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Effects

By Brittany Hernandez,2014-07-18 02:25
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Effects

    Effects

    Dec.2007,Volume1,No.1(Monthly)JournalofMaterialsScienceandEngineering,ISSN1934-8959,USA

    ;Effectsofhighpressuretreatingonthephasetransformationkinetics ;ofaustenitetopearliteinlowcarbonandlowalloysteel ;HANZhen.ti

    ;lCollegeofScience,Yans’hanU}liversi0’,Qinhuangdao066004.China)

    ;Abstract:Theeffectsofhighpressuretreatingollthephase ;transformationfromaustenitetopearliteinlowcarbonand1ow ;alloystee1werestudiedbyDSCmethod.Theresultsshowedthat ;thetransformationtemperatureandactivationenergyof ;austenitetopearliteinlowcarbonandlowalloyslee1were ;increased,whilethephasetransformationtimeandAvrami ;exponentnwerebothdecreasedbyhighpressuretreating.In ;addition,thereasonsofthesephenomenawereanalyzed. ;Keywords:lowcarbonandalloysteel;phasetransformation ;kinetics;highpressuretreating

    ;1.IntrOducti0n

    ;Phasetransformationofsteelhasimportant

    ;practicalapplicationowingtothespecialstructureand

    ;propertiesaffectedbythesolidphasetransformation. ;Someworkshaveindicatedthathighpressuretreating ;affectedsolidificationofalloygreatlyandchangedthe ;distributionofphasesinalloyandthenimprovedthe ;propertiesofalloy[i-31.Researchesontheeffectsof ;highpressuretreatingOllstructuresoflowcarbonsteel ;havebeenreported[4-51

    ;,butthereportsabouttheeffects

    ;ofhighpressuretreatingonthesolidphase

    ;transformationwereveryfew.Lowcarbonandlow ;alloysteelisgenerallyusedinthehotrollingstatement ;andthemainsolidphasetransformationisthe ;transformationfromaustenitetopearlite.Therewere ;manyreportsaboutthesolidphasetransformationof ;steelandironresearchedbyusingthethermal ;expansioncoefficient,thermalsimulationmachineand ;metallographicexaminationI6-8].Buttherewerefew ;reportsaboutthesolidphasetransformationofstee1 ;HANZhenli(1966),female,Bachelor,lecturer;research ;ield:physicalpropertiesformaterials.

    ;andironbyusingdifferentailscanningcalorimetry ;(DSC).Inthepresentworks,theeffectsofhighpressure

    ;treatingonthephasetransformationfromausteniteto ;pearlitein1owcarbonandlowalloysteelwerestudied ;byDSCmethod,Theresultswerehelpfultounderstand ;thephasetransformationformaustenitetopearlitein ;lowcarbonandlowalloysteelunderhighpressure ;treating.

    ;2.Experimentalmaterialsandmethods

    ;Theexperimentmaterialisthelowcarbonand ;1owalloysteel,andthechemicalcompositionofthe ;steel(massfraction,%)is:0.18C,0.34Si,l-42Mn, ;0.022P,0.0l8S.Thesamplewaspressurizedinthe ;graphitecannulaandpyrophyllitewasusedas ;pressuretransmittingmedium.Thehighpressure ;treatingwascarriedonaCSIItypecubicpress.The

    ;pressurewas6GPa,andthetemperaturewas750?.

    ;Thethermalanalysisofthespecimenwascarriedout ;onaSTA449Cthermalanalysisinstrument(DSC)and ;thespecimenswereheatedto850?withcoolingrate

    ;of5?/rain,10?/minand20?/min.respectively.The

    ;phasetransformationtemperatureandtransformation ;timeofthetransformationfromaustenitetopearlitein ;lowcarbonand1owalloystee1weretestedbvDSC

    ;curves.Thestagephasetransformationactivation ;energyfEx)wascalculatedbyDoylemethod9J=

    04567Ex(R.T).. ;logB=IogAE[RF(x)]-L2.315

    ;WhereBisthecoolingrate,F(x)isthefunction ;whichonlyrelatedtophasetransformation,Tisthe ;temperature,Risthegasconstant,Aisthefrequency ;61

    ;.

    ;E

    ;........

    ;ff

    ;........

    ;e

    ;..

