Experimental and simulational studies of the relationship between stress and microstructure in carbon steel
著者 Che Le
著者別名 車, 磊
journal or
publication title
博士学位論文要旨 論文内容の要旨および論文審査 結果の要旨／金沢大学大学院自然科学研究科
volume 平成20年6月
page range 50‑54
year 2008‑06‑01
URL http://hdl.handle.net/2297/26795
氏名 学位の種類 学位記番号 学位授与の日付 学位授与の要件 学位授与の題目
車嘉 博士（工学）
博甲第９４７号 平成１９年９月２８日
課程博士(学位規則第４条第１項）
ExperimentalandSimulationalStudiesoftheRelationshipbetweenStressand
MicrostructuremCarbonSteel
(実験およびシミュレーションによる炭素鋼の応力と組織の関係に関する研究）
廣瀬幸雄（自然科学研究科・特任教授）
山越憲一（自然科学研究科・教授)，佐々木敏彦（教育学部・教授)，
北川和夫（自然科学研究科・教授)，安達正明（自然科学研究科・教授）
論文審査委員（主査）
論文審査委員（副査）
Abstract
Thisthesisisaimedtostudystress-microstructurerelationshipsmmechanicamydefOrmed carbonsteelsusingtheX-raydiffractiontechnique，Ｔｂinvestigatestress-microstructure rclationshipanditseffectonmechanicalbehaviorofcarbonsteels,fOurkindsofspecimenwith differentvolumefractionsandparticlesizesofsphcroidalcementite，arepreparedStressesin thecementitephasearemeasuredbyconventionalX-raydiffractioninstrumentafteraspecific trcatmentonthcspecimensurface,Theeffectsofvolumefractionandparticlesizeofspheroidal cemcntitcontheinter-phascstressstateareestimatedincarbonsteelsundermsimfOur-point bendingandtensiletests・Tbestimatethestressstatesmtwophases,theX-rayelasticconstants oftwophasesinsingle-phascstate(PXEC)aredeterminedpreviouslybytheexperimental X-rayelasticconstantsofthoseincompositestate(CXEC)．
Forabetterunderstandmgofthematerialmcchanicalresponse，theplasticitydifference betweentheferriteandthecementiteduringthedefOnnationprocessingisinvestigatedthrough estimatingmisfitofplasticstrambetweenthemmdirectlybyX-raymeasurement・Associating withtheopticalobscrvation,thedefOnnationbehaviorsofsphcroidalcementiteparticleinthe plasticallydefOrmedsteelarecharacterizedfromitsresidualstressstateevolution・
Finallyltheeffectsofvolumefractionandparticlesizeofthespheriodalcementiteonintemal stressstatesincarbonsteclsu､derthethermalandmechanicalloadingsarealsosimulatedusing acomputationalmodelwhichappliesthefiniteelementmethodatthemicroscale．
論文要旨
Imncarbidc,usuallycanedcementite,hastllechcncalfbnnulaofFC3Cmisfbundasa nnnorphasemalInostallsteels・A1tllougllminoLitgreatlyaffectstheplopertiesofsteel becauseFe3CismucllharderandlnolerigidtllanaretheotllerphasesmstecL
IthasbeenintroducedmthepreⅥousstudiesthatcementitehasobviouseffectsontlle intemalstressesgeneratedduringtheplasticdefbnnationofsteels,andthatthestressstates maybeattributedtotheinhomogeneousmechanicalprOpertiesofsteels・Inthesesmdies，
steelswithspheroidalandlamellarcementiteareusedtoanalyzelheＣｆfectofcementitc particlesizeontheintemalstressstate・Hisobscrvedthattheresidualstressmthematlixof tllesteelwitlllamenarcementiteishigllertllanthatintllesteelwithspheloidalcementite・Yet，
thereismlackofcompalisoninfbnnalionabouttheresidualstressmtheircementiteparticles・
