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Microstructure Evolution and Mechanical Properties of HR3C Steel during Long-term Aging at High Temperature
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ４,２ １( ８):７ ６ ５ Ｇ ７ ７ ３
Mi c r o s t r u c t u r eEv o l u t i onand Me chan i c a lPr ope r t i e so fHR３C S t e e ldu r i ngLong Ｇ t e rm Ag i nga tHi r a t u r e ghTempe B i n WANG１ ２, Zh e ng Ｇ dongL IU１, Sh i Ｇ c hangCHENG１, Chun Ｇmi ngL IU１, J i ng Ｇ z hong WANG１ ,
( １． I ns t i t u t eo fS t r uc t u r a lMa t e r i a l s,Ch i naI r onandS t e e lRe s e a r chI ns t i t u t eGr oup,Be i i ng１０００８１,Ch i na; j , , , , ) ２． Schoo lo fMa t e r i a l sand Me t a l l u r r t he a s t e r nUn i ve r s i t i aon i ng Ch i na gy No y Shenyang１１０００４ L
Ab s t r a c t:Mi c r o s t r uc t u r ee vo l u t i onandt hechange si nme chan i c a lp r ope r t i e so fHR３Cs t e e ldu r i ngl ong Ｇ t e rmag i nga t , ６５０ ７００and７５０ ℃ we r ei nve s t i t ed．Thep r e c i i t a t edpha s e so ft heag i ngs t e e li nc l uded M２３C６ c a r b i de s,Z Ｇpha s e ga p andat r a c eamoun to fNb( C, N)．TheM２３C６ c a r b i de swe r ed i s t r i bu t edma i n l tt heg r a i nbounda r i l eZ Ｇpha s e ya y,wh wa sma i n l ns i det heg r a i ns．Amoun t so fbo t h M２３C６ c a r b i de sandZ Ｇpha s edu r i ngt heag i ngp r o c e s si nc r e a s edwi t h yi i nc r e a s i ngag i ngpe r i odandt empe r a t u r e． Coa r s en i ngo fM２３C６c a r b i de swa si n f l uenc eds i i f i c an t l i ngt imeand gn ybyag t empe r a t u r e,wh i l et hes i z eo ft heZ Ｇpha s ewa sr e l a t i ve l e s sa f f e c t edbyt heag i ngt imeandt empe r a t u r e,wh i chhad yl as t e adys t r eng t hen i nge f f e c t．Coa r s en i ngo ft heM２３C６c a r b i de swa st hema i nr e a s onf o rt hede c l i nei nh i empe r a Ｇ ght t u r ey i e l ds t r eng t hdu r i ngl ong Ｇ t e rmag i nga t７５０ ℃．The M２３C６ c a r b i de swe r el i nkedi n t oac on t i nuouscha i na l ong t heg r a i nbounda r i cha c c oun t edf o rt hede c r e a s eo ft oughne s sdu r i ngag i ng． ywh Ke r d s:HR３Cs t e e l;mi c r o s t r uc t u r ee vo l u t i on;me chan i c a lp r ope r t i ng y;ag ywo DOI:１０ １３２２８/ boyuan i s sn１００６ Ｇ ７０６x ２０１３００８９ j
HR３Cs t e e l,a２５Cr Ｇ ２０Ni Ｇ t t en i t i che a t Ｇ ypeaus r e s i s t an ts t e e lwi t hexc e l l en tr e s i s t anc et os t e amco r Ｇ r o s i onandar e l a t i ve l i t u r es t r eng t h,i san yh ghrup exc e l l en tma t e r i a lf o rus ei nsupe rhe a t e randr ehe a Ｇ [ ] t e ro fUSCun i t s１－５ ．Pr ev i ouss t ud i e shavef ocus ed ma i n l heimpa c to ft hec omponen t sandsome yont [] i nd i v i dua lpr e c i i t a t edpha s e s６ ．Fo rexamp l e,Pa rk p [] e ta l ７ d i s cus s edt heimpo r t an tr o l eo fn i t r ogeni n s t e e lt hr ough t he c r e ep behav i o rc ompa r i son o f HR３Cs t e e landSUS３１０Ss t e e l( ２５Cr Ｇ ２０Ni)wi t hou t [] t ud i edt hemi Ｇ n i ob i umandn i t r ogen． I s edae ta l ８ s c r o s t ruc t u r a ls t ab i l i t ft h i ss t e e ldu r i ngl ong Ｇ t e rm yo ag i nga t５００－７５０ ℃．