Effect of Annealing Time on Microstructure and Mechanical Properties of Cold-Rolled Niobium and Titanium Bearing Micro-alloyed Steel Strips

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

JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL􀆰２ ０ １ ３,２ ０( ９):８ ６ Ｇ ９ ２

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

E f f e c to fAnn e a l i n imeo nMi c r o s t r u c t u r ea ndMe c h a n i c a lPr o e r t i e so f gT p Co l d ＧRo l l e dNi ob i umandT i t an i umBe a r i ng Mi c r o Ｇ a l l o e dS t e e lS t r i s y p CHENJun, 　SHEN Xi n Ｇ un, 　J IFeng Ｇ i n, 　TANGShua i, 　LIU Zhen Ｇ Ｇ dong j q yu, 　WANG Guo ( S t a t eKeyLabo r a t o r fRo l l i ngandAu t oma t i on,No r t he a s t e r nUn i ve r s i t i aon i ng,Ch i na) yo y,Shenyang１１０８１９,L

Ab s t r a c t:Ef f e c t so fanne a l i ngt imeon mi c r o s t r uc t u r eo fc o l d Ｇ r o l l edn i ob i umＧ t i t an i um be a r i ng mi c r o Ｇ a l l oyeds t e e l s t r i r ei nve s t i t ed by op t i c a l mi c r o s c opy,s c ann i ng e l e c t r on mi c r o s c opy,e l e c t r on ba ck Ｇ s c a t t e rd i f f r a c t i on ps we ga ( EBSD)andt r ansmi s s i one l e c t r on mi c r o s c opy．Thec omp l e t er e c r s t a l l i z a t i onanne a l i ngt empe r a t u r eo f６７０ ℃ and y c omp l e t eanne a l i ngt imeo f９mi nwe r ede t e rmi nedus i ngVi cke r s Ｇha r dne s st e s t i ngandEBSDana l s i s．Thef e r r i t emi Ｇ y c r o s t r uc t u r ewi t hsphe r i cc emen t i t epa r t i c l e sandnano Ｇ s c a l ep r e c i i t a t e so fNb( C, N)i nma t r i xwa sob t a i ned．Thek i Ｇ p ne t i c so ft hef e r r i t eg r a i ng r owt hi sl owe r edduet of e r r i t eg r a i nbounda r i e sp i nnedbyt hec emen t i t epa r t i c l e s,s ot he f e r r i t eg r a i ns i z eo f５ 􀆰５μmr ema i nsunchangedamongt heanne a l i ngt imer ang i ngf r om９t o３０mi n． I nadd i t i on,t he s t r eng t ho ft e s t eds t e e la l s oke epsunchanged wi t ht hei nc r e a s eo fanne a l i ngt ime．Theh i ry i e l ds t r eng t ho fap Ｇ ghe r ox ima t e l anbeob t a i nedbyg r a i nr e f i nemen tandp r e c i i t a t i onha r den i ngandt heh i re l onga t i ono f p y４２０ MPac p ghe app r ox ima t e l r k Ｇha r den i ngexponen to fapp r ox ima t e l 􀆰２c anbega i nedduet og r a i nr e f i nemen tand y４０％ andwo y０ r e s enc eo fc emen t i t epa r t i c l e s,i nd i c a t i ngt ha tt heba l anc eo fs t r eng t h,duc t i l i t o rmi ngp r ope r t sr e a l i z ed． p yandf yi Ke r d s:Nb ＧTibe a r i ngmi c r o Ｇ a l l oyeds t e e l;c o l dr o l l i ng;anne a l i ng;mi c r o s t r uc t u r e;me chan i c a lp r ope r t y ywo

　　Mo r eandmo r er e s e a r c h e r sa thomea nda b r o a dp a y a t t en t i ont o mi c r o Ｇ a l l oyeds t e e l sduet ot he i rh i gh s t r eng t h, be t t e rl owＧ t empe r a t u r et oughne s s and , , we l dab i l i t t c．Theho tde f o rma t i on t r ans f o rma Ｇ y e t i on and p r e c i i t a t i on behav i o r so f mi c r o Ｇ a l l oyed p [ ] s t e e l swe r eunde r s t ood１－７ andt hee f f e c to ft he rmo Ｇ me chan i c a lc on t r o l pr o c e s s on mi c r o s t ruc t u r e and me chan i c a lpr ope r t i e so fmi c r o Ｇ a l l oyeds t e e l swa sa l Ｇ [ ８－１０] , s oi nve s t i a t e d ．H o w e v e r t h e r e o r t s a b o u t g p e f f e c to fanne a l i ngt imeon mi c r o s t ruc t u r eand me Ｇ chan i c a lp r ope r t i e so fc o l d Ｇ r o l l ed Nb ＧTibe a r i ng mi Ｇ c r o Ｇ a l l oyeds t e e ls t r i r eex t r eme l ew．Some ps we yf [ １１－１５] r e s e a r che r s i nve s t i t edt hee f f e c to fc emen t i t e ga a r t i c l e son me c h a n i c a lp r op e r t i e si nu l t r a f i n eg r a i n e d p s t e e l s．M CZhaoe ta li nd i c a t edt ha tt hef e r r i t eg r a i n c oa r s en i ngha r d l c cu r r edun t i lc emen t i t epa r t i c l e s yo [ ] spa c i ngr e a ched ac e r t a i nc r i t i c a lva l ue１２ ,and R Song e ta li nd i c a t edt ha tt he wo rk Ｇ ha r den i ng r a t e c ou l dbei nc r e a s edowi ngt ot heex i s t enc eo ff i neand d i spe r s i vec emen t i t e pa r t i c l e sandt he p l a s t i c i t f yo [ １５] u l t r a f i neg r a i neds t e e l sc ou l dbeimp r oved ．And f o ru l t r a f i neg r a i neds t e e l s,t heduc t i l i t ssha r l yi p y