TY1isisbecausetllestressmthelamellarcementitecouldnotbedetemmnedprecisely9dueto thestrongpeakbroademngcausedbytlleelasticandplasticstrains・nlequantitative compansonsplovidedmtlletheoreticalstudiesarealsorestrictedtostressesbetweenｔｈｃ
－５０－
Splleloidalandlamemarcementiteparticlesbecauseofthcwidevalietyoftlleirshapes・
MOIeov則becausetlledefbnnationandstrengthofsteclsisprofbundlyaffbctedbytllc
presenceofcementite，itisinevitabletotakeintoaccounttlledefbnnationbehaviolsof
cenlentite・Tlledefbnnabilityofcemcntiteincarbonsteel,howevcLiscompmcatcdbecauseof itsdepcndenceontempcratureandmiCrostructuralmolphology6Hrplasticallydefmmed peallitesteel,ithasbeenrecoglizedtllatthereisaneffectofthiCknessofthecementiteplates ontheirdefOnnability:tensiledefOnnationoftllickcelnentitelame]Uafavolsbrittlefipacture，
whereascompressionordrawingandlhincenlentitealeabletodefbmplasticanybefbre fractureocculs.Ⅲhasalsobeenobservedtllataproportionofthccementitedissolvesmthe
high-defbmledpealliteandspheriodizedsteeLInthesestudies,thedefbrmationactivityof
cementitcareusuallydisCussedbystudyingchangesinthedislocationsub-structureof cenlentiteplatestlⅡougllOpticalteChnologiessucllasscammngelectlonmicroscopy(SEM）
andtransmittingelectronmcroscOpy(IEM)．
Withthisaim,tllisthesisistodiscusstheeffectsofccmentiteonthemecllanicalprOperties ofcarbonsteelshougllestimatmgthestressevolutionbellaviorofthecementitephasein defblmedsteels､Inaddition,itspulposeisalsotoidentifytlledefbmlationbehaviorof cementiteparticlesmplasticallydefbnnedsteclsandtocolrelateittotlleresidualstlessstate evolutionlllethesisconsistsof7chapters，andtheimportantcontentsandrcsultsof
eachchapteraresummarizcdasfO11ows：
Chapterlisthegeneralintroductionofthisthesis、InthischapteLbackground，
objectivesandcontentsofthethesisareintroducedbriefly6
InChaptcrZ，atecllniquefOrspecificsurfacetreatmentisintroduced，Thissurface treatmenttechniquemakesacontributiontostudyingtheconstitUentphase,ｗｈｉｃｈｈａｓ ａｎｅｓｐｅｃｉａｌｌｏｗｖｏｌｕｍｅｆｍｃtionincompositematerials，usingtheX-raydiffraction technique・miswellknownthatstressesinthecementiteareusuallydifficulttomeasure bydiffractionmethodbecauscofthelowvolumefractionofcementiteinsteel・Inthe presentstudylasurfacetreaｔｍｅｎｔｉｓｕｓｅｄｔｏｒｅａｌｉｚｅｔｈｅｓｔｒｅｓｓｍeasurementonthe cementitcbyX-rayundertheconventionalconditions・Thcsurfacctreatmentincludes
thefOurstepsofsandpapering,electrocllemicalpolishing,wetpolishingandchemical etClmg・Afterthesurfacetreatment，availabilityofthisteclmiquconthestress measurementisalsodiscussed・Itincludcsobservationonnlicrographofthespecimen，ｓ ｓｕｒｆａｃｅｂｙＳＥＭ，measurementonsurfaceroughness，confinnationondiffraction intensityofthecementiteandinvcstigationonstress-strainrelationshipsinthetwo phases・Resultsshowthatthedifficultyofmeasurementonstressstateinthccementite phaseisremovedsuccessfilllybyapplyingthistechniqueJtｉｓａｌｓｏｐｒｏｖｅｄｔｈatthis methodissimplerthaninstrumentmodification,andtheeffectivenessandreliabilityfOr stressmeasurementoncementitephaseareimproved・Howeverぅtheshortcomingofthis techniqueisthatitisnotsuitablefCrspecimcnswithacomplicatedstructure・
