灰鑄鐵的凝固結(jié)晶過(guò)程-外文文獻(xiàn)翻譯

1、山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文外文文獻(xiàn)：SolidificationofgraycastironSolidificationofgraycastironAbstractThisarticleinvestigatesthesolidificationofhypo,eutecticandhypereutecticgraycastirons,usingnoveltechniquesdevelopedbytheauthors.Thenatureoftherevealedmacroandmicrostructuresuggeststhatthesolidificationmechanismisdif

2、ferentfromthatusuallyaccepted.Keywords:Solidification;Grayiron1.IntroductionSeveralauthorshavestudiedthesolidificationofeutecticgraycastironofflakegraphitemorphology(GI)1刀.Commonly,theeutecticsolidificationunitisrepresentedbyanearlysphericalshapeofausteniteandgraphite,asshowninFig.1.Thereisgeneralag

3、reementtoconsiderthatausteniteandgraphitegrowcooperatively,beingbothincontactwiththeliquidphase.ThispictureofthesolidificationofGIissupportedbythemorphologyofthegraphiteflakes,thatresemblearosette,asshowninFig.2,andbythefactthattheinclusions,generallyassociatedtothemicrosegregationatthelasttofreezem

4、elt,arelocatedbetweensuchunits.SteadsreagentrevealsthemicrosegregationofphosphorusinGI,anditcandelineatetheunitsschematicallyrepresentedinFig.1inhighPirons,usuallyreferredtoaseutectells8.Sinceaustenitedendritesarenotreadilydiscernible,exceptingrayironscontainingtypesndgraphite,theirformationandgrowt

5、hcharacteristicsinGIhavereceivedlimitedattention.SomeresearchershaveconsideredtheroleofaustenitedendritesinthesolidificationofGI2,6,7.ThereisnodoubtthatausteniteofhypoeutecticGIgrowsdendritically.Ontheotherhand,mostoftheliteratureworkstatethataustenitecangrowwithothermorphologieswhenthecarboncontent

6、reachesorexceedstheeutectic3,7.Duringthelastyearstheauthorsofthepresentarticlecarriedoutinvestigationsthatchallengedthevalidityofthemorefirmlyestablishedmodelsofthesolidificationofductileiron(DI)9T1.Theuseofaspeciallydevelopedtechnique,thatallowsto山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文revealthesolidificationmacrostructu

7、reofDI,combinedwiththeuseofcolormetallographytechniquesthatrevealthemicrosegregationpattern,showedthatthemacrostructureofDIisformedbyrelativelylargeaustenitegrains,thatcontainaverylargenumbersofgraphitenodules.Thiswasthecaseforhypoeutectic,eutectic,andalsohypereutecticDI.Theobjectiveofthisstudyistoi

8、nvestigatethesolidificationmechanismofGIbyusingthemicroandmacroscopictechniques,successfullyappliedforDIinearlierstudies.Experimentalmethods2.1. MaterialsThemeltsutilizedinthepresentstudywereproducedbyusinga50kgmediumfrequencyinductionmeltingfurnace.Lowmanganesepigiron,steelscrapandferroalloyswereus

9、edasrawmaterials.Meltswerecastinresinbondedsandmouldstoproduceroundbarsof20,30and46mmdiameter.Table1liststhechemicalcompositionofthealloysused.ThemeltswerealloyedwithCuandNiinordertoprovideenoughaustemperabilitytocarryouttheDAASmacrographytechnique,whichisdescribedbelow.2.2. MicrographictechniqueThe

10、coloretchingtechniquerevealsthesolidificationmicrostructurethroughtheuseofareagentthatbringsupthemicrosegregationpatternsgeneratedduringsolidification12.Theetchingreagentismadeof10gNaOH,40gKOH,10gpicricacidand50mldistilledwater.Itmustbepreparedandhandledwithgreatcare,sinceitiscausticandtoxic.Etching

