316-paper-钢管在线加速冷却技术开发-english version

DevelopmentofOnlineAccelerated-CoolingProcessforSeamlessTubeGuanghongYinAbstract：Theeffectofchemicalcomposition,andaswellasofproductionprocessparameters,onthemicrostructureandmechanicalpropertiesisinvestigatedunderacceleratedcoolingconditions.TheresultsshowthatacceleratedcoolingaftermandrelmillingusingthespraycoolingmethodcanproduceidealN80oilcasing,andthequenching-temperingtreatmentisnolongernecessary.1BackgroundThepurposeofthermaldeformationappliedtosteelsisnotonlytoobtaintheexpectedgrainsize,butalsotoimprovethemechanicalpropertiesofsteels.Thermalmechanicaltreatments(TMT)arejustsuchaprocessbyusingboththethermalandthedeformationeffectproducedduringmanufacturing.Amongthem,thermalmechanicalcontrolledprocess（TMCP）fallsintothiscategory.TMCPisacomplextechniquethatincludescontrolledrolling（CR）andacceleratedcooling（ACC）[1].Nowadays,TMCPhasbeensuccessfullyappliedtotheproductionofstructuralsteels,forexample,steelplates,strips,etc.,however,astoseamlesssteeltube,TMCPhasalwaysbeenfarawayfromindustrialproductionowingtoitscomplexityandparticularityofshape,ofthermomechanicalprocessandofmanufacturingequipment[2].Eversince1980,researchershaveendeavoredtotheinvestigationontheTMCPofseamlesssteeltube.Itisclearnowthaton-linenormalization（OLN）andon-lineacceleratedcooling（OALC）arethetwomainmethodstorealizeTMCP.On-linenormalization（OLN）isdescribedasfollows,firstly,the2tubeiscooledtobelowthetransformationtemperatureAc1,throughthephasetransformationofaustenitetoferriteaftermandrelmillingandbeforereheating,thenphasetransformsagainafteraustenitizationatthereheatingfurnace,thustheaustenitegrainsizeisrefinedthroughthepathsofphasetransformation.[2,4-6]。On-lineacceleratedcooling（OALC）[2,3,5-7]isaprocessthatthedeformedausteniteobtainedatthenon-recrystallizationtemperature（Tnr）goesthroughthetransformationtemperatureregionof750～500℃withaheatingrateof10～50℃/s,resultingintherefinedmicrostructureandimprovedstrengthandductility.BecauseTMCPcouldrealizetheon-lineheattreatment,includingOLNandOALC,replacefortheexpensivequenching-temperingtreatment[8],andboostproductionefficiencywhilelowerproductexpense,hereafter,theapplicationprospectispromising.TheresearchaimstothefeasibilityofrealizingOLNandOALContheproductlineofBaosteelΦ140rollingmillunit,togetherwiththedevelopmentofN80casingsteelsuitableforTMCP.2SteeldevelopmentsThesteelcompositionshouldbedesignedandthesteelspeciesshouldbedevelopedbeforethestudyofthefeasibilityofTMCPinBaosteel.Thekeypointofsteeldevelopmentisthatthemicrostructureofthesteelshouldkeepdynamicrecrystallizaitonwhenrollingat1000℃,guaranteeingagainstthephenomenonofmixinggainsize.SuchelementsasC、V、Ti、NassuresmuchprecipitationofthecarbideornitrideofVandTitopinthegrainboundaryandtorefinethegrainsizeathightemperatures,andthusTMCPcouldbeconvenientlyrealizedontheproductionlineattheabsentofOLN.Anotherkeypointisthatthedeformedgrainsrecrystallizeneither3staticallynordynamicallywithin10safterthefinalrollingatabout850℃,andthen,finebainitemicrostructurecouldbeobtainedafterrapidcoolingtothetemperatureregionof400～600℃,asaresult,therequirementforstrengthofN80gradecasingcouldbereached.2.1CompositiondesignAsforN80casingaccordingtotheAPIstandard,s≥552MPa,b≥689MPa.Tosatisfysuchmechanicalpropertiesfromthepointofcomposition,thecarboncontentshouldnotbetoolow,otherwisethestrengthshouldbetoolow.Itisconsideredthatthecarboncontentfallsinto0.2-0.4％,Mn1.0-2.0％,andthemicroalloyingelementsV,Ti,Nb,Mo,acertainamountasseeninTable1.Tabel1CompositionofthetestedsteelCSiMnVTiNbMoNAl0.220.40.10.51.02.00.050.25≤0.05≤0.05≤0.40.0150.030.0050.052.2DynamicrecrystallizationAccordingtothehot-rollingparametersof139.70mm7.72mmtube,theequivalentstrainscalculatedareshowninTable2.Thetubetemperatureismeasuredbyusinganinfraredtemperaturerecorder,andtheresultsarelistedinTable3.Table2equivalentstrainscalculatedfordifferentprocessesofhot-rollingBeforedeformation,mmAfterdeformation,mmLongitudinal1Radial2Circumferential3EquivalentHODD0，thicknessS0OD,Dz，thicknessSzPiercing*///////3.64Reducingofhollowbillet184.0018.75179.0018.750.0310-0.0310.035Mandrelmilling179.0018.75151.507.750.99-0.88-0.111.08StretchReducing151.507.75141.607.720.075-0.004-0.0710.084*Accordingtoliteratures.4Table3Tubetemperaturesfordifferentprocessesofhotrolling℃RotaryhearthfurnaceBeforepiercingBeforeReducingofhollowbilletBeforeMandrelmillingReheatingfurnaceBeforestretchreducing1260123011621044970903Figure1showsthedynamicrecrystallizationunderastrainrateof4.3s-1（T-H）.Itcanbeseenthatcompletedynamicrecrystallizationoccursafterpiercing（1230℃，H=3.64）,andduringmandrelmillingonlyoccursincompletedynamicrecrystallization（1040℃，H=1.08）;dynamicrecrystallizationdoesnottakeplacebothafterreducingofhollowbillet(1160℃，H=0.035)andafterstretchreducing（900℃,H=0.084）,thusthework-hardenedmicrostructureiskept.Fig.1dynamicrecrystallizationofhot-deformedaustenite(T-H)2.3MicrostructureandpropertiesTable4and5showthehot-rollingparametersandthecorrespondingmechanicalproperties,respectively.ThemicrostructureisshowninFig.2Table4Hot-rollin