ＩｎＣｈａｐｔｅｒ３,fOrabetteraccuracyonestimatingthestressstatesofeacllphaseinthe compositematerial，theX-rayelasticconstantsofmaterialinthesingle-phasestate
－５１－
（pnC)areinvestigatedBecauseitisdifficulttoobtainasingle-phasecementitebulk material，thePXECofcenlcntitehavenevcrbeenreporteduntilnow6hthepresent studylfirstlylX-rayclasticconstantsofmatcrialinthecompositcstatc(CXEC)fOrthc fCrriteandthecementitephaｓｅｓｉｎｆＯｕｒｋindsofspecimensaredeterminedbya fOur-pomtbendingexperiment；secondly§ｔｈｅＰＸＥＣｆＯｒｔｈｅｔｗｏｐｈａｓｅｓａｒｅｃａｌｃｕlated fromtheCXECusmgtherelationsllipbetwcenthemthatwasreportedinthepreviOus
study6ExperimentalresultsindicatethatCXECfOrallofthenlicrostructuresmeasureｄ ｍｔｈｉｓｓtudyarealmosttllesame､Forthc211ferritepeak,ｔｈｅＰＸＥＣａｒｅｓｉｍｉｌａｒｆＯｒａｌｌ ｏｆｔｈｅｍｉcrostructures;fDrthe250celnentitepeak,theyraredetenninedintherangeof ０．２２~O26andEhG,intherangcofZ62~Ｚ８２ＧＰａ・
ＩｎＣｈａｐｔｅｒ４,effectsofthemicrostmctureofcementiteontheinter-phasestressstate incarbonsteelsarediscussed，becauseitisconcludedfiompreviousstudiesthatthe microstructuralfeatureofcementiteaffectsstronglyontllemecllanicalpropertiesofcarbon steels.]Fbrthcfirsttilnc,ａｓｗｅｋｎｏｗうthecffectsofbothvolumefiFactionandparticle sizeofspheroidalcementiteonstressstatesofcarbonsteelsarebothestinlatedbyX-ray6
ThefindmgsleadtotllefC11owmgconclusions：
（１）hthcloadingprocess,thcmacroscopicstrcssincreascswithincreasingthc volumefractionofthecementiteparticlcfOragivenparticlesizeandplasticstrainand increaseswithdecreasingparticlesize，fOragivensimilarvolumefractionof cenlentite;thcphascstressintheferriteincreases,butthatinthecementitedecreases
withincreaslngvolumefractionoftllecementitefora画venparticlesizeandplastic strai､;fDragivensimilarvolumefractionofcementite,thestressesintheferriteand cementitemcreasewithdecreasingcementiteparticlesizc．
（２）Aftertheloadingrelaxation,ｆｂｒａｇＭｎｐａｒｔｉｃｌｅｓｉｚｅａｎｄｐｌａｓｔｉｃｓtrain,the
residualstressintheferriteincreases，butthatinthecementitedecreaseswith increasingvolumefractionofthecementite;ｆbragivenvolumefractionofcementite，
thcrcsidualstressesintheferriteandthecementiteincreasewithdecreasingcementite
particlesize、
hChapter5,dcfOnnabilityofspheroidalcementiteiscllaracterizedbyresidualstress
measurement・ItisdifferentfromthepreviousStudies，ｉｎｗｈｉｃhthedefOnnation activitiesofcementiteareusuallydiscussedbystudyingcllangesinthedislocation sub-structureofcemcntiteplatesthroughopticaltechnologiessuchasscanningelectron microscopy(SEM)andtranslnittingclcctronmicroscopy(rEM).Theaimofourstudy istoidentifythedefOnnationbehaviorsofthecementiteparticlebyX-raydiffractioｎ
ａｎｄｔｏｃｏｒｒｅｌａｔｅｉｔｔｏｔｈｅｒｅｓｉｄｕａｌstressstateevolution・IT1estressstateevolutionsfCr bothphasesduringanm-sjZzJfour‐pointbendingtestandafterauniaxialtcnsiletestare wellfOllowedbyX-raydiffraction・Aftereachtensileloading，opticalobservationis
