advances in the metallurgy and applications of adi

JournalofMetallurgicalEngineering(ME)Volume2Issue1,January2013www.mejournal.org

1

AdvancesintheMetallurgyandApplicationsofADIAdelNofalCentralMetallurgicalR&DInstitute(CMRDI)P.O.Box87Helwan,Cairo,Egyptadelnofal@hotmail.comAbstractTheexcellentpropertycombinationofADIhasopenednewhorizonsforcastirontoreplacesteelcastingsandforgingsinmany engineering applications with considerable costbenefits.Thankstotheextensiveresearcheffortsmadeoverthepastfewyears,newprocessingtechniqueshaveopenedevenmoreopportunitiesforthisveryprospectivematerialtoacquirebettercombinationsofstrength,ductility,toughness,wearresistanceaswellasmachinability.This review analyses the key features of those novelprocessing techniquesand the resultednewapplicationsofADI.Thesurveyfirstlydiscussesthepossiblestrengtheningmechanism of ADI with special emphasis on the TRIPphenomena, associated with the deformation of ADI.Strength and toughness properties could be improvedthroughthedevelopmentof:

Ausformed ADI; where mechanical processingcomponent was added to the conventional heattreatmentasadriving force toaccelerate the rateofstageIaustempering.

Squeeze cast ADI; where superior quality ADIcastingswere produced through squeeze casting ofmoltenironinapermanentmold,followedbyinsituheattreatmentofthehotknockedoutcastingsintheausteniterange followedbynormalaustempering inasaltbath.

Twostepaustempering toachieve finerausferriteathigherundercoolingduringaustempering treatmentfollowed by austempering at higher temperaturewherehigherausteniticcarbonispromoted.

ThemachinabilityandductilityofADImaybeconsiderablyenhanced through the development of dual phasemicrostructures (ferrite + ausferriteor ferritemartensite bypartial austenitization in the( + + graphite) regionfollowedbynormalaustempering.The abrasion resistance could be remarkably increasedthroughthedevelopmentof:

Carbidic ADIductile iron containing carbidessubsequentlyaustempered to formausferriticmatrixwithanengineeredamountsofcarbides

Bainitic/martensitic (B/M) ADI containing lessexpensivealloyingelementssuchasSiandMnintherangeof2.53.0%

This report discusses as well the recent trials to producethinwallADIcastings.

KeywordsADI; Austemperd Ductile Cast Iron; Heat Treatment;Ausforming;Austempering

Introduction

The ascastmechanicalpropertiesofductile iron canbe significantly improved through an austemperingheat treatment. This has led to the birth of a newmember of the cast iron family; the austemperedductile iron (ADI), with its unique microstructure;spheroidalgraphiteinanausferriticmatrix[1].The austempering transformation in ADI can bedescribedastwostagereaction: StageIReaction: c + HC(toughening) StageIReaction: HC + carbides(embrittlement)The morphology of the final twophase matrixmicrostructure is determined by the number, shapeandsizeof the initially formed ferriteplatelets in thefirststageaustemperingreactions.Thecontrolof thisstage of transformation will, therefore, ultimatelycontrol the final microstructure and mechanicalproperties.TherateofferriteformationduringstageIaustemperingmaybecontrolledbychemical,thermalormechanicalprocessingvariables.

www.mejournal.orgJournalofMetallurgicalEngineering(ME)Volume2Issue1,January2013

2

SincetheannouncementofthefirstproductionofADIin the late decades of the last century, aworldwideexplosioninresearchstarted,whichprovidedasoundfoundation for expanding the production of thisprospectivematerial inmany industrializedcountriesduring the 1990s and beyond. By the turn of thecentury, the ADI market had begun to rapidlyacceleratefromamodestbeginningintheearly1970stoanestimatedworldwideproductionlevelof300,000tonsbytheendoftheyear2010[24].The mechanical properties of ADI depend on anumberofinterlinkedfactors,includingprimarilytheaustenitizing and austempering temperatures andtimes together with the ascast microstructure, thecomposition and the section size. Of these, theaustempering temperature is themost important.[5].These variations in properties can be related to thechanges in microstructure. At low austemperingtemperatures,anacicular(needlelike)ferriticphaseisformed with only a small amount of retainedaustenite. At the very lowest austemperingtemperatures, the structure may also contain somemartensite. This type of microstructure can providehigh tensile strength and hardness but only limitedductility and poor machinability. With increasedaustempering temperatures, the ferrite becomescoarserwith increased amountsof retained austenite(upto~40%);withatypicalausferritestructure.Thisresults in a substantial increase in ductility andmachinability with a reduction in strength andhardness.Oncetheaustemperingtemperatureexceedsacertainvalue(typically375380C),thestageIIreactionoccursvery rapidly, resulting in a reduction in the retainedaustenite and a corresponding decrease in ductility.TheuniquepropertiesofADIarecloselyrelatedtotheretainedaustenitecontentwhich iscontrolledmainlybytheaustemperingtemperatureandtime.[6]Thankstotheextensiveeffortsmadeoverthepastfewyears, new processing techniques have opened evenmore opportunities for this prespective material toacquire better combinations of strength, ductility,toughness,wear resistance as well as machinability.TheselectionofADIisusuallybasedonawiderangeoffactorssuchasproperties,density,costandothers.Figure 1 demonstrates the competitive edge of ADIcompared with forged steel and cast and forgedaluminumalloys[7].

(a)

(b)

FIG.1COMPARISONOFTHECOST(A)ANDWEIGHT(B)PERUNITOFYIELDSTRENGTHFORDIFFERENTMATERIALS[7]

Strengthening Mechanism of ADI

ADI has found and still is finding so manyapplications, where it proved to be an excellentengineeringmaterials.ThepracticeofADIproductionseems to be ahead of the theory. The strengtheningmechanismsofADIarestillunder investigation.Themain constituents of ADI matrix are acicular ferriteandcarbonenrichedaustenite(with thepossibilityofsome martensite formations at low austemperingtemperatures), both main constituents are of low ormediumstrength.The mysteryof thehighstrengthofADI,andhowitmayresultfromtheseconstituentshave been earlier related to the precipitationhardening arising from the formation of very tinyprecipitatessuchasM6C typecarbidesandothers[8].Thedensityoftheseprecipitates,however,seemstobetoolowtoresultinsuchsuperiorstrengthproperties.Recently[9],extensiveuseofTEMhasshedmorelighton the strengthening mechanisms of the mainstructural constituents of ADI, Fig. 2. Thestrengthening mechanism of ferrite was related tostrain hardening caused by very high dislocationdensity, accompanied by high density very smalldislocation loops. In the same time austenitestrengthening is caused by solution hardeningmechanism supported by grain refining due totwinning, which results in some extra


3

(a)(b) (c)FIG.2TEMMICROGRAPHSOFADISTRUCTURALCONSTITUENTS:(a)FERRITENEEDLE(X22,000)SATURATEDWITHDISLOCATIONSANDDISLOCATIONLOOPS.(b)ANAUSTENITEGRAIN(X35,000)WITHCHARACTERISTICCONTRASTFROMTWINSANDSTACKING

FAULTS.(c)DISTORTEDMARTENSITE(X140,000)WITHVERYTHINMICTOTWINS[9]

coherent grain boundaries.Moreover, stacking faultsrepresentingobstacles fordislocationmovementmayplaysomestrengtheningrole.Moreover, the austenite tomartensite transformationatlowaustemperingtemperatureisaccompaniedwithhigh lattice distortion and consequently high strainenergy.Themartensitegrainswouldbedividedintoavery large number of ultra thin microtwins. Theresulting huge amount of coherent grain boundarieswillimpedethedislocationmovement.