de t e r i o r a t edduet og r a i ns i z er e f i nedt o１－２ μm． , Howeve r f o rco l d Ｇ r o l l ed Nb ＧTibe a r i ng mi c r o Ｇ a l Ｇ l oyeds t e e ls t r i hei nve s t i t i ono ft hef o rma t i on ps,t ga o fc emen t i t epa r t i c l e sdur i nganne a l i ngande f f e c to f c emen t i t epa r t i c l e sonr e c r t a l l i z edg r a i ns i z ei sf ew． ys Sot hep r e s en ti nve s t i t i onp l aysas i i f i c an tr o l e ga gn i ncomme r c i a lapp l i c a t i ono fco l d Ｇ r o l l edNb ＧTibe a r Ｇ i ng mi c r o Ｇ a l l oyeds t e e ls t r i ps． 　　Thee f f e c t so fanne a l i ngt imeonmi c r os t ruc t ur e andme chan i c a lp r ope r t i e so fco l d Ｇ r o l l edNb ＧTibe a r Ｇ i ng mi c r o Ｇ a l l oyeds t e e ls t r i r ei nve s t i t ed by ps we ga op t i c a lmi c r os copy ( OM),s c ann i nge l e c t r onmi c r os Ｇ ( ) , ( ) copy SEM e l e c t r onb a c k Ｇ s c a t t e rd i f f r a c t i on EBSD , andt r ansmi s s i one l e c t r on mi c r os copy ( TEM )．The Vi cke r s Ｇha rdne s st e s t i ng and EBSD ana l i s we r e ys us edt ode t e rmi necomp l e t er e c r t a l l i z a t i onanne a Ｇ ys l i ngt empe r a t ur eandcomp l e t eanne a l i ngt ime,r e Ｇ spe c t i ve l o rma t i on me chan i sm o fc emen t i t e y．Thef r t i c l e si nf e r r i t ema t r i xwa sana l z ed． I twa sf ound pa y t ha tt hef e r r i t eg r a i ncoa r s en i ng wa ssupp r e s s eddue t og r a i n bounda r i e sp i nnedby c emen t i t e pa r t i c l e s, andt h i si st hema i nr e a sont ha tt hef e r r i t eg r a i ns i z e

Founda t i onI t em: I t em Spons o r edbyFundamen t a lRe s e a r chFundsf o rCen t r a lUn i ve r s i t i e so fCh i na ( N１１０６０７００３) B i o r aphy: CHENJun( １９８２—),Ma l e,Do c t o r; 　E Ｇma i l:j unc １９８４１０１１＠１６３ 􀆰c om;　Re c e i v e dDa t e:Febr ua r y１２,２０１２ g

I s sue９　　　Ef f e c to fAnne a l i ngTimeonCo l d ＧRo l l edNi ob i umandTi t an i um Be a r i ng Mi c r o Ｇ a l l oyedS t e e lS t r i ps　

o fapp r ox ima t e l 􀆰５μmr ema i nsunchangedf o rd i f Ｇ y５ f e r en tanne a l i ngt ime．Theba l anc eo fs t r eng t h,duc Ｇ t i l i t o rmi ngp r ope r t i e si sr e a l i z edduet oapp r o Ｇ yandf r i a t eg r a i nr e f i nemen t,p r e c i i t a t i onha r den i ngand p p r e s enc eo fc emen t i t epa r t i c l e s． p

１　Exp e r imen t a lDe t a i l s

　 　 Thechemi c a lc ompo s i t i onso f Nb ＧTibe a r i ng mi c r o Ｇ a l l oyeds t e e la r eg i veni nT a b l e１．Th et e s t e d s t e e lwa s mi c r o a l l o e dw i t hn i ob i um a ndt i t a n i um f o r y [ １６－１７] r a i nr e f i nemen tandpr e c i i t a t i onha r den i ng ． g p

C

Tab l e１　Ch emi c a lc ompo s i t i on so ft e s t e ds t e e l (ma s spe r c en t,％ ) 　 S i

