Carbidic Austempered Ductile iron_ADI.doc

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Carbidic Austempered Ductile iron (CADI)

Presented at DIS Meeting on November 14, 2000

John R. Keough, PE and Kathy L. Hayrynen, PhDApplied Process Inc. Technologies Div. Livonia, !ichigan, "#A

ABSTRACT$ar%idic Auste&pered Ductile Iron '$ADI( is a )a&ily o) ductile cast irons produced *ith car%ides, '%oth ther&allyand &echanically introduced(, that are su%se+uently Auste&pered to ehi%it ade+uate toughness and ecellent*ear resistance.

INTRODUCTION#ince a%out -/ industry has discovered various &aterial0process co&%inations that ehi%it surprisingly good *earresistance %ut de)y classi)ication as either *hite irons or Auste&pered Ductile Irons. They co&%ine various ther&aland &echanical &eans )or introducing car%ides in, and on ductile iron co&ponents. They are su%se+uently heattreated %y the Auste&pering process.

This paper atte&pts to de)ine this class o) $ar%idic Auste&pered Ductile Irons and to de)ine )or the reader the stateo) the art to date.

CARBIDIC AUSTEMERED DUCTI!E IRON (CADI)#ince the early -/1s several &anu)acturers have %een using various techni+ues to eploit the advantages o) the*ear resistance o) car%ides and the toughness o) the Aus)errite &atri produced %y the Auste&pering process.

"#at is Austemperin$%Auste&pering is a high per)or&ance isother&al heat treat&ent that i&parts superior per)or&ance to )errous &etals.The classic de)inition descri%es that as an isother&al heat treat&ent. &i$ure 'co&pares and contrastsconventional 2+uench and te&per3 heat treat&ent and Auste&pering in a generic )errous &aterial.In conventional +uench and te&pering 'red line( the co&ponent is heated to red heat and a )ully Austenitic

condition. It is then +uenched rapidly to a te&perature %elo* the !artensite start line. At this point the )ace centeredcu%ic Austenite trans)or&s to a taller, %ody centered tetragonal !artensite. This unte&pered !artensite is very hardand %rittle. This can cause di))iculty as the eterior o) the part trans)or&s )irst. !o&ents later, the inside o) the parttrans)or&s to !artensite and )orces the eterior to 2&ove3. This nonuni)or& trans)or&ation can result in severedistortion or crac4ing. '$ast irons are particulary vulnera%le to crac4ing during +uenching(. The !artensitic structureis su%se+uently te&pered to produce the desired co&%ination o) strength and toughness.The Auste&pering process 'green line( %egins si&ilarly *ith austeniti5ation )ollo*ed %y rapid cooling to avoid the)or&ation o) Pearlite. Ho*ever, there the si&ilarity ends. In the Auste&pering process the +uenching &edia is heldat a te&perature a%ove the !artensite start te&perature. This results in the 6$$ austenite cooling to the +uenchte&perature. The +uenched &aterial is then held at that te&perature )or a ti&e necessary to produce the desiredacicular structure. In steels, that structure is %ainite, a structure o) acicular )errite and car%ide. In cast irons, *iththeir higher silicon content, an inter&ediate structure called Aus)errite results. Aus)errite consists o) acicular )erriteand car%on sta%ili5ed Austenite. This isother&al trans)or&ation results in uni)or& trans)or&ation o) the structure

throughout the part . Thus crac4ing during +uench trans)or&ation is virtually eli&inated.In Auste&pered cast iron, this Aus)errite has very good a%rasive *ear properties %ecause o) its tendancy to 2straintrans)or&3 on the a%raded sur)ace. Auste&pered Ductile Iron 'ADI( can co&pete *ith &uch harder &aterials.Ho*ever, even ADI can %e %ested %y &aterials containing car%ides. 7ut, car%idic irons tend to %e very %rittle.