11、iscarriedoutat1203(278F)forabout2min.Fig.1.Schematic川ustrationofthesolidificationunitofeutecticGI.山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文Fig.2.Morphologyofgraphite?akesofeutecticGI.2.3. MacrographictechniqueInordertoallowtheobservationofthemacrostructureofDIitisnecessarytocarryoutathermalprocesscalledDAAS(DirectAustemper

12、ingAfterSolidification)9.Inthisprocess,thecastpartsareshakenoutfromthemouldshortaftercasting,whentheirtemperatureisapproximately950C,andtransferredtoafurnaceheldat900C,wheretheyremainfor30mintoallowtemperaturestabilization.Thepartsarethenaustemperedinamoltensaltbathheldat360C,for90min.Arelativelyhig

13、haustemperingtemperatureisusedtoobtainahighamountofretainedausteniteaftertreatment.AftertheDAAStreatment,thematrixmicrostructureshowsafinemixtureofferriteneedlesandretainedaustenite.AschematicofthethermalcycleisshowninFig.3a.TheDAAStreatmentiscertainlylaboriousandcannotbeusedunderusualmoldingcircums

14、tances.Nevertheless,itistheonlymethodcapableofrevealinglowalloyductilecastironmacrostructures,tothebestoftheauthorsknowledge.Afterthisprocedure,theretainedaustenitekeepsthecrystallineorientationdefinedduringsolidification.Therefore,etchingwithPicral(5%)revealsthegrainstructureofthesolidificationaust

15、enite.Itmustbeemphasizedthatsuchmacrostructurewillbenotvisibleafteraconventionalaustemperingtreatment,asthatshownschematicallyinFig.3b,sincethemicrostructurewillbeformedstartingfromafinegrainrecrystallizedaustenitestructureobtainedafteraustenitizing.ThistechniquehasnotbeenappliedbeforetoGI.Asafirsta

16、pproachitwillbeusedonGIfollowingthesameproceduredevelopedforDI.山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文Fig.3.(a)DAASthermalcycle,(b)regularaustemperingthermalcycle.TjibleTjibleI IMeli.Meli.Chemis.1caiYipLuiiionChemis.1caiYipLuiiionw.L%w.L%CECSi.CECSi.MDCUNiNi11,211911,2119口比3.943.9423工$40J3d40J3d曲內(nèi)Q,46Q,46Eumjlk4.27MS2,*5

17、0,22Eumjlk4.27MS2,*50,22也心口E5E5H Hpereuipereui3 3ik4.64ik4.6433J3J3 3昌IMSIMSd d6,6,CL:carbonequiknLCL:carbonequiknL3.ResultsanddiscussionFig.4a-cshowtheunetchedmicrostructureofthe30mmdiametersamplesofhypoeutectic,eutectic,andhypereutecticmelts,respectively.PredominatelytypeAlamellargraphitestructure

18、isobservedinallcases.Fig.5acshowthemacrostructurerevealedbytheDAAStechniqueonthesamesamplesofFig.4.Inallcases,arelativelylargegrainedmacrostructureisobservedonthesamplesurface,includingthehypereutecticalloy.Thisis,tothebestofourknowledge,thefirsttimesuchstructureisrevealedonsandcastGIsamplessolidi?e

19、dnormally.Thegrains,orsolidificationunits,aremuchlargerthanexpectedforthesolidificationmodelbasedonnearlysphericalunits(eutecticcells)representedinFig.1.Asitwasmentionedbefore,theeutecticcellsareusuallyrevealedthroughthemicrosegregationofphosphorusbytheapplicationoftheSteadreagent.Nevertheless,itisi

20、mportanttopointoutthatthismethoddoesnotprovethatareasseparatedbymicrosegregationofphosphorusareinfactdifferentgrains,becauseitdoesnotetchdi?erentiallygrains,orvolumes,ofdifferentcrystalorientation.Itisremarkablethatthegrainstructurehassimilarsizeamongsamplesofthesamediameter,regardlessitscarbonequiv

21、alent.TheonlydifferenceisthatthehypoeutecticGIshowsamorepronouncedcolumnarstructure.Fig.6showsthemacrostructureof山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文thesamplesof20,30and46mmdiameterofthehypereutecticmelt.Notethatthegrainsizeslightlyincreaseswhenthediameterincreases.Fig.4.Microstructureofunetchedsamplesof30mmroundbars.