Mn

P

０ 􀆰０５５ ０ 􀆰２７ １ 􀆰３２ ０ 􀆰００６

S

Ti

Nb

N

０ 􀆰００６ ０ 􀆰０２ ０ 􀆰０３２ ０ 􀆰００６４

　　Thet e s t eds t e e lwa scu tf r om c on t i nuousc a s t Ｇ i ngb i l l e t s．The s eb i l l e t swe r ehe l da t１２００ ℃f o r２h andt henr o l l edandc oo l edus i ngtwo Ｇ h i gh４５０ mm expe r imen t a lho tr o l l i ng mi l lwi t hu l t r a Ｇ f a s tc oo l i ng ( UFC)s s t e m． T h er e d u c t i o ns c h e d u l e i s７ ０→５ ０→ y ３５→２５→１８→１４→t emp e r a t u r ewa i t i ng→１２→８ 􀆰５→６→ ５ mm．Thei n i t i a lr o l l i ngt empe r a t u r eandf i n i sh i ng t empe r a t ur ef o rr ough r o l l i ng a r e app r ox ima t e l y , , １１５０ ℃ andh i rt han１１００ ℃ r e spe c t i ve l ghe y and bo t ht empe r a t u r e sf o rf i n i sh r o l l i ng a r e app r ox i Ｇ , ma t e l nd８５０ ℃ r e s e c t i v e l ep l a t e swe r e y９５０a p y．Th f i r s tcoo l edt o６００ ℃ us i ng UFCandt henc oo l edt o r oomt empe r a t u r eus i nga i rc oo l i nga f t e rr o l l i ngi n o r de rt oke epsu f f i c i en tNbi ns o l u t i on．Andt heho t Ｇ r o l l edp l a t ewi t ht h i ckne s so f６ 􀆰０７mmf o rc o l dr o l l Ｇ i ng wa sob t a i nedandi t s mi c r o s t ruc t u r eand TEM image sa r eana l ed． yz 　　Theho t Ｇ r o l l edp l a t ewa sc o l dr o l l edt o１ 􀆰５ mm i nt h i ckne s sus i ngaf ou r Ｇ h i hc o l dr o l l i n m l land g g i t hewho l er educ t i oni sapp r ox ima t e l 􀆰２９％． Some y７５ c o l d Ｇ r o l l eds t r i r eanne a l eda t５００,５５０,６００, ps we ６２０,６４０,６６０,６８０,７００,７５０,８００,and８５０ ℃ f o r ６ mi nbyus i ngat ubet e s i s t anc ef u rna c eo fSKＧ yper ２ Ｇ １２．TheVi cke r s Ｇ ha r dne s so fanne a l eds amp l e swa s t e s t edus i ngaVi cke r s Ｇ du r ome t e ro fHVＧ ５０andt he c omp l e t er e c r t a l l i z a t i onanne a l i ngt empe r a t u r ewa s ys de t e rmi ned． Somec o l d Ｇ r o l l eds t r i r eanne a l eda t pswe t hec omp l e t er e c r t a l l i z a t i onanne a l i ngt empe r a t u r e ys f o r３,６,９,１２,１５,２０,and３０ mi ni no r de rt oi n Ｇ ve s t i t et hee f f e c to fanne a l i ngt imeon mi c r o s t ruc Ｇ ga t u r eand me chan i c a lpr ope r t i e so fc o l d Ｇ r o l l ed Nb ＧTi be a r i ng mi c r o Ｇ a l l oyeds t e e ls t r i ps． 　　Samp l e swe r ec u tf r om ho tr o l l e dp l a t e sa ndc o l d Ｇ

􀅰 ８７ 􀅰

r o l l edanne a l eds t r i he i rsur f a c e sa l ongt h i ckＧ psandt ne s sd i r e c t i on ( ND)andr o l l i ngd i r e c t i on ( RD)we r e l i shedandt hene t chedi n４％ n i t a lso l u t i onf o rob Ｇ po s e r va t i ono f OM ( LEICA DMIRM )and FEＧSEM ( ULTR ATM ５５)．Somes amp l e s we r ee l e c t r opo l Ｇ ( ) i shedus i ngt hee l e c t r opo l i she r El e c t r oMe t４ f o r EBSDana l i s．Thee l e c t r o l t econs i s t so fpe r ch l o r i c ys y a c i do fapp r ox ima t e l 􀆰５％ andabso l u t ee t hy la l Ｇ y１２ , , c oho lo fa r ox ima t e l 􀆰５％ andt hevo l t a ee l e c t r i c pp y８７ g cur r en tandt imef o re l e c t r opo l i s h i nga r ea r ox ima t e l pp y １５V,１ 􀆰２Aand２５s,r e spe c t i ve l I nadd i t i on,t he y． ５００μmＧ t h i cks r es l i c e swe r ecu tf r om s amp l e s, qua andt hent h i nnedby me chan i c a labr a s i ont oapp r ox i Ｇ ma t e l l e c t r opo l i s he du s i ngatwi n Ｇ e te l e c Ｇ y５０μmande j t r opo l i s he r( S t r u e r sT e nuPo l Ｇ ５)．Thee l e c t r o l t ec on Ｇ y s i s t so fapp r ox ima t e l r ch l o r i ca c i dand９１％ y９％ pe abso l u t ee t hy la l coho l,andt het empe r a t ur eo fe l e c Ｇ t r o l t e,vo l t ageande l e c t r i ccur r en tf o re l e c t r opo l i s Ｇ y h i nga r eabou t－４０℃ ,３５Vand５５mA,r e s e c t i v e l p y． 　　 Me chan i c a lp r ope r t i e si n RD we r et e s t edus i ng CMTＧ ５１０５e l e c t r on un i ve r s a lt e s t i ng ma ch i necon Ｇ t r o l l edbycompu t e r．S t anda rdt ens i l es amp l e swi t h wi d t ho f１０ mm,o r i i na lgaugel eng t ho f２５ mm g andpa r a l l e ll eng t ho f５０ mm we r et e s t eda tr oom / t emp e r a t u r ea tac r o s sb e ams e e do f５ mm m i n ． The p , i e l ds t r eng t h t ens i l es t r eng t hande l onga t i ona f t e r y f r a c t ur ewe r ea l lde t e rmi ned．

