FoundationItemItemSponsoredbyNationalNaturalScienceFoundationofChina(５１０７１０７８)ResearchFundofKeyLaboratoryforAdvancedTechnologyinEnvironmentalProtectionofJiangsuProvinceofChina(AE２０１０３５)NaturalScienceFoundationofJiangsuProvinceofChina(BK２０１２２５０)

BiographyYANGZiＧrun(１９８１mdash)MaleDoctorAssociateProfessor　EＧmail１２３１２３９５３１６３1049008com　ReceivedDateApril１０２０１２CorrespondingAuthorWANGShuＧqi(１９６２mdash)MaleProfessor　EＧmailshuqi_wangujs1049008edu1049008cn

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JOURNALOFIRONANDSTEELRESEARCHINTERNATIONAL1049008２０１３２０(１０)８１Ｇ８６10512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273105127310512731051273

WearBehaviorandMechanismofSpheroidalGraphiteCastIronYANGZiＧrun１　LIDongＧsheng２　WANGLan２　WANGShuＧqi２　WEIMinＧxian２

(１SchoolofMaterialsEngineeringYanchengInstituteofTechnologyYancheng２２４０５１JiangsuChina２SchoolofMaterialsScienceandEngineeringJiangsuUniversityZhenjiang２１２０１３JiangsuChina)

AbstractWearbehaviorandmechanismofspheroidalgraphitecastironwerestudiedonapinＧonＧdiskelevatedtemＧperatureweartesterThephaseandmorphologyofwornsurfaceswereexaminedbyXＧraydiffractionandscanningelectronmicroscopyResultsshowthatwithanincreaseofloadwearrateofspheroidalgraphitecastirongraduallyincreasesunderlowloadsrapidlyincreasesorpotentiallyincreasesunderhighloadswearrateincreaseswithinＧcreasingambienttemperatureAt２５－２００adhesivewearprevailsoxidativewearandadhesivewearcoexistat４００Asloadsurpasses１５０Nat４００ extrusivewearappearsTheelevatedＧtemperaturewearofspheroidalgraphitecastironisaphysicalandchemicalprocessincludingthefollowingreactionsxFe＋y２O２mdashFexOy２C＋O２mdash２COandFexOy＋yCOmdashxFe＋yCO２Henceat４００theamountofgraphiteandtriboＧoxidesaresubstanＧtiallyreducedbecauseofreductivefunctionofgraphiteItcanbesuggestedthatwearＧreducedeffectofgraphiteandtriboＧoxidesisimpairedKeywordsspheroidalgraphitecastironwearbehaviorwearmechanismtriboＧoxidemicrostructure

　 　SpheroidalgraphitecastironpossessesgoodmechanicalpropertiesespeciallyhighenoughplasＧticitytoughnessandhigherstrengththancarbonsteelHencespheroidalgraphitecastironasanimＧportantferrousalloyispopularlyadoptedinvariousengineeringapplicationssuchasautomobileagriＧculturalmachineryandmining[１]　　WearisoneoftheimportantfailurepatternsforthemovingmechanicspartsWearofsteelshasbeenextensivelystudiedand wearbehaviorand mechaＧnism ofsteelsareclearlyknown[２－１０]Howeverrarestudyconcerninggraphitecastironwascarriedout[１１－１４]ARRiahiandATAlpas[１１]suggestedthefirstwearmapforgreycastironWearmechanismswereclassifiedinto ultraＧmild mild and severewearInultraＧmild wearacompactedoxidefilmcoveredcontactingsurfacesmildwearwasalsodeＧfinedasoxidativewearSeverewearappearedwhenoxidelayerdidnotstablyformduetodelaminationoftriboＧoxidesTheexcellentwearresistanceofgreycastironduringdryslidingunderlowloadingcondiＧ

tionswasattributedtographiteflakesandformationofagraphitefilmYCLiuetal[１２]studiedtheinfluＧenceofsurfaceoxidationonthewearresistanceofcastironsandfoundthatoxidationincreasedwearratewhencastironwasofhighstrengthandhardＧnessbutwhencastironwasoflowstrengthandhardnessoxidationreducedwearrateWhetheroxiＧdationincreasedorreducedweardependedongraphＧitemorphologymicrostructureandhardnessofmaＧtrixK HirasataandK Hayashi[１３]studiedfrictionandwearofseveralkindsofcastironsundersevereslidingconditionsandfoundthatthewearrateswerestronglydependentonhardnessvariationBKPrasＧad[１４]studiedtheeffectofmicrostructuralfeaturesandtestconditionsonthe wearofcastironandfoundthatthegoverningphenomenaofwearmightbeduetoadhesivewearwhichgeneratedoxideparＧticulatesthatfurtherledtoabrasivewear　 　 Thereforetillnowthe wearbehaviorandmechanismofgraphitecastironhavenotbeenclearＧlyunderstoodThepurposeofthisresearchisto

studythedrysliding wearbehaviorofspheriordgraphiteironThe wear mechanism ofspheroidalgraphitecastironwasalsodiscussedtherelationＧshipbetweentriboＧoxidesandgraphitewereexplored

１　ExperimentalProcedure　　Pinsof６mmindiameterand１２mminlengthwere made of commercial QT８００Ｇ２ spheroidalgraphitecastironwhileD２steelwasselectedasdiscsof７０mmindiameterand８mminthicknessTheirchemicalcompositionsarelistedinTable１TheasＧcastandheatＧtreatedmicrostructuresofthespheroidalgraphitecastiron (QT８００Ｇ２)areillusＧ

tratedinFig1049008１TheasＧcastmicrostructureofthespheroidalgraphitecastironisshowninFig1049008１(a)Thespheroidalgraphitecastironwasaustenitizedat９００for２０mincooledinoilthentemperedat２００５００and７５０ for２hrespectivelyBesidesspheroidalgraphitetemperedmartensite(HRC５５)[Fig1049008１(b)]temperedtroosite(HRC４０)[Fig1049008１(c)]andtemperedsorbite(HRC２０)[Fig1049008１ (d)]wereachievedCommercialD２steelwasaustenitizedat１１５０ for２０minoilquenchedandtemperedthreetimesat５５０ for２htoachievetemperedtroositewithanhardnessofHRC６０　　WeartestswereperformedonanMGＧ２０００type

　　　Table１　Chemicalcompositionsofspheroidalgraphitecastiron(pin)andD２steel(disk)　　　 (masspercent)

Materials C Cr Mo V Si Mn S P

QT８００Ｇ２ ３1049008４０－３1049008８０ － － － ２1049008４０－３1049008００ ０1049008５０－０1049008８０ le０1049008０５ le０1049008０５D２ １1049008４５－１1049008７０ １１1049008００－１２1049008５０ ０1049008４０－０1049008６０ ０1049008１５－０1049008３０ le０1049008４０ le０1049008４０ le０1049008０３０ le０1049008０３０

Fig1049008１　MicrostructuresofspheroidalironofasＧcast(a)andastemperedat２００ (b)５００ (c)and５７０ (d)

pinＧonＧdischightemperatureweartesterThewearparameterswereasfollowsslidingdistanceof１1049008２times１０３ mvelocityof１msambienttemperaturerangeof２５－４００andloadrangeof５０－２００NWearwasdeterminedbymeasuringthemasslossofpinspeciＧmenusinganelectronicbalance (０1049008０１ mg)Masslosswasconvertedintovolumelossusingthedensityofspheroidalgraphitecastiron(７1049008３０gcm３)ThewearratewasdefinedasvolumelossbyunitdisＧtance(mm３mm)DataforeachwearvaluewascalＧ

culatedfromtheaverageofthreetestsMomentoffrictionforcebetweenthepinanddiskduringwearwasmeasuredbyasensorandautomaticallyrecorＧdedbyapersonalcomputerthentransformedtofrictioncoefficientStructuresandmorphologyofwornsurfacesandsubsurfacewereidentifiedbyusingaDMaxＧ２５００pctypeXＧraydiffractometer(XRD)andaJSMＧ７００１Ftypescanningelectronmicroscope(SEM)respectivelyHardnessofpinspecimen was measＧuredbyusinganHRＧ１５０AtypeRockwellapparatus

1048944２８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

２　Results２1049008１　Wearrate　　Fig1049008２showsthewearrateofspheroidalgraphＧitecastironundervarioustestingconditionsItcanbeobservedthatwearrateincreasedwithincreasingambienttemperatureSpheroidalgraphitecastirontemperedat２００and５００presentedasimilarreguＧlarityWearratesat２５and２００approachedeach

otherButthewearrateat４００ firstslowlyinＧcreasedandthenabruptlyincreasedattheloadof１５０and１２５Nrespectively [Fig1049008２ (a)and (b)]Forspheroidalgraphitecastirontemperedat５７０ wearratewasfoundtoincreaserapidlyunderacerＧtainload(criticalload)atvariousambienttemperaＧturesAsambienttemperatureincreasedthecritiＧcalloads were１５０１２５and５０ Nrespectively[Fig1049008２(c)]

Fig1049008２　Wearratesofspheroidalgraphitecastirontemperedatvarioustemperingtemperaturesof２００ (a)５００ (b)and５７０ (c)underdifferenttestingconditions

　　ComparisonofwearrateofdifferenttemperedmicrostructuresatvariousambienttemperaturesisshowninFig1049008３At２５thewearrateoftemperedsorbiteoutclassedtempered martensiteandtemＧperedtroositeUndertheloadof２５－１５０NtemＧpered martensiteandtemperedtroositepresentednearlythesamewearrateWhentheloadsurpassed１５０NtemperedtroositeincreasedrapidlybuttemＧperedmartensitekeptaslowincrease[Fig1049008３(a)]

