简介：Themicrostructureandpropertiesofacombinedprecipitationhardeningultrahighstrengthsteelwithnano-sizedcarbidesandintermetallicswerestudiedsystematically.Theresultsshowthataftertemperingat300℃lotsofε-carbidesareprecipitatedinthemartensite,thestrengthrisesandthetoughnessfallsslightly.Aftertemperingat430℃,muchcoarsercementitelaminaareprecipitatedinmartensiticlaths,whichcausestheimpacttoughnessfallstotheminimumvalue.WithtemperaturefurtherincreasingthecementitesaredissolvedandM2Ccarbides,β-NiAlintermetallicsandreverseaustenitebegintoprecipitate.Thetensilestrengthandyieldstrengthachievethepeakvalueat470℃,490℃respectively.Thetestedsteelachieveatensilestrengthof2120MPa,ayieldstrengthof1950MPaandimpactenergyof54J/cm2afteroptimumtemperingat510℃.Whentemperingtemperatureisabove530℃theM2Ccarbidesandreverseausteniteiscoarsening.Aftertemperingat560℃thereverseaustenitereachesthemaximumvolumefractioninpresentwork.