Howeve r,r e l a t i ve l imi t ed yl , s t ud i e shavebe enc onduc t edont henumbe r mo r Ｇ l ogyand g r owt hl aw o ft hep r e c i i t a t ed pha s e s pho p andt her e l a t i onsh i twe ent hep r e c i i t a t edpha s e p be p andt heme chan i c a lp r ope r t i e so ft hes t e e ldur i ngt he h i Ｇ t empe r a t u r el ong Ｇ t e rm ag i ng o f HR３C s t e e l． gh Th e r e f o r e,f u r t h e rs t ud i e sont h emi c r o s t r u c t u r ee vo l u Ｇ t i onandpr ope r t so ft h i ss t e e ldu r i ngl ong Ｇ ychange t e rmag i nga r es t i l lr equ i r ed． I nt h i ss t udy,bychemＧ
[] i c a lpha s eana l i s９ ,s c ann i nge l e c t r on mi c r os copy ys ( SEM),t r ansmi s s i one l e c t r on mi c r os copy (TEM ) ando t he rt e chno l og i e s,t het s,t opog r aphy,p r e Ｇ ype c i i t a t i onl oc a t i on,p r e c i i t a t i onamoun tandevo l u Ｇ p p t i onp r oc e s so ft hep r e c i i t a t e d h a s ed u r i n t h ea Ｇ p p g g i ng o f HR３Cs t e e lwe r eobs e r vedandana l ed．I n yz add i t i on,t hee f f e c t so ft hep r e c i i t a t edpha s eevo l u Ｇ p t i onont hepe r f o rmanc eo ft hes t e e lwe r ed i s cus s ed．
１ Exp e r imen t a lPr o c e du r e s
２５kgt e s ts t e e lwa ssme l t edi nava cuumi nduc Ｇ t i onf urna c eandf o r n t oaba rwi t ht hed i ame t e r gedi o f１６mm．Thechemi c a lcompos i t i onswe r eana l ed yz t obe C ０ ０５１,S i０ ２８, Mn１ ３０,Ni２０ ６０,Cr ２４ ０１,Nb０ ３７andN０ ２４ ( ma s s％ )．Af t e rt heso Ｇ l u t i ont r e a tmen ta t１２３０ ℃ f o r３０ mi n,t he mi c r o Ｇ s t ruc t ur eo fs t e e li sshowni nF i １,i nwh i cht he r e g wa sani r r egu l a rshapedp r imepha s ei ns i det heg r a i n wi t has i z eo f１００－８００nm．Ene r Ｇ d i spe r s i veXＧ r ay gy ( ) spe c t r os copy EDS ana l i sshowst ha tt hecon Ｇ ys t en t so fn i ob i umandchr omi um we r er e l a t i ve l i yh gh
Founda t i onI t em: I t em Spons o r edbyNa t i ona lHi ＧTe chRe s e a r chandDeve l opmen tPr og r am ( ８６３Pr og r am)o fCh i na ( ２０１２AA０３A５０１); gh I n t e r na t i ona lSc i enc eandTe chno l ogyCoope r a t i onPr og r amo fCh i na ( ２０１２DFG５１６７０) B i o r aphy: B i n WANG,Do c t o r; E Ｇma i l: b i nk i ng２００９＠f oxma i l c om; Re c e i v e dDa t e:Ma r ch２８,２０１３ g
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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 ２１
F i １ Op t i c a lmi c r o s c opyima e( a)andEDSpa t t e rn ( b)o fs t e e la f t e rs o l u t i ont r e a tmen t g g
i nt h i spr imepha s e．Ac c o r d i ngt or e su l t sf r om p r ev i Ｇ [ １０] , ouss t udy t hep r imepha s eshou l dbet heund i s Ｇ so l vedZ Ｇ s e．Nop r e c i i t a t edpha s ewa sf ounda t pha p t heg r a i nbounda r i e s．Af t e rs o l u t i ont r e a tmen t,t he spe c imenswe r eageda t６５０,７００and７５０ ℃f o r１０, １００,３００,１０００,３０００and６０００h,r e spe c t i ve l y． , Ch a r a c tt e s ta tr o omt emp e r a t u r e as ho r t Ｇ pyimp t e rmh i Ｇ t emp e r a t u r et e n s i l et e s ta t７００ ℃ a ndc hemi Ｇ gh c a lph a s eana l i so ft heageds amp l e s we r ec a r r i ed ys ou t．Theimpa c t eds amp l e swe r eus eda sme t a l l ur i Ｇ g c a ls amp l e sande t chedi nCuCl２ ＋HCl＋H２Oso l u Ｇ t i on．Ana l i so ft hemi c r o s t ruc t u r eandimpa c tf r a c Ｇ ys t u r e mo r l ogy wa sc onduc t ed unde r an S Ｇ ４３００ pho s c ann i nge l e c t r on mi c r o s c ope．Thes amp l ef o rt r ans Ｇ mi s s i one l e c t r on mi c r o s c opy wa spo l i shed me chan i Ｇ , c a l l l e Ｇ e t t ede l e c t r o l t i c a l l e r vedun Ｇ y doub j y yandobs de ran HＧ ８００t r ansmi s s i one l e c t r on mi c r o s c ope．