22、(a)Hypoeutecticmelt,(b)eutecticmelt,(c)hypereutecticmelt.山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文Fig.5.Macrostructureof30mmdiameterroundbars.(a)Hypoeutecticmelt,(b)eutecticmelt,(c)hypereutecticmelt.Thepresenceofsuchlargegrainsindicatesthatlargeportionsofthesamplehavethe山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文sameaustenitecrystallineorientation.

23、Itshouldthenbepossibletofindindicationsofaustenitegrowthinsideasolidificationgrain.Thiswasinvestigatedbytracingthemicrosegregationinsideeachgrainbyusingthecolormetallographytechnique.TheresultsshowthepresenceofaustenitedendritesforGIofallcarbonequivalentvaluesinvestigated.Asanexample,Fig.7showstheso

24、lidificationmicrostructureofthehypereutecticmelt.Itisremarkablethatthegraphitecoloniesdonotshowaninterdendriticmorphology,butareimmersedinthedendritesteminmanyplaces,aspointedbythearrows.Thisexplainswhysuchdendriteshavenotbeenidentifiedbefore,throughtheobservationofthedistributionofflakegraphite.Ita

25、lsosuggeststhatflakegraphitemaygrowtosomeextent,mostprobablyduringthelaststagesofsolidificationorduringsolidstategraphitization,notincontactwiththemeltbutbyCdiffusionthroughanausteniteenvelope.山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文Fig.6.Macrostructureofroundbarsofhypereutecticmelt.(a)20mm,(b)30mm,(c)46mm.Thepresenceofsu

26、chlargegrainsandthemorphologyofmicrosegregationpatternssuggestthattheso-calledeutecticcellsarenotactualindividualsolidificationunits,butlargegroupsofthemhaveacommonorigininaverylargeaustenitedendrite.TheobservationsleadtoproposethefollowingexplanationofGIsolidification.Verythinorskinnyaustenitedendr

27、itesnucleateandgrowtolargeextentat,orbelow,thetemperaturespointedonFig.8.Anygraphiteparticlesthatmaybepresentinthemeltatthisstageareengulfedbythisdendriticarray.ThisismostprobablyeffectivelytakingplaceinthecaseofhypereutecticGI.Existingparticlesattheintradendriticmelt,ornewlynucleatedgraphitenucleia

28、tthesupersaturatedintradendriticmelt,makecontactwithaustenitebranchesandbegincooperativegrowth,formingtheunitscalledeutecticcells.Itispossibletospeculatethat,forbothhypereutecticandhypoeutecticGI,thereisnotanucleationeventforeutecticcells,butthesolidificationprocessisdominatedbytheinitialgrowthofrel

29、ativelylargeaustenitedendritesthatprovidealargedensityofausteniteseedsonwhichtheformerlycalledeutecticcellscanform.Theseunitsarenotsolidificationgrains,asitiscommonlyaccepted.Agreatnumberofthemarepresentintoeachgrain.山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文NoausteniteNoaustenitenucleationatnucleationat, ,HypoeutecticHyper

30、eutecticHypoeutecticHypereutecticFig.8.SchematicsectionoftheeutecticregionoftheFeCequilibriumdiagram.Theproposedmechanismissupportedbyobservationsofotherauthors.RuffandWallace2pointoutthataustenitedendritesarepresentingrayironofhypo,hyperandeutecticcomposition,andthattheocleationofeutecticaustenitet