２　Re s u l t sandDi s c u s s i on

２ 􀆰１　Mi c r o s t r u c t u r eo fho t Ｇ r o l l e dp l a t e s 　　Theop t i c a lmi c r os t ruc t ur eandTEMimage so f ( ho tr o l l ed p l a t e sa r eshowni nF i 􀆰１．F i 􀆰１ a) g g showst ha tt hemi c r os t ruc t ur econs i s t so fpo l l ygona , f e r r i t e a c i cu l a rf e r r i t e and pe a r l i t e．Some cub i c TiNＧ enr i ched c a rbon i t r i de sa r e obs e r ved,bu tt he r oundandf i ne NbCＧ enr i chedc a rbon i t r i de sa r eno t ( ) obs e r vedi nF i 􀆰１ b ． I tc anbededuc edt ha tal a r g ge amoun to fn i ob i umex i s t si nso l u t i on,andus i ngu l Ｇ t r a Ｇ f a s tcoo l i ngcou l dke epsu f f i c i en tn i ob i umi nso Ｇ [ １８] ( , ) l u t i on ． Sot hep r e c i i t a t i ono fNb C N c anoc cur p dur i nganne a l i ng． ２ 􀆰２　Re c r s t a l l i z a t i ont empe r a t u r e y 　　TheVi c ke r s Ｇha r dn e s so fc o l d Ｇ r o l l e dNb ＧT ib e a r i ng mi c r o Ｇ a l l oyeds t e e ls t r i a l eda td i f f e r en tt emＧ psanne r a t ur e sf o r６ mi ni sshowni nF i 􀆰２．TheVi cke r s Ｇ pe g ha rdne s sf i r s t l l i t l s c endsowi ngt or e cove r ys gh yde y a t５００－６２０ ℃ ,t hensha r l s c endsowi ngt or e Ｇ p yde c r t a l l i z a t i ona t６２０－６８０ ℃ andr ema i nsne a r l ys y unchangeda t６８０－８５０ ℃ a tl a s t．Andt hecomp l e t e r e c r s t a l l i z a t i o na n n e a l i n t e m e r a t u r eo f ６ ７ ０ ℃ c a n y g p

􀅰 ８８ 􀅰

　　　　　　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　

F i 􀆰１　Op t i c a lmi c r o s t r u c t u r e( a)andTEMima e( b)o fho tr o l l e dp l a t e so fNb ＧT ib e a r i ngmi c r o Ｇ a l l o e ds t e e l g g y

bede t e rmi ned．

F i 􀆰２　Ef f e c to fann e a l i ngt emp e r a t u r e sonVi ck e r s Ｇha r dn e s s g o fc o l d Ｇ r o l l e dNb ＧT imi c r o Ｇ a l l o e ds t e e ls t r i y p

２ 􀆰３　Comp l e t eanne a l i ngt ime 　　Theg r a i nbound a r i e smi s o r i e n t a t i on ma so fc o l d Ｇ p , r o l l eds t r i sa n n e a l e da t６ ７ ０ ℃ f o r３ ６a n d９ m i n p a r eshowni nF i 􀆰３．F i 􀆰３ ( a)showst henumbe r g g f r a c t i ono fl owＧ ang l eg r a i nbounda r i e s(＜１５ °) i sl a r Ｇ rf o ranne a l i ngt imeo f３ mi n,i nd i c a t i ngt ha tt he ge r e c r t a l l i z a t i ondoe sno toc cura tt he s ez one s．Af ew ys band i ngz one swi t hah i i t fl owＧ ang l eg r a i n ghdens yo ( ) , bounda r i e sa r eobs e r vedi nF i 􀆰３ b showi ngt ha t g r e c r t a l l i z a t i ono c c u r sa tmo s tz on e s． F i 􀆰３ ( c)s hows ys g t ha tt heb and i ngz on e swi t hah i e n s i t fl owＧ ang l e ghd yo , r a i nbounda r i e sc anno tbeobs e r ved i nd i c a t i ngt ha t g

Gr eyl i ne s:mi s o r i en t a t i on ＜１５ °; 　B l a ckl i ne s:mi s o r i en t a t i on ＞１５ °． ( a)３ mi n; 　 ( b)６ mi n; 　 ( c)９ mi n．

F i 􀆰３　Gr a i nbounda r i e smi s o r i en t a t i onmapo fc o l d Ｇ r o l l e dNb ＧT ib e a r i ngmi c r o Ｇ a l l o e ds t e e ls t r i sann e a l e da t g y p ６７０ ℃ f o rd i f f e r en tt ime

t hec omp l e t e l e c r t a l l i z edf e r r i t eg r a i nc anbeob Ｇ yr ys t a i neda f t e ranne a l i nga t６７０ ℃ f o r９ mi n． ２ 􀆰４　Mi c r o s t r u c t u r eo fc o l d Ｇ r o l l e dNb ＧT ib e a r i ng mi Ｇ c r o Ｇ a l l o e ds t e e ls t r i s y p 　 　Ba s edonEBSDana l i s,t hec omp l e t e l e c r Ｇ ys yr ys t a l l i z edf e r r i t eg r a i nc anbeob t a i neda f t e ranne a l i ng

a t６７０ ℃f o r９mi n,andi t sop t i c a lmi c r os t ruc t ur ei s ( showni nF i 􀆰４ b)．Theop t i c a lmi c r os t ruc t ur e sa f Ｇ g t e ranne a l i nga t６７０ ℃f o r１２,１５,２０and３０mi na r e showni nF i 􀆰４ ( c)t o( f)． I tc anbef oundt ha tt he g f e r r i t eg r a i ndoe sno tg r owobv i ous l t hi nc r e a s i ng ywi t heanne a l i ng t imea f t e rr e c r t a l l i z a t i on,andt he ys f e r r i t eg r a i ns i z ewa sme a sur edus i ngi n t e r c ep tl i ne a r