"#at is Carbidic ADI (CADI)%$ADI is a ductile cast iron containing car%ides, 'that are either ther&ally or &echanically induced(, that issu%se+uently Auste&pered to produce an Aus)erritic &atri *ith an engineered a&ount o) car%ides.

!ethods o) car%ide introduction include8

As$ast $ar%ides

o Internal 'che&ical or inverse( chill

o #ur)ace chill 'li&ited depth, directional(
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!echanically Introduced $ar%ides

o $astin, crushed !$ycar%ides

o $astin, engineered car%ides 'shapes(

9elded

o Hard)ace *eld&ent

o 9eld&ent *ith !$ygrains

AsCast CarbidesInternal 'che&ical or inverse( chillIron created as ductile iron and treated *ith &agnesiu& and0or rare earths to result in spheroidal graphite can %einduced to produce a car%idic &icrostructure %y a variety o) &ethods. These include alloying *ith car%ide sta%ili5erssuch as chro&iu&, &oly%denu&, titaniu& and others, controlling the cooling during sha4eout or ad:usting thecar%on e+uivalent to produce a hypoeutectic iron che&istry. The car%ides produced )ro& this techni+ue can %e2dissolved3 to a controlled etent %y su%se+uent Auste&per heat treat&ent.&i$ure sho*s a $ADI sa&ple *ith ascast car%ides that *as su%se+uently Auste&pered at ;//o6 *ith ;= car%ides and a continuous Aus)errie &atri. This &icrostructure *ould %e slightly less *earresistant than the iron in&i$ure %ut *ith greater toughness.&i$ure +sho*s a si&ilar iron *ith car%ides )urtherdissolved to ?/=. &i$ure ,sho*s the *ear resistance o) a typical $ADI vs ascast gray and ductile iron and variousgrades o) ADI. Table 'sho*s a ta%le o) typical unnotched $harpy i&pact values including $ADI.

Directional Sur-ace C#ill CarbidesThese car%ides are produced %y placing &edia *ith high ther&al conductivity and ther&al capacity ad:acent to thesur)ace o) the solidi)ying iron. As the &olten iron contacts this sur)ace the solidi)ication rate is su))iciently high tocreate car%ides perpendicular to that sur)ace and etending into the %ody o) the part. These co&ponents &ay0or&ay not %e )ree o) car%ides in the ther&al center o) the part. Depth o) chill can, and is, controlled %y controlling thechill sche&e and the che&ical analysis o) the iron. These car%ides can %e 2dissolved3 to a controlled etent %ysu%se+uent Auste&per heat treat&ent.

Mec#anicall. Introduced CarbidesCastin/ crus#ed M0C.carbidesThis process, to the authors1 4no*ledge is only practiced %y license to #advi4 $orporation. In this process, crushed!$ycar%ides are strategically placed in the &old cavity at the desired location. The &etal then )ills in around thecar%ides resulting in a continuous iron &atri *ith discrete car%ides &echanically trapped in it. The speci)ic &ethodused to contain the car%ides 2in place3 during &old )illing is not 4no*n to the authors. This &ethod allo*s theengineer the option o) placing car%ides only *here needed resulting in a traditional ductile iron &atri throughout therest o) the casting. These particular car%ides are essentially una))ected %y su%se+uent auste&per heat treat&ent.

Castin/ en$ineered carbides (s#apes)This process re+uires the setting o) engineered car%ides into the &old *ith special core prints or other techni+ues.

These engineered car%ides &ay have %ac4 dra)ts or 4eyed )eatures that allo* the& to %e &echanically loc4ed intothe &etal once it solidi)ies. These car%ides are then una))ected %y su%se+uent auste&per heat treat&ent.