２ Exp e r imen t a lRe s u l t s
f o rt het imepe r i odo fbo t h１００and６０００h,p r oba Ｇ ( , ) , b l c aus et heNb C N pha s ewa sr a r e andt he ybe d i f f r a c t i onpe ako ft he M２３C６ c a rb i de swa sh i ghand cove r edt ha to ft heNb( C, N)pha s e．
F i ２ XRDpa t t e rn so fe x t r a c t e ds e c ondpha s epa r t i c l e si n g s t e e la f t e ra i nga t７００ ℃ f o r１０,１００and６０００h g
２ １ Mi c r o s t r u c t u r ee v o l u t i ondu r i ngl ong Ｇ t e rma i ng ２ １ ２ Evo l u t i onof pr e c ipi t a t ed pha s ea tgra i n g ２ １ １ Type sofs e c ondpha s ei ns t e e lwi t hdi e r Ｇ b oundary f f en tagi ngt ime Af t e ra i nga t７００ ℃ ,p r e c i i t a t e dpha s ea e a r e d g p pp , TheXRD pa t t e rnso ft heex t r a c t ed powde ro f a l ongt heg r a i nbounda r ． A i n f o r１ ０－１ ０ ０ ０h t h e y g g , HR３Cs t e e lageda t７００ ℃ f o r１０ １００and６０００h amoun tands i z eo ft hepha s epr e c i i t a t eda tg r a i n p a r eshowni nF i ２．Thema i np r e c i i t a t edpha s e si n bounda r nc r e a s eds i i f i c an t l n i t i a lpa r t i cuＧ g p yi gn y．Thei t hes t e e lwe r e M２３ C６ c a rb i de s,Z Ｇ s e (NbCrN) l a t e s( F i s ３( a)and３( b))we r ec onn e c t e dandg r a du a l Ｇ pha g ( , ) ( , andat r a c eamoun to fNb C N pha s e on l nt he l r ewi n t os t r i i chwe r ed i s t r i bu t eda l ongt he yi yg ps wh s amp l ea e df o r１０h)． Fu r t h e rmo r e,f o rt h e１０hs t a t e, g r a i nbounda r i e scon t i nuous l rs emi Ｇ con t i nuous l g yo y ( ( ) ( ) ) , t hed i f f r a c t i oni n t ens i t o ft h eZ Ｇ h a s e w a ss i n i f i Ｇ F i ３ c and３ d ．Fr om １０００t o６０００h t he y p g gs c an t l t r ong e rt h a nt h a to ft h e M２３C６ c a r b i d e s,wh i l e coa r s en i ng o ft he p r e c i i t a t ed pha s ea tt he g r a i n ys p f o rt he１００and６０００hag i ngs t a t e s,t hed i f f r a c t i on bounda r nc r e a s eds l i t l F i ３( d)t o３( f))． yi gh y( gs i n t ens i t ft he M２３C６ c a rb i de si nt hes t e e lwa se l e Ｇ Thes t e e l mo r l ogy changeds l i t l r a i n yo pho gh y．The g va t eds i i f i c a n t l Th i si nd i c a t e st h a tal a r eamoun to f bounda r r e c i i t a t ewa sd i s t r i bu t edi nacon t i nuous gn y． g yp p M２３C６c a rb i de shadp r e c i i t a t eddu r i ngt he s etwoag Ｇ s t r i o rmf o rag i ngo f１０００handd i s t r i bu t edd i s Ｇ p pf ( , ) i ngp r o c e s s e s．The Nb C N pha s e wa sno tf ound con t i nuous l o rag i ngo f３０００－６０００hwi t hasphe Ｇ yf
I s sue８ Mi c r o s t r uc t u r eEvo l u t i onand Me chan i c a lPr ope r t i e so fHR３CS t e e ldu r i ngLong Ｇ t e rm Ag i ng
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( a)１０h; ( b)１００h; ( c)３００h; ( d)１０００h; ( e)３０００h; ( f)６０００h．
F i ３ SEMima e so fp r e c i i t a t e dpha s ea tg r a i nbounda r i e sa e da t７００ ℃ f o rd i f f e r en tt ime g g p g
