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Frictional properties of new developed cold work tool steel for high tensile strength steelforming die.pdf

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Frictional properties of new developed cold work tool steel for high tensile strength steelforming die.pdf

Wear27120112884–2889ContentslistsavailableatScienceDirectWearjournalhomepagewww.elsevier.com/locate/wearFrictionalpropertiesofnewdevelopedcoldstrengthKunichikaaShimanebaArticleReceivedReceivedAcceptedAvailableonline25June2011KeywordsToolDieGallingAdhesiveStampingSelflubricationsteelexperimentalexcellentSKD111.TheapplicationofhightensilestrengthsteelhereafterabbreviatedasHTSSisbeingabruptlyincreasedtoproducethemorerigidautomobileswithoutincreasingbodyweightsintheworldwideautomobileindustry.Thistrendcomesfromthatautomobilemanufacturerstionthroughdueasfacturerswearofmachinabilityment.astypeandmethodingresistanceandmachinabilityaswellasshowingexcellentperformanceinwidevariousapplicationssuchasforming,pressingandothercoldworkingapplications.Recently,SMAGIChasbeenacceptedinvariousapplicationfieldsofcoldformingprocessesassocalledanecomaterialandespecially,hasanexcellentreputa00431648/doiarerequiredforhigherglobalenvironmentprotecandimprovementofcollisionsafetywhiletheysuppresscostsimprovingfuelconsumptionofautomobiles.However,HTSSismuchmoredifficultmaterialtobeformedtohigherstrengthcomparedtocurrentusedmaterialssuchplainstructuralsteels.TheaboverequiresautomobilemanutogetnewdiematerialstoensuredurabilityintermsofresistanceandseizureresistanceforpressformingoperationHTSS.Moreover,requirementformoldsteelmaterialsistoimproveandeasyheattreatmentandgoodsurfacetreatAccordingtothisrequirement,thecurrentmaterialssuchconventionalD2equivalenttoJISSKD11anditsimprovedmaterialsareimpossibletoattaingoodwearresistancemachinabilitysimultaneously,however,thenewalloydesigncouldaccomplishthebreakthroughbasedon11alloyelementsaddition.SLDMAGICTMhereafterabbreviatedas∗Correspondingauthor.Tel.810854221919fax810854226374.EmailaddressKunichikaKubotahitachimetals.co.jpK.Kubota.tioninlargesizemoldsforautomobilebodyindustries.Themethodofdevelopingalloydesignisreportedelsewhere13.Inthisreport,rolesofalloyingelementsofnewlydevelopedSMAGICareinvestigatedbasedontheselflubricationwithoutcoatingFig.1.2.MaterialsandmethodsAppliedmaterialsforexperimentsarecoldworktoolsteelsbasedondevelopedsteelSMAGIC.Table1showsthechemicalcompositionofeachcoldworktoolsteels.Fig.2showsthecalculatedphasediagramofSKD11andSMAGIC.PhasediagramofotherconventionalsteelsisalmostsametoSKD11.BecauseevenconventionalsteelishighCandhighCrone,thephasediagramismorecomplexthanthesimpleFe–CsteelbecauseofexistenceoftwotypesofcarbideswhichareM7C3andM23C6.Machinabilityhasbeenestimatedbytwowaysfacemillandendmilltests.MachinabilitywithbothmillingwereestimatedbyverticaltypemachinecenterMatsuuraBT40showninFig.2withcuttingspeedof120and100m/min.ASTME618iswellknownasstandardevaluationofmachinability,however,thesetwotypes–seefrontmatter©2011ElsevierB.V.Allrightsreserved.10.1016/j.wear.2011.06.007