Study On Oxidation Behavior And Creep Property Of9Cr-9Co-5W-2.2Al Creep Resistance Steels

The large use of the9-12%Cr ferritic heat-resistant steels is in the power generationindustry because of their low cost, high thermal conductivity and low thermal expansioncoefficient. The power plant design has sought lower CO2emissions and high efficiency byelevating steam condition to even higher ranges of pressure and temperature. The combine ofhigh creep strength and oxidation resistance is needed in the applying of the new materials.However, it is no way for the9-12%Cr ferritic heat-resistant steels to have the goodperformance of the combine of creep strengh and oxidation resistance. So, it is essential todevelop the new ferritic steels to meet the requirement for higher temperature applications ofthe9-12%Cr ferritic heat-resistant steels. This experiment was carried out to research theoxidation behaviour and creep property of the9Cr-9Co-5W-2.2Al ferritic alloy.The creep testing results showed that the creep strength of the test steel is good at650℃、630℃、610℃, the creep strength has not reduced at the long creep time. The phenomenonof the mircostructure degradation is present at the test temperture.The number of theprecipitates increased in the ferrite grains and the features of the lath martensite is not obviouswith the creep process. The Laves phases precipitated inhomogeneously in the ferrite andmartensite grains, the ripe rate of the Laves phases was very quickly and the phases were thebig particles usually,so the Laves phases do not has the ieadl effect of the strength. The M23C6carbide preciitated in the martensite grains mainly,the sizes of the particles were small and theripe rate of the carbides were slow,so The M23C6carbides could have the good effect of thestrength.The oxidated testing results showed that the Al2O3scale formed on the surface of the teststeel in the air and wet air(10%H2O+air) at650℃after the3000h. The Al2O3scale was socompact that its growth was slow, the weight of the oxidated test steel did not increaseobviously. The scaling rates of the Al2O3scale in the air and wet air and the thickness of thescale were almost same, so the H2O had not the influnce on the growth of the Al2O3scale.