Study On Creep Property And Oxidation Behaviour Of 9Cr-6Co-2W-1Mo Ferritic Creep-Resistant Steels

650?ultra-supercritical coal-fired power generation technology could effectively improve the efficiency of thermal power unit,and reduce power pollutants discharge.It's not only an important initiative for optimizing and readjusting industrial structure,but also the important content of national energy strategy.The 9-12%Cr ferritic heat resistant steels are being considered as a candidate material for the next generation of high-temperature structural components because of their low cost,high thermal conductivity and high performance-cost ratio.However,it is no way for the 9-12%Cr ferritic heat-resistant steels to have the good performance of the combine of creep strengh and oxidation resistance in the 650?grade power plant.So,it is essential to develop the new ferritic steels to meet the requirement for higher temperature applications of the 9-12%Cr ferritic heat-resistant steels.In this paper,the Thermo-Calc software is used to calculate phase diagram and design the 9Cr-3Co-2W-lMo ferritic alloy.This experiment was carried out to research the oxidation behaviour and creep property of the 9Cr-6Co-2W-1Mo ferritic alloy.Results as following:?1?After the process of heat treatment,the test steel is a single martensite structure,and the MX phase and M₂₃C₆ phase has small size and distributes in the matrix.According to the Larson-Mille,Monkman-Grant,Norton and the new power law equation,the long-term creep strengths of test steel under the condtion of 650?10⁵ h is more than 100 MPa.?2?In the process of creep,the microstructures of test steel have coarsening and the lath character of martensite gradually disappear.The precipitation of LAVES phase takes place during creep at prior austenite grain boundaries and matensite lath boundaries from supersaturated solid solution of 9Cr-6Co-2W-1Mo steel,then the subsequent large coarsening of LAVES phases and M₂₃C₆ phase results in the breakdown in creep rupture strength observed in the long-term creep.?3?Multi-stage oxidation kinetics is observed for the test steel at 650?in air after10627 h,the outer layer is composed of CoFe₂O₄,Fe₂O₃ and Fe₃O₄,the lining lay is Fe₂O₃ and Cr₂O₃.Multi-stage oxidation kinetics is observed for the test steel at 650?in the wet air?20%H₂O+air?after 3469 h,the outer layer is Fe₂O₃,the lining lay is?FeCr?₂O₃.The oxidation resistance of test steel is better than that of P92 steel in the wet air?20%H₂O+air?at 650?when oxidation for longer time.In the air and the wet air?20%H₂O+air?environment at temperatures between 600?to 700?the oxidation behavior of the 9Cr-6Co-2W-1Mo steel tended to exhibit an anomalous temperature dependence of the oxidation behavior.?4?The pre-oxidation steel and the no pre-oxidation steel air at 650?for 500 h have differenr oxidation resistance.The steel by pre-oxidation treatment in argon gas at650?for 0.5 h had lesser weight gain than no pre-oxidation.