I s sue９　　　Ef f e c to fAnne a l i ngTimeonCo l d ＧRo l l edNi ob i umandTi t an i um Be a r i ng Mi c r o Ｇ a l l oyedS t e e lS t r i ps　

􀅰 ８９ 􀅰

( a)６ mi n; 　 ( b)９ mi n; 　 ( c)１２ mi n; 　 ( d)１５ mi n; 　 ( e)２０ mi n; 　 ( f)３０ mi n．

F i 􀆰４　Op t i c a lmi c r o s t r u c t u r eo fc o l d Ｇ r o l l e dNb ＧT ib e a r i ngmi c r o Ｇ a l l o e ds t e e ls t r i sann e a l e da t６７０ ℃ f o rd i f f e r en tt ime g y p

me t hod,a sshowni nF i 􀆰５．F i 􀆰５showst ha tt he g g ave r agef e r r i t eg r a i ns i z eo f５ 􀆰５μm a lmo s tr ema i ns unchangedwi t hi nc r e a s i ngt heanne a l i ngt ime． I nad Ｇ

F i 􀆰５　Fe r r i t eg r a i ns i z ef o rd i f f e r en tann e a l i ngt ime g

d i t i on,al a r ramoun to fc emen t i t epa r t i c l e sc anbe ge , obs e r vedi n ma t r i x a sshowni nF i 􀆰４andF i 􀆰６, g g and t he s ec emen t i t e pa r t i c l e sc an obs t ruc tg r a i n coa r s en i ng． 　 　 Fo r co l d Ｇ r o l l ed Nb ＧTi be a r i ng mi c r o Ｇ a l l oyed s t e e ls t r i a l eda t６７０ ℃ f o r６,９,１２,１５,２０ psanne and３０ mi n,al a r ramoun to fc emen t i t epa r t i c l e s ge ( ) de t e rmi nedby TEM ana l i si nF i 􀆰７ d i s t r i bu t ed ys g a tt hef e r r i t eg r a i nbounda r i e s( a r r ow B)andi ns i de ( ) t hef e r r i t eg r a i ns a r r ow A a r eobs e r vedi nF i 􀆰６ g ( a)． I nadd i t i on,t hez one swi t hah i i t fc e Ｇ ghdens yo men t i t epa r t i c l e s( a r r owsCandD)i nwh i cht hef e r Ｇ r i t eg r a i ns i z ei ssma l l e rt han o t he r sa r ea l so ob Ｇ s e r vedi nF i 􀆰６ ( b)and ( e), i nd i c a t i ngt ha tt hec eme n Ｇ g

( a)６ mi n; 　 ( b)９ mi n; 　 ( c)１２ mi n; 　 ( d)１５ mi n; 　 ( e)２０ mi n; 　 ( f)３０ mi n．

F i 􀆰６　SEMima e so fc o l d Ｇ r o l l e dNb ＧT ib e a r i ngmi c r o Ｇ a l l o e ds t e e ls t r i sann e a l e da t６７０ ℃ f o rd i f f e r en tt ime g g y p

􀅰 ９０ 􀅰

　　　　　　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　

F i 􀆰７　TEMima e so fc o l d Ｇ r o l l e dNb ＧT ib e a r i ngmi c r o Ｇ a l l o e ds t e e ls t r i sann e a l e da t６７０ ℃ f o r９mi n g g y p

t i t e pa r t i c l e sc an e f f e c t i ve l t ruc tf e r r i t eg r a i n y obs c oa r s en i ng． 　　Theb l ock Ｇ f o rm pe a r l i t ei nho tr o l l edp l a t e sbe Ｇ , c ome sband Ｇ shapeda f t e rc o l dr o l l i ng andt heband Ｇ shapedpe a r l i t ebe c ome ssphe r i cpa r t i c l e sowi ngt o t hede compo s i t i oni nl o c a lz one sdu r i ng anne a l i ng． Tha ti swhyt hec emen t i t epa r t i c l e sd i s t r i bu t ei nl i ne a tmos tz one si nF i 􀆰６．Thek i ne t i c so ff e r r i t eg r a i n g c oa r s en i ng i sr educ ed owi ng t ot he f e r r i t eg r a i n bounda r i e se f f e c t i ve l i nned by t he s ec emen t i t e yp [ ] r t i c l e s１２ ,l e a d i ngt ot h en e a r l c h a ng e da v e r a e pa y un g