　　At２００ temperedmartensiteandtemperedtroositeshowedsimilarwearrateinentireloadrangebuttheyweresubstantiallylowerthanthatoftemperedsorbite[Fig1049008３(b)]At４００thewearratesofvariＧousmicrostructureswerealmostthesameundertheloadof２５－５０NAstheloadsurpassed５０Nthewearrateoftemperedsorbiterapidlyincreasedbuttemperedmartensiteandtemperedtroositerevealedagradualincreaseandfewerdifferenceofwearrates

Fig1049008３　Comparisonsofwearratesofspheroidalgraphitecastironwithvarioustemperedmicrostructuresatdifferentambienttemperaturesof２５ (a)２００ (b)and４００ (c)

Wearratesoftempered martensiteandtemperedtroositerapidlyincreasedundertheloadsof１２５and１５０Nrespectively[Fig1049008３(c)]　 　Fig1049008４exhibitsaveragefrictioncoefficientofspheroidalgraphitecastironwith５００ temperedmicrostructure underdifferenttesting conditionsAveragefrictioncoefficientsgraduallyincreasewithincreasingloadandambienttemperatureTheaverＧ

agefrictioncoefficientsubstantiallyreducedto０1049008３３undertheloadof１５０Nat４００

２1049008２　Phaseandmorphologyofwornsurfaces　　XRDpatternsofwornsurfacesofspheroidalgraphitecastironwith５００temperedmicrostructureatvariousambienttemperaturesareillustratedinFig1049008５ItcanbenoticedthattrivialFeOandFe３O４appＧ

1048944３８1048944Issue１０　　　　　　　　　WearBehaviorandMechanismofSpheroidalGraphiteCastIron　

Fig1049008４　Averagefrictioncoefficientofspheroidalironwith５００temperedmicrostructureundervarious

testingconditions

earedonwornsurfacesat２５－２００ [Fig1049008５(a)and(b)]Asambienttemperaturereached４００ theintensityofoxidesincreasedbutitwasapparentlylowerthantheintensityofironThismeansthattriboＧoxidesincreasedbuttheiramount wasstillless[Fig1049008５(c)]　 　 Morphology of wornsurfacesofspheroidalgraphitecastironwith５００temperedmicrostrucＧtureundervarioustestingconditionsisshowninFig1049008６At２５－２００wornsurfacesmainlypresenＧtedtearingＧformadhesivetracewithasmallamountofblackgraphitethatissupposedtobeaheadstreamoftearingUnderahighloadtraceoxidespresentedascattereddistributiononwornsurfaces[Fig1049008６(a)－(d)]At４００asmallamountofoxidesformedon

Fig1049008５　XＧraydiffractionpatternsforwornsurfacesofspheroidalironwith５００temperedmicrostructureatambienttemperaturesof２５ (a)２００ (b)and４００ (c)

(a)５０N２５　 (b)２００N２５　 (c)５０N２００　 (d)２００N２００　 (e)５０N４００　 (f)１５０N４００Fig1049008６　Morphologyforwornsurfacesofspheroidalironwith５００temperedmicrostructureundervariousconditions

certainpartsofwornsurfaces[Fig1049008６(e)]Whenaloadof１５０ N wasappliedwornsurfacesturnedsmootherandfurrowsexistedalongtheslidingdiＧrection[Fig1049008６(f)]

２1049008３　Sectionmorphologyofwornsurfacesandweardebris　　Fig1049008７exhibitssectionmorphologyofwornsurＧfacesundervarioustestingconditionsAt２５ therewasalmostnotriboＧoxidelayeronwornsurfaces

1048944４８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

(a)５０N２５　 (b)２００N２５　 (c)５０N２００　 (d)２００N２００　 (e)５０N４００　 (f)１５０N４００Fig1049008７　Morphologyforsubsurfaceofspheroidalironwith５００temperedmicrostructureundervariousconditions

[Fig1049008７(a)and(b)]At２００scatteredtriboＧoxＧidelayercanbefoundinthepartofwornsurfaceandreachedathicknesslessthan３μm [Fig1049008７ (c)and(d)]At４００theamountoftriboＧoxidesrelＧativelyincreasedbuttotalquantitywaslessInthiscasetriboＧoxidelayerpresented a discontinuousformandlessthan５μminthickness[Fig1049008７ (e)]Whentheloadof１５０NwasappliedstretchedＧformgraphiteappearedindicatingthatasevereplasticdeformationoccurredinsubsurface[Fig1049008７(f)]

３　Discussion　　At２５－２００thereisnoortracetriboＧoxidesonwornsurfacesmetalＧmetalcontactcannotbeavoiＧdedAdhesivewearispredominantwearmechanismTheincreaseofambienttemperatureandfrictionheatwouldreducesurfacehardnessofspheroidalgraphitecastironThuswearrateat２００ismarＧginallyhigherthanthatat２５UnderalowloadalowerincreaseofwearratemaybeattributedtothelubricatingroleofgraphiteHoweverunderahigherloadgraphiteandortheboundarybetweengraphiteand matrixreadilyfractureunderfrictionforcetoleadtorapidincreaseofwearrate　　At４００ triboＧoxideswouldincreaseduetotheelevationofambienttemperatureAlthoughtheamountoftriboＧoxidesrelativelyincreasedtheywerefarlowerthanthoseofsteelsunderthesamecondiＧtions[８－１０]Theirquantityandthickness(＜５μm)werenotenoughtoentirelyavoidthemetalＧmetalcontactInthiscaseoxidativewearandadhesivewearcoexistedAstheloadsurpassed１５０NextruＧsivewearappeared

　　DuringslidinggraphiteisseverelydamagedThespheroidalgraphiteonwornsurfaceswouldbestretchedbyforceCrackswouldappearandpropaＧgatealongtheboundarybetweengraphiteandmaＧtrixthusgraphitedelaminatedfromwornsurfacesWeardebrisofgraphitewouldbegroundtopowderUndertheconditionofhightemperatureandloadgraphitepowderwouldreactwithFe２O３andFe３O４

formedonwornsurfaces　　２C＋Fe３O４mdash３Fe＋２CO２uarr (１)　　３C＋２Fe２O３mdash４Fe＋３CO２uarr (２)　　２C＋O２mdash２CO (３)　　４CO＋Fe３O４mdash３Fe＋４CO２ (４)　　３CO＋Fe２O３mdash２Fe＋３CO２ (５)　　Fig1049008８presentsΔGθ

TＧT diagramofFeＧCＧOsysＧtemasafunctionofambienttemperatureForthereactions(３)(４)and(５)ΔGθ

T＜０thusreactionsspontaneouslyproceedFromthermaldynamicsreＧsultsitcanbesuggestedthatduringthewearofsphＧ

Fig1049008８　ΔGθTＧTdiagramofFeＧCＧOsystem

1048944５８1048944Issue１０　　　　　　　　　WearBehaviorandMechanismofSpheroidalGraphiteCastIron　

eroidalgraphitecastironat４００graphiteisfirstoxidizedtoCOthenreductionreactionsamongCOFe２O３andFe３O４occurThusoxidesaredifficulttoexistonwornsurfaceofspheroidalgraphitecastironwhichcanexpoundthelesstriboＧoxidesintheXRDresultsofwornsurfaces　　AllinallgraphitewasreportedtopossessluＧbricationrole during wearThelubrication rolewouldappearat２５－２００andlowloadThuswearratewasreducedWhenahighloadwasappliedgraphiteandortheboundarybetweengraphiteandmatrixwouldfracturethusthewearincreasedSoitisreadilytoexplainthereasonthatwearrategraduallyincreasedunderalowloadandrapidlyinＧcreasedunderahighloadAt４００duetodeoxiＧdizationfunctionofgraphitetheamountofgraphiteand triboＧoxides would apparently decreasethewearＧreducedrolewouldbeimpairedItcanbesugＧgestedthatelevatedtemperaturewearofspheroidalgraphitecastironisaphysicalandchemicalprocessincludingthefollowingreactionsxFe＋y２O２mdashFexOy２C＋O２mdash２COandFexOy ＋yCOmdashxFe＋yCO２

４　Conclusions　　１)WearrateofspheroidalgraphitecastirongraduallyincreasedunderalowloadandrapidlyenhancedorpotentiallyenhancedunderahighloadWithanincreaseofambienttemperaturewearrateincreasedMicrostructures ofspheroidalgraphitecastironpresentedanobviousinfluenceon wearrateWearresistanceincreasedaccordingtothefolＧlowingordertemperedsorbitetemperedtroostiteandtempered martensiteFriction coefficientinＧcreasedwithincreasingambienttemperatureanddeＧscendedwithincreasingload　　２)At２５－２００noortracetriboＧoxidesexisＧtedonwornsurfacesofspheroidalgraphitecastironadhesivewearprevailedAt４００triboＧoxidesrelＧativelyincreasedbuttheiramountandthickness(＜５μm)werenotenoughtoavoidthemetalＧmetalcontactthusoxidativewearandadhesivewearcoＧexistedAstheloadsurpassed１５０ Nextrusivewearappeared　　３)Graphitepossessedlubricatingfunctiontoreducewearat２５－２００andalowloadAsahighload wasappliedwearrateincreasedbecauseof

fractureofgraphiteandorboundarybetweengraphＧiteandmatrixAt４００ theamountofgraphiteandtriboＧoxidessubstantiallydecreasedduetothedeoxidationroleofgraphiteHencethe wearＧreＧducedfunctionofgraphiteandtriboＧoxideswereimＧpairedElevatedＧtemperature wear of spheroidalgraphitecastironcanbesuggestedtobeaphysicalandchemicalprocessincludingthefollowingreacＧtionsxFe＋y２O２mdashFexOy２C＋O２mdash２CO andFexOy＋yCOmdashxFe＋yCO２