31、akesplaceorandneartheprimaryaustenitedendritesDioszegietal.7statethatforhypoeutecticalloystheplacefortheeutecticnucleationisbelievedtobeclosetotheinterfaceofprimaryausteniteinthesegregatedliquid.Thesestudiesdonotstatethatthereisnonewnucleationofaustenite,buttheysuggestthatthereisalinkbetweenaustenit

32、edendritesandthenucleationofeutecticaustenite.Numerousexperimentshavedemonstratedthatthenumberofeutecticcellsperunitareaisincreasedbytheadditionofinoculantstothemelt.Thesolidificationmodelproposedinthisworkdoesnotdenythismechanism.Itisclearthattheinoculationprocessincreasesthenucleationrateofgraphit

33、e,thenalargernumberofgraphitenucleiwouldcauseamorefrequentinteractionbetweenaustenitebranchesandgraphite,leadingtoalargernumberofsmallerunitsofcoupledeutecticcells.Asitiswellknowntheobservationsoftheeutecticcellsisveryusefultorelatesolidificationstructurecharacteristicswithpropertiesofthecastpart.山東

34、建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文ConclusionsTheDAASmacrographictechniquehasbeensuccessfullyappliedtorevealthemacrostructureofhypo,hyperandeutecticflakegraycastirons.Themacrostructureofsandcasthypo,hyperandeutecticGIshowrelativelylargegrainsinallFig.7.Blackandwhiteprintofhypereutecticmeltaftercoloretching.cases.Colorm

35、etallographytechniqueswereusedtorevealtheaustenitedendriteslocationsanditsinteractionwithgraphiteflakes.Graphiteflakesfrequentlycrossaustenitedendritestems,suggestingthatsuchflakescancontinuegrowingaftertheyhavebeenenvelopedbyaustenite.Thisstudyprovesthataustenitedendritegrowthispredominantnotonlyfo

36、rhypoeutecticbutalsoforhypereutecticgrayirons.Theunitsusuallycalledeutectellsarenotsolidificationgrains,asitiscommonlyaccepted.Agreatnumberofthemarepresentintoeachgrain.References1 MorroghH,OlfieldW.IronSteel1959;32:479.2 RuffGF,WallaceJF.AFSTrans1976;84:705.3 AngusHT.CastIron:PhysicalandEngineering

37、Properties.Butterworths;1976.p.5.4 StefanescuDM.MetalsHandbook,Casting.ASMInternational;1988.p.168.5 RoviglioneAN.DoctoralThesis.NationalUniversityofLaPlata,Argentina.1998.6 MiyakeH,OkadaA.AFSTrans1998;106:581.7 DiooszegiA.MillbergA,SvenssonIL.ProceedingsoftheInternationalConferenceonTheScienceofCas

38、tingandSolidification,2001;p.269.8 MooreJC.MetalsHandbook,Metallography,structuresandphasediagrams.ASM10山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文International;1973.p.93.9 BoeriRE,SikoraJA.IntJCastMetalsRes2001;13:307.10 RiveraGL,BoeriRE,SikoraJA.MaterSciTechnol2022;18:691.11 RiveraGL,BoeriRE,SikoraJA.AFSTrans2022:111.12 Ri

39、veraGL,BoeriRE,SikoraJA.CastMetals1995;8:1.中文譯文：灰鑄鐵的凝固結(jié)晶過(guò)程摘要：本文作者用由自己開(kāi)展出的新奇的技術(shù)研究了亞共晶、共晶和過(guò)共晶灰鑄鐵的結(jié)晶過(guò)程.這些被揭示的宏觀及微觀結(jié)構(gòu)說(shuō)明灰鑄鐵的結(jié)晶機(jī)理與我們通常所接受的說(shuō)法并不相符.關(guān)鍵詞：凝固結(jié)晶；灰鑄鐵1.導(dǎo)言：有幾位作者之前已經(jīng)研究了成片狀石墨形態(tài)共晶灰鑄鐵的凝固結(jié)晶過(guò)程.通常,共晶灰鑄鐵的結(jié)晶單元呈現(xiàn)出近似奧氏體與石墨的球狀形態(tài),如圖1所示.大家普遍認(rèn)為奧氏體和石墨是同步生長(zhǎng)的,原因是它們同時(shí)與液相接觸.這種設(shè)想一方面被呈玫瑰狀的層狀石墨形態(tài)如圖2所支持；另一方面也被存在于品間的夾雜物所支持