Strain Hardening of ADI

Short treatment times lead to inferior mechanicalproperties due to the presence of untemperedmartensite. The same trend is produced with thecombination of long times and high austemperingtemperatures, in this case as a result of austenitedecomposition into ferrite plus coarse carbides thattakes place during the heat treatment. At lowaustempering temperatures (~300C), the austenite isplastically stabledue to the higherCcontent and tothe finer distribution of this phase in themicrostructure(V


4

associated with the straininduced martensitictransformationduring the tensile test.Thegeneratedstrain by the volume expansion accompanying themartensitictransformationstimulatesnewmartensitictransformation resulting in the increase in theinstantaneousnvaluewithstrain.Asaconsequenceofchanges in the structure in the course of tensiledeformation,itisbelievedthattheinitialsegmentoflnstress versus ln strain corresponding to the lowerplastic strain (Fig. 3) is characterized by the plasticdeformation of the retained austenite. At higherstrains, as previously reported, the deformationprocessismodifiedbytheformationofstraininducedmartensite,whichtakesplacewhenthedeformationofaustenitehasbeenexhausted[12].

FIG.3LNTRUESTRESSVERSUSLNTRUESTRAIN[12]

FIG.4VARIATIONOFINSTANTANEOUSVALUEOFNWITH

PLASTICSTRAIN[12]The difference between the two lines in Fig. 3 canestimate the energy consumed in the TRIP process[10]. The lower the Ccontent of the austenite, thesmaller is the strain necessary to produce themechanical transformation of the austenite and thesmalleristheenergyconsumedinTRIP.Twotypesofmartensite induced by deformation have beenreported [10]. The first is of the lath type which

nucleatesat twinboundariesor twin intersection; thesecondhasaplatemorphologyandseems to form inregions affected by the homogeneous precipitationduring the austempering treatmentofquasicoherentepsiloncarbides inaustenite.This lattermartensite isoftemperedtype,containingepsiloncarbidesofsizeslargerthanthosefoundintheparentaustenitebeforedeformation.ImprovedtoughnessofADIresultsfrom:

reducedferriteparticlesize increased carbon content in the retained

austenite,which increases the strainhardeningabilityandstrainhardeningcoefficient

stabilityoftheretainedaustenite[14]Formation of strain inducedmartensite is known toenhance the toughness inTRIPsteels. InADI,due tothe high Ccontent, the martensite formed is brittleand it isdebatable if the formationof strain inducedmartensite can improve the toughness. Thecontribution of strain induced martensite to thetoughness of ADI has been recently discussed [15].Themartensite containingADI can be visualized asfiber reinforced ductilematerial. Even if the fiber isbrittle,itwillnotmakethecompositebrittle,aslongasthefiberisshorterthanacriticallength,as itwillnotbe loaded to its maximum strength and will not,therefore, fracture.According to thisargument, if theretainedaustenite regionsarenotmassive, thenonlyveryshortlengthofthinmartensitewillformandwillimprovethetoughnessofADI.Thus, ADI austempered at lower temperature andhaving finerausferritic structure shouldbenefit fromthemartensite formation,while that treatedathighertemperatures and consisting of massive retainedaustenite together with coarse ferrite will not. Theretained austenite in upper bainite can easilytransformtostraininducedmartensite[16].Increasing the cold rolling (CR) reductions, theamountofretainedaustenite(r)wasdecreasedduetopartialtransformationofrtomartensite,Figs.5and6indicate that the amount of mechanically generatedmartensiteincreaseswithincreasingtheCRreduction[n].As canbe seen fromFigures 7 and 8, the elongationand impact toughness decrease, while the ultimatetensilestrengthandhardnessincreasewithincreasingCR reduction. This is attributed to increase of thehardening of the investigated ADI with cold


5

deformationprocesses(deformationbandsandtwins)and deformation induced martensite. It must bementioned that the observed changes in themechanical properties at light cold deformation (7%reduction) aremainly attributed to the hardening ofthisalloybyplasticdeformationconcentratedinr.Atthis light deformation the amount of mechanicallyformedmartensiteisverysmall(Fig.5)[11].

FIG.5VARIATIONOFVOLUMEFRACTIONSOFRETAINEDAUSTENITEANDMECHANICALLYFORMEDMARTENSITE

WITHCOLDREDUCTIONPCT.[11]

X =28.7% 19%Red FIG.6MICROSTRUCTURESOFADIAFTERTWODIFFERENTREDUCTIONSSHOWINGMARKEDDECREASEOFRAT19%

REDUCTION[12]

1050

1100

1150

1200

1250

1300

1350

0 5 10 15 20 25 30Cold Deformation%

UTS

5

6

7

8

Elo

ngat

ion

UTSElongation

FIG.7VARIATIONOFELONGATIONANDULTIMATETENSILE

STRENGTHWITHCOLDREDUCTIONPCT

300

320

340

360

380

400

420

440

460

0 5 10 15 20 25 30Cold Deformation %

Har

dnes

s

26

28

30

32

34

36

38

40

42

44

Impa

ct T

ough

ness

Hardness

impact

FIG.8VARIATIONOFVICKERSHARDNESSANDIMPACT

TOUGHNESSWITHCOLDREDUCTIONPCT

Good wear resistance is usually obtained in anymaterial by ensuring a high hardness. Lowaustemperingtemperatures(235250C)producehardADI (~480550 BHN) and such grades would beselected when good wear resistance is the mainrequirement. As the austempering temperatureincreases, the hardness decreases, resulting in morewear. However, the softer grades of ADI (typically280320BHN)containlargeamountsofausteniteandthis canworkhardenand/or transform tomartensitewhen subjected to mechanical strain at the surface,withwearresistancesignificantlybetterthanwouldbeexpected.Althoughthiseffectisadisadvantagewhenmachining, it can be very beneficial for certainADIcomponents, since as the surface isworn away, it iscontinuously replacedbya freshly formed,hardenedlayer.WithincreasingapplicationsofADIasasubstituteforforged steels in manufacturing industries, strainhardening of ADI is attracting more attention andmoreresearch isrequired forbetterunderstandingofthis phenomena. This may be attributed to thefollowingfactors:

22242628303234363840

0 5 10 15 20 25 30Cold Deformation %

Ret

aine

d A

uste

nite

2

4

6

8

10

12

14

16

18

Mar

tens

iteAusteniteMartensite

7%Re X =36%


6

ADI components such as transmission gears,crackshafts, train car wheels are subjected toextensivemachiningduringmanufacturingandthe strainhardening behavior of ADI hasprofound influenceonmachining tool life andpartsurfacefinish.

Inmanyapplications,ADIcomponentsundergosubstantial plastic strains (e.g. fatigue, wear).The total life cycle of those components are,therefore, influenced by the strainhardeningcharacteristicsofthematerial.

Strainhardening of the ADI matrix causesstraininduced martensite formation and thiscontributestothehighwearresistanceofADI.

The following discussion will attempt to report theextensive efforts made over the last few years tooptimize the machinability, strength, and toughnessandabrasionresistanceofADI.Thenovelapplicationsassociated with these developments will be shortlydiscussed.Machinable ADI

When ADI first started to be used for engineeringapplications,thereweremanydifficultiesexperiencedintryingtomachineit,andsomeofthesedoubtlesslypersisttothisday.ThehardestgradesofADIreachahardnessof ~50HRCwhichwouldpose a challengefor anyhighvolumemachiningoperation.Althoughthe softer grades ofADI have a typical hardness of300350 BHN, their matrix structure contains up to40% retained austenite.When subjected to strains inservice,aswasmentionedinsection(3)ofthissurvey,thisphaserapidlyworkhardensandcantransformtomartensite [12,17,18], this can thereby reduce themachinability compared with a steel of equivalenthardness. The volume fraction of high carbonaustenitepresentinthemicrostructureofaustemperedductile iron(ADI) isoneofthe importantfactorsthatinfluence the mechanical and physical properties ofthe alloy. Formation of martensite by TRIP(transformationinducedplasticity)mechanismduringthemachiningoperation, inwhicha largeamountofstress is applied to the microstructure, results indecreaseinmachinabilityofADI.ItisconsideredthatthelimiteduseofADIforhighvolumeapplicationsispartlydue tomachiningdifficulties.Thiswasoneofthe motivations in the recent developments of amachinableADI[1926].AlackofexperienceofthehighvolumemachiningofADIaddsuncertaintytothecostsandproductionrates

