Effect of Finishing Rolling Temperature on Microstructure and Mechanical Properties of Microalloyed TRIP Steels

􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇􀪇

JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL􀆰２ ０ １ ３,２ ０( １ ０):７ ５ Ｇ ８ ０

􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉􀪉 􀪉

Ef f e c to fF i n i s h i ngRo l l i ngTempe r a t u r eon Mi c r o s t r u c t u r eand Me chan i c a lPr ope r t i e so fMi c r o a l l o e dTRIPS t e e l s y MIZhen Ｇ l i, 　J IANG Ha i Ｇ t ao, 　LIZh i Ｇ chao, 　CHEN Me i Ｇ f ang, 　WANGZh i Ｇ gang ( Na t i ona lEng i ne e r i ngRe s e a r chCen t e rf o rAdvanc edRo l l i ngTe chno l ogy,Un i ve r s i t fSc i enc eand yo Te chno l ogyBe i i ng,Be i i ng１０００８３,Ch i na) j j

Ab s t r a c t:Di f f e r en ts amp l e so fTRIP ( t r ans f o rma t i oni nduc edp l a s t i c i t t e e lob t a i nedbytwod i f f e r en tho t Ｇ r o l l i ng y)s s chedu l e sa r ei nve s t i t edbyus i ngaSEM ( s c a nn i nge l e c t r onmi c r o s c op e)．Th emi c r o s t r u c t u r ei sc h a r a c t e r i z e dbyu s i ng ga anOM ( op t i c a lmi c r o s c ope)f o rpha s ed i s t r i bu t i onandbyEBSD ( e l e c t r onba cks c a t t e rd i f f r a c t i on)f o rt ex t u r eand s emapp i ng．ODF ( o r i en t a t i ond i s t r i bu t i onf unc t i on)g r aphsa r eus edt oi nve s t i t et hee f f e c to fr e c r s t a l l i z a t i on pha ga y behav i o ro ft heho t Ｇ de f o rmedaus t en i t eonpha s et r ans f o rma t i ondu r i ngt hec on t r o l l edc oo l i ngp r o c e s s．Theme chan i c a l behav i o ri si n t e r r e t edi nt e rmso ft hes t r eng t ho fbo t hha r dands o f tpha s e s,i nc omb i na t i onwi t ht hequan t i t o c a Ｇ p y,l t i onandt r ans f o rma t i onk i ne t i c so ft heme chan i c a l l nduc ed ma r t ens i t e( TRIPe f f e c t)．Ther e su l t sshowt ha tmo r e yi aus t en i t eg r a i nsex i s ti nt hes t e e l sob t a i neda tf i n i sh i ngr o l l i ngt empe r a t u r e( FRT)o f７５０ ℃ ,wh i chi nhe r i t edt hede Ｇ f o rma t i ons t r uc t u r ea f t e rt heho t Ｇ r o l l i ngp r o c e s s．Thei ns t an t ane ousn va l ue ( ni )o ft ho s es t e e l si skep th i r i nga ghdu l a r angeo fs t r a i nbe f o r ef a i l u r e,wh i l et het ens i l es t r eng t handt o t a le l onga t i ono ft hes t e e l swi t hr e spe c tt ot hed i f Ｇ ger f e r en tf i n i sh i ngr o l l i ngt empe r a t u r e sdono tshowanys i i f i c an td i f f e r enc e s． gn Ke r d s:TRIP;ho tr o l l i ng;mu l t i s emi c r o s t r uc t u r e;me chan i c a lbehav i o r;EBSD pha ywo

　　TRIP ( t r ans f o rma t i oni nduc edp l a s t i c i t t e e l s y)s , s s e s samu l t i s emi c r o s t ruc t u r ec ons i s t i ngt Ｇ po pha yp i c a l l ff e r r i t e( α ＧFe),ba i n i t eand me t a s t ab l er e Ｇ yo [ １－５] ( ) t a i nedaus t en i t e γ ＧFe ．Ther o l l i ngp r o c e s s i ng r ame t e r s,e spe c i a l l hef i n i sh i ngr o l l i ngt empe r a Ｇ pa yt ( ) , t u r e FRT p l ayanimpo r t an tr o l ei nt hef o rma t i on o ft hemu l t i s emi c r o s t ruc t u r eo fTRIPs t e e l．Mo Ｇ pha r eove r,t he op t imum me chan i c a lp r ope r t i e s( h i gh s t r eng t handexc e l l en tp l a s t i c i t fTRIPs t e e la r e y)o ma i n l t e rmi nedbyi t s mi c r o s t ruc t u r e,e spe c i a l l yde y t hevo l umef r a c t i onands t ab i l i t fr e t a i nedaus t en Ｇ yo i t e．Thec a rbonr e e c t edf r omt heg r owi ngf e r r i t eand j ba i n i t i cf e r r i t een r i che st heaus t en i t ep r og r e s s i ve l y [ ６] ands t ab i l i z e st heaus t en i t ea tr oom t empe r a t u r e ． Fe r r i t ewi t hbc cs t ruc t u r ec anbed i s t i ngu i shedi n t o , twot si n t e r c r i t i c a lf e r r i t eex i s t i ngbe f o r eTRIP ype s t e e l sa r ecoo l edi n t o ba i n i t ef o rmi ng t empe r a t u r e r eg i on,andpr oeu t e c t o i df e r r i t ef o rmi ngdu r i ngt he [] c oo l i ngp r oc e s s７ ．Ba i n i t ei st r ans f o rmedf r om t he