40、,這些夾雜物與最后結(jié)晶時(shí)的顯微偏析有關(guān)并存在于上述品問(wèn).斯泰得的反響物揭示了灰鑄鐵中磷的顯微偏析,它可以描畫出圖1中含磷量高的灰鑄鐵的金相所大體上呈現(xiàn)出的特征,通常被稱為共晶團(tuán).由于奧氏體的樹枝狀結(jié)晶不易被區(qū)分,除了在含有“D型或“E型石墨的灰鑄鐵中,其他情況下它們的形成和生長(zhǎng)特征沒(méi)有受到太多的關(guān)注.有一些研究人員也對(duì)奧氏體樹枝狀晶在灰鑄鐵結(jié)晶過(guò)程中的作用進(jìn)行過(guò)研究.毫無(wú)疑問(wèn),亞共晶灰鑄鐵中的奧氏體是以樹枝狀生長(zhǎng)的.另一方面,許多文獻(xiàn)說(shuō)明.奧氏體在碳含量到達(dá)或超過(guò)共品點(diǎn)時(shí)會(huì)生長(zhǎng)成其它不同的形態(tài).去年,本文的作者們完成了一個(gè)研究,挑戰(zhàn)了被更加穩(wěn)固的建立的可鍛鑄鐵11山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及

41、譯文的凝固結(jié)晶模型的權(quán)威性.一項(xiàng)被特殊開(kāi)展出的技術(shù)的應(yīng)用,使得揭示可鍛鑄鐵的結(jié)晶宏觀結(jié)構(gòu)成為可能,同時(shí)彩色金相技術(shù)的應(yīng)用展現(xiàn)出了顯微偏析的圖案.通過(guò)這些技術(shù)說(shuō)明,可鍛鑄鐵的宏觀組織是由相互關(guān)聯(lián)的粗大奧氏體晶粒形成的,其中包含著數(shù)量眾多的石墨球.這就是亞共晶、共晶、過(guò)共晶可鍛鑄鐵的事實(shí).這個(gè)研究的目的就是研究灰鑄鐵的凝固結(jié)晶機(jī)理,通過(guò)使用顯微和目視的各種技術(shù)來(lái)完成.這些技術(shù)在之前的對(duì)可鍛鑄鐵的研究中被非常成功的應(yīng)用.2.實(shí)驗(yàn)方法2.1實(shí)驗(yàn)材料現(xiàn)在研究中所用的鐵液是用50kg中頻感應(yīng)爐生產(chǎn)的.低鉆生鐵、廢鋼和鐵合金都被用作成產(chǎn)的原料.鐵液被澆注入樹脂砂模中來(lái)生產(chǎn)直徑分別為20、30、和60mm勺棒

42、條.表1列出了所用合金的化學(xué)成分.鐵液中參加銅和鍥是為了提供足夠的等溫淬火性能來(lái)獲得DAA法觀檢測(cè)技術(shù),這項(xiàng)技術(shù)將在下面進(jìn)行介紹.2.2微觀技術(shù)彩色腐蝕技術(shù)通過(guò)應(yīng)用一種試劑揭示了凝固結(jié)晶的微觀結(jié)構(gòu).這種試劑可以顯現(xiàn)出凝固過(guò)程中產(chǎn)生的顯微偏析的圖案.這種腐蝕試劑是由10gNaOH40gKOH10g苦味酸和50ml蒸儲(chǔ)水組成的.這種腐蝕劑必須要被妥善制備和保管,由于它是有腐蝕性并且有毒的.腐蝕劑要在120c(278F)下彳溫2分鐘才能取出圖1共晶灰鑄鐵凝固結(jié)晶單元示意圖12山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文圖2共晶灰鑄鐵石墨形態(tài)2.3宏觀技術(shù)為了能夠觀察可鍛鑄鐵的宏觀結(jié)構(gòu),我們需要提出一種熱處理過(guò)