    ;ctsof

    ;

    ;h

    ;

    ;i

    ;

    ;ghpre

    ;s

;

    ;suretreatingonthephasetransformationkineticsofaustenitetopearliteinlow

    carbonandlowalloysteel

    ;factor,XiSthevolumefractionoftransformationphase ;Xiiscalculatedby:Xi=Si|S.whereSiistheareaofthe ;radiationofheatpeakintheDSCcurvefromthe ;beginningofphasetransformationtoacertain ;temperature.SiSthetota1areaoftheradiationofheat ;peakintheDSCcurve.1ogAE[RF(x)]isaconstant

    ;whenXiSaconstant.The1ogBT..curvewas

    ;obtainedusingtemperaturesmeasuredfromthe ;DSCcurve.Theslopeoftheplotwasobtainedandthe ;stepphasetransformationactivationenergyExwas ;calculated.Avramiexponentnunderacertain ;temperatureisn=.d{ln[.1n(1X)]}/dlnBl0.SOthe

    ;slopeofplotofcurveIn[ln(1X)]-lnBisn.The

    ;hardnessandthemicrostructureofthespecimenswere ;analyzedbvHR150Ahardnesstester.

    ;NEOPHOT21opticalmicroscopeandH800

    ;transmissionelectronmicroscoperespectively. ;3.Resultsanddiscussion

    ;3.1Phasetransformationatconstantcooling

;rate

    ;Fig.1showstheDSCcurvesofthelowcarbon ;and1OWalloystee1.ItcanbefoundthatthereiSa ;exothermalpeakinthecurve,wheneverthecooling ;rateswas5?/min,10?/minor20?/min.Itcan

    ;beconsideredthattheexothermalpeakiscausedby ;thetransformationfromaustenitetopearlite.Fromthe ;DSCcurve,thebeginningtemperature,thepeak ;temperature,theendingtemperatureofphase ;transformationaswellasthephasetransformation ;timewereobtained,whicharepresentedinTableland ;Table2,respectively.

    ;.D

    ;

    ;?

    ;E

    ;?

    ;0

    ;

    ;Z

    ;?

    ;

;?

    ;

    ;?

    ;

    ;Z

    ;1rc

    ;(a)Normalpressure

    ;f’c

    ;(b)Highpressure

    ;Fig.1DSCcurvesoflowcarbonandalloysteel

    ;underdifferentpressures ;62

    ;Table1Temperatureofphasetransformationatdifferentcoolingrates

    ;Effectsofhighpressuretreatingonthephasetransf

    ;ormationkineticsofaustenite ;

    ;t

    ;

    ;op

    ;ea

    ;

    ;rl

;

    ;ite

    ;

    ;in

    ;

    ;lo

    ;

    ;w

    ;

    ;ca

    ;

    ;rb

    ;

    ;on

    ;

    ;a,tl.waIloysteeI

    ;Table2Thephasetransformationtime(S)

    ;atdifferentconditions ;Presu!~C/min)

    ;Itcanbeconcludedfromtheexperimentaldata

    ;thatthehigherthecoolingrateis

    ;,the1owerthe

    ;beginningtemperature,thepeaktemperatureandthe ;endmgtemperatureofphasetransformationare.Under ;ngnpf.essuretreating,thetemperatureof ;transformationfromaustenitetopearliteincreased ;and

    ;thephasetransformationtime.

    ;Becameshorter.when

    ;thecoolingrateis5~C/min

    ;,thebeginningtemperature’

    ;thepeaktemperature,theendingtemperatureofDhase ;tranformationincreaseby9.68~C,9.57~Cand11.62~C. ;respectively,whilethephasetransf0rn1atiOntime ;shorten23.4s

    ;3.2Phasetransformationactivationenergy ;Fg?2showsthecurvesofphasetransf0atiOn

    ;Volumefraction(Xi)versustemperaturefr)inthestee1 ;atdifferentheatingratesdeterminedbytheDSC ;.

    ;AccordingtotemperaturedatainFig.2,Theplotof ;Log(B)atdifferentphasetransformationv01ume ;rractionsanddifferenttemperaturewereobtained ;.as

;showninFig.3,which

    ;Temnerature

    ;TemoeratureT/?

    ;Fig?2Relationshipbetweenthetransform ;atjonvo1ume

    ;fractionandtemperatureunder

    ;?

    ;?

    ;differentcoolingrates

    ;T/10K.

    ;T/104K

    ;Fjg.3TheplotofLog(B)--Tatdifferentphase

    ;transformationvolumefraction

    ;ShowedalinerrelationofLog(B)VST.Bythis

    ;lope,thetransformationactivationenergy(Ex)is

    ;caJculatedbyDoylemethod

    ;,asshowninFig.4.Itcan

    ;beseenfromFig.4thatthephasetransf0mation ;actiVationenergyfortwosamplesalemuchhighe ;rat

    ;63

    ;gI1.JJ0SrI00暑星0qT_

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