f e r r i t eg r a i ns i z ewi t hi nc r e a s i ngt heanne a l i ngt ime． 　 　TEMimage so fco l d Ｇ r o l l ed Nb ＧTibe a r i ng mi Ｇ c r o Ｇ a l l oyeds t e e ls t r i sa n n e a l e da t６ ７ ０ ℃ f o r９ m i n p a r eshowni nF i 􀆰７．Thecha r a c t e r i s t i c EDX spe c Ｇ g t rum o fsphe r i c pa r t i c l e s ma rked a sa r r ow A i n F i 􀆰７ ( a)i sshowni nF i 􀆰８ ( a),i nd i c a t i ngt ha tt he g g , a t omi cpe r c en t age so fC Feand Mna r eapp r ox i Ｇ ma t e l 􀆰３０％ ,７０ 􀆰１５％ and６ 􀆰６４％ ,r e spe c t i ve l y２３ y． Sot hesphe r i cpa r t i c l e sa r ema i nc emen t i t epa r t i c l e s． , I nadd i t i on t hef i neandd i spe r s i ver ound p r e c i i Ｇ p t a t e s[ a r r owBi nF i 􀆰７ ( c)]wh i c hma eNb( C, N) g yb

( a)Cemen t i t epa r t i c l ema rkeda sa r r ow Ai nF i 􀆰７ ( a); 　 ( b)Pr e c i i t a t ema rkeda sa r r owBi nF i 􀆰７ ( c)． g p g

F i 􀆰８　Cha r a c t e r i s t i cEDXs e c t r ao fc emen t i t epa r t i c l e sandp r e c i i t a t e s g p p

de t e rmi nedbyEDXana l i sc ana l s obeobs e r ved． ys ２ 􀆰５　Me chan i c a lpr ope r t i e so fc o l d Ｇ r o l l e dNb ＧT ib e a r Ｇ i ngmi c r o Ｇ a l l o e ds t e e ls t r i s y p 　　Thee f f e c to fa nn e a l i ngt imeons t r e ng t ha nde l on Ｇ a t i ono fc o l d Ｇ r o l l e d Nb ＧT ib e a r i ng mi c r o Ｇ a l l o e ds t e e l g y s t r i sshowni nF i 􀆰９． Be f o r et hec omp l e t er e c r Ｇ psi g ys t a l l i z a t i on ( anne a l i ngt imel owe rt han９ mi n),t h e

l owe ry i e l ds t r e ng t h and u l t ima t et e n s i l es t r e ng t ho f t e s t e ds t e e lsha r l s c end wi t hi nc r e a s i ngt hean Ｇ p y de ne a l i ngt imeowi ngt od i s appe a r anc eo fwo rk Ｇha rden Ｇ ed mi c r os t ruc t ur e．Af t e rt hecomp l e t er e c r t a l l i z a Ｇ ys t i on ( anne a l i ngt imeh i rt han９ mi n),t hel owe r ghe i e l ds t r eng t handu l t ima t et ens i l es t r eng t ho ft e s t ed y s t e e lr ema i na lmos tunchanged wi t hp r o l ong i ngt he anne a l i ngt ime,andt h i sr e su l ti si ngoodag r e emen t

I s sue９　　　Ef f e c to fAnne a l i ngTimeonCo l d ＧRo l l edNi ob i umandTi t an i um Be a r i ng Mi c r o Ｇ a l l oyedS t e e lS t r i ps　

􀅰 ９１ 􀅰

F i 􀆰９　Ef f e c to fann e a l i ngt imeons t r eng t h( a)ande l ong a t i on ( b)o fc o l d Ｇ r o l l e dNb ＧT ib e a r i ngmi c r o Ｇ a l l o e ds t e e ls t r i s g y p

w i t ht hen e a r l c h a ng e df e r r i t eg r a i ns i z eo f５ 􀆰５μm, yun [ １９] and me e t st he Ha l l ＧPe t ch r e l a t i onsh i he p ．Att s amet ime,t he h i r va l ue o ft he l owe ry i e l d ghe s t r eng t ho fapp r ox ima t e l anbeob t a i ned y４２０ MPac duet og r a i nr e f i nemen tandp r e c i i t a t i onha r den i ng． p 　　F i 􀆰９ ( b)showst ha tt heh i re l onga t i ono f g ghe app r ox ima t e l hep r oduc to fs t r eng t hand y４０％ andt duc t i l i t ang i ngf r om１８t o２０GPa􀅰 ％ c anbeob Ｇ yr t a i nedamongt heanne a l i ngt imer ang i ngf r om ９t o ３０ mi n．Ononehand,f o rt hef e r r i t eg r a i ns i z eo f ５ 􀆰５μm,t hephenomenono ft heduc t i l i t r l Ｇ ysha p yde [ ] s c end i ngi nu l t r a f i neg r a i neds t e e l sc anno to c cu r１１ ． Ont heo t he rhand,t heduc t i l i t ft e s t eds t e e lc an yo beimp r oved by c emen t i t e pa r t i c l e sd i s t r i bu t edi n [ ] ma t r i x１４ ．Sot he h i h e r r o d u c to fs t r e n t h a n d g p g duc t i l i t anbeob t a i ned． yc 　 　I na dd i t i on,t h ewo r k Ｇ h a r d e n i nge xpon e n to fc o l d Ｇ r o l l e dNb ＧT ib e a r i ng mi c r o Ｇ a l l o e ds t e e ls t r i sa nn e a l e d y p f o rd i f f e r e n tt imei ss howni nF i 􀆰１０．Thewo rk Ｇ ha r d Ｇ g en i ngexponen to ft e s t eds t e e li supt oapp r ox ima t e l y ０ 􀆰２,i nd i c a t i ngt ha tt hec apab i l i t fun i f o rm e l on Ｇ yo t i onandne ck i ngr e s i s t a n c eo ft e s t e ds t e e li sb e t t e r． ga