and the early experiences of ADI exposed someinconsistencies in themachinability.Theseproblems,however,canbeminimizedbycollaborationbetweena knowledgeable foundryman, heat treater andmachiningexpert.The influence of austenitizing and austemperingtemperatures on the machinability of ADI wasrecently reported [27,28]. The production ofmachinableADI has attracted the attention ofmanyresearchers in the last few years by optimizing thecomposition and heat treatment cycles of cast iron.Muhlberger developed [19] and patented [20] amachinable grade ADI by careful selection of thecomposition (low Mn) and heat treatment variablesand this development was exploited in at least oneEuropean foundry [21,22]. More recently, two othergradesofmachinableADIhavebeendevelopedintheUS[23,24],specificallyaimingatincreasingtheuseofADI for automotive applications such as chassiscomponentsandcrankshafts.There are some differences between the twoapproaches,butthecommonfeatureisthatthematrixstructure contains a considerable amounto ferrite inboth cases.Thenewgrade, referred toasMADITM isclaimedtohaveuniquemachiningcharacteristicsandlower machining costs than ascast ductile iron orregular ADI under appropriate conditions of speedand feed. Inplantmachining trials have shown thatMADI at 243 BHN could be machined on existingmachinelinesdesignedforductileirongrade654512.In a continuing effort to address the deficiencies ofregular ADI, extensive efforts have been recentlymade to develop the dualphase (ferriticausferritic)gradesofADIwithenhancedmachinabilitypropertiesto compete with forged steel for power trainapplications [2936]. The properties of dual phasematrix(DPM)ADIhavebeenthesubjectofextensivestudies[3748].ADI offers an excellent compromise between thevalues of proof stress and elongation; both are veryhighlyappreciated in the fieldofsuspensionparts intheautomotive industry [49].ManypotentialusesofADI in competitionwith forged steel and aluminumalloys can be opened due to strong possibilities ofweightandvolumereductions.A car steering knuckle, which has high safetyrequirements, isanewpotentialapplication forADI,where the impact resistance is theprinciple criteriondetermining part size and design.


7

TABLE1POINTSOFIMPROVEMENT[33]

FDN ADI MixedStructure

Tensilestrength MPa 510 1060 700

Proofstress(0.2%) MPa 380 725 550

Elongation % 14.5 14.5 14.5

Hardness HB 207 321 250

Machinability +++ + ++

Impact(Charpy) J/cm2 140 180 160

Deflection(drop) mm/kJ 38 21 30

The main advantage in using ADI is a question ofweight and cost. Ferritic ductile iron (FDI) is lessexpensive than forged steel but requires heaviersectionsduetoitslowerstrength.ReplacementofFDIwith ADI results in 30% improvement of energyabsorbed,but theplasticdeformationbecomes lower.Higher deformations are required for suspensionparts, inparticular for legalpurposes in a contextofaccident and hence there has been a real interest toproduceADIwithenhancedductilityproperties.Recently[33],anewADIwassuggestedwithoptimalductility through the development of dualphasemicrostructures(ferriteausferriteorferritemartensite)by the proper heat treatment. Such dual phase(duplex)microstructures areobtained by intercriticalannealing (partial austenitization) in the ( + +graphite) region followed by austempering at 250400C,andhence,coloniesofproeutectoid ferriteareintroduced within an ausferrite matrix. Superiorstrengthductility combination was achieved in ADIwith duplex microstructure compared withconventionalductile irons.Moreover, tensilestrengthand elongationof ferriticductile iron (FDI) couldbedoubledinaferriteausferriteduplexADI.Suchironswere also found to exhibit superior mechanicalproperties to those exhibited by ductile irons withferritemartensitematrices.Recently, an attemptwasmadetoinvestigatetheeffectofalloyingelementsNi,Mo and Cu on the properties of ADI produced byintercriticalannealingandhighestductility(16%)andimpactstrength (145 J)wereachieved inADIalloyedwith1%Niand0.25%Mo[3436].Thewearresistanceof ADIs with dual matrix structures was found todecreasewith the increaseofproeutectoid ferriteand

decrease of ausferrite content [37]. The properties ofthenewmixed structure compared tobothADI andferrite ductile iron (FDI) is shown in Table 1 [33],whichemphasizesthemainpointsofimprovement.

ReplacementofFDIwithADI structure resultsin an improvement of tensile strength, yieldstrengthandimpactenergy.

ReplacementofconventionalADIwiththatofamixed structure leads, to hardness reduction(and hence bettermachinability) togetherwithan increase in impact deformation. For anidenticalheat treatmentcycle, thepropertiesofADIwith mixed structureseem toeffectivelydepend on the Sicontent. The lowSi gradeseemsmoreattractiveas ithastensilestrength,proof strength, and hardness comparablewiththoseofpearliticstructureswithelongationandimpact strength close to those of FDI. Thehigherstrengthvaluesmaybeattributedtothemore complete austempering transformationtogether with the absence of any pearliticstructure in the last to freezezones.Moreover,the lowSicontentreduces thehardeningeffectof Si on ferrite, which leads to significantdeterioration of impact strength. The low Sitype has higher impact energy than FDI andhigherimpactdeformationthanADI[33].

The ADI with the mixed (ferriteausferrite)structureprovidesasatisfactorysolutionwhereFDI does not have the necessary impactresistanceorADIdoesnotprovidetherequireddeformationlevelortherequiredmachinability.


8

Very limited research related to the strainhardeningcharacteristicsofconventionalADI isavailable in theliterature [10, 17].Using theHolloman equation, thestrainhardeningbehaviorofADIsubjectedtoanoveltwostepaustemperingprocesswasanalyzed[50].Thestrain hardening exponent values of ADI with twostep austempering process was shown to result inlowerductilityandstrainhardeningexponentvalues,compared to the conventional singlestepaustempering process. This resultwas related to theamount and morphology of microstructuralconstituents and the interaction intensities betweencarbonatomsanddislocation in thematrix.Recently[51], the strainhardeningbehaviorofADIwithdualmatrix structure (DMS)was investigated, it seems tobeaffectedbythevariationsinthevolumefractionaswell as morphologies of phases, the degree ofausferrite connectivity and interaction intensitiesbetweencarbonatomsanddislocationinthematrix.Ithasbeen reported that fully ferritic (austenite free)ADIcouldbeproducedbyaustemperingat260Candthen tempered at 484C for 2 hrs, withoutcompromising the mechanical properties [52]. Theprocess was rather sensitive to the austemperingtemperature, initial austempering at 385C andtemperingat thesame temperatureof484C resultedin a drastic reduction in the ductility and fracturetoughness of the material. The machinability,however, was improved in both cases. Furtherdevelopment in this direction may lead toconsiderable enhancement of the machinabilitypropertiesofADI.

Enhancement of Strength Properties of ADI

AusformedAustemperedDuctileIron(AADI)It has been shown [5,53] that the rate of ferriteformation during stage I austempering may becontrolledbythefollowingprocessingvariables:

Chemical includingalloycontentselectionforhardenability purposes together with theaustenitization temperature selection whichcontrolsthematrixcarboncontent.

Thermal includingaustempering temperatureandtime.

Mechanicalincludingmechanicaldeformationintroduced into theaustemperingschedule justafter quenching, but before any substantialtransformation of austenite (ausforming)(Fig.9).