Carbidic "eldments

1ard-ace "eldmentThis process starts *ith a conventional ductile iron casting, typically *ith a )ully, or &ostly )erritic &atri. The castingis then hard)ace *elded in the area o) greatest *ear. This results in a car%idic *eld and a heat a))ected area at the*eld0casting inter)ace as sho*n in &i$ure 2.#u%se+uent Auste&per heat treat&ent has little or no e))ect on the*eld structure 'depending on the che&ical analysis o) the *eld &aterial chosen( %ut the heat a))ected 5one iseli&inated and a )ully Aus)erritic &atri results in all areas other than the *eld itsel) as sho*n in &i$ure 3.In so&e*eld applications po*dered &etal car%ides can %e purged into the &olten *eld to provide additional *earresistance.
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Table '4 Typical unnotched $harpy i&pact values ')tl%s(. Tested at @o6 'o$(.Bac5 to Article

?/>;= $ar%ide;// $ADI

-/

$ar%uri5ed B/

;;/< Ductile Iron

>;

Crade ? ADI

@/

Crade - ADI

/

>;- Ductile Iron

;

OTENTIA! A!ICATIONS &OR CADIThe current applications )or $ADI are li&ited, %ut gro*ing. Agricultural co&ponents have %een produced in $ADI*ith ascast car%ides since the early -/s. A #andvi4 licensee has produced li&ited production +uantities o) $ADIparts *ith castin, crushed car%ides as *ell. Research into chillcar%ide $ADI ca&sha)ts is ongoing. Ho*ever, thevisi%ility o) $ADI has %een greatly increased o) late *ith the pu%lic launch o) $ADI in progra&s at John Deere.In the 6e%ruary /// issue o) #AE )) High*ay !aga5ine John Deere announced the use o) $ADI ele&ents in itsrevolutionary ne* rotary co&%ine '&i$ure 6(.Then, in John Deere1s *ners $ircle !aga5ine '!arch ///( they pu%licly announced the use o) $ADI in theirLa5er Rip ripper points. These t*o events accelerated ongoing e))orts in the industry in %oth research andproduction.$ADI presents so&e intriguing product possi%ilities. Potential applications in vehicles include ca&sha)ts and ca&)ollo*ers. Agricultural applications &ay include rippers, teeth, plo* points, *ear plates and harvester, pic4er and%aler co&ponents. Possi%le railroad applications include contact suspension co&ponents and railcar0hopper car*ear plates. In construction and &ining potential applications include digger teeth and scari)iers, cutters, &illha&&ers, )lails, guards, covers, chutes, plates, housings, transport tu%es and el%o*s, rollers and crusher rollers.Ceneral industrial applications could include pu&p co&ponents, *ear housings and plates, conveyor *ear parts,s4ids and s4id rails, rollers and %last parts.

"1AT ARE T1E RIS7S 8 DISAD9ANTA:ES O& CADI%

$ADI ehi%its only li&ited &achina%ility 'possi%ly grinding only(

I) alloying is used the returns &ust %e segregated

Additional operations and costs &ay %e incurred i) car%ides are *elded on or castin

"1AT ARE T1E AD9ANTA:ES O& CADI%
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&i$ure 4 CADI >it# 2,? carbide and a ,@@& ADI matri0= (T#ese carbides >ere produced ascast)=Bac5 to Article

&i$ure *4 CADI >it# +,? carbide and a ,@@& Aus-errite matri0 (T#ese carbides >ere produced ascast)=Bac5 to Article
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&i$ure +4 CADI >it# *@? carbide and a ,@@& Aus-errite matri0= (T#ese carbides >ere produced ascast)=Bac5 to Article
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&i$ure ,4 Abrasie >ear resistance o- CADI s= ascast and Austempered $ra. and ductile irons=Bac5 to Article

&i$ure 24 Microstructure o- #ard-ace >elded ductile iron s#o>in$ t#eCarbidic >eld (li$#t) and t#e pearlitic #eat a--ected one (dar5)=

Bac5 to Article

&i$ure 34 (Ri$#t) Microstructure o- #ard-ace >elded ductile iron t#at #as been subsein$ t#e Carbidic >eld (li$#t) and t#e Aus-errite matri0 (dar5)=

Bac5 to Article
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Carbidic Austempered Ductile iron_ADI.doc