机械英语翻译 毕业设计之用Word文档下载推荐.docx
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机械英语翻译 毕业设计之用Word文档下载推荐.docx
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I.VONHAGENandM.KELLER
ThedevelopmentofAF22duplexsteeltubesusedunderseveremultiplecorrosionconditionsinoilandgaswellswasexamined.Theconditionsofhot-andcold-formingprocessesandtheirinfluenceonthemechanicalpropertiesoftubesaresummarizedonthebasisofbothlaboratoryexperimentsandpracticalexperiencesobtainedwithtubefabrication.Theeffectofprecipitationonthemechanicalpropertiesofhot-finishedtubesisshown,andstepsarediscussedtoavoidthisprecipitation.TheanisotropicbehaviorofmechanicalpropertiesandtheformationofresidualstressesofAF22tubes,aswellastheinfluenceofheattreatmentontheseproperties,arediscussedindetail.
INTRODUCTION
Forapproximatelyeightyears,MannesmannhasbeenproducingandtestingtubesmadefromAF22duplexsteelforuseinhighlycorrosivemedia.Besidesbeingusedinthechemicalindustry,theseproductsareofspecialimportanceintheexploitationofpetroleumandnaturalgas.。
Duetotheoilpriceexplosionatthebeginningoftheseventiesandinthemid-seventies,theexploitationoflowergradefieldswithmajororminorpercentagesofaggressivemediaalsobecameeconomical.Inaddition,thereinforcedexplorationactivitytendedtomoveinthedirectionofstillgreaterdepths.ThesefactshadconsiderableeffectonthetypesandpropertiesofOCTGmaterialsusedintheprocess.TableIgivesasurveyofOCTGmaterialsasprocessedtodayby
Mannesmann,intheusualgrades,asindicatedbytherelativeAPI(AmericanPetroleumInstitute)specifications.AscanbeseenfromTableI,theaustenitic-ferriteAF22gradeslendthemselvesexceptionallywelltoextraordinarycorrosionstresseswithinthefieldofsourgases.ItisclearlyvisiblethatAF22tubesaremadeintwogrades.The448MPa(65ksi)versionrepresentsthesolution-annealedcondition,whereasthe896MPa(130ksi)variantrepresentsthestrain-hardenedcondition
HOT-FORMINGPROPERTY
IntheearlydevelopmentalstageinthemanufactureoftubesmadefromAF22duplexsteel,thefirstpriority--apartfromfindingoutthemostsuitablealloyingvariant--wastoascertainthedeformationbehaviorinthehotandcoldconditions,inordertobeabletoselect,fromamongthemanufacturingprocessesavailable,thosemostappropriateforthepurposesunderconsideration.22duplexsteelasfavoredbyMannesmannhasthechemicalcompositionlistedinTableI.
Thehot-formingpropertyofthissteelhasbeendeterminedonthebasisoftwoprocedures:
(1)hottorsionand
(2)hottensiletests.Figure1showstheresultsofhottorsiontests.Thenumberofrevolutionsuntiltheoccurrenceoffracture,whichisameasureforplasticity,hasbeenplottedagainstthedeformationtemperature,inthisinstancethetesttemperature.Thediagramrevealsthat,beginningwithtemperatures>
1100℃(>
2012)theplasticityincreasesrapidlyFigure2showstheresultsofhottensiletestsperformedonthegleeblemachine.Inthisparticularinstance,thereductionofareaplottedagainstthetesttemperaturehasbeentakenasameasuringstandardforthehot-formingproperty.Accordingly,theoptimumtemperaturerangeforhotformingisthatbetween1100and1250(2012and2282)Thesignificantdecreaseofhotplasticityattemperaturesabove1250(2282)isduetotheaustenite-ferriteratiovaryingwithincreasingtemperaturestothedetrimentoftheaustenite.Above1250(2282F)therelativelysmallamountsofaustenitearetobefoundatthegrainboundariesoftheferrite,thusimpairingtheductilityoftheAF22material.
HOT-FORMINGPROCESS
Theabove-citedoptimumhot-formingrangebetween1100and1250(2012and2282F)whichisrelativelysmallincomparisonwithmanyothersteels,allowsonlysuchpipe-manufacturingprocesseswheretheformingoperationscanbeaccomplishedwithinashortperiodoftimeandwithoutmajorlossesoftemperature.Forthesereasons,thehot-extrusionandplug-rollingprocessesaresuggestedforbothofthesehot-formingprocesses,andtheselectionofoneortheotherprocessdependsontherequireddimensionsThehot-extrusionprocessisabletosupplysizesofuptoapproximately200mminoutsidediameterandwallthicknessesofuptonearly25mm.greaterdeliverylengths,theplugmillprocessisapplied.Overlappingbetweenbothprocessesforsizerequirementsispossible.ThemajorityofAF22tubesareproducedinaccordancewiththehot-extrusionprocess,inordertobesubsequentlysubjectedtofurthertreatment.However,inordertoachieveanoptimummicrostructure,thehot-finishedtubesmustbepreviouslysolutionannealed.