FIG.9SCHEMATICREPRESENTATIONOFTHEAUSFORMING

PROCESS[5]

FIG. 10 SEM MICROGRAPHS OF ADI ALLOYED WITH 2% NI

AUSTEMPERED AT 375C FOR 1 MINUTE. (A) CONVENTIONALLY PROCESSED; (B) AUSFORMED TO 25%

REDUCTION. ARROWS INDICATE THE BRITTLE MARTENSITE FORMED IN MANY ZONES IN THE CONVENTIONALLY

PROCESSED ADI [53]Naturally, anoptimum finalmicrostructure couldbeproducedbyincludingelementsofallthreeprocessingvariables. It has been shown [5760] thatmechanicalprocessing ofADI can act as a control valve for thestage I austempering reaction. In ausformedaustempered ductile iron (AADI), mechanicaldeformation is utilized to affect the microstructureand, consequently, the mechanical properties ofductile irondue toaccelerationofausferrite reaction,refining the microstructure and increase of thestructuralhomogeneity.A recentwork [57]hasshown thatausformingup to25% reduction in height during a rolling operationcontributed to add a mechanical processingcomponent to the conventional ADI heat treatment,thus increasing the rate of ausferrite formation andleading to a much finer and more homogeneousausferriteproduct (Fig. 10).The effectof ausformingonthestrengthvalueswasquitedramatic(Fig.11)(upto 70 and 50% increase in the yield and ultimatestrengthrespectively).Amechanism involvingbotharefinedmicrostructural scale as a result of enhancedferritenucleationtogetherwithanelevateddislocation


9

density was suggested [21]. Hardenability elementssuch as Ni and Mo are usually added to increasehardenabilityofthicksectioncastings,andausformingtohigherdegreesofdeformationwasfoundnecessarytoalleviatethedeleteriouseffectsofalloysegregationonductility[58].

FIG. 11 YIELD STRENGTH VS AUSTEMPERING TIME AND

AUSFORMING REDUCTION FOR ADIS ALLOYED WITH 2% NI.

It ismorepractical that theadvantageofausformingwouldbetakenbyforgingratherthanbyrolling.Theforgingprocessmaybeperformedon castpreforms,austenitized and quenched to the austemperingtemperature, inserted intoadie,pressedor forged tothe final shape and then returned back into theaustempering bath to complete the acceleratedtransformation. Minimal deformation degrees byconventional forging standards, i.e.anaverage strainof25%wouldbesufficientfortheformingpartoftheprocessingsequence. Ithasbeenreported [59] that insituationswherevery severedeformationoccurs, theworkpiece may not need to be returned to theaustemperingbath to complete the transformation toausferrite, as the latterwill have been completed bythetimetheworkpieceisextractedfromthedie.Theideaofcreatingpreformsinductileironandthenausforming them to final shape could be quiteeffective for relatively simple shaped castings thatmust meet high demanding strength and ductilityrequirements, e.g. connecting rods for automotiveapplications.Itisunderstoodthatcertaindeviationsindesignelementsofbothpreformaswellasthediesetshould be involved compared to the design ofconventional ADI process. The abovementionedconcepthasbeenutilizedtoproducetanktrackcenterguides[60]usingafiniteelementsimulationtechniquetomatchboth thepreformdesignand thediedesignso that a uniform equivalent stain throughout the

castingaveraged~20%.No inclinationtofractureorcrackinghasbeenreported.SqueezeCastingofADIADI was produced without an austenitizing stepbasedonapatentpublishedin1985byP.B.Magalhaes[61]. In this process, casting in a permanent moldallowedtheejectionofthepartatatemperaturelevelabove 850C where a completely austenitic rangecouldbeguaranteed.Subsequentquenching ina saltbathwouldleadtotheADIausferriticmicrostructure.Based on this process, a novel technique has beensimultaneously developed at TUAachen FoundryInstitute [62] and component CPC Finland [63] toproducesuperiorqualityADIcastings,usingsqueezecastingofmoltenmetal inpermanentmold, followedby insituheat treatmentofthehotknockoutcastingin the austenite range, followed by normalaustempering in a salt bath. Figure 12 shows aschematicrepresentationoftheprocess[62].This technique seems to have some uniqueadvantages,suchas:

Soundcastingscanbeproducedwithout feedersor gating system as the solidification expansionwasusedtocounteractsolidificationshrinkage.

Increased heat transfer avoids formation ofmacro and microsegregation, which decreasesthemechanicalpropertiesofADI.

Chemical composition of ductile iron can beselected toavoidanymetastablesolidification inspiteoftheextremelyfastsolidification.

Theproductionprocessisshorterandlessenergyconsuming as the elimination of sand from theprocesswouldallowthehotcastingscomingoutfrom the permanent mold to be directlyintroducedtotheheattreatmentfurnace.

The structure of the SQADI ismuch finer (thegraphite aswell as the ausferrite),whichmeansbetter mechanical properties (ultimate tensilestrength,elongationandfatiguestrength).

The casting surface is entirely free from anysurfacedefects,whichagainmeanshigherfatiguestrength.

Themachinabilityisbetter. Moreenvironmentallyfriendly.


10

TABLE2SOMETENSILETESTRESULTSOFSQUEEZECASTTESTSAMPLESCOMPAREDTOENSTANDARD[63]

Test1 EN Test2 ENTensilestrength,MPa 1238 1200 1115 1000Yieldstrength,MPa 968 850 839 700Elongation,% 13.4 2 15.3 5Hardness,HB 388 340/440 363 300/360

TABLE3COMPARISONOFDIFFERENTSUSPENSIONFORKMATERIALS[63]

GJS6005 SQADI(Tested) MicroalloyedSteelTensilestrength,MPa 600 950 1000Yieldstrength,MPa 370 750 550Elongation,% 10 11 12

FIG.12PROCESSSTEPSANDTEMPERATUREREGIMEOFTHE

SQPROCESSANDTHEINSITUHEATTREATMENT[62]Table 2 [63] shows some tensile test results of asqueezecastedringgeartestsamplescomparedtoENstandard.Fiat suspension forkwas tested for fatiguestrength and amazing results were achieved. Thiscomponenthadtopassthetestwithoutcracksloadedwith 250 KN after lifetime of 300,000 cycles. Thesqueeze cast forks couldpass the testwith 5000KNwithout failureup to 310million cycles.The tensileproperties were much higher than pearlitic ductileironorevenbetterthanmicroalloyedsteelsasshowninTable3 [63],yield strengthwasmuchhigher thansteelandelongationaboutthesame.TwostepAustemperingofADIThe mechanical properties of ADI are mainlydependenton:

Thefinenessofferriteandausteniteinausferrite Theaustenitecarbon(X,C)where:

XisthevolumefractionofausteniteCistheausteniteCcontent

Both these factors depend on the austemperingtemperature. Higher undercoolings enhance thenucleation of ferrite from the parent austenite andhencepromotes finerausferrite structurewithhigheryieldand tensilestrengthbut lowerductility.On theotherside,higheraustemperingtemperaturesresultincoarser feathery ferrite and austenite with lowerstrength but higher ductility properties. Moreover,higher austempering temperatures lead to higher(X,C) parameter which, in turn, increases fracturetoughnessandfatiguestrengthofADI.It is possible, therefore, to optimize the mechanicalpropertiesofADIbyausferrite refinementaswellasincreasing the austenite carbon. Hence, the novelconceptoftwostepaustemperingwasconceived[64],which involves first quenching the alloy to a lowertemperature (250270C) after austenitization, thusincreasing the undercooling, and then, once thenucleationof ferrite is complete, immediately raisingthe temperature of the quenchingmedia to a highertemperaturetoenhancefasterdiffusionofcarbonandincrease austenite carbon (X,C) in the matrix. AschematicofthisprocessisshowninFig.13.The twostep austempering process has resulted inhigher wear resistance in ADI compared to theconventional singlestep austempering process. An


11

analytical model for the abrasion wear behavior ofADI revealed the dependence of wear behavior ofADIon themicrostructuralparameters, especially theparameterXC /dwhered istheferriticcellsizeaswell as the strainhardening exponent (nvalue).ThemajorwearresistantmechanisminADIwasshowntobe the microstructural refinement in ausferrite andsolution strengthening effect (high Ccontent inaustenite) along with strain hardening effect of theaustenitephase[6566].

f g

c a

d e

a h

Tem

pera

ture

Time

a-b heating to austenitization temperature

b-c austenitizing c-d quenching to the supercooled

temperature d-e few minutes holding at the first

austempering temperature e-f heating immediately to second

austempering temperature f-g holding at second

austempering temperature (~2 hr)

g-h air cooling to room temperature

FIG. 13 SCHEMATIC OF THE TWO STEP AUSTEMPERING

PROCESS

Meanwhile, the twostep austempering processresultedinhighercrackgrowthrateandlowerfatiguethreshold than the single stepADIproces.The crackgrowth rate increment due to the twostepaustemperingprocessincreaseswiththeaustemperingtemperature [67].Moreover, it has been shown in arecent publication carried out at (CMRDI) that thetwostep austemperingprocess increases the fracturetoughnessofADI,wheretheincrementinthefracturetoughness by the twostep process is morepronouncedinunalloyedirons[68].The improved toughness was correlated to reducedferrite grain size, increased carbon content of theretainedausteniteaswellasitsstability[33].