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[２]　QuinnTFJSullivanJLRowsonDMDevelopmentsintheOxidationalTheoryofMildWear[J]TribologyInternational１９８０１３(４)１５３

[３]　WilsonJEStottFHWoodGCTheDevelopmentofWearProtectiveOxidesandTheirInfluenceonSlidingFriction [J]ProceedingstheRoyalofSociety１９８０３６９A５５７

[４]　InmanIADattaSDuHLetalMicroscopyofGlazedLayＧersFormedDuringHighTemperatureSlidingWearat７５０ [J]Wear２００３２５４(５６)４６１

[５]　StraffeliniGTrabuccoDMolinariAOxidativeWearofHeatＧTreatedSteels[J]Wear２００１２５０(１Ｇ１２)４８５

[６]　BarrauOBoherCAnalysisoftheFrictionandWearBehavＧiourofHotWorkToolSteelforForging[J]Wear２００３２５５(７Ｇ１２)１４４４

[７]　GarzaＧMontesＧdeＧOcaNFRainforthW MWearMechanismsExperiencedbyaWorkRollGradeHighSpeedunderDifferentEnvironmentalCondition[J]Wear２００９２６７(１Ｇ４)４４１

[８]　WangSQWeiM XWangFetalTransitionofElevatedTemperatureWear MechanismsandtheOxidativeDelaminaＧtionWearinHotＧWorkingDieSteels[J]TribologyInternaＧtional２０１０４３(３)５７７

[９]　WangSQWeiM XZhaoY TEffectsoftheTriboＧOxideand Matrixon DrySliding WearCharacteristicsand MechaＧnismsofaCastSteel[J]Wear２０１０２６９(５６)４２４

[１０]　WeiMXChenKMWangSQetalAnalysisforWearBeＧhaviorsofOxidativeWear[J]TribologyLetters２０１１４２(１)１

[１１]　RiahiA RAlpasA TWearMapforGreyCastIron [J]Wear２００３２５５４０１

[１２]　LiuYCSchisslerJMMathiaGTheInfluenceofSurfaceOxidationontheWearResistanceofCastIron[J]TribologyInternational１９９５２８(７)４３３

[１３]　HirasataKHayashiKFrictionandWearofSeveralKindsofCastIronsUnderSevereSlidingConditions[J]Wear２００７２６３(１Ｇ６)７９０

[１４]　PrasadBKSlidingWearReponseofCastIronasInfluencedbyMicrostructuralFeaturesandTestCondition[J]MaterialsScienceandEngineering２００７４５６A(１２)３７３

1048944６８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

studythedrysliding wearbehaviorofspheriordgraphiteironThe wear mechanism ofspheroidalgraphitecastironwasalsodiscussedtherelationＧshipbetweentriboＧoxidesandgraphitewereexplored

１　ExperimentalProcedure　　Pinsof６mmindiameterand１２mminlengthwere made of commercial QT８００Ｇ２ spheroidalgraphitecastironwhileD２steelwasselectedasdiscsof７０mmindiameterand８mminthicknessTheirchemicalcompositionsarelistedinTable１TheasＧcastandheatＧtreatedmicrostructuresofthespheroidalgraphitecastiron (QT８００Ｇ２)areillusＧ

tratedinFig1049008１TheasＧcastmicrostructureofthespheroidalgraphitecastironisshowninFig1049008１(a)Thespheroidalgraphitecastironwasaustenitizedat９００for２０mincooledinoilthentemperedat２００５００and７５０ for２hrespectivelyBesidesspheroidalgraphitetemperedmartensite(HRC５５)[Fig1049008１(b)]temperedtroosite(HRC４０)[Fig1049008１(c)]andtemperedsorbite(HRC２０)[Fig1049008１ (d)]wereachievedCommercialD２steelwasaustenitizedat１１５０ for２０minoilquenchedandtemperedthreetimesat５５０ for２htoachievetemperedtroositewithanhardnessofHRC６０　　WeartestswereperformedonanMGＧ２０００type

　　　Table１　Chemicalcompositionsofspheroidalgraphitecastiron(pin)andD２steel(disk)　　　 (masspercent)

Materials C Cr Mo V Si Mn S P

QT８００Ｇ２ ３1049008４０－３1049008８０ － － － ２1049008４０－３1049008００ ０1049008５０－０1049008８０ le０1049008０５ le０1049008０５D２ １1049008４５－１1049008７０ １１1049008００－１２1049008５０ ０1049008４０－０1049008６０ ０1049008１５－０1049008３０ le０1049008４０ le０1049008４０ le０1049008０３０ le０1049008０３０

Fig1049008１　MicrostructuresofspheroidalironofasＧcast(a)andastemperedat２００ (b)５００ (c)and５７０ (d)

pinＧonＧdischightemperatureweartesterThewearparameterswereasfollowsslidingdistanceof１1049008２times１０３ mvelocityof１msambienttemperaturerangeof２５－４００andloadrangeof５０－２００NWearwasdeterminedbymeasuringthemasslossofpinspeciＧmenusinganelectronicbalance (０1049008０１ mg)Masslosswasconvertedintovolumelossusingthedensityofspheroidalgraphitecastiron(７1049008３０gcm３)ThewearratewasdefinedasvolumelossbyunitdisＧtance(mm３mm)DataforeachwearvaluewascalＧ

culatedfromtheaverageofthreetestsMomentoffrictionforcebetweenthepinanddiskduringwearwasmeasuredbyasensorandautomaticallyrecorＧdedbyapersonalcomputerthentransformedtofrictioncoefficientStructuresandmorphologyofwornsurfacesandsubsurfacewereidentifiedbyusingaDMaxＧ２５００pctypeXＧraydiffractometer(XRD)andaJSMＧ７００１Ftypescanningelectronmicroscope(SEM)respectivelyHardnessofpinspecimen was measＧuredbyusinganHRＧ１５０AtypeRockwellapparatus

1048944２８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

２　Results２1049008１　Wearrate　　Fig1049008２showsthewearrateofspheroidalgraphＧitecastironundervarioustestingconditionsItcanbeobservedthatwearrateincreasedwithincreasingambienttemperatureSpheroidalgraphitecastirontemperedat２００and５００presentedasimilarreguＧlarityWearratesat２５and２００approachedeach

otherButthewearrateat４００ firstslowlyinＧcreasedandthenabruptlyincreasedattheloadof１５０and１２５Nrespectively [Fig1049008２ (a)and (b)]Forspheroidalgraphitecastirontemperedat５７０ wearratewasfoundtoincreaserapidlyunderacerＧtainload(criticalload)atvariousambienttemperaＧturesAsambienttemperatureincreasedthecritiＧcalloads were１５０１２５and５０ Nrespectively[Fig1049008２(c)]

Fig1049008２　Wearratesofspheroidalgraphitecastirontemperedatvarioustemperingtemperaturesof２００ (a)５００ (b)and５７０ (c)underdifferenttestingconditions

　　ComparisonofwearrateofdifferenttemperedmicrostructuresatvariousambienttemperaturesisshowninFig1049008３At２５thewearrateoftemperedsorbiteoutclassedtempered martensiteandtemＧperedtroositeUndertheloadof２５－１５０NtemＧpered martensiteandtemperedtroositepresentednearlythesamewearrateWhentheloadsurpassed１５０NtemperedtroositeincreasedrapidlybuttemＧperedmartensitekeptaslowincrease[Fig1049008３(a)]

　　At２００ temperedmartensiteandtemperedtroositeshowedsimilarwearrateinentireloadrangebuttheyweresubstantiallylowerthanthatoftemperedsorbite[Fig1049008３(b)]At４００thewearratesofvariＧousmicrostructureswerealmostthesameundertheloadof２５－５０NAstheloadsurpassed５０Nthewearrateoftemperedsorbiterapidlyincreasedbuttemperedmartensiteandtemperedtroositerevealedagradualincreaseandfewerdifferenceofwearrates

Fig1049008３　Comparisonsofwearratesofspheroidalgraphitecastironwithvarioustemperedmicrostructuresatdifferentambienttemperaturesof２５ (a)２００ (b)and４００ (c)

Wearratesoftempered martensiteandtemperedtroositerapidlyincreasedundertheloadsof１２５and１５０Nrespectively[Fig1049008３(c)]　 　Fig1049008４exhibitsaveragefrictioncoefficientofspheroidalgraphitecastironwith５００ temperedmicrostructure underdifferenttesting conditionsAveragefrictioncoefficientsgraduallyincreasewithincreasingloadandambienttemperatureTheaverＧ

agefrictioncoefficientsubstantiallyreducedto０1049008３３undertheloadof１５０Nat４００

２1049008２　Phaseandmorphologyofwornsurfaces　　XRDpatternsofwornsurfacesofspheroidalgraphitecastironwith５００temperedmicrostructureatvariousambienttemperaturesareillustratedinFig1049008５ItcanbenoticedthattrivialFeOandFe３O４appＧ

1048944３８1048944Issue１０　　　　　　　　　WearBehaviorandMechanismofSpheroidalGraphiteCastIron　