３　Conc l u s i on s 　 　 １) The comp l e t er e c r t a l l i z a t i on anne a l i ng ys t empe r a t ur eo f６７０ ℃ andanne a l i ngt imeo f９mi no f co l d Ｇ r o l l ed Nb ＧTibe a r i ng mi c r o Ｇ a l l oyeds t e e ls t r i ps c anbede t e rmi neda c cur a t e l i ngVi cke r s Ｇha rdne s s yus , t e s t i ngandEBSDana l i sr e spe c t i ve l e r r i t e ys y．Thef mi c r os t ruc t ur ewi t hc emen t i t epa r t i c l e sandp r e c i i Ｇ p t a t e so fNb( C,N)i n ma t r i xc anbeob t a i neda f t e r anne a l i nga t６７０ ℃ f o r９ mi n． 　　２)Thef e r r i t eg r a i ns i z eo f５ 􀆰５μmr ema i nsa l Ｇ mos tunchangedamongt heanne a l i ngt imer ang i ng f r om９t o３０mi nbe c aus et hek i ne t i c so ff e r r i t eg r a i n coa r s en i ngi sl owe r edduet og r a i nbounda r i e sp i nned byc emen t i t epa r t i c l e s． ) 　　３ Theh i rv a l u eo fl owe ry i e l ds t r e ng t ho fa Ｇ ghe p r ox ima t e l anbeob t a i nedbyg r a i nr e f i ne Ｇ p y４２０ MPac men tandp r e c i i t a t i onha rden i ng．Theh i re l on Ｇ p ghe t i on o fapp r ox ima t e l rk Ｇha rden i ng ga y ４０％ and wo exponen to fapp r ox ima t e l 􀆰２c anbega i nedduet o y０ app r op r i a t eg r a i nr e f i nemen t and p r e s enc eo fc e Ｇ men t i t epa r t i c l e s．Theba l anc eo fs t r eng t h,duc t i l i t y andf o rmi ngp r ope r t i e si sr e a l i z edduet oapp r op r i a t e , r a i nr e f i nemen t p r e c i i t a t i onha rden i ngandp r e s Ｇ g p enc eo fc emen t i t epa r t i c l e s． Re f e r enc e s:

[ １] 　CHEN L i Ｇ i ng,ZHAO Yang,XU Xi ang Ｇ i u,e ta l．Dynami c q q Re c r t a l l i z a t i onandPr e c i i t a t i onBehav i o r so faKi ndo fLow ys p Ca r bon VＧMi c r oa l l oyed S t e e l[ J]．Ac t a Me t a l l ur i c aS i n i c a, g ２０１０,４６( １０):１２１５ ( i nCh i ne s e)． [ ２] 　Ve r vynck tS,Ve r bekenK,Th i bauxP,e ta l．Re c r t a l l i z a t i on Ｇ ys

F i 􀆰１０　L i n e a rr e r e s s i onc u r v e sf o rwo rk Ｇha r d en i ng g g e xpon en to fc o l d Ｇ r o l l e dNb ＧT ib e a r i ngmi c r o Ｇ a l l o e yd s t e e ls t r i sa n n e a l e da t ６ ７ ０ ℃ f o rd i f f e r e n t t i m e p

Pr e c i i t a t i onI n t e r a c t i onDur i ng Aus t en i t e Ho tDe f o rma t i ono f p aNb Mi c r oa l l oyedS t e e l[ J]．Ma t e rSc iEng,２０１１,５２８A( １６/ １７):５５１９． [ ３] 　YuanX Q,L i uZY,J i aoS H,e ta l．Ef f e c t so fNanoPr e c i i Ｇ p t a t e si nAus t en i t eonFe r r i t eTr ans f o rma t i onS t a r tTempe r a t ur e Dur i ngCon t i nuousCoo l i ngi n Nb ＧTiMi c r o Ｇ a l l oyedS t e e l s[ J]． I S I JI n t,２００７,４７( １１):１６５８．

