inhibits the premature segregation of Ni,Cr,Si,and Mo at grain boundaries by reducing their diffusion coefficients,thereby suppressing the generation of intergranular M_(6) C carbides during aging at 783 K,achieving superior thermal stability.In contrast,N-free steel exhibits microstructural instability due to theγ→M_(6) C+ferrite transformation during aging at 783 K.At 823 and 873 K,it is concluded that the diffusion of alloying elements accelerates,resulting in the formation of M_(6) C and ferrite in N-doping steel and subsequent microstructural instability.It contributes to a decrease in impact toughness,as microcracks tend to form at the ferrite domain and M_(6) C/ferrite interface with high strain concentration.Notably,when aged at 923 K,N-doping steel exhibits a cellular structure composed of M_(23) C_(6) and M_(6) C carbonitrides,with Nb(C,N)serving as the nucleation site within the grains.This differs from the intragranularχ-phase observed in N-free steel,as the nucleation driving force of theχ-phase decreases with an increasing N content.The study offers valuable insights for the development of fastener materials intended for utilization in lead-cooled fast reactors.展开更多
基金funded by the LingChuang Research Project of China National Nuclear Corporation and the Natural Science Foun-dation of Liaoning Province(No.2023-MS-019).
文摘High-temperature long-term microstructural instability is an urgent problem to be solved for high-silicon Fe-Cr-Ni austenitic stainless steel.In this study,we propose a novel strategy to improve the microstructural thermal stability of Si-modified Fe-Cr-Ni austenitic steels via N doping.The microstructural evolution behaviors of N-free and N-doping steels were systematically investigated during aging at 783-923 K.The findings indicate that N doping results in substantial grain refinement and improves the strength of the steel.Importantly,it is found that N doping inhibits the premature segregation of Ni,Cr,Si,and Mo at grain boundaries by reducing their diffusion coefficients,thereby suppressing the generation of intergranular M_(6) C carbides during aging at 783 K,achieving superior thermal stability.In contrast,N-free steel exhibits microstructural instability due to theγ→M_(6) C+ferrite transformation during aging at 783 K.At 823 and 873 K,it is concluded that the diffusion of alloying elements accelerates,resulting in the formation of M_(6) C and ferrite in N-doping steel and subsequent microstructural instability.It contributes to a decrease in impact toughness,as microcracks tend to form at the ferrite domain and M_(6) C/ferrite interface with high strain concentration.Notably,when aged at 923 K,N-doping steel exhibits a cellular structure composed of M_(23) C_(6) and M_(6) C carbonitrides,with Nb(C,N)serving as the nucleation site within the grains.This differs from the intragranularχ-phase observed in N-free steel,as the nucleation driving force of theχ-phase decreases with an increasing N content.The study offers valuable insights for the development of fastener materials intended for utilization in lead-cooled fast reactors.