Fig1049008４　Averagefrictioncoefficientofspheroidalironwith５００temperedmicrostructureundervarious

testingconditions

earedonwornsurfacesat２５－２００ [Fig1049008５(a)and(b)]Asambienttemperaturereached４００ theintensityofoxidesincreasedbutitwasapparentlylowerthantheintensityofironThismeansthattriboＧoxidesincreasedbuttheiramount wasstillless[Fig1049008５(c)]　 　 Morphology of wornsurfacesofspheroidalgraphitecastironwith５００temperedmicrostrucＧtureundervarioustestingconditionsisshowninFig1049008６At２５－２００wornsurfacesmainlypresenＧtedtearingＧformadhesivetracewithasmallamountofblackgraphitethatissupposedtobeaheadstreamoftearingUnderahighloadtraceoxidespresentedascattereddistributiononwornsurfaces[Fig1049008６(a)－(d)]At４００asmallamountofoxidesformedon

Fig1049008５　XＧraydiffractionpatternsforwornsurfacesofspheroidalironwith５００temperedmicrostructureatambienttemperaturesof２５ (a)２００ (b)and４００ (c)

(a)５０N２５　 (b)２００N２５　 (c)５０N２００　 (d)２００N２００　 (e)５０N４００　 (f)１５０N４００Fig1049008６　Morphologyforwornsurfacesofspheroidalironwith５００temperedmicrostructureundervariousconditions

certainpartsofwornsurfaces[Fig1049008６(e)]Whenaloadof１５０ N wasappliedwornsurfacesturnedsmootherandfurrowsexistedalongtheslidingdiＧrection[Fig1049008６(f)]

２1049008３　Sectionmorphologyofwornsurfacesandweardebris　　Fig1049008７exhibitssectionmorphologyofwornsurＧfacesundervarioustestingconditionsAt２５ therewasalmostnotriboＧoxidelayeronwornsurfaces

1048944４８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

(a)５０N２５　 (b)２００N２５　 (c)５０N２００　 (d)２００N２００　 (e)５０N４００　 (f)１５０N４００Fig1049008７　Morphologyforsubsurfaceofspheroidalironwith５００temperedmicrostructureundervariousconditions

[Fig1049008７(a)and(b)]At２００scatteredtriboＧoxＧidelayercanbefoundinthepartofwornsurfaceandreachedathicknesslessthan３μm [Fig1049008７ (c)and(d)]At４００theamountoftriboＧoxidesrelＧativelyincreasedbuttotalquantitywaslessInthiscasetriboＧoxidelayerpresented a discontinuousformandlessthan５μminthickness[Fig1049008７ (e)]Whentheloadof１５０NwasappliedstretchedＧformgraphiteappearedindicatingthatasevereplasticdeformationoccurredinsubsurface[Fig1049008７(f)]

３　Discussion　　At２５－２００thereisnoortracetriboＧoxidesonwornsurfacesmetalＧmetalcontactcannotbeavoiＧdedAdhesivewearispredominantwearmechanismTheincreaseofambienttemperatureandfrictionheatwouldreducesurfacehardnessofspheroidalgraphitecastironThuswearrateat２００ismarＧginallyhigherthanthatat２５UnderalowloadalowerincreaseofwearratemaybeattributedtothelubricatingroleofgraphiteHoweverunderahigherloadgraphiteandortheboundarybetweengraphiteand matrixreadilyfractureunderfrictionforcetoleadtorapidincreaseofwearrate　　At４００ triboＧoxideswouldincreaseduetotheelevationofambienttemperatureAlthoughtheamountoftriboＧoxidesrelativelyincreasedtheywerefarlowerthanthoseofsteelsunderthesamecondiＧtions[８－１０]Theirquantityandthickness(＜５μm)werenotenoughtoentirelyavoidthemetalＧmetalcontactInthiscaseoxidativewearandadhesivewearcoexistedAstheloadsurpassed１５０NextruＧsivewearappeared

　　DuringslidinggraphiteisseverelydamagedThespheroidalgraphiteonwornsurfaceswouldbestretchedbyforceCrackswouldappearandpropaＧgatealongtheboundarybetweengraphiteandmaＧtrixthusgraphitedelaminatedfromwornsurfacesWeardebrisofgraphitewouldbegroundtopowderUndertheconditionofhightemperatureandloadgraphitepowderwouldreactwithFe２O３andFe３O４

formedonwornsurfaces　　２C＋Fe３O４mdash３Fe＋２CO２uarr (１)　　３C＋２Fe２O３mdash４Fe＋３CO２uarr (２)　　２C＋O２mdash２CO (３)　　４CO＋Fe３O４mdash３Fe＋４CO２ (４)　　３CO＋Fe２O３mdash２Fe＋３CO２ (５)　　Fig1049008８presentsΔGθ

TＧT diagramofFeＧCＧOsysＧtemasafunctionofambienttemperatureForthereactions(３)(４)and(５)ΔGθ

T＜０thusreactionsspontaneouslyproceedFromthermaldynamicsreＧsultsitcanbesuggestedthatduringthewearofsphＧ

Fig1049008８　ΔGθTＧTdiagramofFeＧCＧOsystem

1048944５８1048944Issue１０　　　　　　　　　WearBehaviorandMechanismofSpheroidalGraphiteCastIron　

eroidalgraphitecastironat４００graphiteisfirstoxidizedtoCOthenreductionreactionsamongCOFe２O３andFe３O４occurThusoxidesaredifficulttoexistonwornsurfaceofspheroidalgraphitecastironwhichcanexpoundthelesstriboＧoxidesintheXRDresultsofwornsurfaces　　AllinallgraphitewasreportedtopossessluＧbricationrole during wearThelubrication rolewouldappearat２５－２００andlowloadThuswearratewasreducedWhenahighloadwasappliedgraphiteandortheboundarybetweengraphiteandmatrixwouldfracturethusthewearincreasedSoitisreadilytoexplainthereasonthatwearrategraduallyincreasedunderalowloadandrapidlyinＧcreasedunderahighloadAt４００duetodeoxiＧdizationfunctionofgraphitetheamountofgraphiteand triboＧoxides would apparently decreasethewearＧreducedrolewouldbeimpairedItcanbesugＧgestedthatelevatedtemperaturewearofspheroidalgraphitecastironisaphysicalandchemicalprocessincludingthefollowingreactionsxFe＋y２O２mdashFexOy２C＋O２mdash２COandFexOy ＋yCOmdashxFe＋yCO２

４　Conclusions　　１)WearrateofspheroidalgraphitecastirongraduallyincreasedunderalowloadandrapidlyenhancedorpotentiallyenhancedunderahighloadWithanincreaseofambienttemperaturewearrateincreasedMicrostructures ofspheroidalgraphitecastironpresentedanobviousinfluenceon wearrateWearresistanceincreasedaccordingtothefolＧlowingordertemperedsorbitetemperedtroostiteandtempered martensiteFriction coefficientinＧcreasedwithincreasingambienttemperatureanddeＧscendedwithincreasingload　　２)At２５－２００noortracetriboＧoxidesexisＧtedonwornsurfacesofspheroidalgraphitecastironadhesivewearprevailedAt４００triboＧoxidesrelＧativelyincreasedbuttheiramountandthickness(＜５μm)werenotenoughtoavoidthemetalＧmetalcontactthusoxidativewearandadhesivewearcoＧexistedAstheloadsurpassed１５０ Nextrusivewearappeared　　３)Graphitepossessedlubricatingfunctiontoreducewearat２５－２００andalowloadAsahighload wasappliedwearrateincreasedbecauseof

fractureofgraphiteandorboundarybetweengraphＧiteandmatrixAt４００ theamountofgraphiteandtriboＧoxidessubstantiallydecreasedduetothedeoxidationroleofgraphiteHencethe wearＧreＧducedfunctionofgraphiteandtriboＧoxideswereimＧpairedElevatedＧtemperature wear of spheroidalgraphitecastironcanbesuggestedtobeaphysicalandchemicalprocessincludingthefollowingreacＧtionsxFe＋y２O２mdashFexOy２C＋O２mdash２CO andFexOy＋yCOmdashxFe＋yCO２

References

[１]　SantisADBartolomeoODIacovielloDetalQuantitativeShapeEvaluationofGraphiteParticlesin DuctileIron [J]JournalofMaterialsProcessingTechnology２００８１９６(１２３)２９２

[２]　QuinnTFJSullivanJLRowsonDMDevelopmentsintheOxidationalTheoryofMildWear[J]TribologyInternational１９８０１３(４)１５３

[３]　WilsonJEStottFHWoodGCTheDevelopmentofWearProtectiveOxidesandTheirInfluenceonSlidingFriction [J]ProceedingstheRoyalofSociety１９８０３６９A５５７

[４]　InmanIADattaSDuHLetalMicroscopyofGlazedLayＧersFormedDuringHighTemperatureSlidingWearat７５０ [J]Wear２００３２５４(５６)４６１

[５]　StraffeliniGTrabuccoDMolinariAOxidativeWearofHeatＧTreatedSteels[J]Wear２００１２５０(１Ｇ１２)４８５

[６]　BarrauOBoherCAnalysisoftheFrictionandWearBehavＧiourofHotWorkToolSteelforForging[J]Wear２００３２５５(７Ｇ１２)１４４４

[７]　GarzaＧMontesＧdeＧOcaNFRainforthW MWearMechanismsExperiencedbyaWorkRollGradeHighSpeedunderDifferentEnvironmentalCondition[J]Wear２００９２６７(１Ｇ４)４４１

[８]　WangSQWeiM XWangFetalTransitionofElevatedTemperatureWear MechanismsandtheOxidativeDelaminaＧtionWearinHotＧWorkingDieSteels[J]TribologyInternaＧtional２０１０４３(３)５７７