43、程,被稱為DAAS結(jié)晶后直接淬火.在這個(gè)過(guò)程中,當(dāng)溫度大約到達(dá)950c時(shí),鑄件被從鑄模中振出并被放到900c的加熱爐中保溫30min,以便讓溫度穩(wěn)定下來(lái).然后將鑄件放入360c的鹽浴中奧氏體等溫淬火90分鐘.相應(yīng)的高的奧氏體等溫淬火溫度是為了在熱處理后獲得大量的剩余奧氏體.經(jīng)過(guò)DAASftt理后,鑄件的顯微組織表現(xiàn)出一種很好的針狀鐵素體和剩余奧氏體的混合體.一個(gè)熱處理冷卻圖如圖3a所示.DAASt理當(dāng)然是一種費(fèi)力的方法,不應(yīng)用于通常的鑄造情形下.然而,據(jù)筆者所知,它是現(xiàn)在唯一一種能夠揭示低合金可鍛鑄鐵宏觀組織的方法.經(jīng)過(guò)這一過(guò)程后,剩余奧氏體保持了凝固時(shí)的結(jié)晶傾向.因此,含有苦味酸的腐蝕劑揭示

44、了結(jié)晶后奧氏體的晶粒結(jié)構(gòu).必須被強(qiáng)調(diào)的是這樣的宏觀組織是不能在傳統(tǒng)的奧氏體等溫淬火后觀察到的,如圖3b所示,由于其中的顯微組織會(huì)在奧氏體化后經(jīng)歷一次奧氏體晶粒重結(jié)晶過(guò)程.這項(xiàng)技術(shù)還沒(méi)有被應(yīng)用于灰鑄鐵.作為第一種途徑,它將像在可鍛鑄鐵中的開(kāi)展一樣被應(yīng)用于灰鑄鐵.圖3aDAAS熱處理冷卻圖b常規(guī)奧氏體等溫淬火冷卻圖13山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文TdbkIChnnicjlcumpo-.itLotiMdiChemiul閭MpoiWon(.%CECSLMuCiiNiH,pwu怔die3陽(yáng)LM2,H4.口0,96Euifcdc4.273282史U.220.射0t5Hypereutstic4643.

45、61Jrll通藤L帕口確CL:CL:cdrbojiequiknl.3.結(jié)論與分析圖4a-c表現(xiàn)了未被腐蝕的直徑為30mm勺分別為亞共晶、共晶、過(guò)共晶的試樣的顯微組織結(jié)構(gòu).在所有的情況下都可以看到大量的層狀石墨.圖5a-c展示了在圖4中所示的相同試樣上采用DAA豉術(shù)所獲得的宏觀組織結(jié)構(gòu).在所有情況中,晶粒生長(zhǎng)的相比照擬大的組織都是在試樣的外表發(fā)現(xiàn)的,包括過(guò)共晶合金.這就是說(shuō),據(jù)我們所知,這是第一次正式在砂型鑄件中發(fā)現(xiàn)這種組織.這些晶?；蛘呓Y(jié)晶單元的尺寸要比我們基于圖1中所示的球形晶粒建立的結(jié)晶模型的預(yù)想大得多.如前所述,共晶團(tuán)通常是被由于參加穩(wěn)定劑產(chǎn)生的磷的顯微偏析所表現(xiàn)出來(lái)的.然而,需要指出的

