3.5NI钢物性

UnlessotherwisestatedthispagecontainsVersion1.0content(Readmoreaboutversions)2.3.7ThermalconductivitiesDefinitionandunitsThethermalconductivity,λ,ofasubstancemaybedefinedasthequantityofheattransmitted,Q,duetounittemperaturegradient,inunittimeundersteadyconditionsinadirectionnormaltoasurfaceofunitarea,whentheheattransferisdependentonlyonthetemperaturegradient.λ=−Q∂T∂nInthissectionthermalconductivityvaluesareassembledformetallic,semi-conductingandinsulatingelements,representativegroupsofalloys,refractoriesandmiscellaneousconstructionalandinsulatingmaterials,someliquidsandsomegases.ThevaluesareexpressedintheSIunitWm−1K−1throughout.Factorsforconvertingtootherunitsareasfollows:1Wm−1K−1=0.01Jcmcm−2s−1K−1=0.002388calcmcm−2s−1K−1=0.8598kcalmm−2h−1K−1=0.001926Btuinft−2s−1°F−1=6.933Btuinft−2h−1°F−1=0.5778Btuftft−2h−1°F−1=0.0001605Btuftft−2s−1°F−1MoreextensivecollectionsofthermalconductivitydatawillbefoundinTouloukianetal.(1970a,bandc).ThermalconductivitiesofmetallicelementsThethermalconductivityvaluesinthetablebelowareformetallicelementsinthepurestpolycrystallineconditionforwhichreliablemeasurementshavebeenreported.Entriesinitalicsrelatetotheliquidphase.Thethermalconductivitiesoflesspuresamplesoftheseelementswillbelowerthanthevaluesgivenbelow.Thermalconductivityinvariablydecreaseswithdecreasingpurity;suchdependencebeingweakatambientandhighertemperaturesbutverystrongatcryogenictemperatures.λ/(Wm−1K−1)MetalTemperature/K173.2273.2373.2573.2973.2Aluminium24123624023392Antimony3325.5221927Beryllium36721816812993Bismuth118.27.21317Cadmium10097958945Caesium37362020.617.7Cerium8111316—Chromium12096.5928266Cobalt130105896953Copper420403395381354Dysprosium910.5———Erbium1415———Gadolinium1210———Gallium†43413345—Gold324319313299272Hafnium2523222121Holmium141617——Indium92847642—Iridium156147145139—Iron9983.5725634Lanthanum121314.5——Lead3736343221Lithium9486824759Lutetium1817———Magnesium160157154150—Manganese78———Mercury29.57.89.411.7—Molybdenum145139135127113Nickel11394836771Niobium5353555864Osmium93888787—Palladium7272737993Platinum7372727378Plutonium468——Potassium105104534532Praseodymium9.91213.4——Rhenium5249474445Rhodium156151147137—Rubidium5958322922Ruthenium12311711510898Samarium10131314—Scandium1516———Silver432428422407377Sodium141142887860Tantalum58575858.560Technetium—515050—Terbium1110.5———Thallium514744——Thorium5554545658Thulium1617———Tin7668633240Titanium2622211921Tungsten188177163139119Uranium2427293343Vanadium3231313338Yttrium16.517———Zinc11711711210466Zirconium2623222123†Valuesforthea-axiswhichapproximatetothepolycrystal;thosefortheb-axisare91and88andforthec-axisare16.5and16at173.2and273.2K.Thermalconductivitiesofsinglecrystalsofsomenon-cubicmetalsatnormaltemperatureλ/(Wm−1K−1)MetalThermalconductivityindirectionofc-axisa-axisb-axisBismuth5.49.3Cadmium83.05104Dysprosium11.6510.25Erbium18.412.6Gadolinium10.710.3Gallium16.040.888.3Holmium22.113.6Lutetium23.313.8Mercury(at227.7K)33.025.9Terbium14.59.45Thulium24.214.1Tin51.874.0ThermalconductivitiesofalloysAtlowtemperaturesthethermalconductivityofagivenmetaltendstoincreaseinproportiontothereciprocalofitsresidualresistivityρ0.Manymetals,especiallygoodelectricalconductors,havethermalconductivitiesthatfollowthesimplerelationλ=L0σTatverylowtemperaturesandattemperatureshigherthantheirDebyetemperature;L0beingtheLorentzcoefficient2.45×10−8Ws−1K−2,σtheelectricalconductivityinSm−1andTtheabsolutetemperature.Thisbehaviourenablesthethermalconductivitiesofmetallicsamplestobeestimatedfairlyreliablyfromsimpleelectricalresistivitymeasurements.Asthethermalconductivitiesofalloysdependstronglyontheirmechanicalandthermalhistory(heattreatment)aswellasontheirchemicalcomposition,thevaluestabulatedbelowshouldberegardedastypicalforthecompositionslisted.Formanygroupsofalloysthethermalconductivityofaparticularsample,nearroomtemperatureandabove,canbeestimatedwithinabout6%fromitsmoreeasilymeasuredelectricalconductivityusingtherelationλ=LσT+C.TheoptimumvaluesforLandCfordifferentalloytypesareasfollows:MainconstituentmetalL/(10−8Ws−1K−2)C/(Wm−1K−1)Aluminium........................2.2210.5Copper.........................2.397.5Alpha-iron.......................2.439.2Gamma-iron......................2.394.2Magnesium......................2.219.6Nickel.........................2.138.4Nickel-chromium(nimonictype)............2.206.0Titanium........................2.302.9Zirconium.......................2.502.2Formoredetailedinformationontherelationshipbetweenthethermalandelectricalconductivitiesofalloyssee:Powell(1965),HustandClark(1971).ThermalconductivitiesofalloysatambientandelevatedtemperaturesAlloyComposition/weightpercentλ/(Wm−1K−1)atTemperature/KAlCCrCuFeMgMnNiSiWZnOther2733735737739731273AluminiumalloysAluminium100———————————236240233———Alpaxgamma87———0.30.30.3—12———188188184———Lo-Ex85——10.50.9—111.8———172175173———Y-alloy92——3.80.41.3—1.80.4———180188194———RR5993——2.31.21.5—1.20.9———168176186———RR5789——2.20.32.50.5—0.3—5—161171178———CopperalloysCopper———100————————403395381—354—Brass———70——————30—106128146