r en taus t en i t e．Pa r en taus t en i t ei sgov e r n e dbyo r i Ｇ pa ( ) e n t a t i onr e l a t i on s ORs t ha ta r ed e s c r i b e dbyanumb e r o fequ i va l en tva r i an t s,andbys e l e c t i onamongt hos e [] va r i an t s８ ．Re t a i nedaus t en i t ei st heso l epha s et ha t ha st hef c cs t ruc t ur ei nTRIPs t e e l． [] 　 　S Za e f f e r e r７ haves t ud i edt het r ans f o rma t i on me chan i smsandco r r e l a t i onbe twe en mi c r os t ruc t ur e and me chan i c a lp r ope r t i e so faco l d Ｇ r o l l edandan Ｇ , n e a l e dTRI Ps t e e l．Howe v e rt het r an s f o rma t i onme c ha Ｇ n i smso fho t Ｇ r o l l edTRIPs t e e lhaveno tbe eni nve s t i Ｇ , t edt ho r ough l r e f o r e i nt h i s wo rkt hebc c ga y．The andf c cs t ruc t ur e sa r ed i s t i ngu i shedby EBSD ( e l e c Ｇ t r onba cks c a t t e rd i f f r a c t i on)．S i nc et he mi c r os t ruc Ｇ t ur ei sde t e rmi nedbyt hecompos i t i onsandcoo l i ng cond i t i ons,twoho t Ｇ r o l l eds chedu l e sa r eemp l oyedt o r oduc et heTRIPs t e e l st oi nve s t i t et hee f f e c to f p ga f i n i sh i ng r o l l i ng t empe r a t ur e on t he i r mi c r os t ruc Ｇ t ur e s．Fur t he rmo r e,t het ex t ur ei nf c candbc cpha Ｇ s e si sa l sos t ud i eds i nc et her e t a i nedau s t e n i t ec an

Founda t i onI t em: I t em Spons o r edbyNa t i ona lNa t ur a lSc i enc eFounda t i ono fCh i na ( ５０８０４００５);Cen t r a lCo l l eg i a t eBa s i cSc i en t i f i cRe s e a r ch Bur s a r fCh i na ( FRF ＧTP Ｇ １１ Ｇ ００５B) yo B i o r aphy:MIZhen Ｇ l i( １９７１—),Fema l e,Do c t o r,Pr o f e s s o r; 　E Ｇma i l:mi z l＠ne r c a r 􀆰us t b 􀆰edu 􀆰cn;　Re c e i v e dDa t e: May１７,２０１２ g

　　　　J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l　　　　　　　　　　　　　　Vo l 􀆰２０　

􀅰 ７６ 􀅰

c a t u r et hes i t u a t i ono ft h ep a r e n tph a s et os omee x t e n t． p

１　Exp e r imen t a lPr o c e du r e

　 　 Thechemi c a lc ompo s i t i on o ft hei nve s t i t ed ga s t e e li sl i s t edi nTab l e１．Thes t e e lwa sf ab r i c a t edby va cuum i nduc t i on me l t i ng．The s t e e li ngo t s we r e he a t edt o１２００ ℃ f o r２h,ho tr o l l eda c c o r d i ngt o twok i ndso fs chedu l e ss epa r a t e l henf o r y,andt ged t of o rmap l a t ewi t hat h i ckne s so f３０ mm．Theho t r o l l i ngs chedu l e sa r el i s t edi n Tab l e２．TRIPs t e e l s a f t e rr o l l i nga r ec oo l edby３s t eps;a i rc oo l i nga f t e r １s ts t epo fr ap i dc oo l i ngi st oob t a i nenoughf e r r i t e, and２ndr ap i dc oo l i ngs t epi st og i veasu f f i c i en tr a t e , t o ob t a i n ba i n i t e．Fo rs imp l i c i t he s t e e l s ho t y t r o l l edbys chedu l ea th i rFRTa r enamedSH and ghe t hes t e e l sho tr o l l ed by s c h e du l ea tl owe rFRT a r e ( ) n ame dSL．Af t e rt h ec on t r o l l e dc o o l i ngp r o c e s sF i 􀆰１ , g t heTRIPp l a t e swe r es imi l a r l o i l eda t４００ ℃． yc 　　Theme t a l l og r aph i cspe c imenswe r epo l i s h e da nd