ADI with Enhanced Wear Resistance

CarbidicADI(CADI)CADI is ductile iron containing carbides that issubsequently austempered to produce an ausferriticmatrix with an engineered amount of carbides.Volume fraction of carbides may be controlled by

partial dissolution during the subsequentaustenitizationprocessandhencetheproperabrasionresistance/toughness combination may be reached.CADIexhibitsexcellentwearresistanceandadequatetoughness. The abrasion resistance of this newmaterial is superior to thatof theADI and increaseswith increased carbide content. In anumberofwearapplications, it can compete favorablywith highCrabrasionresistantironswithimprovedtoughness[6976].Several methods have been suggested to introducecarbidestothestructureofADI[3840].(a) As cast carbides can be introduced to the

structureofADI throughalloyingwithcarbidepromoting elements such as Cr, Mo, Ti, etc.,controllingthecoolingrateduringsolidification,adjusting the carbon equivalent to producehypoteutectic composition or through surfacechilling.

Recently,ithasbeenreportedthatgoodbalancebetweenwear resistance and impact toughnesscould be achieved through the selection ofCrcontent/austempering temperature combination[69].

(b) Carbides precipitated during austempering:extending the second stage austempering willresult in theprecipitationof finecarbides fromthehighcarbonaustenite:HC+.

(c) Mechanically introduced carbides; crushed MxCycarbidesarestrategicallyplaced in themoldcavity at the desired location. The metal thenfills in around the carbides resulting in acontinuous iron matrix with discrete carbidesmechanically trapped. This method allows theengineer the option of placing carbides onlywhereneeded resulting in conventionalductileironmatrix throughout the rest of the casting.Theseparticularcarbidesareessentiallyaffectedby subsequent austempering process. Thistechnique iscurrentlyonlypracticedby licenseto Sadvik corporation and the specificmethodused to contain the carbides in place duringmoldfillingneedsfurtherinvestigation.

(d) Fully or mostly ferritic matrix is hard facewelded in the area of greatest wear, whichresults in a carbidic weld and a heat affectedzone at the weld/casting interface. Subsequentaustemperheat treatmenthas littleorno effectontheweldstructure,dependingonthe


12

TABLE4PROSPECTSANDPOTENTIALSOFCADI[69]

chemical composition of the weld materialchosen, whereas the heat affected zone iseliminatedanda fullyausferriticmatrix resultsinallareasexcept theweldarea itself. Insomeweldapplications,powderedmetalcarbidescanbe purged into the molten weld to provideadditionalwearresistance[69].

The advantages, disadvantages, marketopportunitiesaswellaspotentialapplicationsofCADIareillustratedinTable4[69].

Bainitic/Martensite(B/M)DualphaseADIA new grade of wear resistant ductile iron, withproperties similar to those of ADI was recentlydevelopedbycombining lessexpensivealloyingwitha controlled heat treatment to produce a bainiticmartensitic dualphase structure. Alloying elementssuch as Si and Mn promote bainitic transformationwereadded in the rangeof2.53.0%each.Moreover,such alloying facilitates the separation of bainitictransformation from martensitic one. Manganesesignificantly reduces the Ms temperature, dissolvesunlimitedlyintoausteniteandimproveshardenability.AtMncontentshigher than3.0%,austenite increaseson the account of bainite and carbides starts toprecipitate. Manganese carbides formation isrestrained effectively by silicon,which promotes theformation of bainitic ferrite and the enrichment ofasutenite with carbon. The resulting increase inaustenite stability will reduce the possibility of

manganese carbides formation and manganesedissolves in austenite and ferrite. The pearliteformation is avoided by controlled cooling heattreatment;consistingofthreestages:(1) Water spraying quenching is applied for rapid

cooling from austenitization temperature toabout 300C in a fewminuteswhich suppressanypearlitetransformation.

(2) Soaking in a heat preservation setting forbainitic transformation over a range oftemperature forms the spraying endtemperatureto200Cfor2hrs.

(3) Aircoolingtoroomtemperatureformartensitictransformation.

The resulting microstructure containing bainite,martensite and 810 vol. % retained austenite alongwith the graphite spheroids will give an excellentcombinationofhardness and toughnesswhich reach51.5HRCand21.7J/cm2respectivelyandthiscouldbeattributedtothefollowingfactors[77,78]:i) The bainite needles split the undecompensed

austenite and effectively decrease the size ofmartensite leading to improved strength andtoughness.

ii) High toughness of bainite restricts thepropagationofcracksoriginatingmainlyat thegraphite/matrix interface and hence toughenstheiron.


13

iii) Thepresenceofretainedaustenite (810vol.%)contributestothetougheningeffect.

TheimpactwearresistanceoftheB/Mductileironwasfound to be comparable with that of the highchromiumcastironandtwicethatofmanganesesteel.Underconditionsof low impact load,suchas that inthecaseofgrindingballsand liners in thesmallandmediumdiameterballmills, theB/Mductile ironcanreplace the manganese steel as a wear resistantmaterial. In such application, the B/M ductile ironshowsgoodworkhardeningeffectduetothepresenceoftheretainedaustenite.Thesurfaceworkhardeningeffectcanconsiderablyimprovethewearresistanceofthe hardened surfaces, while the core of the ballsremainstough.Currently,thereisanincreasinginterest[79]intheascast austenitebainite ductile iron, produced byalloyingwith>3.0%Ni,andupto0.8%Moandupto1.0%Cu.Thetensilestrengthandelongationoftheascastalloyedductileironwereshowntobehigherthanthose of irons subjected to hotshakeout from sandmolds at 250C andheld for twohours.The inferiorproperties in the second casewere attributed to theincreasedlevelsofretainedaustenite.

Thin-Wall ADI Castings

To achieve fuel economy in automotive industry,reducingthevehicleweighthasbeenamajorresearcharea of interest over the last few decades.Althoughthe general trend has been to use low densitymaterials (aluminum, magnesium and composites)instead of cast iron and steel in the automotiveindustry, numerous examples have been recentlynoted in the literature where iron castings startedagain to replace aluminum in the industry. Thiscomparison is encouraged by the increased strength,ductility,stiffness,vibrationdampingcapacity,aswellasreducedcost[80].Iftheyieldstress/costratioofthevariousmaterialsiscompared,thenewmemberoftheductile iron family, theADI, ismost of the time thewinner.Whenmechanicalproperties,densityandcostare included inmaterialevaluation,ductile ironmayoffermoreadvantages thanaluminum,particularly ifthinwallductileironpartscouldbeproducedwithoutfurther heat treatment processes. The potentials forductile iron applications for lightweight automotivecomponents have been limited by the capability toproduceascast free thinwallparts (23mm) [81,82].Production of thinwall ductile iron castings stillrepresents a daily challenge in modern foundries.