􀅰 ９２ 􀅰

　　　　　　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　

[ ４] 　HongSG,KangK B,Pa rkC G．S t r a i n Ｇ I nduc edPr e c i i t a t i on p o fNbCi nNbandNb ＧTiMi c r oa l l oyedHSLAS t e e l s[ J]． Sc r i t a p Ma t e r,２００２,４６( ２):１６３． [ ５] 　L i u W J,J ona sJJ．AS t r e s sRe l axa t i on Me t hodf o rFo l l owi ng Ca r bon i t r i dePr e c i i t a t i oni n Aus t en i t ea t Ho t Wo rk i ng TemＧ p r a t ur e s[ J]．Me t a l lTr ans,１９８８,１９A( ６):１４０３． pe [ ６] 　Pand i tA,Mur uga i rA S,e ta l．S t r a i nI nduc ed yan A,Podde Pr e c i i t a t i ono fComp l exCa r bon i t r i de si n Nb ＧVand Ti ＧV Mi Ｇ p c r oa l l oyedS t e e l s[ J]． Sc r i t a Ma t e r,２００５,５３( １１):１３０９． p [ ７] 　XU Yun Ｇ bo,YU Yong Ｇme i,WU Di,e ta l．The rmodynami c s Ca l cu l a t i onso fPr e c i i t a t i onBehav i o ri nNbMi c r oa l l oyedS t e e l s p [ J]．Ch i ne s eJ our na lo fMa t e r i a l sRe s e a r ch,２００６,２０( １):１０４ ( i nCh i ne s e)． [ ８] 　Zr n i kJ,Kva cka lA,e ta l． Ef f e c to fThe rmome Ｇ jT,Pongpaybu chan i c a lPr o c e s s i ngont heMi c r o s t r uc t ur eandMe chan i c a lPr op Ｇ e r t i e so fNb ＧTiMi c r oa l l oyedS t e e l[ J]．Ma t e rSc iEng,２００１, ３１９ Ｇ ３２１A:３２１． [ ９] 　Ma t aJ,Kuz i akR,P i e t r z l l i ngo ft heI n f l uenc eo f j yk M．Mode The rmome chan i c a lPr o c e s s i ngo fNb ＧMi c r oa l l oyedS t e e lont he Re su l t i ng Me chan i c a lPr ope r t i e s[ J]．J Ma t e rPr o c e s s Te ch, １９９８,８０ Ｇ ８１:５２４． [ １０] 　Gome zM,Va l l e sP,Med i naSeba s t i ánF． Evo l u t i ono fMi c r o Ｇ s t r uc t ur eand Pr e c i i t a t i on S t a t e Dur i ng The rmome chan i c a l p Pr o c e s s i ngo faX８０ Mi c r oa l l oyedS t e e l[ J]．Ma t e rSc iEng, ２０１１,５２８A( １３/１４):４７６１． [ １１] 　SongR,PongeD,Ra abeD．Me chan i c a lPr ope r t i e so fan Ul Ｇ t r a f i neGr a i nedC ＧMnS t e e lPr o c e s s edby Wa rm De f o rma t i on J]．Ac t a Ma t e r,２００５,５３( １８):４８８１． andAnne a l i ng [

[ １２] 　Zhao M C,Hanamur a T,Qi u H,e ta l．Gr a i n Gr owt hand /Cemen Ha l l ＧPe t ch Re l a t i on i n Dua l ＧS i z ed Fe r r i t e t i t eS t e e l Wi t hNano ＧS i z edCemen t i t ePa r t i c l e si na He t e r ogeneousand Dens eDi s t r i bu t i on [ J]． Sc r i t a Ma t e r,２００６,５４( ６):１１９３． p [ １３] 　Sh i nD H,Pa rkK T,Kim YS．Fo rma t i ono fF i neCemen t i t e Pr e c i i t a t e si nan Ul t r a Ｇ f i ne Gr a i ned Low Ca r bonS t e e l[ J]． p Sc r i t a Ma t e r,２００３,４８( ５):４６９． p [ １４] 　Zh a oM C,Ha n amu r aT,Qi u H,e ta l．De e nd e n c eo fS t r e ng t h p andS t r eng t h ＧEl onga t i on Ba l anc eont he Vo l umeFr a c t i ono f /Cemen Cemen t i t e Pa r t i c l e si n Ul t r a f i ne Gr a i ned Fe r r i t e t i t e S t e e l s[ J]． Sc r i t a Ma t e r,２００６,５４( ７):１３８５． p [ １５] 　SongR,PongeD,Ra abeD． Imp r ovemen to ft heWo rkHa r d Ｇ en i ngRa t eo fUl t r a f i neGr a i nedS t e e l sThr oughSe c ondPha s e Pa r t i c l e s[ J]． Sc r i t a Ma t e r,２００５,５２( １１):１０７５． p [ １６] 　Jun HJ,KangK B,Pa rkCG．Ef f e c t so fCoo l i ngRa t eand I s o t he rma lHo l d i ngont hePr e c i i t a t i onBehav i o rDur i ngCon Ｇ p t i nuousCa s t i ngo fNb ＧTiBe a r i ng HSLA S t e e l s[ J]．Sc r i t a p Ma t e r,２００３,４９( １１):１０８１． [ １７] 　KangK B,Kwon O,Le e W B,e ta l．Ef f e c to fPr e c i i t a t i on p ont heRe c r t a l l i z a t i onBehav i o ro faNbCon t a i n i ngS t e e l[ J]． ys Sc r i t a Ma t e r,１９９７,３６( １１):１３０３． p [ １８] 　ChenJ,TangS,L i uZ Y,e ta l．S t r a i n Ｇ I nduc edPr e c i i t a t i on p Ki ne t i c so fNb( C, N)andPr e c i i t a t e sEvo l u t i oni n Aus t en i t e p o fNb ＧTi Mi c r o Ｇ a l l oyed S t e e l s[ J]．J Ma t e rSc i,２０１２,４７ ( １１):４６４０． [ １９] 　And r ewsK W．Emp i r i c a lFo rmu l a ef o rt heCa l cu l a t i ono fSome Tr ans f o rma t i onTempe r a t ur e[ J]． JI r onS t e e lI ns t,１９６５,２０３ ( ７):７２１．