[９]　WangSQWeiM XZhaoY TEffectsoftheTriboＧOxideand Matrixon DrySliding WearCharacteristicsand MechaＧnismsofaCastSteel[J]Wear２０１０２６９(５６)４２４

[１０]　WeiMXChenKMWangSQetalAnalysisforWearBeＧhaviorsofOxidativeWear[J]TribologyLetters２０１１４２(１)１

[１１]　RiahiA RAlpasA TWearMapforGreyCastIron [J]Wear２００３２５５４０１

[１２]　LiuYCSchisslerJMMathiaGTheInfluenceofSurfaceOxidationontheWearResistanceofCastIron[J]TribologyInternational１９９５２８(７)４３３

[１３]　HirasataKHayashiKFrictionandWearofSeveralKindsofCastIronsUnderSevereSlidingConditions[J]Wear２００７２６３(１Ｇ６)７９０

[１４]　PrasadBKSlidingWearReponseofCastIronasInfluencedbyMicrostructuralFeaturesandTestCondition[J]MaterialsScienceandEngineering２００７４５６A(１２)３７３

1048944６８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

２　Results２1049008１　Wearrate　　Fig1049008２showsthewearrateofspheroidalgraphＧitecastironundervarioustestingconditionsItcanbeobservedthatwearrateincreasedwithincreasingambienttemperatureSpheroidalgraphitecastirontemperedat２００and５００presentedasimilarreguＧlarityWearratesat２５and２００approachedeach

otherButthewearrateat４００ firstslowlyinＧcreasedandthenabruptlyincreasedattheloadof１５０and１２５Nrespectively [Fig1049008２ (a)and (b)]Forspheroidalgraphitecastirontemperedat５７０ wearratewasfoundtoincreaserapidlyunderacerＧtainload(criticalload)atvariousambienttemperaＧturesAsambienttemperatureincreasedthecritiＧcalloads were１５０１２５and５０ Nrespectively[Fig1049008２(c)]

Fig1049008２　Wearratesofspheroidalgraphitecastirontemperedatvarioustemperingtemperaturesof２００ (a)５００ (b)and５７０ (c)underdifferenttestingconditions

　　ComparisonofwearrateofdifferenttemperedmicrostructuresatvariousambienttemperaturesisshowninFig1049008３At２５thewearrateoftemperedsorbiteoutclassedtempered martensiteandtemＧperedtroositeUndertheloadof２５－１５０NtemＧpered martensiteandtemperedtroositepresentednearlythesamewearrateWhentheloadsurpassed１５０NtemperedtroositeincreasedrapidlybuttemＧperedmartensitekeptaslowincrease[Fig1049008３(a)]

　　At２００ temperedmartensiteandtemperedtroositeshowedsimilarwearrateinentireloadrangebuttheyweresubstantiallylowerthanthatoftemperedsorbite[Fig1049008３(b)]At４００thewearratesofvariＧousmicrostructureswerealmostthesameundertheloadof２５－５０NAstheloadsurpassed５０Nthewearrateoftemperedsorbiterapidlyincreasedbuttemperedmartensiteandtemperedtroositerevealedagradualincreaseandfewerdifferenceofwearrates

Fig1049008３　Comparisonsofwearratesofspheroidalgraphitecastironwithvarioustemperedmicrostructuresatdifferentambienttemperaturesof２５ (a)２００ (b)and４００ (c)

Wearratesoftempered martensiteandtemperedtroositerapidlyincreasedundertheloadsof１２５and１５０Nrespectively[Fig1049008３(c)]　 　Fig1049008４exhibitsaveragefrictioncoefficientofspheroidalgraphitecastironwith５００ temperedmicrostructure underdifferenttesting conditionsAveragefrictioncoefficientsgraduallyincreasewithincreasingloadandambienttemperatureTheaverＧ

agefrictioncoefficientsubstantiallyreducedto０1049008３３undertheloadof１５０Nat４００

２1049008２　Phaseandmorphologyofwornsurfaces　　XRDpatternsofwornsurfacesofspheroidalgraphitecastironwith５００temperedmicrostructureatvariousambienttemperaturesareillustratedinFig1049008５ItcanbenoticedthattrivialFeOandFe３O４appＧ

1048944３８1048944Issue１０　　　　　　　　　WearBehaviorandMechanismofSpheroidalGraphiteCastIron　

Fig1049008４　Averagefrictioncoefficientofspheroidalironwith５００temperedmicrostructureundervarious

testingconditions

earedonwornsurfacesat２５－２００ [Fig1049008５(a)and(b)]Asambienttemperaturereached４００ theintensityofoxidesincreasedbutitwasapparentlylowerthantheintensityofironThismeansthattriboＧoxidesincreasedbuttheiramount wasstillless[Fig1049008５(c)]　 　 Morphology of wornsurfacesofspheroidalgraphitecastironwith５００temperedmicrostrucＧtureundervarioustestingconditionsisshowninFig1049008６At２５－２００wornsurfacesmainlypresenＧtedtearingＧformadhesivetracewithasmallamountofblackgraphitethatissupposedtobeaheadstreamoftearingUnderahighloadtraceoxidespresentedascattereddistributiononwornsurfaces[Fig1049008６(a)－(d)]At４００asmallamountofoxidesformedon

Fig1049008５　XＧraydiffractionpatternsforwornsurfacesofspheroidalironwith５００temperedmicrostructureatambienttemperaturesof２５ (a)２００ (b)and４００ (c)

(a)５０N２５　 (b)２００N２５　 (c)５０N２００　 (d)２００N２００　 (e)５０N４００　 (f)１５０N４００Fig1049008６　Morphologyforwornsurfacesofspheroidalironwith５００temperedmicrostructureundervariousconditions

certainpartsofwornsurfaces[Fig1049008６(e)]Whenaloadof１５０ N wasappliedwornsurfacesturnedsmootherandfurrowsexistedalongtheslidingdiＧrection[Fig1049008６(f)]

２1049008３　Sectionmorphologyofwornsurfacesandweardebris　　Fig1049008７exhibitssectionmorphologyofwornsurＧfacesundervarioustestingconditionsAt２５ therewasalmostnotriboＧoxidelayeronwornsurfaces

1048944４８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

(a)５０N２５　 (b)２００N２５　 (c)５０N２００　 (d)２００N２００　 (e)５０N４００　 (f)１５０N４００Fig1049008７　Morphologyforsubsurfaceofspheroidalironwith５００temperedmicrostructureundervariousconditions

[Fig1049008７(a)and(b)]At２００scatteredtriboＧoxＧidelayercanbefoundinthepartofwornsurfaceandreachedathicknesslessthan３μm [Fig1049008７ (c)and(d)]At４００theamountoftriboＧoxidesrelＧativelyincreasedbuttotalquantitywaslessInthiscasetriboＧoxidelayerpresented a discontinuousformandlessthan５μminthickness[Fig1049008７ (e)]Whentheloadof１５０NwasappliedstretchedＧformgraphiteappearedindicatingthatasevereplasticdeformationoccurredinsubsurface[Fig1049008７(f)]

３　Discussion　　At２５－２００thereisnoortracetriboＧoxidesonwornsurfacesmetalＧmetalcontactcannotbeavoiＧdedAdhesivewearispredominantwearmechanismTheincreaseofambienttemperatureandfrictionheatwouldreducesurfacehardnessofspheroidalgraphitecastironThuswearrateat２００ismarＧginallyhigherthanthatat２５UnderalowloadalowerincreaseofwearratemaybeattributedtothelubricatingroleofgraphiteHoweverunderahigherloadgraphiteandortheboundarybetweengraphiteand matrixreadilyfractureunderfrictionforcetoleadtorapidincreaseofwearrate　　At４００ triboＧoxideswouldincreaseduetotheelevationofambienttemperatureAlthoughtheamountoftriboＧoxidesrelativelyincreasedtheywerefarlowerthanthoseofsteelsunderthesamecondiＧtions[８－１０]Theirquantityandthickness(＜５μm)werenotenoughtoentirelyavoidthemetalＧmetalcontactInthiscaseoxidativewearandadhesivewearcoexistedAstheloadsurpassed１５０NextruＧsivewearappeared

　　DuringslidinggraphiteisseverelydamagedThespheroidalgraphiteonwornsurfaceswouldbestretchedbyforceCrackswouldappearandpropaＧgatealongtheboundarybetweengraphiteandmaＧtrixthusgraphitedelaminatedfromwornsurfacesWeardebrisofgraphitewouldbegroundtopowderUndertheconditionofhightemperatureandloadgraphitepowderwouldreactwithFe２O３andFe３O４

formedonwornsurfaces　　２C＋Fe３O４mdash３Fe＋２CO２uarr (１)　　３C＋２Fe２O３mdash４Fe＋３CO２uarr (２)　　２C＋O２mdash２CO (３)　　４CO＋Fe３O４mdash３Fe＋４CO２ (４)　　３CO＋Fe２O３mdash２Fe＋３CO２ (５)　　Fig1049008８presentsΔGθ

TＧT diagramofFeＧCＧOsysＧtemasafunctionofambienttemperatureForthereactions(３)(４)and(５)ΔGθ

T＜０thusreactionsspontaneouslyproceedFromthermaldynamicsreＧsultsitcanbesuggestedthatduringthewearofsphＧ