Review of the recent literature shows that thinwallductile ironhasbeensuccessfullyproducedformanyyears, thanks to the optimization of some criticalproduction parameters: pouring temperature,chemical composition, thermal conductivity of themolding materials, type and amount of inoculatingmaterial in combination with the spheroidizingmethod adopted, casting design and other foundrybasicpractices[83,84].When the commercial introduction of ADI in 1972,consistent efforts have been made to identify newapplicationsof thisnewemergingmaterial,however,difficultieshavebeen encountered inproducingADIthicker than 100 mm due to the segregation ofhardenability elements added to prevent pearliteformation. Such difficulty in obtaining the requiredaustemperability and the heterogeneousmicrostructuresdonotrepresentarealproblemwhenproducing thin wall ADI castings due to theinsignificant segregation tendency associated withrapidsolidificationofthosethinwallcastings.Theuseof ADI in thinwall and high strength parts has,however,beenmentionedinaverylimitednumberofreference[85,86].Successfulcasewasrecentlyreported[85],whereahollowconnectingrodforatwocylindercar engine and a frontupright for a racing carweresuccessfullymade of thinwallADI,which confirmsthe capability of ADI to build complex thin walledparts of high strength. With recent development ininoculation theoryandpractice, itbecamepossible tocast thinwallductile ironpartscompletely free fromcarbides.Consequently, further improvements in thepropertiesofthinwallADIcastingscouldbeachievedwiththeaustemperingprocess.Inarecentstudy[87],the results of a R&D program on the effect of wallthickness (310mm)andsiliconcontent (2.42.7%)onthepropertiesofADIhasbeen reported. Ithasbeenshown that thinwall ADI castings austempered at360Candcontaining lowsiliconcanexhibitultimatestrength exceeding 1100 MPa with more than 10%elongation. This is an indication that austemperedthinwallductile iron isbecominga logicalchoice fortheproductionofsmall,lightweightandcosteffectiveautomotive components. However, more data aboutthemetallurgyof thinwallADIcastings seems tobeofpracticalinterest.Recently [88],2mmADIplateswithahomogeneousausferriticandnodulecountof300nodules/mm2wereproducedatCMRDI.Itwasfoundthatdecreasingthewall thickness leads to reduced amounts of retained


14

austenite and structure refinement, which in turnincrease the hardness. Increasing the austemperingtemperaturefrom350Cto400Cresulted inreducedtensilestrengthvalues(950and1000MPafor8and2mmwallthickness,respectively)to(775and875MPaforthesamewallthickness),increasedimpactstrength(from 40 to 80) and from 100 to 125 J at wallthicknesses of 2 and 8mm, respectively, apparentlydue to increased amounts of retained austenite athigheraustemperingtemperatures.

Concluding Remarks

1. Extensive research work over the past decadehashelpedtodevelopthepropertycombinationofADIinthreedirections:

increasedstrength,ductilityandtoughness enhanced wear resistance/toughness

combination improvedmachinability

2. ADIoffershigh levelsofmechanicalpropertiesatacompetitivecost.WhenthehighstrengthofADI is taken intoaccount, itcould successfullycompetewithlightweightalloys,astheadditiveweight required to giveunit strength is lower.Moreover, when the relative cost of ADIrequiredtogiveunitstrengthisconsidered,ADIseems to be one of the cheapest alloys. Thesepointshaveyettobefullyappreciatedbymanydesign engineers. Currently, novel processingtechniques adopted in achieve better strengthand toughness properties include ausforming,coldrolling, twostep austempering, squeezecastingandothers.

3. Thecurrentresearchworkaimingatimprovingmachinability ofADI looks rather vital for thefutureofthismaterial.Theavailablemachiningtechniques required for forging steel are notalways suitable for ADI components,particularly on a high volume machining linededicated to the production of one specificproduct. This problem can beminimizedwiththe development of ferritic or ferritic +ausferriticADIstructures.

4. Carbidic as well bainitic/martensitic ADI offeropportunities for superior wear resistance,combined with reasonable toughness, whichmayopennewapplicationsforADI.

REFERENCES

[1] R.A. Harding, The production, properties andautomotiveapplicationsforaustemperedductile iron,AsiaEurope Environment Forum Conf., Jakarta,Indonesia,2325Nov.(2005).

[2] T.Dorn,J.R.Keough,T.SchroederandA.Thoma,Thecurrentstateofworldwidestandards forductile iron,2003KeithD.MillsSymposiumonDuctileIron,HiltonHead,SC,USA,2023Oct.(2003).

[3] K.L.HayrynenandJ.R.Keough,Austemperedductileiron the stateof the industry in2003,2003KeithD.Mills Symposium on Ductile Iron, Hilton Head, SC,USA,2023Oct.(2003).

[4] K.L.HayrynenandJ.R.Keough,Is ittimeforagrade800 ADI in North America?, AFS Trans., vol. 113,paper03089,(2005),pp.851875.

[5] K.B. Rundman, Austempered ductile iron microstructureandmechanicalproperties,inCasting1997 InternationalADI and SimulationConference,HelsinkiUniversityofTechnology,Finland(1997)Ed.K.Holmberg,paper2,42pp.

[6] R.A. Harding, Control of the retained austenitecontentofADI;inAFSInc.,1991WorldConferenceonAustempered Ductile Iron, 1214 March (1951),Bloomingdale,Chicago,IL,pp.2231.

[7] J.R. Keough and K.L. Hayrynen, Automotiveapplications of austempered ductile iron (ADI): acritical review in Designing and AchievingLightweight Vehicles (SP1684). SAE Technical Paper(2000)010.0764.

[8] M.Kaczorowski,D.Myszka:Thenanostructuralstudyof ADI in transmission electron microscope, PraceITMat.(2003)ss.1016.

[9] A. Krzyska and M. Kaczorowski, The mystery ofADI, Archieves of Foundry Engineers, vol. 7, Issue4/2007,pp.111114(2007).

[10] J.Aranzabal,I.Gutierrez,J.M.RodriguezIbabeandJ.J.Urcola, Influence of the amount andmorphology ofretained austenite on themechancial properties of anaustemperedductileiron,MetallurgicalandMaterialsTransactionsA,vol.28A,May(1997),pp.11431156.

[11] H.NasrEldin,A.Nofal,A.RamadanandM.Ibrahim,Structurecharacteristicsandmechanicalpropertiesofcold rolled austempered ductile iron alloyed withnickel,CanadianMetallurgicalQuarterly,vol.43,No.2,pp.203218(2004).

[12] A.Nofal,H.NasrEldinandM.Ibrahim,Coldrollingof austempered ductile iron, Journal of Materials


15

ScienceandTechnology,vol.11,No.2,pp.8696(2003).[13] J.Arnazabal,I.Gutierrez,J.M.RodriguezIbabeandJ.J.

Urcola, Influenceofheat treatmentonmicrostructureand toughnessofaustemperedductile iron,MaterialsScienceandTechnology,8,(1992),pp.263273.

[14] K.S. Ravishankar, K. Rajendra Udupa and P. PrasadRao, Development of austempered ductile iron forhigh strength and fracture toughness by two stepaustemperingprocess,TheProceedings of theWorldFoundryCongress,Chinnai, India710February2008,pp.3540.

[15] S. Chatterjee and H.K.D.H. Bhadeshia, TRIPassistedSteelsCrackingofHighCarbonMartensite;,Mater.Sci.Tech.,(2006),vol.22,No.6,pp.695699.

[16] S. Daber and P. Prasad Rao, Formation of Straininduced Martensite in Austempered Ductile Iron; J.Mater.Sci.(2008),43,pp.357367.

[17] J.L. Garin and R.L. Mannheim, Straininducedmartensite in ADI alloy, Journal of MaterialsProcessingTechnology,143144,pp.347351(2003).

[18] Z.Zhongkui,S.Quingzhou,M.HailongandZ.Junxian,Experimental study of MAchineable ADI,Proceedings of the 8th International Symposium onScience and Processing of Cast Iron, Beijing, China,(2006),pp.464467.

[19] H. Muhlberger, Process in the production,understanding and applications of Germaniteaustempered ductile iron,ASME andAmax Inc., 2ndInt.Conf.onAustemperedDuctileIron:YourMeanstoImproved Performance, University of Michigan, AnnArbor,M1,1719March1986,Illinois,1986,5593.

[20] K.SchmdthGmbHandothers,Nodularcastironwithamixedausteniticbainiticstructureandmethodforitsproduction, German patent/2853870, filed 13December1978.

[21] F. Zanardi, The development of machinable ADI inItaly, 2002 World Conference on ADI, Ductile IronSocietyand theAmericanFoundrySociety,Louisville,KY(USA),Sept.2627,2002,4pp.