SOLUTIONANNEALING
Asalreadymentioned,theaustenite-ferriteratioundergoeschangesattemperaturesabove1000(1832)AsmayAsmaybeseenfromFigure5,theamountofaustenite,intheorderof60pctatatemperatureof1000(1832)decreasestoaslittleasapproximately20petat1300(2372)Thetwocurveswereobtainedfromtwodifferentmelts.Austeniticcontentsrangingbetweenabout40and60pethavebeenfoundtobemostfavorableforthecorrosionchemicalproperties.Consequently,thefigurerevealsamaximumsolution-annealingtemperatureof1100(2012)Theminimumsolution-annealingtemperaturerangeislimitedbytheoccurrenceofsigmaphase,resultingattemperaturesoflessthan980(1796)ThesigmaphasehasanegativeeffectonmechanicalpropertiesaswellasonthecoldworkabilityofduplexsteelssuchastheAF22alloy.Inordertoensureasufficientmarginofsecurityduringthemanufacturingprocess,withaviewtoavoidingsigma-phaseprecipitationsofthetubes,asolutionannealingtemperatureof1050(1922)withsubsequentwaterquenchingmustbeused.
InFigure6,theamountofsigmaphasehasbeenplottedagainstannealingtemperatureandannealingtime.Itisevidentthat,alreadyatholdingtimesof2minutes,occurrenceofsigmaphasecanbeobserved.Thismeansthatthecriticaltemperaturerangeduringthecoolingprocessmustbepassedthroughquickly.
ThenegativeeffectofthesigmaphaseonthetoughnessofAF22duplexsteelcanbeseenfromFigure7,wheretheimpactenergyhasbeenplottedagainstthesolutionannealingtemperature.Thesteepdecreaseoftheimpactvaluesatannealingtemperaturesbelow1000(1832)revealsthattheupperlimitofthesigma-phaserangeissomewherebetween980and1000(1796and1832Inoperativepractice,ithasbecomeobviousthatverynegligibleamountsofsigmaphasehaveadetrimentaleffectontoughnessproperties.Theusualholdingtimeforsolutionannealingis15to20minutes.Theserelativelylongtimesarenecessaryinordertoguaranteeauniformheatingofthetubes.Laboratorytimesof2minutesaresufficientinordertocompletelydissolvethesigmaphase.Thishasalsobeenconfirmedbyproductiontrials.
875FEMBRITTLEMENT
Duringthecoolingoperationofthetubesdowntoroomtemperatureafurthercriticaltemperaturerangehastobepassedthrough,whichisknownas875embrittlement.(Thisoccursat468)Figure8showsthetensilestrengthandtheimpactenergyofAF22tubesafterannealingbetween100and850(212and1562)atdifferentholdingtimesandaftersubsequentwaterquenching.Theincreaseoftensilestrengthandthedecreaseofimpactenergyareclearlyvisibleinthetemperaturerangearound468(875).Thisisduetosubmicroscopicsegregations,thetypeofwhichhasnotyetbeenexactlydefined.Fortheheattreatmentduringthemanufacturingprocess,theexistenceof875embrittlementmeansthatthetubeshavetobequicklycooleddownto-300(-572)
STRAINHARDENING
Inthesolution-annealedcondition,therequirementsoftheAPISpecificationarecompliedwithforAF22duplexsteelofgrade448MPa(65ksi).Asmentionedearlier,thehighertensilepropertiesareobtainedbycoldreduction.Figure9showsthework-hardeningbehaviorofAF22steel.ThecurveshavebeenobtainedbylaboratorydeformingtestsbycoldrollingAF22platesdowntovariousendthicknesses.Itcanberecognizedthat,afteracoldreductionofabout33pct,essentiallythemaximumdegreeofworkhardeningisachieved.Figure10shows,fortheyieldstrength,thecomparisonbetweenlaboratoryvaluesandvaluesobtainedfromcold-pilgeredtubes.Thescatterband,inthecaseof>
50pethigherdeformationdegrees,islargelyabovethelaboratorycurve,whichisconditionedbythevaryingtypesofcoldworking.Becauseoftheimpactlikedeformationinthepilgerprocess(assumingequaldeformationdegrees)obviouslyhigherstrain-hardeningvaluesareobtainedthanwiththeaidofcoldrolling.
Asidefromcold-pilgerrolling,strain-hardenedAF22tubesalsocanbeproducedbycolddrawing.Figure11containsthecold-workscatterbandsofcold-drawnpilgeredAF22tubes.Asthefigurereveals,thecold-workscatterbandsarenarroweddownbecauseofacoldworkperformedintwosteps,withintermediatesolutionannealing.Furthermore,itbecomesobviousthatthework-hardeningbehaviorduringthedrawingprocessexhibitsasteepercurvethantheonethatresultsfrompilgering.Theless-pronouncedincreaseofthestrain-hardeningcurveastheresultofcoldpilgeringintwostepsmeans,forthepracticeoftubemanufacturing,ahigherdegreeofproductionsafety.Supposingausualyieldstrengthrangeof,forexample,896to1034MPa(130to150ksi),itcanbededucedfromFigure11that,forpilgering,alargerrangeofmanufactureexists.Thisisimportantbecausethetubesusedforcoldpilgeringmayrevealcircumferentialwallthicknessvariations,whichwouldlocallyleadtodifferentdegreesofdeformationonanindividualtube.
Thetoughness
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