From the viewpoint of energy-saving and environment protection,it is necessary to develop Ultra Super Critical(USC) fossil-fired power plants.In order to ensure the reliable operation of power plants under high steam conditions,good mechanical properties(particularly high creep strength),corrosion resistance and fabricability are generally required for the heat resistant steels used in USC boilers.Among these heat-resistant steels,S30432 austenitic heat-resistant steels are of interest due to high creep strength,excellent oxidation and corrosion resistance at temperatures up to 650 -700℃.In this paper,the strengthening mechanism of S30432 austenitic heat-resistant steel was investigated based on the precipitation behavior of S30432 during aging and creep at 650℃.Results show that the microstructure of as-supplied S30432 steel is austenite,the main precipitation consists of only Nb(C,N).After aged for 10 000 h or crept for 10 712 h,there is a slight increase in the size of fine Nb(C,N),but the transformation from Nb(C,N) to NbCrN does not occur.Aging and creep results in the precipitation ofε-Cu and M_(23)C_6.The coarsening velocity ofε-Cu particles diminishes greatly and they are still very fine in the long-term creep range.With the increase of aging and creep time M_(23)C_6 carbides tend to coarsen gradually.The size of M_(23)C_6 is larger and the coarsening is easier in contrast toε-Cu and Nb(C,N).Nb(C,N) precipitates in the as-supplied microstructure,while aging and creep result in the precipitation ofε-Cu and M_(23)C_6.High creep rupture strength of S30432 steel is attributed to the precipitation hardening ofε-Cu,Nb(C,N) and M_(23)C_6.Extremely,ε-Cu plays an important role in improving the creep rupture strength of S30432,and at least 61%of the creep rupture strength of S30432 at 650℃results from the precipitation hardening ofε-Cu particles. From the viewpoint of energy-saving and environment protection, it is necessary to develop Ultra Super Critical (USC) fossil-fired power plants. In order to ensure the reliable operation of power plants under high steam conditions, good mechanical properties (particularly high creep corrosion resistance and fabricability are generally required for the heat resistant steels used in USC boilers. Among these heat-resistant steels, S30432 austenitic heat-resistant steels are of interest due to high creep strength, excellent oxidation and corrosion resistance at temperatures up to 650-700 ° C. In this paper, the strengthening mechanism of S30432 austenitic heat-resistant steel was investigated based on the precipitation behavior of S30432 during aging and creep at 650 ° C. Results show that the microstructure of as-supplied S30432 steel is austenite , the main precipitate consists of only Nb (C, N). After aged for 10 000 h or crept for 10 712 h, there is a slight increase in the size of fine Nb (C , N the transformation from Nb (C, N) to NbCrN does not occur. Aging and creep results in the precipitation of ε-Cu and M_ (23) C_6. The coarsening velocity of ε-Cu particles diminishes greatly and they are still very fine in the long-term creep range. The increase of aging and creep time M_ (23) C_6 carbides tend to coarsen gradually. The size of M_ (23) C_6 is larger and the coarsening is easier in contrast to ε-Cu and Nb (C, N) .Nb (C, N) precipitates in the as-supplied microstructure, while aging and creep result in the precipitation of ε-Cu and M_ (23) C_6.High creep rupture strength of S30432 steel is attributed to the precipitation hardening of ε-Cu, Nb (C, N) and M_ (23) C_6.Extremely, ε-Cu plays an important role in improving the creep rupture strength of S30432, and at least 61% of the creep rupture strength of S30432 at 650 ° C results from the precipitation hardening of ε-Cu particles.