[22] F.Zanardi,MachinableADIinItaly,AFSTransactions2005,paper05209(05),13pages.

[23] A.P. Druschitz and D.C. Fitzgerald, MADITM:Introducing a new machinable austempered ductileiron, NonFerrous Castings (SP1734), SAE WorldCongress, Detroit, Michigan, 36, 2003 SAE TechnicalPaper2003010831.

[24] A.P. Druschitz and D.C. Fitzgerald, A machinableaustempered cast iron article having improved

machinability, fatigue performance and resistance toenvironmental cracking and amethod ofmaking thesame, International Patent Application WO2004/022792 A2, 18 March 2004. Also US PatentApplication:2004112479,June17,2004.

[25] F. Zanardi, Fatigue properties and machinability ofADI,LaMetallurgicaItaliana,10/2005,2732.

[26] Z. Zhoo, Q. Sun, H. Ma and J. Zhu, Experimentalstudy ofmachinableADI, Science and Processing ofCastIron(SPCI8)Symposium,Beijing(2006).

[27] J.R.KeoughandK.L.Hayrymen,Developmentsinthetechnology and engineering applications ofaustemperedductileiron(ADI),Proceedingsofthe8thInternationalSymposiumonScienceandProcessingofCastIron,Beijing,China(2006),pp.474479.

[28] M.CemalCakir,AliBayram,YahyaIsikandBarisSalar,The effects of austempering temperature and timeonto machinability of austempered ductile iron,Materials Science and Engineering A407, (2005), 147153.

[29] T.KobayashiandS.Yamada,Effectofholdingtimeinthe (+) temperature rangeon toughnessof speciallyaustemperedductileiron,Metall.Mat.Trans.A,(1996),27A(7),pp.19611971.

[30] D.RousiereandJ.Aranazabal,Developmentofmixed(ferritic+ausferritic)structuresforspheroidalgraphiteirons,MetallurgicalScienceandTechnology,vol.18(a),(2000),2429.

[31] A.M. Rashidi and M. MoshrefiTorbati, Effect oftempering conditionson themechanicalproperties ofductile cast ironwith dualmatrix structures (DMS),MaterialsLetter,vol.45,(2000),203207.

[32] K.Kocatepe,M.Cerah andM. Erdogan, The tensilefracture behavior of intercritically annealed andquenched + tempered ferritic ductile iron with dualmatrixstructure,MaterialsandDesign,July(2005).

[33] J. Aranzabal, G. Serramoglia, C.A. Goria and D.Rousiere, Development of a new mixed (ferriticausferritic) ductile iron for automotive suspensionparts, Int. J. of Cast Metals Research, 2003, 16 (13),185192.

[34] M.J. Prez, M.M. Cisneras, M.F. Lpez, S. Rodriguezand V. Vzquez, Austempered ductile iron withduplexmatrix,Proceedingsof the8th Int.SymposiumonScienceandProcessingofCastIron(SPCI8),Beijing,China,Oct.1619(2006),139144.

[35] C. Valds, M.J. Perez Lpez, M. Figueroa and L.E.Ramirez, Austemperedductile ironwithdualmatrix


16

structure, Revista Mexicana De Fisica S55(1), May(2009),pp.4851.

[36] M.Figueroa,M.J.Prez,K.L.Fraga,C.V.ValdsandE.Almanza, Impact strength of thin wall ductile ironwithdualmatrixstructure,RevistaMexicanaDeFisicaS55(1),May(2009),pp.105109.

[37] Y.Sahin,M.ErdoganandV.Kilicli, Wearbehaviorofaustemperedductile ironwithdualmatrixstructures,MaterialsScienceandEngineeringA444(2007),3138.

[38] K.Kocatepe,M.Cerah andM. Erdogan, The tensilefracture behavior of intercritically annealed andquenched + tempered ferritic ductile iron with dualmatrixstructure,MaterialsandDesign(2005).

[39] R.C.Voigt,L.M. Eldoky andH.S.Chiou, Fracture ofductile cast irons with dual matrix structure, AFSTrans.(1986),94,pp.645656.

[40] T.KobayashiandH.Yamamoto,Developmentofhightoughness in austempered type ductile cast iron andevaluation of its properties, Metall. Mat. Trans. A,(1988),19A(2),pp.319327.

[41] R. Kazerooni, A. Nazarboland and R. Elliot, Use ofaustenitizingtemperatureincontrolofaustemperingofMnMoCualloyedductileiron,Mat.Sci.Tech.,(1997),13(12),pp.10071015.

[42] M.Hafiz,TensilepropertiesandfractureofferriticSGironhavingdifferentshellstructure,Z.Metallk.,(2001),92(11),pp.12581261.

[43] M.Cerah,K.KocatepeandM.Erdogan, Influenceofmartensite volume fraction and tempering time ontensilepropertiesofpartiallyaustenitized in the (+)temperature range and quenched + tempered ferriticductileiron,J.Mat.Sci.,(2005),40(13),pp.34533459.

[44] M.Erdogan,K.KocatepeandM.Cerah, Influenceofintercritical austenitizing and tempering time andmartensite volume fractions on tensile properties offerriticductile ironwithdualmatrix structure, Int. J.CastMet.Res,(2001),19(4),pp.248253.

[45] V. Kilicli and M. Erdogan, Tensile properties ofpartially austenitized and austempered ductile ironswith dual matrix structures, Mat. Sci. Tech. (2006),22(8),pp.919928.

[46] V. Kilicli and M. Erdogan, The effect of ausferritevolume fraction and its morphology on the tensileproperties of partially austenitized and austemperedductile ironswithdualmatrix structures, Int. J.CastMet.Res.(2000).

[47] M. Erdogan, V. Kilicli and B. Emir, Transformationcharacteristics of ductile iron austempered from

intercritical austenitizing temperature ranges, J.Mat.Sci.,(2007).

[48] Z.R.He,G.X.LinandS. Ji, Deformationand fracturebehavior of cast ironwith optimizedmicrostructure,Mat.Charac.(1997),38(45),pp.251258.

[49] J.R. Keough, Austempered materials and theirapplicationstodrivelineandsuspensioncomponents,SAE International Offhighway and PowerplantCongress,Sept.2000,SAETechnicalPaper2000012563.

[50] J.Yang,andS.K.Putatunda,Influendceofanoveltwostep austempering process on the strain hardeningbehaviorofaustemperedductilecast iron(ADI),Mat.Sci.Eng.A,(2004),A382(12),pp.265279.

[51] V. Kilicli and M. Erdogan, The strainhardeningbehavior of partially austenitized and austemperedductileironswithdualmatrixstructures,J.ofMaterialEngineeringandPerformance,vol.17(2),April (2008),pp.240249.

[52] S.K. Patatunda, S. Kesani, R. Tackett and G. Lawes,Development of austenite free ADI (austemperedductile cast iron),Materials Science and EngineeringA435436(2006),112122.

[53] D.J.Moore,K.B.RundmanandT.N.Rouns,TheEffectofThermomechanicalProcessingonBainiteFormationin Several Austempered Ductile Irons, FirstInternationalConferenceinADI,ASM,pp.1331(1985).

[54] J.D.DelaO,C.M. Burke,B.Lagather,D.J.Moore andK.B. Rundman, Thermomechanical Processing ofAustempered Ductile Iron: ThermomechanicalProcessing and Mechanical Properties ofHypereutectoid Steels andCast Irons, TheMinerals,Metals and Materials Society, pp. 79100, Sept. 1418(1997).

[55] J. Aachary and D. Venugopalan, MicrostructuralDevelopment and Austempering Kinetics of DuctileIron during Thermomechanical Processing,Metallurgical and Materials Trans. A, vol. 31A, pp.25752585,Oct.(2000).

[56] B.N.Olson,ch.Brucke,J.Parolini,D.J.MooreandK.B.Rundman, AusformedAustempered Ductile Iron(AADI), International Conference on ADI; DIS andAFS,Louisville,KY,USA,2960,Sept.,pp.2527(2002).