Fig1049008８　ΔGθTＧTdiagramofFeＧCＧOsystem

1048944５８1048944Issue１０　　　　　　　　　WearBehaviorandMechanismofSpheroidalGraphiteCastIron　

eroidalgraphitecastironat４００graphiteisfirstoxidizedtoCOthenreductionreactionsamongCOFe２O３andFe３O４occurThusoxidesaredifficulttoexistonwornsurfaceofspheroidalgraphitecastironwhichcanexpoundthelesstriboＧoxidesintheXRDresultsofwornsurfaces　　AllinallgraphitewasreportedtopossessluＧbricationrole during wearThelubrication rolewouldappearat２５－２００andlowloadThuswearratewasreducedWhenahighloadwasappliedgraphiteandortheboundarybetweengraphiteandmatrixwouldfracturethusthewearincreasedSoitisreadilytoexplainthereasonthatwearrategraduallyincreasedunderalowloadandrapidlyinＧcreasedunderahighloadAt４００duetodeoxiＧdizationfunctionofgraphitetheamountofgraphiteand triboＧoxides would apparently decreasethewearＧreducedrolewouldbeimpairedItcanbesugＧgestedthatelevatedtemperaturewearofspheroidalgraphitecastironisaphysicalandchemicalprocessincludingthefollowingreactionsxFe＋y２O２mdashFexOy２C＋O２mdash２COandFexOy ＋yCOmdashxFe＋yCO２

４　Conclusions　　１)WearrateofspheroidalgraphitecastirongraduallyincreasedunderalowloadandrapidlyenhancedorpotentiallyenhancedunderahighloadWithanincreaseofambienttemperaturewearrateincreasedMicrostructures ofspheroidalgraphitecastironpresentedanobviousinfluenceon wearrateWearresistanceincreasedaccordingtothefolＧlowingordertemperedsorbitetemperedtroostiteandtempered martensiteFriction coefficientinＧcreasedwithincreasingambienttemperatureanddeＧscendedwithincreasingload　　２)At２５－２００noortracetriboＧoxidesexisＧtedonwornsurfacesofspheroidalgraphitecastironadhesivewearprevailedAt４００triboＧoxidesrelＧativelyincreasedbuttheiramountandthickness(＜５μm)werenotenoughtoavoidthemetalＧmetalcontactthusoxidativewearandadhesivewearcoＧexistedAstheloadsurpassed１５０ Nextrusivewearappeared　　３)Graphitepossessedlubricatingfunctiontoreducewearat２５－２００andalowloadAsahighload wasappliedwearrateincreasedbecauseof

fractureofgraphiteandorboundarybetweengraphＧiteandmatrixAt４００ theamountofgraphiteandtriboＧoxidessubstantiallydecreasedduetothedeoxidationroleofgraphiteHencethe wearＧreＧducedfunctionofgraphiteandtriboＧoxideswereimＧpairedElevatedＧtemperature wear of spheroidalgraphitecastironcanbesuggestedtobeaphysicalandchemicalprocessincludingthefollowingreacＧtionsxFe＋y２O２mdashFexOy２C＋O２mdash２CO andFexOy＋yCOmdashxFe＋yCO２

References

[１]　SantisADBartolomeoODIacovielloDetalQuantitativeShapeEvaluationofGraphiteParticlesin DuctileIron [J]JournalofMaterialsProcessingTechnology２００８１９６(１２３)２９２

[２]　QuinnTFJSullivanJLRowsonDMDevelopmentsintheOxidationalTheoryofMildWear[J]TribologyInternational１９８０１３(４)１５３

[３]　WilsonJEStottFHWoodGCTheDevelopmentofWearProtectiveOxidesandTheirInfluenceonSlidingFriction [J]ProceedingstheRoyalofSociety１９８０３６９A５５７

[４]　InmanIADattaSDuHLetalMicroscopyofGlazedLayＧersFormedDuringHighTemperatureSlidingWearat７５０ [J]Wear２００３２５４(５６)４６１

[５]　StraffeliniGTrabuccoDMolinariAOxidativeWearofHeatＧTreatedSteels[J]Wear２００１２５０(１Ｇ１２)４８５

[６]　BarrauOBoherCAnalysisoftheFrictionandWearBehavＧiourofHotWorkToolSteelforForging[J]Wear２００３２５５(７Ｇ１２)１４４４

[７]　GarzaＧMontesＧdeＧOcaNFRainforthW MWearMechanismsExperiencedbyaWorkRollGradeHighSpeedunderDifferentEnvironmentalCondition[J]Wear２００９２６７(１Ｇ４)４４１

[８]　WangSQWeiM XWangFetalTransitionofElevatedTemperatureWear MechanismsandtheOxidativeDelaminaＧtionWearinHotＧWorkingDieSteels[J]TribologyInternaＧtional２０１０４３(３)５７７

[９]　WangSQWeiM XZhaoY TEffectsoftheTriboＧOxideand Matrixon DrySliding WearCharacteristicsand MechaＧnismsofaCastSteel[J]Wear２０１０２６９(５６)４２４

[１０]　WeiMXChenKMWangSQetalAnalysisforWearBeＧhaviorsofOxidativeWear[J]TribologyLetters２０１１４２(１)１

[１１]　RiahiA RAlpasA TWearMapforGreyCastIron [J]Wear２００３２５５４０１

[１２]　LiuYCSchisslerJMMathiaGTheInfluenceofSurfaceOxidationontheWearResistanceofCastIron[J]TribologyInternational１９９５２８(７)４３３

[１３]　HirasataKHayashiKFrictionandWearofSeveralKindsofCastIronsUnderSevereSlidingConditions[J]Wear２００７２６３(１Ｇ６)７９０

[１４]　PrasadBKSlidingWearReponseofCastIronasInfluencedbyMicrostructuralFeaturesandTestCondition[J]MaterialsScienceandEngineering２００７４５６A(１２)３７３

1048944６８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

Fig1049008４　Averagefrictioncoefficientofspheroidalironwith５００temperedmicrostructureundervarious

testingconditions

earedonwornsurfacesat２５－２００ [Fig1049008５(a)and(b)]Asambienttemperaturereached４００ theintensityofoxidesincreasedbutitwasapparentlylowerthantheintensityofironThismeansthattriboＧoxidesincreasedbuttheiramount wasstillless[Fig1049008５(c)]　 　 Morphology of wornsurfacesofspheroidalgraphitecastironwith５００temperedmicrostrucＧtureundervarioustestingconditionsisshowninFig1049008６At２５－２００wornsurfacesmainlypresenＧtedtearingＧformadhesivetracewithasmallamountofblackgraphitethatissupposedtobeaheadstreamoftearingUnderahighloadtraceoxidespresentedascattereddistributiononwornsurfaces[Fig1049008６(a)－(d)]At４００asmallamountofoxidesformedon

Fig1049008５　XＧraydiffractionpatternsforwornsurfacesofspheroidalironwith５００temperedmicrostructureatambienttemperaturesof２５ (a)２００ (b)and４００ (c)

(a)５０N２５　 (b)２００N２５　 (c)５０N２００　 (d)２００N２００　 (e)５０N４００　 (f)１５０N４００Fig1049008６　Morphologyforwornsurfacesofspheroidalironwith５００temperedmicrostructureundervariousconditions

certainpartsofwornsurfaces[Fig1049008６(e)]Whenaloadof１５０ N wasappliedwornsurfacesturnedsmootherandfurrowsexistedalongtheslidingdiＧrection[Fig1049008６(f)]

２1049008３　Sectionmorphologyofwornsurfacesandweardebris　　Fig1049008７exhibitssectionmorphologyofwornsurＧfacesundervarioustestingconditionsAt２５ therewasalmostnotriboＧoxidelayeronwornsurfaces

1048944４８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

(a)５０N２５　 (b)２００N２５　 (c)５０N２００　 (d)２００N２００　 (e)５０N４００　 (f)１５０N４００Fig1049008７　Morphologyforsubsurfaceofspheroidalironwith５００temperedmicrostructureundervariousconditions

[Fig1049008７(a)and(b)]At２００scatteredtriboＧoxＧidelayercanbefoundinthepartofwornsurfaceandreachedathicknesslessthan３μm [Fig1049008７ (c)and(d)]At４００theamountoftriboＧoxidesrelＧativelyincreasedbuttotalquantitywaslessInthiscasetriboＧoxidelayerpresented a discontinuousformandlessthan５μminthickness[Fig1049008７ (e)]Whentheloadof１５０NwasappliedstretchedＧformgraphiteappearedindicatingthatasevereplasticdeformationoccurredinsubsurface[Fig1049008７(f)]

３　Discussion　　At２５－２００thereisnoortracetriboＧoxidesonwornsurfacesmetalＧmetalcontactcannotbeavoiＧdedAdhesivewearispredominantwearmechanismTheincreaseofambienttemperatureandfrictionheatwouldreducesurfacehardnessofspheroidalgraphitecastironThuswearrateat２００ismarＧginallyhigherthanthatat２５UnderalowloadalowerincreaseofwearratemaybeattributedtothelubricatingroleofgraphiteHoweverunderahigherloadgraphiteandortheboundarybetweengraphiteand matrixreadilyfractureunderfrictionforcetoleadtorapidincreaseofwearrate　　At４００ triboＧoxideswouldincreaseduetotheelevationofambienttemperatureAlthoughtheamountoftriboＧoxidesrelativelyincreasedtheywerefarlowerthanthoseofsteelsunderthesamecondiＧtions[８－１０]Theirquantityandthickness(＜５μm)werenotenoughtoentirelyavoidthemetalＧmetalcontactInthiscaseoxidativewearandadhesivewearcoexistedAstheloadsurpassed１５０NextruＧsivewearappeared