steelformingdieKubotaa,∗,TakuyaOhbab,ShigekazuMoritoMetallurgicalResearchLaboratory,HitachiMetals,Ltd.21072Yasugicho,Yasugishi,DepartmentofMaterialsScience,ShimaneUniversity,1060Nishikawatsu,Matsue,Shimanerticleinfohistory18November2010inrevisedform29April20116June2011steelsteelweardieabstractCurrentlydevelopedtoolrespondingtoAISID2typeantigallingproperty.Thetioncoefficientandshowsandcomparedwithtypicaldevelopedsteel.TheantigallingIntroductionworktoolsteelforhightensileb6928601,Japan6908504,JapanSLDMAGICTMwasexaminedandcomparedwithotherSKD11cortoolsteelsfromtheviewpointofmachinability,frictionpropertyandresultsindicatedtheSLDMAGICshowsverylowkineticfricmachinability.Theantigallingpropertyofthealloywasstudiedandmodelalloyseliminatingcharacteristicelementsfromthenewlypropertyofthealloywasdiscussedwitharoleofelementsincluded.©2011ElsevierB.V.Allrightsreserved.SMAGICTM,thenameofthenewalloy,canattainbetterwearK.Kubotaetal./Wear27120112884–28892885diagramFig.test.TableChemicalofmoldscuttingtioniswhilemillingconditionTemperaturetingusedFig.test.Fig.1.Calculatedphase2.Detailconditionsoffacemillingtestandschematicdrawingofmachining1compositionoftypicalcoldworktoolsteelsinJapan.SMAGICFe–1.0C–8.3Cr–Ni–Mo–W–Al–Cu–SSKD11Fe–1.5C–12.0Cr–Mo–V8CrSteelFe–1.0C–8.3Cr–Mo–V10CrSteelFe–1.2C–10Cr–Mo–V–SconditionsareselectedbecausemachiningmethodsofdiesandaremainlyintermittentcuttingascomparedtocontinuousofASTME618.DetailsoffacemillingconditionforevaluaofwornwidthoftipweresummarizedinFig.2.Thisconditionsetuponseversidebecausecuttingvolumemustbesuppressedsamedamagemodeiskept.Fig.3showsthedetailsofendconditionformeasurementofcuttingtemperature.Thisissetupasforeasysideoftemperaturemeasurement.oftheendmillwasmeasuredatoppositesideofcutedgebyradiationthermometer.Thefrictiontests,whichwereforevaluatingtheantigallingproperty,wereperformedwith3.Detailconditionsofendmillingtestandschematicdrawingofmachiningofcolddiesteels.Fig.4.Heattreatmentdiagramofdiesteelsforgallingtest.CrankPressKomatsu80tonaftertheheattreatmentshowninFig.4.Fig.5showsthedetailconditionofsocalledhatshapedbendingmethod14asthegallingtest.Strokespeedis40spm,wrinkledepressionforceis2.2ton,strokelengthis60mmwithoutlubricant.Inaddition,worksareadoptedas590and980gradeHTSSofthickness1.6mmwhosesurfacestateareRa0.04H9262mpolishedby1000thgridsandpaperandwithoutZnplating.SurfacetextureismeasuredbysurfaceroughnessmeasurementequipmentTokyoseimitsu,Surfcom.Determinationofgallinglengthaftergallingtestissumoflengthwhichsequentialamplitudeover2.5H9262mexists.Measurement,whichisexecuted1pathbyawork,isnearendpointonwhichgallingistendtooccurstrongly,asmentionedbelow.Thegallingrateisdefinedastheratioofgallinglengthtolengthmeasured.Schematicdrawingofballondisktypetest,whichwasalsoperformedwithfrictiontestingmachineOrienticCorporation,EFMIII1020,showninFig.6.DetailsconditionsofthisexperiFig.5.SchematicdrawingofhatbendingtestwhichevaluatesantigallingpropertiesofdiesteelbyHTSSforming.2886K.Kubotaetal./Wear27120112884–2889Fig.6.Schematicdrawingofballondiskfrictiontestanddetailsofconditions.BothofsurfaceroughnessareaboutR0.2H9262m..menttouseareatedetchedis3.3.1.abilityshowsing.Moreover,samechipsthetributebythisonlythatMAGIC,20sideredFig.8.Resultoftooltemperaturemeasurementinthecaseofendmillingtestofannealedstate.temperature.Judgingfromthecolorofchips,temperatureofSMAGICisabout300◦Cwhileothersarenear500◦C.Sato12alsoverifiedforhardenedstatemachiningthatwornwidthoftipforSMAGICismuchlessthanthatforSKD11andedgetemperatureofSMAGICwasabout50◦ClowerthanthatofSKD11bysimilarmeasurementmethod.aThesearebasedonJISstandardR1613whichisequivalentASTMG99,however,selectionofmaterialisexecutedbyactualreference.areshowninFig.6.ObservationofmicrostructureperformedbyScanningElectronMicrocopyhereafterabbreviasSEM,HitachiS3500afterthespecimensarepolishedandbyNital.Analysisofaveragechemicalcompositionofsteelsexecutedbywetchemicalmethod.ResultsanddiscussionsMachinabilityatannealedconditionFirst,facemillingtestisexecutedinordertoevaluatemachinofeachcoldworktoolsteelsattheannealedcondition.Fig.7theresultofwornwidthoffacemillingcutterafterthetestWornwidthofSMAGICistheleastdatuminallofthesesteels.wornwidthof10Crsteel,whichcontainssulfurastheofSMAGIC,isthesecondleast.However,thecolorofcutofSMAGICisonlygoldwhileallofothersareblue3,4.Atviewpointofabrasivewear,amountofcarbidesmainlyconwearpromotion.WorstresultofSKD11maybeexplainedthispointbecauselargeamountsofCandCrarecontainedinalloy.However,excellenceofSMAGICcannotbeexplainedbyabrasivemodebecausewornwidthofSMAGICislessthanof8Crsteelinspiteofsameamountofcarbides.Fig.8showsedgetemperatureduringendmillingtest.AsforSedgetemperatureduringendmillingisexceptionallyabout◦Clowerthantheseofothersteels.Fromtheseresults,itisconthatdifferenceofchipcolorindicatesdifferenceofcuttingFig.7.Resultofworntipwidthafterfacemillingtestatannealedstate.3.2.FrictionalpropertyunderHTSSformingofactualuseHatshapedbendingtestusing80toncrankpressmachineisexecutedtoevaluateantigallingproperty.Fig.9showstheresultofthetest.Gallingisaphenomenonthatgivesdamagetothesurfaceofworksheetbyhardwelddepositonthecornerofdiewhileworksliding.Thetensiongeneratedontheworksheetiscontrolledbyholdingforceinordertosuppresswrinkle.GallingdoesnotoccurinSMAGICwhileotherdiematerialsoccurundertheconditionafter3timesforming.TwokindsofHTSSgrade,590and980MPa,areutilizedasworkforthistest.Fig.10showsanexampleofsurfaceroughnessmeasurementonthedashlineinFig.9.Here,thedefinitionofgallinglengthisthesumoflengthinwhichamplitudeisover2.5H9262m.Fig.11showsthatgallingratedefinedinexperimentalprocedureincreaseswiththeincreaseofwrinklesuppressionforce.Criticalgallingforceisdefinedasthewinklesuppressionforceofgallingrateaccomplishedover1.Fig.12showscriticalgallingforcefordiematerialsandHTSSgrade.InbothcasesofHTSSgrade,SMAGICissuperiortoSKD11.ThisresultsuggeststhatfrictionforcedecreasesinthecaseofSMAGIC.InthecaseofsameFig.9.Opticalphotographofsheetsurfaceafterbendingtest60spm,1.5tonwrinklesuppressionforce,580MPagradeHTSS.K.Kubotaetal./Wear27120112884–28892887Fig.10.ResultofsurfaceroughnessmeasurementofworkonthedashlineinFig.9aftergallingtestanddeterminationofgallingareainthecaseofSKD11inFig.9.Fig.minute.dieoflargerofcriticalhigheringcanmetalliciftheisFig.of11.Influenceofwrinklesuppressionforceongallingrateat60strokespermaterial,criticalforceofhighergradeHTSSishigherthanthatlowerone.Incaseofhighergradework,elasticregionbecomesandplasticdeformationbecomessmaller.Thustheformationnascentmetallicsurfaceonworksheetisavoidedandthenthegallingforcerises.However,intheactualfieldofstamping,gradeworkishardtobedeformedbecausetheactualformforceisdeterminantforcefortheantigallingproperty.Here,itbeconsideredinfluenceofonlybothformationrateofnascentsurfaceandactualformingforceongallingphenomenon,manyotherconditionsareregardedasconstant.Thereasonwhyactualformingforceisdominantfortheantigallingpropertythatworkshapemustbekeptthesameshapebypreventing12.ComparativeresultofdiematerialsandHTSSgradesoncriticalgallingvaluewinklesuppressingforce.thespringbackandthatis,theformationrateofnascentmetallicsurfaceiskeptconstantregardlesstoworkstrengthwhileactualformingforcerises.Fig.13showsthemicrostructureofSMAGICandSKD11observedbySEM.Carbidesareindicatedbyarrowsforbothfigures.FiguresshowthatcarbidesofSMAGICarefinerthanthatofSKD11.Distancesofcarbidesweremeasuredandaverageddistancesare3.8H9262mforSMAGICand5.8H9262mforSKD11,respectively.ConsideringlowercarboncontentcomparedwithSKD11,averagedistanceofcarbideinSMAGICisexpectedlongerthanthatinSKD11,butnot.Inourpreviouspaper1,shorteraveragedistancebetweencarbidesinSMAGICincreasesabrasivewearresistance.Sincetheantigallingpropertyistheadhesivemode,theshorterdistanceofcarbide,whichincreasesabrasivewearresistanceonharderside2,cannotexplaintheexcellentantigallingpropertyofSMAGIC.Fig.14indicatestheresultoffrictionalpropertiesbythefixedballondisktestwithoutlubricant.Diskspecimensweremadefromthediesusedinthehatbendingtest.InthecaseofSMAGIC,frictioncoefficientislowerthantheseofconventionalsteels.Theincrementalgradientoffrictioncoefficientmeansincreaseofadhesionareaincontactzone.Thefrictiontestresultsuggeststhatantigallingpropertyisimprovedbyselflubrication.Inthemanycasesofactualuse,thewearvolumewasreducedbyhalfinthebothwithandwithoutthesurfacetreatment,thedielifewasexpandedfromdoubleto100times.3,4Asmentionedabove,machinabilityofSMAGICisalsoevaluatedassuperiortootherconventionalsteels.Moreover,bothdistortionandthisdeviationcausedbyheattreatmentaremuchsmallerthanotherconventionalsteels.Inthecaseofmanufacturingdiesandmolds,thesepropertiesaredemandedasforprecisionofclearancebetweenshearedges,andcontributelifeofshearedgesinactualuse.3.3.InfluenceofchemicalcompositiononfrictioncoefficientInordertoclarifytheeffectofelementsonfrictioncoefficientofSMAGICwereinvestigatedwithuseofmodelalloysshowninTable2.Table2isobtainedbychemicalanalysisusing10kgingotwithhotworkingatthesametemperatureastheactualmanufacTable2Chemicalcompositionoftestedsteelmanufacturedby10kgingot.SMAGICFe–1.0C–8.3Cr–Ni–Mo–W–Al–Cu–SSKD11Fe–1.5C–12.0Cr–Mo–V8CrSteelFe–1.0C–8.3Cr–Mo–V–CuFe–1.0C–8.3Cr–Ni–Mo–W–Al–S–WMoFe–1.0C–8.3Cr–Ni–Al–Cu–S–SFe–1.0C–8.3Cr–Ni–Mo–W–Al–Cu–AlFe–1.0C–8.3Cr–Ni–Mo–W–Cu–S

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