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Tab l e１　Ch emi c a lc ompo s i t i ono fi nv e s t i a t e ds t e e l g (ma s spe r c en t,％ ) 　 S i

０ 􀆰２１ １ 􀆰４８

Mn

１ 􀆰４６

Nb

０ 􀆰０４４

Mo

P

０ 􀆰１６

０ 􀆰０１０

S

０ 􀆰００９７

Tab l e２　Ho tr o l l i ngs ch e du l e sf o ri nv e s t i a t e ds t e e l s g / Reduc Pa s s Th i ckne s s t i on/ numbe r mm ％ １

３０

３３

３

１３

３５

２

２０

３５

４

８ 􀆰５

３５

６

４

２６

５

５ 􀆰５

３６

Tempe r a t ur e f o rh i gh FRT/℃

Tempe r a t ur e f o rl ow FRT/℃

１１００

１０００

１１５０ １０５０ ９９０ ９３０

８７０

１０５０ ９５０ ９００ ８５０ ８００

F i 􀆰１　Con t r o l l e dc o o l i ngp r o c e s sa f t e rf i n i s hr o l l i ng g

e t ched wi t hl ep r al i i d９ ．The mi c r os t ruc t ur e so f qu t hei nve s t i t eds t e e l s we r ei den t i f i ed by us i ng an ga op t i c a lmi c r os cope (OM )andas c ann i ng e l e c t r on mi c r os cope ( SEM)．Thes amp l e sf o rSEMi nve s t i Ｇ ga t i on and EBSD me a sur emen t s we r ep r epa r ed by r i nd i ngf o l l owe dbye l e c t r opo l i s h i ng．HKLs o f twa r e g , wa sus edt od i s t i ngu i sht hef e r r i t e ba i n i t eandaus Ｇ t en i t epha s e s． []

２　Exp e r imen t a lRe s u l t s

２ 􀆰１　Mi c r o s t r u c t u r echa r a c t e r i z a t i on ２ 􀆰１ 􀆰１　Re t a i nedau s t en i t e 　　Aus t en i t es t ab i l i t ton l t r ong l yno ydependss yon i t sowncha r a c t e r i s t i c s( vo l umef r a c t i on,g r a i ns i z e, ) s emo r l ogyandc a rboncon t en t bu ta l sode Ｇ pha pho t e rna lf a c t o r sl i ket hes t i f f ne s so ft he pendsonex sur r ound i ngpha s e s,andt hec r t a l l og r aph i co r i en Ｇ ys t a t i ono ft heg r a i nswi t hr e spe c tt ot hel oad i ngd i r e c Ｇ [] t i on１ ．Thetwod i f f e r en tTRIPs t e e l s we r ee t ched wi t hl epr al i i dt oobs e r vet hed i s t r i bu t i ono fba i n Ｇ qu , i t eandaus t en i t eg r a i n s wh i c hi ss howni nF i 􀆰２．The g l oc a t i onso fr e t a i nedaus t en i t eobs e r vedi nt heexpe r Ｇ

F—Fe r r i t e; 　B—Ba i n i t e; 　Ar—Re t a i nedaus t en i t e． ( a)SL; 　 ( b)SH ．

F i 􀆰２　Mi c r o s t r u c t u r eo fd i f f e r en tTRIPs t e e l se t ch e dwi t hl ep r al i i dob t a i n e dbyOM g qu

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I s sue１０　　　　　　　　Ef f e c to fF i n i sh i ngRo l l i ngTempe r a t u r eon Mi c r oa l l oyedTRIPS t e e l s　

imen t a ls amp l e sdemons t r a t edi nF i 􀆰３ ( a)c anbe g d i v i dedi n t ot hr e ec a t ego r i e s:su r r oundedbyba i n i t e , , l a t hs be twe enba i n i t eandf e r r i t e andsu r r ounded bys eve r a lf e r r i t eg r a i ns．The s eaus t en i t eg r a i nswi l l undoub t ed l h a v ed i s t i n c te f f e c to nt h et r a n s f o r m a Ｇ y [] t i on me chan i sm du r i ng t het ens i l e de f o rma t i on７ ． Theaus t en i t eg r a i nssu r r oundedbyba i n i t esha r el a r Ｇ e rs i z ed u e t oc a r b o ne n r i c h m e n td u r i n t h eb a i n i t e g g t r ans f o rma t i on,wh i l et ho s esu r r ounded by f e r r i t e a r e muchsma l l e r．Thede c r e a s i ngg r a i ns i z e mi t gh

r educ et he Mst empe r a t ur e１ ．Thes i z eo faus t en i t e , r a i n i n S i s l a r e r a n d t h ev o l u m e e r c e n t o f a u s Ｇ g g p L t en i t eo fSLi sa l soh i rt hant ha to fSH a sshown ghe i n Tab l e３．Theaus t en i t echa r a c t e r i s t i c sa r ea l so showni nt hei nve r s e po l ef i u r e s Ｇ b a s e d m a si g p n , F i 􀆰４ wh i chdemons t r a t e st ha tt heaus t en i t eg r a i n s g i nSH a r er oundwh i l et ho s ei nSLa r ec o a r s eande l ong a Ｇ t e d．Th i s may beexp l a i nedbyt her e c r t a l l i z a t i on ys behav i o ro ft heho tde f o rmedaus t en i t e． 　　Be s i d e st hes ha eo ft heau s t e n i t eg r a i n s,t hes l i t p gh []