　　DuringslidinggraphiteisseverelydamagedThespheroidalgraphiteonwornsurfaceswouldbestretchedbyforceCrackswouldappearandpropaＧgatealongtheboundarybetweengraphiteandmaＧtrixthusgraphitedelaminatedfromwornsurfacesWeardebrisofgraphitewouldbegroundtopowderUndertheconditionofhightemperatureandloadgraphitepowderwouldreactwithFe２O３andFe３O４

formedonwornsurfaces　　２C＋Fe３O４mdash３Fe＋２CO２uarr (１)　　３C＋２Fe２O３mdash４Fe＋３CO２uarr (２)　　２C＋O２mdash２CO (３)　　４CO＋Fe３O４mdash３Fe＋４CO２ (４)　　３CO＋Fe２O３mdash２Fe＋３CO２ (５)　　Fig1049008８presentsΔGθ

TＧT diagramofFeＧCＧOsysＧtemasafunctionofambienttemperatureForthereactions(３)(４)and(５)ΔGθ

T＜０thusreactionsspontaneouslyproceedFromthermaldynamicsreＧsultsitcanbesuggestedthatduringthewearofsphＧ

Fig1049008８　ΔGθTＧTdiagramofFeＧCＧOsystem

1048944５８1048944Issue１０　　　　　　　　　WearBehaviorandMechanismofSpheroidalGraphiteCastIron　

eroidalgraphitecastironat４００graphiteisfirstoxidizedtoCOthenreductionreactionsamongCOFe２O３andFe３O４occurThusoxidesaredifficulttoexistonwornsurfaceofspheroidalgraphitecastironwhichcanexpoundthelesstriboＧoxidesintheXRDresultsofwornsurfaces　　AllinallgraphitewasreportedtopossessluＧbricationrole during wearThelubrication rolewouldappearat２５－２００andlowloadThuswearratewasreducedWhenahighloadwasappliedgraphiteandortheboundarybetweengraphiteandmatrixwouldfracturethusthewearincreasedSoitisreadilytoexplainthereasonthatwearrategraduallyincreasedunderalowloadandrapidlyinＧcreasedunderahighloadAt４００duetodeoxiＧdizationfunctionofgraphitetheamountofgraphiteand triboＧoxides would apparently decreasethewearＧreducedrolewouldbeimpairedItcanbesugＧgestedthatelevatedtemperaturewearofspheroidalgraphitecastironisaphysicalandchemicalprocessincludingthefollowingreactionsxFe＋y２O２mdashFexOy２C＋O２mdash２COandFexOy ＋yCOmdashxFe＋yCO２

４　Conclusions　　１)WearrateofspheroidalgraphitecastirongraduallyincreasedunderalowloadandrapidlyenhancedorpotentiallyenhancedunderahighloadWithanincreaseofambienttemperaturewearrateincreasedMicrostructures ofspheroidalgraphitecastironpresentedanobviousinfluenceon wearrateWearresistanceincreasedaccordingtothefolＧlowingordertemperedsorbitetemperedtroostiteandtempered martensiteFriction coefficientinＧcreasedwithincreasingambienttemperatureanddeＧscendedwithincreasingload　　２)At２５－２００noortracetriboＧoxidesexisＧtedonwornsurfacesofspheroidalgraphitecastironadhesivewearprevailedAt４００triboＧoxidesrelＧativelyincreasedbuttheiramountandthickness(＜５μm)werenotenoughtoavoidthemetalＧmetalcontactthusoxidativewearandadhesivewearcoＧexistedAstheloadsurpassed１５０ Nextrusivewearappeared　　３)Graphitepossessedlubricatingfunctiontoreducewearat２５－２００andalowloadAsahighload wasappliedwearrateincreasedbecauseof

fractureofgraphiteandorboundarybetweengraphＧiteandmatrixAt４００ theamountofgraphiteandtriboＧoxidessubstantiallydecreasedduetothedeoxidationroleofgraphiteHencethe wearＧreＧducedfunctionofgraphiteandtriboＧoxideswereimＧpairedElevatedＧtemperature wear of spheroidalgraphitecastironcanbesuggestedtobeaphysicalandchemicalprocessincludingthefollowingreacＧtionsxFe＋y２O２mdashFexOy２C＋O２mdash２CO andFexOy＋yCOmdashxFe＋yCO２

References

[１]　SantisADBartolomeoODIacovielloDetalQuantitativeShapeEvaluationofGraphiteParticlesin DuctileIron [J]JournalofMaterialsProcessingTechnology２００８１９６(１２３)２９２

[２]　QuinnTFJSullivanJLRowsonDMDevelopmentsintheOxidationalTheoryofMildWear[J]TribologyInternational１９８０１３(４)１５３

[３]　WilsonJEStottFHWoodGCTheDevelopmentofWearProtectiveOxidesandTheirInfluenceonSlidingFriction [J]ProceedingstheRoyalofSociety１９８０３６９A５５７

[４]　InmanIADattaSDuHLetalMicroscopyofGlazedLayＧersFormedDuringHighTemperatureSlidingWearat７５０ [J]Wear２００３２５４(５６)４６１

[５]　StraffeliniGTrabuccoDMolinariAOxidativeWearofHeatＧTreatedSteels[J]Wear２００１２５０(１Ｇ１２)４８５

[６]　BarrauOBoherCAnalysisoftheFrictionandWearBehavＧiourofHotWorkToolSteelforForging[J]Wear２００３２５５(７Ｇ１２)１４４４

[７]　GarzaＧMontesＧdeＧOcaNFRainforthW MWearMechanismsExperiencedbyaWorkRollGradeHighSpeedunderDifferentEnvironmentalCondition[J]Wear２００９２６７(１Ｇ４)４４１

[８]　WangSQWeiM XWangFetalTransitionofElevatedTemperatureWear MechanismsandtheOxidativeDelaminaＧtionWearinHotＧWorkingDieSteels[J]TribologyInternaＧtional２０１０４３(３)５７７

[９]　WangSQWeiM XZhaoY TEffectsoftheTriboＧOxideand Matrixon DrySliding WearCharacteristicsand MechaＧnismsofaCastSteel[J]Wear２０１０２６９(５６)４２４

[１０]　WeiMXChenKMWangSQetalAnalysisforWearBeＧhaviorsofOxidativeWear[J]TribologyLetters２０１１４２(１)１

[１１]　RiahiA RAlpasA TWearMapforGreyCastIron [J]Wear２００３２５５４０１

[１２]　LiuYCSchisslerJMMathiaGTheInfluenceofSurfaceOxidationontheWearResistanceofCastIron[J]TribologyInternational１９９５２８(７)４３３

[１３]　HirasataKHayashiKFrictionandWearofSeveralKindsofCastIronsUnderSevereSlidingConditions[J]Wear２００７２６３(１Ｇ６)７９０

[１４]　PrasadBKSlidingWearReponseofCastIronasInfluencedbyMicrostructuralFeaturesandTestCondition[J]MaterialsScienceandEngineering２００７４５６A(１２)３７３

1048944６８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

(a)５０N２５　 (b)２００N２５　 (c)５０N２００　 (d)２００N２００　 (e)５０N４００　 (f)１５０N４００Fig1049008７　Morphologyforsubsurfaceofspheroidalironwith５００temperedmicrostructureundervariousconditions

[Fig1049008７(a)and(b)]At２００scatteredtriboＧoxＧidelayercanbefoundinthepartofwornsurfaceandreachedathicknesslessthan３μm [Fig1049008７ (c)and(d)]At４００theamountoftriboＧoxidesrelＧativelyincreasedbuttotalquantitywaslessInthiscasetriboＧoxidelayerpresented a discontinuousformandlessthan５μminthickness[Fig1049008７ (e)]Whentheloadof１５０NwasappliedstretchedＧformgraphiteappearedindicatingthatasevereplasticdeformationoccurredinsubsurface[Fig1049008７(f)]

３　Discussion　　At２５－２００thereisnoortracetriboＧoxidesonwornsurfacesmetalＧmetalcontactcannotbeavoiＧdedAdhesivewearispredominantwearmechanismTheincreaseofambienttemperatureandfrictionheatwouldreducesurfacehardnessofspheroidalgraphitecastironThuswearrateat２００ismarＧginallyhigherthanthatat２５UnderalowloadalowerincreaseofwearratemaybeattributedtothelubricatingroleofgraphiteHoweverunderahigherloadgraphiteandortheboundarybetweengraphiteand matrixreadilyfractureunderfrictionforcetoleadtorapidincreaseofwearrate　　At４００ triboＧoxideswouldincreaseduetotheelevationofambienttemperatureAlthoughtheamountoftriboＧoxidesrelativelyincreasedtheywerefarlowerthanthoseofsteelsunderthesamecondiＧtions[８－１０]Theirquantityandthickness(＜５μm)werenotenoughtoentirelyavoidthemetalＧmetalcontactInthiscaseoxidativewearandadhesivewearcoexistedAstheloadsurpassed１５０NextruＧsivewearappeared

　　DuringslidinggraphiteisseverelydamagedThespheroidalgraphiteonwornsurfaceswouldbestretchedbyforceCrackswouldappearandpropaＧgatealongtheboundarybetweengraphiteandmaＧtrixthusgraphitedelaminatedfromwornsurfacesWeardebrisofgraphitewouldbegroundtopowderUndertheconditionofhightemperatureandloadgraphitepowderwouldreactwithFe２O３andFe３O４

formedonwornsurfaces　　２C＋Fe３O４mdash３Fe＋２CO２uarr (１)　　３C＋２Fe２O３mdash４Fe＋３CO２uarr (２)　　２C＋O２mdash２CO (３)　　４CO＋Fe３O４mdash３Fe＋４CO２ (４)　　３CO＋Fe２O３mdash２Fe＋３CO２ (５)　　Fig1049008８presentsΔGθ

