407-paper-Effect of ultrasonic treatment on solidi

SECRETARIATUSE;Headershouldbeblank.SECRETARIATUSE;FootershouldbeblankEffectofultrasonictreatmentonsolidificationstructureofsteelsLIUQingmei,ZHANGYong,SONGYaoling，QIFeipeng,ZHAIQijie(SchoolofMaterialsScienceandEngineering,ShanghaiUniversity,Shanghai20072，China)Abstract:Inthispaper,therecentresearchprogressconductedintheeffectofultrasonictreatmentonstructurerefinementofsteelsisbrieflygeneralized.Theresultsshowtothatultrasonictreatmentintothemeltscanrefinesolidificationstructureoflow-carbon,high-carbonandstainlesssteel.And,themechanicalpropertiesofsteelsareimprovedremarkably.Keywords:Ultrasonic;Structurerefinement;equiaxedgrain0IntroductionInrecentyears,manykindsofphysicalfieldsareusedinthesolidificationprocessofmetals.Andasakindofhigh-frequencyacousticwave,itisdemonstratedthatultrasoniccreatesthecavitation,acousticstreamingandelectricaleffectswhenitpropagatesintotheliquidmedium[1,2].Thus,ultrasonictreatmentshowsexcellentresultsonrefininggrainstructureandimprovingmechanicalproperties[3-8].Inthispaper,weimposeultrasonicvibrationondifferentsteelsduringsolidificationandcharacterizetheeffectofultrasoniconmetalsinvirtueoftheresultsofmicrostructureandotherproperties.Basedonexperimentalresults,themechanismofultrasonicvibrationonsteelsisdiscussedbriefly.1EFFECTOFULTRASONICTREATMENTOFLOW-CARBONSTEELThecompositionoflow-carbonsteelis0.05%CandFe.Themicrostructureoflow-carbonsteelwithoutandwith700WUTisshowninFig1.Itisfoundthatwithoutacousticvibration,themicrostructureiscoarseanditsaveragegrainsizeisseveralmillimeters.Upon700WUT,thecoarsestructureisbrokenupintofinerequiaxedgrains.2EFFECTOFULTRASONICTREATMENTOFHIGH-CARBONSTEELFig1Microstructureoflow-carbonsteelwithvariousprocesses(a)0W(b)700W50μm(a)50μm(b)SECRETARIATUSE;Headershouldbeblank.SECRETARIATUSE;FootershouldbeblankMicrostructureofT10steel(C:0.99%)withoutandwith700WultrasonictreatmentisdepictedinFig2.Itisshownthatwithoutultrasonictreatment,grainsarecoarsewithanaveragesizeof820μm(Fig2(a)).However,whentheappliedultrasonicpoweris700W,theT10grainsaftertreatmentarefineequiaxedmorphologywithaveragesizeof315μm(Fig2(b)).Table1listssomemechanicalcharacteristicsastensilestrengthandductilityofT10steelwithoutandwithultrasonictreatment.Fromthistable,itisseenthattensilestrengthisimprovedfrom635MPawithoutultrasonictreatmentto870MPawith700Wultrasonictreatment,whichhasanincrementofabout37%.Correspondingly,theultrasonictreatmentresultsalsointheductility1.8timesfrom9.4%to16.7%.SEMfractographsofsampleswithoutandwithultrasonictreatmentareshowninFig3.Thebrittlefeatureisobviouslydisplayedinthefractographsamplewithoutultrasonictreatment(Fig3(a)).Comparatively,thesamplewithultrasonictreatmentsexhibitsthecombinationofductileandbrittlefracturesurfacesthatarecoveredwithdimples(Fig3(b)).Table1MechanicalpropertiesofT10steelwithvariousprocessesTS/MPa/EL/%/WITHOUTUT6359.4WITHUT87016.7(a)(b)Fig2MicrostructureofT10steelwithvariousprocesses(a)0W(b)700WSECRETARIATUSE;Headershouldbeblank.SECRETARIATUSE;Footershouldbeblank3EFFECTOFULTRASONICTREATMENTOFAUSTENITICSTRINLESSSTEELFig4offersthecomparisonofEBSDresultswithoutandwith700WUT.Intheevaluation,neighboringpointsshowingadifferenceinorientationlargerthat150aredefinedasgrainboundariesandcolorblack,andsimilarlyneighboringpointswithadifferenceinorientationlargerthan20aredefinedassub-grainboundariesandcolorgrey.Inaddition,somescatteredpointsingrainsrepresentdislocations.Hence,forexample,arrowheadAandBrepresentthegrainboundary，arrowheadCisthesub-grainboundaryandarrowheadDandEdenotedislocations.ItcanbeobservedinFig4(a)thatwithoutUT,grainsarecoarsecolumnarstructureandalargenumberofdislocationsaredistributedingrainsnon-uniformly.After700WUT,however,thereisanincreaseintheoccurrenceofgrainboundariesandanapproximatelyequiaxedstructurewithafineraveragesizeareachieved.Also,thenumberofdislocationsingrainsisdecreasedremarkably,whereasalargeincreaseinthenumberofsub-grainboundariescanbeseeningrains.Table2listssomemechanicalcharacteristicsastensilestrength(TS),elongationpercent(EL)andreductionofareaatfracture(RA)ofthesteelsinbothconditions.Asshowninthistable,thetensilestrengthofthesampleisimprovedfrom649MPawithoutUTto731MPawith700WUT.Andcorrespondingelongationpercentisenhancedfrom70.9%to79.5%.Moreover,thefractureareawithUTissmallerthanthatwithoutUT.Theresultsindicateagoodcorrelationbetweenthesolidificationstructureandmechanicalproperties.TheSEMmicrographsoffracturesurfacefeaturesofthesteelstreatedwithoutandwith600WUTareshowninFig5.Itcanbeconcludedfromthefracturesurfacefeaturesthatbothtensiletestsamplesrepresentacharacteristicofductilefailure.ButthesurfaceductilefeatureofsampletreatedwithUTismoreobviousthanthatofsampleuntreatedwithultrasonic.FractureofthesampletreatedwithUTispredominantlyductilewithevidenceofplasticdeformationandmicroscopicfeaturescomprisingagreatdealofdeepdimples(Fig5(b)).(a)(b)Fig3FracturemorphologiesofT10steelwithvariousprocesses(a)0W(b)700WSECRETARIATUSE;Headershouldbeblank.SECRETARIATUSE;FootershouldbeblankTable2Mechanicalpropertiesof1Cr18Ni9Tiwithvar