( a)SL; 　 ( b)SH ．

F i 􀆰３　I nv e r s epo l ef i r emap sandg r a i nbounda r i s t r i bu t i onmap so fau s t en i t ei nd i f f e r en tTRIPs t e e l s g gu yd Tab l e３　Me chan i c a lp r op e r t i e s,v o l umef r a c t i onands i z eo fau s t en i t e

Yi e l ds t r eng t h/ Tens i l es t r eng t h/ Samp l e MPa MPa

SL

SH

５８４ ５３３

７８０

７５８

To t a le l onga t i on/ ％

Tens i l es t r eng t h×t o t a l e l onga t i on/( GPa􀅰 ％ )

Vo l umef r a c t i on o fγ/％

S i z eo f γ/μm

３３ 􀆰４

２５ 􀆰３

６ 􀆰４４

０ 􀆰３６

３４ 􀆰０

２６ 􀆰５

８ 􀆰８４

０ 􀆰４１

( a)SL; 　 ( b)SH ．

F i 􀆰４　I nv e r s epo l ef i r emap so fb c cpha s e si nd i f f e r en tTRIPs t e e l s g gu

r ays c a l eva r i a t i oni naus t en i t eg r a i nsa swe l la st he g t ex t u r eo fr e t a i nedaus t en i t ec anshowt hevo l umeo f [ ] aus t en i t eg r a i nsunde r i ngr e c r t a l l i z a t i on１０ ．The go ys r ays c a l eo fani nd i v i dua laus t en i t eg r a i ni s much g r e ri nSH a sshowni nF i 􀆰４,andon l eve r a la c Ｇ pu g ys c i den t a lg r a i ns wi t hg r ays c a l eva r i a t i ona r ef ound,

wh i chi l l us t r a t e st ha t mos to ft heaus t en i t ei n SH havef i n i shedr e c r t a l l i z a t i on．Ont hecon t r a r ys y,a l a r rpe r c en t ageo faus t en i t eg r a i nsi nt heSL TRIP ge s t e e lf l uc t ua t ei ng r ays c a l e． ２ 􀆰１ 􀆰２　Fe r r i t e 　　Asshowni nF i 􀆰３,t hepo l lf e r r i t ei nt he g ygona