TＧT diagramofFeＧCＧOsysＧtemasafunctionofambienttemperatureForthereactions(３)(４)and(５)ΔGθ

T＜０thusreactionsspontaneouslyproceedFromthermaldynamicsreＧsultsitcanbesuggestedthatduringthewearofsphＧ

Fig1049008８　ΔGθTＧTdiagramofFeＧCＧOsystem

1048944５８1048944Issue１０　　　　　　　　　WearBehaviorandMechanismofSpheroidalGraphiteCastIron　

eroidalgraphitecastironat４００graphiteisfirstoxidizedtoCOthenreductionreactionsamongCOFe２O３andFe３O４occurThusoxidesaredifficulttoexistonwornsurfaceofspheroidalgraphitecastironwhichcanexpoundthelesstriboＧoxidesintheXRDresultsofwornsurfaces　　AllinallgraphitewasreportedtopossessluＧbricationrole during wearThelubrication rolewouldappearat２５－２００andlowloadThuswearratewasreducedWhenahighloadwasappliedgraphiteandortheboundarybetweengraphiteandmatrixwouldfracturethusthewearincreasedSoitisreadilytoexplainthereasonthatwearrategraduallyincreasedunderalowloadandrapidlyinＧcreasedunderahighloadAt４００duetodeoxiＧdizationfunctionofgraphitetheamountofgraphiteand triboＧoxides would apparently decreasethewearＧreducedrolewouldbeimpairedItcanbesugＧgestedthatelevatedtemperaturewearofspheroidalgraphitecastironisaphysicalandchemicalprocessincludingthefollowingreactionsxFe＋y２O２mdashFexOy２C＋O２mdash２COandFexOy ＋yCOmdashxFe＋yCO２

４　Conclusions　　１)WearrateofspheroidalgraphitecastirongraduallyincreasedunderalowloadandrapidlyenhancedorpotentiallyenhancedunderahighloadWithanincreaseofambienttemperaturewearrateincreasedMicrostructures ofspheroidalgraphitecastironpresentedanobviousinfluenceon wearrateWearresistanceincreasedaccordingtothefolＧlowingordertemperedsorbitetemperedtroostiteandtempered martensiteFriction coefficientinＧcreasedwithincreasingambienttemperatureanddeＧscendedwithincreasingload　　２)At２５－２００noortracetriboＧoxidesexisＧtedonwornsurfacesofspheroidalgraphitecastironadhesivewearprevailedAt４００triboＧoxidesrelＧativelyincreasedbuttheiramountandthickness(＜５μm)werenotenoughtoavoidthemetalＧmetalcontactthusoxidativewearandadhesivewearcoＧexistedAstheloadsurpassed１５０ Nextrusivewearappeared　　３)Graphitepossessedlubricatingfunctiontoreducewearat２５－２００andalowloadAsahighload wasappliedwearrateincreasedbecauseof

fractureofgraphiteandorboundarybetweengraphＧiteandmatrixAt４００ theamountofgraphiteandtriboＧoxidessubstantiallydecreasedduetothedeoxidationroleofgraphiteHencethe wearＧreＧducedfunctionofgraphiteandtriboＧoxideswereimＧpairedElevatedＧtemperature wear of spheroidalgraphitecastironcanbesuggestedtobeaphysicalandchemicalprocessincludingthefollowingreacＧtionsxFe＋y２O２mdashFexOy２C＋O２mdash２CO andFexOy＋yCOmdashxFe＋yCO２

References

[１]　SantisADBartolomeoODIacovielloDetalQuantitativeShapeEvaluationofGraphiteParticlesin DuctileIron [J]JournalofMaterialsProcessingTechnology２００８１９６(１２３)２９２

[２]　QuinnTFJSullivanJLRowsonDMDevelopmentsintheOxidationalTheoryofMildWear[J]TribologyInternational１９８０１３(４)１５３

[３]　WilsonJEStottFHWoodGCTheDevelopmentofWearProtectiveOxidesandTheirInfluenceonSlidingFriction [J]ProceedingstheRoyalofSociety１９８０３６９A５５７

[４]　InmanIADattaSDuHLetalMicroscopyofGlazedLayＧersFormedDuringHighTemperatureSlidingWearat７５０ [J]Wear２００３２５４(５６)４６１

[５]　StraffeliniGTrabuccoDMolinariAOxidativeWearofHeatＧTreatedSteels[J]Wear２００１２５０(１Ｇ１２)４８５

[６]　BarrauOBoherCAnalysisoftheFrictionandWearBehavＧiourofHotWorkToolSteelforForging[J]Wear２００３２５５(７Ｇ１２)１４４４

[７]　GarzaＧMontesＧdeＧOcaNFRainforthW MWearMechanismsExperiencedbyaWorkRollGradeHighSpeedunderDifferentEnvironmentalCondition[J]Wear２００９２６７(１Ｇ４)４４１

[８]　WangSQWeiM XWangFetalTransitionofElevatedTemperatureWear MechanismsandtheOxidativeDelaminaＧtionWearinHotＧWorkingDieSteels[J]TribologyInternaＧtional２０１０４３(３)５７７

[９]　WangSQWeiM XZhaoY TEffectsoftheTriboＧOxideand Matrixon DrySliding WearCharacteristicsand MechaＧnismsofaCastSteel[J]Wear２０１０２６９(５６)４２４

[１０]　WeiMXChenKMWangSQetalAnalysisforWearBeＧhaviorsofOxidativeWear[J]TribologyLetters２０１１４２(１)１

[１１]　RiahiA RAlpasA TWearMapforGreyCastIron [J]Wear２００３２５５４０１

[１２]　LiuYCSchisslerJMMathiaGTheInfluenceofSurfaceOxidationontheWearResistanceofCastIron[J]TribologyInternational１９９５２８(７)４３３

[１３]　HirasataKHayashiKFrictionandWearofSeveralKindsofCastIronsUnderSevereSlidingConditions[J]Wear２００７２６３(１Ｇ６)７９０

[１４]　PrasadBKSlidingWearReponseofCastIronasInfluencedbyMicrostructuralFeaturesandTestCondition[J]MaterialsScienceandEngineering２００７４５６A(１２)３７３

1048944６８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０　

eroidalgraphitecastironat４００graphiteisfirstoxidizedtoCOthenreductionreactionsamongCOFe２O３andFe３O４occurThusoxidesaredifficulttoexistonwornsurfaceofspheroidalgraphitecastironwhichcanexpoundthelesstriboＧoxidesintheXRDresultsofwornsurfaces　　AllinallgraphitewasreportedtopossessluＧbricationrole during wearThelubrication rolewouldappearat２５－２００andlowloadThuswearratewasreducedWhenahighloadwasappliedgraphiteandortheboundarybetweengraphiteandmatrixwouldfracturethusthewearincreasedSoitisreadilytoexplainthereasonthatwearrategraduallyincreasedunderalowloadandrapidlyinＧcreasedunderahighloadAt４００duetodeoxiＧdizationfunctionofgraphitetheamountofgraphiteand triboＧoxides would apparently decreasethewearＧreducedrolewouldbeimpairedItcanbesugＧgestedthatelevatedtemperaturewearofspheroidalgraphitecastironisaphysicalandchemicalprocessincludingthefollowingreactionsxFe＋y２O２mdashFexOy２C＋O２mdash２COandFexOy ＋yCOmdashxFe＋yCO２

４　Conclusions　　１)WearrateofspheroidalgraphitecastirongraduallyincreasedunderalowloadandrapidlyenhancedorpotentiallyenhancedunderahighloadWithanincreaseofambienttemperaturewearrateincreasedMicrostructures ofspheroidalgraphitecastironpresentedanobviousinfluenceon wearrateWearresistanceincreasedaccordingtothefolＧlowingordertemperedsorbitetemperedtroostiteandtempered martensiteFriction coefficientinＧcreasedwithincreasingambienttemperatureanddeＧscendedwithincreasingload　　２)At２５－２００noortracetriboＧoxidesexisＧtedonwornsurfacesofspheroidalgraphitecastironadhesivewearprevailedAt４００triboＧoxidesrelＧativelyincreasedbuttheiramountandthickness(＜５μm)werenotenoughtoavoidthemetalＧmetalcontactthusoxidativewearandadhesivewearcoＧexistedAstheloadsurpassed１５０ Nextrusivewearappeared　　３)Graphitepossessedlubricatingfunctiontoreducewearat２５－２００andalowloadAsahighload wasappliedwearrateincreasedbecauseof

fractureofgraphiteandorboundarybetweengraphＧiteandmatrixAt４００ theamountofgraphiteandtriboＧoxidessubstantiallydecreasedduetothedeoxidationroleofgraphiteHencethe wearＧreＧducedfunctionofgraphiteandtriboＧoxideswereimＧpairedElevatedＧtemperature wear of spheroidalgraphitecastironcanbesuggestedtobeaphysicalandchemicalprocessincludingthefollowingreacＧtionsxFe＋y２O２mdashFexOy２C＋O２mdash２CO andFexOy＋yCOmdashxFe＋yCO２

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[１４]　PrasadBKSlidingWearReponseofCastIronasInfluencedbyMicrostructuralFeaturesandTestCondition[J]MaterialsScienceandEngineering２００７４５６A(１２)３７３

1048944６８1048944 　　　　JournalofIronandSteelResearchInternational　　　　　　　　　　　　　　Vol1049008２０