[57] H.NasrEldin,A.NofalandM.Ibrahim,Ausformingof Austempered Ductile Iron Alloyed with Nickel,InternationalJ.ofCastMetalsResearch,vol.19,No.3,pp.137150(2006).

[58] A.A. Nofal, H. Nasr Eldin, and M.M. Ibrahim,ThermomechanicalTreatmentofAustemperedDuctile


17

Iron,Proceedingsofthe8thSymposiumonScienceandProcessingofCastIronSPCI8,Beijing,China,pp.397402Oct.1619(2006).

[59] B.N. Olson, D.J. Moore, K.B. Rundmanb and G.R.Simula, Potential for Practical Applications ofAusforming Austempered Ductile Iron, AFS Trans.,vol.110,02118,pp.965980(2002).

[60] X.LeiandC.J.Lissenden,FiniteElementSimulationofAusformingofAustemperedDuctileIronComponents,Trans.oftheASME,vol.12,pp.420425(2001).

[61] P.B. Magalhaes, Processo de Producao de FerrousFundidos Bainiticos por Austempera Directa, Patentno.85046,Portugal(1985).

[62] R.W. Kaiser and P.R. Sahm, Squeeze CastingDevelopment of Ductile Iron for Increasing ADIProperties, International Scientific Conference onADIFoundrys Offer for Designers and Uses ofCasting, pp. II/39II/44, CracowPoland, 2324 Nov.(2000).

[63] M. Johansson, New ADIProduction Technology,WorldConferenceonADI,DISandAFS,Louisville,KY,USA,2930Sept.(2002).

[64] J.YangandS.K.Putatunda, Improvement inStrengthandToughnessofAustemperedDuctileCastIronbyaNovelTwoStepAustemperingProcess,MaterialsandDesign25,pp.219230(2004).

[65] J.YangandS.K.Putatunda,InfluenceofaNovelTwoStep Austempering Process on the StrainHardeningBehavior of Austempered Ductile Cast Iron (ADI),Materials Science and Engineering A382, pp. 265279(2004).

[66] J.YangandS.K.Putatunda,EffectofMicrostructureonAbrasionWearBehaviorofAustemperedDuctileCastIron (ADI) Processed by a Novel TwoStepAustempering Process, Materials Science andEngineeringA406,pp.217228(2005).

[67] J.Yang and S.K. Putatunda, Near Threshold FatigueCrackGrowthBehavior ofAustemperedDuctileCastIron (ADI) Processed by a Novel TwoStepAustempering Process, Materials Science andEngineeringA393,pp.254268(2005).

[68] K.M.Ibrahim,A.A.NofalandM.M.Ibrahim,EffectofAlloyingAdditionsandTwoStepAustemperingontheMicrostructure and Mechanical Properties of DuctileIron, The 9th Int. Conf. on Mechanical Design andProduction(MDP9),Cairo,Egypt,Jan.810(2008).

[69] K. Hayrynen and K. Brandenberg, CarbidicAustempered Ductile Iron (CADI) the New Wear

Material,Trans.AFS, vol. 111,paperNo. 03088,pp.845850(2003).

[70] J.R. Keough and K.L. Hayrynen, CarbidicAustemperedDuctileIron(CADI),DISMeeting,Nov.14(2000).

[71] M. Chisamera, I. Riposan, C. Ionascu and S. Stan,MottledAustemperedCast Irons (MnCrNi System)ObtainedbyMgFeSiandModifying IronGrits (M16)forMagnesiumTreatmentatHigherWearResistance,International ScientificConference on ADIFoundrysOfferforDesignersandUsersofCastings,III/25III/32,2324Nov.(2000).

[72] S. Laino, J.A. Sikora and R.C. Dommarco,DevelopmentofWearResistantCarbidicAustemperedDuctileIron(CADI),Wear,265(2008).

[73] L.Jinhai,L.Guolu,Z.Huiyou,B.Boqian,X.Xingchuan,Y. Zhaoyu, Z. Yicheng and Y. Xuexian, Study onMicrostructure and Properties of CarbidicAustemperedDuctile Iron (CADI),Proceedingsof69thWorldFoundryCongress,Oct.1620(2010),Hangzhou,China,pp.423426.

[74] L. JinLai, Y. Xuexian, Z. Hui, L. Guolu; Applicationand Prospect ofADI andCADI inMetallurgical andMineIndustries;ModernCastIron,(2008),28,4.

[75] Z.YiCheng,L.KeruiandZ.ZhongChou;Production,ApplicationandDevelopmentForecastofIsothermallyQuenched (Austempered) Ductile Iron in China;ModernCastIron(2007),27(10).

[76] S.Laino,J.SikoraandR.C.Dommarco;AdvancesintheDevelopment of Carbidic ADI, Proceedings of theNinth International Symposium on Science andProcessingofCast Iron (SPCI9),Luxor,Egypt 1013thNov.(2010),pp.187192.

[77] 77.R. Zhou, Y. Jiang, D. Lu, R.F. Zhou and Z. Li,DevelopmentandCharacterizationofaWearResistantBainite/Martensite Ductile Iron by Combination ofAlloying and Controlled Cooling Heat Treatment,Wear250,pp.529534(2001).

[78] 78. S.M.Lee, S.S.Park andB.M.Moon, High Si andMnContaining Austempered Ductile Cast Iron forWear Applications, Proceedings of the 65th WorldFoundryCongress,Gyeongju,Korea,pp.251258(2002).

[79] 79.Z.Ning,S.Ren, J.SunandY.Feng, StudyonAsCastAusteniteBainiteDuctileCast Iron,ProceedingsofScienceandProcessingofCastIron,SPCI8,Beijing,China,pp.134138(2006).

[80] 80.D.M.StefanescuandR.Ruxanda,LightweightIronCastings Can They Replace Aluminum Castings?,


18

Proceedingsofthe65thWorldFoundryCongress(WFC),Gyeongiu,Korea(2002).

[81] 81.E. Fras and M. Gorny, Structure of Thin WallAustempered Ductile Iron (TWADI), Proceedings ofthe 8th International Symposium on Science andProcessingofCastIron(SPCI8),Beijing,China,Oct.1619,pp.157162(2006).

[82] 82.C. Labrecque and M. Gagn, Production ofCarbide Free Thin Wall Ductile Iron Castings, AFSTrans.vol.104,pp.3138(2000).

[83] 83.D.M. Stefonescu, L.P. Dix, R.E. Ruxanda, C.C.Coburn andT.S.Piwonks, TensileProperties ofThinWallDuctileIron,AFSTrans.,vol.187,p.1149(2002).

[84] 84.M.M.Mourad,A.A.Nofal,H.H.AhmedandH.A.Elhashimy, Investigation of the ParametersAffectingtheProductionandPropertiesofThinWallDuctileIronCastings,theArabFoundrySymposium(ARABCAST),

SharmElSheikh,Egypt,710Nov.(2008).[85] 85.R.A. Martinez, R.E. Boeii and J.A. Sikora,

Application of ADI in High Strength Thin WallAutomotive Parts, World Conference on ADI,Louisville,pp.143148,Oct.(2004).

[86] 86.C.Labrecque,M.GagnandA. Jarid, Optimizingthe Mechanical Properties of Thin Wall Ductile IronCastings,AFSTrans.,vol.109,St.Louis,(2005).

[87] 87.M.Gagn,C.Labrecque,M.PopescuandM.Sahoo,Effect of Silicon Content and Wall Thickness on thePropertiesofAustemperedDuctile Irons,AFSTrans.,vol.110,(2006).

[88] 88.M.M. Mourad, K.M. Ibrahim, M.M. Ibrahim andA.A. Nofal, Optimizing the Properties of Thin WallAustempered Ductile Iron, 68th World FoundryCongress(WFC),Chennai,India,pp.161166,710Feb.(2008).

advances in the metallurgy and applications of adi

Documents

austemperedductile iron

squeeze cast adi

ausformed adi

deformation of adi

cast iron family

carbidic adiductile

austempering transformation

final microstructure