􀅰 ７８ 􀅰

　　　　J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l　　　　　　　　　　　　　　Vo l 􀆰２０　

twos t e e l sf o l l owst hes amed i s t r i bu t i on d i s c i l i ne p andsha r es imi l a rs i z e．Af t e rs i xho tr o l l i ngpa s s e s, t he r e mus tbel a r f o rma t i on wi t h i naus t en i t e, gede andd i s l oc a t i onsandd i s l o c a t i onc e l l samongt heaus Ｇ t en i t eg r a i nssupp l u a n t i t i e so fn u c l e a t i o n o i n t s yq p f o rf e r r i t e．Owi ngt ot hel owFRTf o rSL TRIPs t e e l andt hef o l l owedqu i ckc oo l i ngr a t e,de f o rma t i onr e Ｇ c ove r i ngr a t i oi smi l dun t i lt heshe e t sa r ehe l di nt he i n t e rmed i a t et empe r a t u r er eg i on．Wh i l et he TRIP s t e e l sa r equenchedi n t ot heba i n i t et r ans f o rma t i on , z one t hef e r r i t eg r a i nsnex tt oaus t en i t ec on t i nuet o r owt oal a r rs i z eun t i laus t en i t et r ans f o rmst o g ge ba i n i t e．Tha t ′s why t hef e r r i t eg r a i nssu r r ounded wi t haus t en i t ea r emuchl a r rt hant ho s ef o rmedi n ge t hef e r r i t et r ans f o rma t i onz one． ２ 􀆰１ 􀆰３　Ba i n i t e 　　Lowang l eg r a i nbounda r i e s( １ °－３ °)i nba i n i t e showni nF i 􀆰３ ( b)a r e much mo r et hant ho s ei n g s amp l eo fSLshowni nF i 􀆰３ ( a)． Fu r t he rmo r e,r e l Ｇ g a t i vef r equenc od i s o r i en t a t i onang l ei sshowni n yt F i 􀆰５,wh i l el a t t i c ed i s t o r t i on deg r e ei n ba i n i t eo f g s amp l eo f SL i s much h i ra c c o r d i ng t ot he ghe r ays c a l eva r i a t i oni n ba i n i t eshowni nF i 􀆰４ ( a)． g g Muchene r r i i na t edf r om t het r ans f o rma t i oni s gyo g wa i t i ngt ober e l e a s edwhe t he rbyf o rmi ngl owang l e r a i n bounda r i e so r by l a t t i c ed i s t o r t i on．Ba i n i t e g t r ans f o rma t i ono c cu r s wi t has i i f i c an tshapeand gn vo l umechangea s s o c i a t ed wi t hhyd r o s t a t i cs t r e s s e s wh i chl e adt ol ow ang l eg r a i nbounda r i e so rl a t t i c e [] d i s t o r t i on３ ．Thed i f f e r enc e sbe twe ent heba i n i t eex Ｇ i s t enc ef o rmsmaya l s obei n t e r r e t e db t h ed e f o r m Ｇ p y a t i onene r e t a i neddu r i ngt heho tr o l l i ngp r o c e s s． gyr 　 　Theh i t t e rn qua l i t ow ave r age mi Ｇ gh pa yandl ( ) s o r i en t a t i onsa c c o r d i ngt oF i 􀆰４ b i nd i c a t ear e l a Ｇ g t i ve l owd i s l o c a t i ondens i t nba i n i t ewh i chi sdue yl yi t or e cove r i si sbe c aus et heh i r ans f o rma t i on y．Th ght t empe r a t ur ea l l owsqu i cke rc a r bond i f f u s i ont h a tl e a d s t osma l l e rt r ans f o rma t i ons t r e s s e sandl a t t i c ed i s t o r Ｇ

F i 􀆰５　Mi s o r i en t a t i onang l ed i s t r i bu t i onf o rSL g

t i on３ ．Fur t he rmo r e,t heh i r pur i t t t e r ghe y and be c r s t a l l i n i t o fb a i n i t i c f e r r i t e l a t h s i ns a m l e so f S y y p H havemuchl e s sl a t t i c ede f e c t s,wh i l et hel owang l e bounda r i e sa r echao t i c． []

２ 􀆰２　Me chan i c a lbeha v i o r 　 　 Thet ens i l ep r ope r t i e sa r eshowni n Tab l e３． nc r e a s ei n bo t ht he y i e l d Compa r ed wi t h SH ,ani s t r eng t hand u l t ima t et ens i l es t r eng t hc an be ob Ｇ s e r vedf o rt hes amp l eo fSL ．Th i simp r ovemen ti s a c compan i edbyani nc r e a s ei nt hee l onga t i onf r om ３３ 􀆰４％ t o３４ 􀆰０％ f o rt hes amp l eo fSL ．Toana l z e y t hewo rkha rden i ngbehav i o r,i ns t an t aneousn va l ue [ ] i sde t e rmi neda sni １１ : ( 　　　　ni ＝d l og σ/d ε l og １) 　 　ni de s c r i be st hei ns t an t aneousha rden i ngr a t i o． l uev ss t r a i ncur ve sf o rt hetwo F i 􀆰６showsni va g s amp l e s．Thecur ve sshowt ha tbe f o r et het rues t r a i n l uef o rs amp l eo fSHi r e a che sabou t０ 􀆰１３,t heni va s , h i r wh i l et he i rt r e nd sa r ea lmo s tt hes ame．Af t e r ghe l uef o rs amp l eo fSL ke t ha ts t r a i npo i n t,t heniva eps i n c r e a s i ngandp e aka e a r sa tt hes t r a i npo i n to f０ 􀆰２０, pp wh i l et he r ei snod i s t i nc tpe akont hecur vef o rSH ．

F i 􀆰６　I n s t an t an e ou sn v a l u e( ni )v s g t r u es t r a i nf o ri nv e s t i a t e ds t e e l s g

３　Di s c u s s i on ３ 􀆰１　Au s t en i t er e c r s t a l l i z a t i on y 　 　 Theru l eo faus t en i t er e c r t a l l i z a t i on p l aysa ys ve r r t an tr o l ei nt hea c t ua lp r oduc t i onpr oc e s s yimpo con t r o l．The r ea r ea tl e a s ttwop i e c e so fi n f o rma t i on i nedbyEBSDt ha tc anbeus edt oi nve s t i t et he ga ga aus t en i t er e c r t a l l i z a t i onex t en tqua l i t a t i ve l ys y．The r ays c a l eva r i a t i oni ni nd i v i dua lr e t a i ned aus t en i t e g r a i nsdemons t r a t e st hel a t t i c ed i s t o r t i onr e su l t i ng g f r om t he aus t en i t e de f o rma t i on e f f e c t i ve l y．The r owt hme chan i smso fpo l landba i n i t i cf e r r i t e g ygona a r eknownt obequ i t ed i f f e r en tf r ome a cho t he r,ye t t he i rt r ans f o rma t i ont ex t ur e sa r equa l i t a t i ve l v e r y y