madetocolTelatethedetenninedresidualstressstatewiththemicrostructure・The couplingoftechniqueshelpsustocharacterizethedefOnnationcvolutionsofthcferritc andthespheroidalcementiteinthecarbonstｅｅＬＩｎｓｕｍｍａｒｙ，theirdifferentdefbnnation
behaviorsarecharacterizedasfO11ows：
－５２－
othefirststepwheretheferriteandthecenlentitehaveanelasticbehavior，
・mthesecondstcp,theccmentiteisstillelasticandtheferriteisplastic，
。inthetllirdstep，plasticstrainrelaxationoccursintheferritcbutcemcntitestill defmnselasticallyうfinallylthecementitebreaks・
Ｉｎｃhapter6,mternalstressstatesincarbonsteelsunderthethemalandmechanical loadmgsareinvestigatedusingacomputationalmodelwhic]lappliesthefimteelement methodatthemicroscalc、Becausethepreviousstudieshavereportedthatthe miclostmcturalfeatureofcementitealsoaffectsstronglyontlletllemo-mecllanical propertyofcarbonsteclsoHowcv則thestressevolutionsofsteelsundcrthe tllemo-mechanicalloadingsaredifficUlttoinvestigatebecauseoflimitationsofstress measurementinstmncnts・Filrthcnnore,itisimpossibletoindcpcndentlyvarythevarious microstmcturalparamctersandtlmsisolatetheireffectsonstresscvolutions・Withthisaim，
acomputationalmodelwhicllappliesthefiniteelementmetllodattllemicroscaleisusedm tllepresentstudy6EffCctsofvolumehactionandparticlesizeofthespheriodalcelncntiteon thcintemalstressstatesunderthcthennalandmecllanicalloadingsaresimulatedmbverify thercliabilityofthccomputationalsimmations，ｔｈｅｒｅsidualstresscsintheconstitucnt phasesaremeasuredbymeansofX-raystressdiffractionteclmique､Resultsshowthat thecomputationalsimulationsfitwellwiththeexperimentaldata，andthe
microstmcture-basedmodelisvalidated
Asmentionedabove，tmsthesisintroducesaneffectivemethodtoinvestigatestress evolutionbehaviorsofthecementiteincarbonsteelsusingtheX-raydiffraction techniquelYlcstress-microstructurerclationships，espcciallytheeffectsofthevolume fractionandparticlesizcofthecementiteonthestresscvolutionbehaviorsofdefOnned carbonsteelsaresystematicallyinvcstigatedtllrougllexperimentalmeasurementsand computationalsimulations・Theresultsobtainedareexpectedtobecontributiveto promotingthestudyonnlechanicalmetallurgy．
－５３－
学位論文審査結果の要旨
平成１９年８月１日に第１回学位論文審査委員会を開催し,提出された学位論文及び関係資料 に基づき論文内容を詳細に検討した．さらに，平成１９年８月１日に行われた口頭発表後に，第
２回学位論文審査委員会を開き，協議の結果，以下のように判定した．
本論文は材料の弾`性および塑`性変形挙動に対し，ミクロな視点で応力を通して解析を行い，そ れを明らかにしたものである…本研究では特に球状セメンタイト相とフェライト相で構成された 炭素鋼を対象とした．先ず，セメンタイト相からのＸ線回折測定は通常非常に困難であるため，
特殊な表面処理を考案して,実験室の比較的弱いＸ線源での高角度セメンタイトの応力測定を行 う方法を開発した.次に炭素鋼の強度に対する材料の体積割合や形状の大きさの影響を調べるた めに，セメンタイトの体積率と粒径が異なる試験片を作製し，またセメンタイト相とフェライト 相からなる二相材料として扱うことで,材料の強度および応力挙動に対するセメンタイトの体積 割合や大きさの影響を検討した．そしてその残留応力測定を利用して，機械加工を受けた炭素鋼 におけるセメンタイト相とフェライト相の変形挙動を推測できる方法を提案した．さらに材料の 組織をモデルとした有限要素法を用いて，機械変形と熱変形による材料の応力挙動を検討した．
以上の内容は，今後の炭素鋼の工具開発および材料開発に大きく貢献できるものと確信する．
以上，本論文は，博士（工学）の学位論文に値するものと判定する．
－５４－