46、是,這種方法不能證實(shí)被磷的顯微偏析分隔開(kāi)的不同區(qū)域就是不同的晶粒,由于它沒(méi)有侵蝕到不同結(jié)晶傾向的不同晶?；蛘唧w積.值得注意的是無(wú)論碳當(dāng)量如何,相同直徑的試樣有著相似的晶粒組織.唯一不同的是亞共晶灰鑄鐵表現(xiàn)出一種更加明顯的柱狀晶.圖6表現(xiàn)了直徑20、30、60mm過(guò)共晶試樣的宏觀組織形貌.從中可以看出隨著試樣直徑的增加,晶粒尺寸略有增長(zhǎng).14山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文圖4未腐蝕的直徑30m僦棒的顯微組織(a)亞共晶組織(b)共晶組織過(guò)共品組織15山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文圖5直彳30m僦棒的宏觀形貌(a)亞共晶組織(b)共晶組織過(guò)共晶組織這種大晶粒的存在暗示了試樣中有很大一局部都

47、具有相同的奧氏體結(jié)晶傾向.這之后使得找到在凝固結(jié)晶的晶粒中的奧氏體的生長(zhǎng)的線索成為可能.我們可以通過(guò)應(yīng)用彩色金相技術(shù)追蹤每個(gè)晶粒內(nèi)的顯微偏析.結(jié)果說(shuō)明對(duì)于所有碳當(dāng)量的灰鑄鐵來(lái)說(shuō),樹枝狀?yuàn)W氏體的存在值得研究.舉個(gè)例子,圖7展現(xiàn)了過(guò)共品鑄鐵的凝固結(jié)晶宏觀組織.值得注意的是,石墨群沒(méi)有表現(xiàn)出枝晶間的形態(tài),在許多地方反而被浸入樹枝狀晶中,如圖中箭頭所指,這就解釋了為什么這種樹枝品之前僅僅通過(guò)對(duì)層片石墨的觀察沒(méi)有被鑒別出來(lái).這也說(shuō)明層片狀石墨可以在生長(zhǎng)到某種程度時(shí),大多數(shù)是在凝固結(jié)晶的最后一個(gè)過(guò)程或者是在凝固過(guò)程的石墨化過(guò)程中,在不與鐵液接觸的情況下,通過(guò)C的擴(kuò)散穿過(guò)奧氏體的包裹.16山東建筑大學(xué)畢業(yè)論

48、文外文文獻(xiàn)及譯文圖6過(guò)共晶組織試棒的宏觀形貌(a)20mm(b)30mm(c)46mm這么大的晶粒以及顯微偏析的圖案形態(tài)說(shuō)明,所謂的共晶團(tuán)實(shí)際上并不是獨(dú)立的凝固的凝固結(jié)晶單元.但是它們之中的很大一局部是發(fā)源于一個(gè)非常巨大的奧氏體樹枝品.這些觀察引出了下面對(duì)于灰鑄鐵凝固結(jié)晶過(guò)程的解釋.許多細(xì)小的奧氏體樹枝晶形核、生長(zhǎng)到圖8所示溫度或在此溫度以下.任何有可能在鐵液中存在的石墨都被這些樹枝品所吞沒(méi).這也很有可能在過(guò)共晶灰鑄鐵中實(shí)際的發(fā)17山東建筑大學(xué)畢業(yè)論文外文文獻(xiàn)及譯文生.已經(jīng)在樹枝狀晶中存在的石墨或者是在過(guò)飽和樹枝晶中新形核的石墨,與奧氏體的枝干相接處繼而協(xié)同生長(zhǎng),形成了所謂的共品團(tuán).我們有理由這樣猜想：無(wú)論是過(guò)共晶灰鑄鐵還是亞共晶灰鑄鐵,都沒(méi)有一個(gè)對(duì)于共晶團(tuán)的形核過(guò)程.但是凝固結(jié)晶過(guò)程是被相對(duì)大一些的奧氏體樹枝晶的主要的生長(zhǎng)所主宰的,這些樹枝晶在之前所提到的共晶團(tuán)的形成區(qū)域提供了大量的高密度的奧氏體晶核.但是