| As the “energy” and “environmental protection” problem is sharping,development of the higher parameters of ultra supercritical thermal power units is imminent.However,high temperature creep resistance and high temperature oxidation resistance of heat-resistant steel are required because of the improvement of the parameters.Now 9~12% Cr ferritic heat-resistant steel is the development trend of heat-resistant steel materials.In this paper,the Thermo-Calc software is used to calculate phase diagram and design the 9Cr-3Co-2W-1Mo ferritic alloy.This experiment was carried out to research the oxidation behaviour and creep property of the 9Cr-3Co-2W-1Mo ferritic alloy.Results as following:(1)Test steel is dual phase steel composed of tempering martensite and ?-ferrite.In the process of creep,the microstructures have no coarsening and the lath character of martensite gradually disappear.According to the stress-LM curve,the creep rupture life of test steel under the condtion of 650?/100 MPa is more than 100000 hours.(2)The creep fracture mode of test steel under the conditions of 650??700??750?.Laves phase precipitates in the process of creep.With the extension of creep time the size of Laves phase growth,and there is a linear relationship between size and creep time.In addition,Volume fraction is growing fast and then slowiy,eventually reach an equilibrium value.MX phase precipitates in the process of heat treatment.MX phase has small size and distributes in the matrix.(3)The oxidation resistance of test steel is worse than that of P92 steel in the air at 650? when oxidation for longer time.In the early oxidation stage,the oxidation film is FeO3;In the later oxidation stage,the oxidation film is divided into Fe2O3 outer layer and(Cr,Fe)2O3 lining layer because of the outward diffusion.(4)The oxidation resistance is not much different between test steel and P92 steel in wet air(20%H2O + air)at 650?.Oxidation film is divided into Fe2O3 outer layer and(Cr,Fe)2O3 lining layer. |
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