I s sue１０　　　　　　　　Ef f e c to fF i n i sh i ngRo l l i ngTempe r a t u r eon Mi c r oa l l oyedTRIPS t e e l s　

s imi l a r,d i f f e r i ngi nde t a i lon l nadeg r e eo fva r i an t yi s e l e c t i on．Th i si sus e f u lt os t udyt heaus t en i t er e Ｇ c r t a l l i z a t i oni nt e rms o fp r oduc t pha s et ex t u r e ys whent het ex t u r eo f pr oduc t pha s e s( f e r r i t e and ba i n i t e)i s ha r dt od i f f e r en t i a t ef r om e a ch o t he r, , s i nc et heybo t hhavet hebc cs t ruc t u r e． I nde t a i l L

Ma l e t８ po i n t edou tt hei n f l uenc eo fs l i nt heaus Ｇ pi t en i t eont heva r i an ts e l e c t i onphenomenonbo t hon t hema c r os c a l eandont hes c a l eo fi nd i v i dua laus t en Ｇ i t eg r a i ns．I na l lc a s e s,t he i r mode l sp r opo s edi n Ｇ vo l vet hes e l e c t i on o fpa r t i cu l a rva r i an t sba s ed on t hea c t i v i t fspe c i f i cs l i t ems ( i 􀆰e 􀆰as l i l ane yo ps ys pp andas l i i r e c t i on)．Theob t a i nedr e su l t si nd i c a t e pd , , t ha ti nt hec a s eo ft heba i n i t et r ans f o rma t i on t he s e l e c t i oni sba s edonspe c i f i cs l i l ane s．Ba s edon pp t he s ef i nd i ngs,t hee f f e c to fde f o rma t i onandr e c r Ｇ ys t a l l i z a t i ono faus t en i t eg r a i nsont he mi c r o s t ruc t u r e o fmi c r oa l l oyedTRIPs t e e l si sobv i ous． 　 　Jus ta s men t i onede a r l i e r,a lmo s tha l fo ft he aus t en i t ei nt hes t e e l sp r oduc edi nl owFRTs chedu l e i nhe r i t edt hede f o rma t i onbyho t Ｇ r o l l i ng,wh i l et he r e i smuch mo r er e c r t a l l i z edr e t a i nedaus t en i t ef ound ys i nt hes t e e l sp r oduc edi nh i chedu l e．Now, ghFRTs []

􀅰 ７９ 􀅰

t her e c r t a l l i z a t i on behav i o ro ft he ho tde f o rmed ys aus t en i t ewi l lbed i s cus s edi nt e rmso ft ex t ur ei nt he f c candbc cpha s e s．Ac co rd i ngt ot hes t udyo fBev i s [ ] Hu t ch i nson１０ ,br a s s ({ ００１}＜ １１２ ＞ )t ex t ur e, { １１０}＜１１５＞ t ex t ur eand g r os s ({ １１２}＜１１１＞ )

t ex t ur ea r ef o rmedi nnon Ｇ r e c r t a l l i z edaus t en i t er e Ｇ ys i ons,wh i l ecube ({ ００１}＜１００＞ )t ex t ur ei st i Ｇ g yp c a l l o rmedi nr e c r t a l l i z edr eg i onso faus t en i t e． yf ys The r ei sa lmos tnot i c a l l e c r t a l l i z edaus t en i t e yp yr ys t ex t ur ef oundi nt hes amp l e so fSL[ F i 􀆰７ ( a)]．Mo Ｇ g , ( { } ) r eove rt i c a lcube ００１ ＜１００＞ t ex t ur eo fr e Ｇ yp c r t a l l i z edaus t en i t ei sobv i ousi ns amp l e so fSH ys [ F i 􀆰７ ( b)]．Th i si st os ay,whent hes t e e li sr o l l ed g , i nl ow FRT s chedu l e t he de f o rma t i onf o rmedi n aus t en i t er ema i ns suc c e s s f u l l nt he f e r r i t e and yi ba i n i t et r ans f o rma t i on a r e a s,wh i ch wi l li n f l uenc e t heu l t ima t e pha s e sand me chan i c a lp r ope r t i e sr e Ｇ ma rkab l ex t ur ef o rbc cpha s e so fs amp l e so f y．Thet SLcons i s t so fobv i ousα Ｇ f i br e(＜１１０＞∥RD)andγ Ｇ f i br e (＜１１１＞ ∥ND)o r i en t a t i ons．Bycon t r a s t,t he t i c a lf i br ei ns amp l e so fSH i s muchl e s ssha r yp p, wh i chi nd i c a t e st ha tmuchmo r enuc l e a t i oneven t so f aus t en i t ehaveoc cur r ed．

