Study On Creep Property And Oxidation Behavior Of 9Cr-3Co-2W-0.4Si-0.53Mn Martensite Creep-Resistant Steels

With the increasing shortage of energy and the improvement of environmental awareness,it is urgent to increase the thermal efficiency of ultra-supercritical thermal power generators as much as possible.To solve this problem,it is significant to research the heat-resistant steel materials which can be apply on higher temperatures.9%Cr heat-resistant can not balance the creep and oxidation resistance well,beacuse its weakness oxidation resistance at high temperatures.We designed a new type of 9%Cr martensite heat resistant steel,and its oxidation resistance performance and creep resistance performance were studied.The conclusions are as follows:?1?The microstructure of experimental steel is delta-ferrite and tempering martensite after normalizing and tempering heat treatment.The M₂₃C₆ and MX phases are precipitated in heat treatment process,with small size and dispersed in the matrix.According to the three methods the long-term creep strengths of test steels under the condtion of 650?10⁵ h is less than 100MPa.?2?The experimental steel at 650?/675?/725?/750?under the condition of creep fracture mode is ductile fracture.During the creep process,the martensite structure degradation and the lath characteristics gradually disappeared.With the Laves deposit from solid solution,M23C6 and MX gradually grow up that reduce the creep resistant.?3?A protective oxide layer was formed on the surface of the experimental steel after a certain period of oxidation,multi-stage oxidation kinetics is observed for the test steel at 650?in air after 8679h,the outer layer is composed of Fe₂O₃ and FeCr₂O₄,the lining layer is CrMn_1.5O₄ and Cr₂O₃.Multi-stage oxidation kinetics is observed for the test steel at 650?in the wet air?20%H₂O+air?after 1012h,the outer layer is composed of Fe₂O₃ and Fe₃O₄,the lining layer is CrMn_1.5O₄ and Cr₂O₃.?4?There are large differences in the oxide film structure of the experimental steel at different temperatures for the test steel in the wet air?20%H₂O+air?after 600h.The oxide film is composed of Fe₂O₃/Fe₃O₄ at 600?in the wet air?20%H₂O+air?after600h,the oxide film is composed of Fe₂O₃/FeCr₂O₄/Fe₃O₄ at 650?in the wet air?20%H₂O+air?after 600h,the oxide film is composed of CrMn_1.5O₄/Cr₂O₃ at 700?in the wet air?20%H2O+air?after 600h.The main reason for this difference is that temperature affects the diffusion rate of Cr³⁺in the matrix.