( a)Aus t en i t eo fSL; 　 ( b)Aus t en i t eo fSH ; 　 ( c)Al lpha s e so fSL; 　 ( d)Al lpha s e so fSH ．

F i 􀆰７　F i r e so fODF ( o r i en t a t i ond i s t r i bu t i onf unc t i on)wi t hφ２ ＝４５ ° g gu

３ 􀆰２　Re l a t i on s h i e twe e nme chan i c a lpr ope r t i e sand pb mi c r o s t r u c t u r e 　　Op t imum me chan i c a lp r ope r t i e so fTRIPs t e e l s a r eob t a i nedt hr oughun i f o rm wo rkha r den i ngdu r i ng s t r a i n i ng p r o c e s sc aus ed by c on t i nuous aus t en i t e t r ans f o rma t i onove rawi der angeo fs t r a i n． I no t he r

wo rds,t hes t r a i n Ｇha rden i ngc apa c i t sa f f e c t edbo t h yi byt hei n t e r a c t i onsbe twe enha rde randso f t e rpha s e s andbyt he me chan i c a l l nduc edpha s et r ans f o rma Ｇ yi [ １２] t i on ． SEM g r aphso fSL s amp l e sbe f o r eanda f t e r un i ax i a lt ens i l et e s ta r eshowni nF i 􀆰８．Al lt hef e r Ｇ g r i t eg r a i nshavebe ene l onga t ed,wh i c hwa si nc onn e c Ｇ

( a)Be f o r ede f o rma t i on; 　 ( b)Af t e rde f o rma t i on．

F i 􀆰８　Mi c r o s t r u c t u r eo fSL ob t a i n e dbySEM g

􀅰 ８０ 􀅰

　　　　J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l　　　　　　　　　　　　　　Vo l 􀆰２０　

t i onwi t ht heaus t en i t et r ans f o rma t i on．Thei ns t an t a Ｇ neousn va l ue wa s wi de l u s e da sa ni n d i c a t i o no f y [ １３] f o rmab i l i t f she e t ma t e r i a l s ．Ma t e r i a l s wi t h yo be t t e rf o rmab i l i t l lexh i b i th i rn va l ue swh i ch ywi ghe c anbe ma i n t a i nedevent oh i rl eve l so fs t r a i n． ghe Th i sva r i a t i oni ns t ab i l i t faus t en i t ei sp r obab l yo y duet ol owe rc a rbonen r i chmen ti nt r ans f o rmedaus Ｇ t en i t edur i ngt heba i n i t et r ans f o rma t i onp r o c e s s,bu t i tmaya l soa r i s ef r omt heg r a i ns i z e．

４　Conc l u s i on s

　 　１)Almo s tha l fo ft heaus t en i t ei nt hes t e e l s r o d u c e da tl o wf i n a lr o l l i n t e m e r a t u r ei n h e r i t e d p g p t hede f o rma t i onbyho t Ｇ r o l l i ng,wh i l et he r ei smuch mo r er e c r t a l l i z edr e t a i nedaus t en i t ef oundi nt he ys s t e e l sp r oduc eda th i i na lr o l l i ngt empe r a t u r e． ghf { 　　２)B r a s s( ０ ０ １}＜１ １ ２＞)t e x t u r ea nd { １ １ ０}＜１ １ ５＞ t ex t u r ea r e mo r esha r ns t e e l sp r oduc eda tl owe r pi ( ) , FRT ７５０ ℃ a snot i c a l l e c r t a l l i z edaus t en Ｇ yp yr ys i t et ex t ur e wa sf ound． Mo r eove r, t i c a l cube yp ({ ００１}＜１００＞ )t ex t u r eo fr e c r t a l l i z edaus t en i t ei s ys ( ) obv i ousi ns amp l e sp r odu c e da th i e rFRT ８００ ℃ ． gh a l u e 　　３)Ba s e dont h ef a c tt h a tt h ei n s t a n t a n e ou sn v ( ni)i she l dt obeh i ral a r angeo fs t r a i ns, ghove ger

l owe rFRTi sp r i o rf o rho t Ｇ r o l l edTRIPs t e e l st oga i n be t t e rcomp r ehens i veme chan i c a lp r ope r t i e s． Re f e r enc e s:

[ １] 　Kammoun i aA,Sa i ka l t a M,e ta l．Ef f e c to ft he ya W,Dumon Ba i n i t i c Tr ans f o rma t i on Tempe r a t ur e on Re t a i ned Aus t en i t e Fr a c t i onandS t ab i l i t nTiMi c r oa l l oyedTRIPS t e e l s[ J]．Ma Ｇ yi t e r i a l sSc i enc eandEng i ne e r i ng,２００９,５１８A( １/２):８９． [ ２] 　Cabus C,Peg l e H,Ba c r o i x B．Or i en t a t i on Re l a t i onsh i Ｇ p Be twe enAus t en i t eandBa i n i t ei naMu l t i s edS t e e l[ J]．Ma t e r Ｇ pha

i a l sCha r a c t e r i z a t i on,２００７,５８( ４):３３２． [ ３] 　Pa l i z da rY,Co chr aneRC,Br onR,e ta l．TheEf f e c to fDe Ｇ yds l i be r a t eAl umi num Add i t i onsont he Mi c r o s t r uc t ur eo fRo l l ed S t e e lP l a t eCha r a c t e r i z edUs i ngEBSD [ J]．Ma t e r i a l sCha r a c t e r Ｇ i z a t i on,２０１０,６１( ２):１５９． [ ４] 　LIUJ i Ｇ i Ｇ cheng,ZHUFu Ｇ x i an,e ta l． Ef f e c to f yuan,ZHANGZ Coo l i ngMe t hodonMi c r o s t r uc t ur eandMe chan i c a lPr ope r t i e so f Ho t ＧRo l l edC ＧS i ＧMnTRIPS t e e l[ J]． J our na lo fI r onandS t e e l Re s e a r ch,I n t e r na t i ona l,２０１２,１９( １):４１． [ ５] 　J IANG Ha i Ｇ t a o,DING We i,TANG D i,e ta l．Me c h a n i c a lPr op e r t y and Mi c r o s t r uc t ur a lCha r a c t e r i z a t i on o fC ＧMn ＧAl ＧS i Ho t Di p Ga l van i z i ng TRIP S t e e l[ J]．J our na lo fI r on and S t e e l Re Ｇ s e a r ch,I n t e r na t i ona l,２０１２,１９( ８):２９． [ ６] 　HyunJ oJun,Pa rkSH,Cho iSD,e ta l．De c ompo s i t i ono fRe Ｇ t a i nedAus t en i t eDur i ngCo i l i ngPr o c e s so f Ho tRo l l ed TRIP Ｇ Ai dedS t e e l s[ J]．Ma t e r i a l sSc i enc eand Eng i ne e r i ng,２００４, ３７９A( １/２):２０４． [ ７] 　Za e f f e r e rS,Oh l e r tJ,B l e c kW．AS t udyo fMi c r o s t r u c t u r e,T r a n s Ｇ

f o rma t i on Me chan i smsandCo r r e l a t i onBe twe en Mi c r o s t r uc t ur e and Me chan i c a lPr ope r t i e so faLow Al l oyed TRIP S t e e l[ J]． Ac t a Ma t e r i a l i a,２００４,５２( ９):２７６５． [ ８] 　Ma l e tL,Ba r ne t t M R,J a c sPJ,e ta l．Va r i an tSe l e c t i on que Dur i ngt heγ Ｇ t o Ｇ αbPha s eTr ans f o rma t i oni nHo t ＧRo l l edBa i n i t i c TRIP ＧAi dedS t e e l s[ J]． Sc r i t a Ma t e r i a l i a,２００９,６１( ５):５２０． p [ ９] 　DeA K,Spe e rJG,Ma t l o ckDK． Co l o rTi n t ＧEt ch i ngf o rMu l t i Pha s eS t e e l s[ J]．Advma t e rPr o c e s s,２００３,１６１( ２):２７． [ １０] 　Bev i sHu t ch i ns on,LenaRyde,EvaL i ndh,e ta l．Tex t ur ei n Ho tRo l l edAus t en i t eandRe su l t i ngTr ans f o rma t i onPr oduc t s [ １):９． J]．Ma t e r i a l sSc i enc eandEng i ne e r i ng,１９９８,２５７A( [ １１] 　Sc o t tC,Al l a i nS,Fa r a lM,e ta l．TheDeve l opmen to faNew Fe ＧMn ＧC Aus t en i t i cS t e e lf o r Au t o rmo t i ve App l i c a t i ons [ J]． RevuedeMé t a l l ur i e,２００６,１０３( ６):２９３． g [ １２] 　J a c sPJ,Fur nemon tQ,Lan iF,e ta l．Mu l t i s c a l eMe chan Ｇ que i c so f TRIP ＧAs s i s t ed Mu l t i s eS t e e l s:I．Cha r a c t e r i z a t i on pha J]．Ac t a Ma t e r i a l i a,２００７,５５( １１): and Me chan i c a lTe s t i ng [ ３６８１． [ １３] 　Ch i angJ,Lawr enc eB,BoydJD,e ta l．Ef f e c to fMi c r o s t r uc Ｇ t ur eon Re t a i ned Aus t en i t eS t ab i l i t rk Ha r den i ngo f yand Wo TRIPS t e e l s[ J]．Ma t e r i a l sSc i enc eand Eng i ne e r i ng,２０１１, ５２８A( １３/１４):４５１６．