r o i d i z i ngt r end ( F i ３( e)and３( f))． gs Ca l i b r a t i on o ft he TEM d i f f r a c t i on pa t t e rns showed t ha tt he p r e c i i t a t ed pha s ea tt he g r a i n p bounda r sM２３C６c a rb i de,wi t hc omp l i c a t edcub i c ywa , c r s t a ls t r u c t u r e w h i c h r e t a i n e d ac o h e r e n tr e l a Ｇ y
t i onsh i t ht he ma t r i x( γ)．Theo r i en t a t i onr e l a Ｇ p wi t i onsh i twe ent he M２３C６ c a rb i deandt he ma t r i x pbe wa s[ ０１０]M２３C６ ∥ [ ０１０] sshowni nF i ４( d)．Th i s g γa r e su l twa scons i s t en tr e spe c t i ve l t ht ha tr epo r t ed y wi [ ] [ ] byFange ta l １１ andPenge ta l１２ ．Thel a t t i c econ Ｇ
F i ４ M２３C６ c a r b i d emo rpho l o tg r a i nbounda r fs t e e la e da t７００ ℃ f o r１００h ( a),１０００h ( b)and g g ya yo g ６０００h ( c)andc a l i b r a t i ono fTEM d i f f r a c t i onpa t t e rn s( d)
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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 ２１
s t an to ft he M２３C６ c a rb i de swa st hr e et ime st ha to f , t hema t r i x t husi t sd i f f r a c t i onspo tl eng t hwa sone t h i r dt ha to ft hema t r i x,wh i chwa sat i c a lcha r a c Ｇ yp t e r i s t i co fM２３C６c a rb i de s． S imi l a rt ot heevo l u t i ono f t hepr e c i i t a t ed pha s ea tt heg r a i nbounda r r p y unde SEM,t he mo r l ogyevo l u t i ono ft he M２３C６ c a r Ｇ pho b i de sa tt heg r a i nbounda r rTEM wa sa sf o l Ｇ yunde l ows．Fr om app r ox ima t e l o３００ha tt hee a r l y１０t y ag i ngs t age,M２３C６c a rb i de sl e s st han２００nmi ns i z e we r ep r e c i i t a t ed and d i spe r s ed a l ong t he g r a i n p bounda r sshowni nF i ４( a)．Wi t hex t end i ngag Ｇ ya g i ngt ime,t he M２３ C６ c a rb i de sg r ew g r adua l l y and conne c t edt oge t he rt of o rm a s emi Ｇ c on t i nuous o r con t i nuouscha i no f２００－３００nmi nwi d t ha l ongt he r a i nbounda r r om３００t o１０００h,a ss howni nF i ４ g yf g ( ) , b ．Af t e r１０００h t her e l a t i ves i z eo ft heM２３C６c a r Ｇ b i de sc on t i nuedt oi nc r e a s ebu tt heg r owi ngr a t ewa s , r e l a t i ve l s l o w a n dt h e M C c a r b i d e s w e r es h e Ｇ y p ２３ ６ r o i d i z e dg r adua l l t h ex t end i ng ag i ng t ime and y wi f o rmedd i s c on t i nuousp a r t i c l e sa l ongt h eg r a i nbound a Ｇ
r ss howni nF i ４( c)． ya g ２ １ ３ Ev o l u t i o nofi n t r agr anu l a rpr e c i i t a t edpha s e p Asshowni nF i ５,asho r tr od Ｇ l i kef i nepr e c i Ｇ g p , i t a t ed pha s e wi t h ad i s t r i bu t i on wi t h i nt he g r a i n andasma l ls i z eo fapp r ox ima t e l sf ound y４０nm,wa common l nt heag i ngs t a t e so ft hes amp l e．Ac co rd Ｇ yi , i ngt ot hed i f f r a c t i onpa t t e rns t h i ssma l lpr e c i i t a Ｇ p t ed pha s ecou l d bei den t i f i eda st he Z Ｇ s e,and pha compa r edwi t ht hebu l kyZ Ｇ s ei nF i １,t hes i z e pha g o ft h i sZ Ｇ s ei nt heag i ngs t a t e so ft hes amp l ei s pha sma l l e rt hant hebu l kyon e．TheZ Ｇ s ec r s t a ls t r u c Ｇ pha y [ ] t u r ewa st e t r agona l．Sourma i landBhade sh i a１３ a l so r epo r t edt h i sf i nei n t r ag r anu l a r l r e c i i t a t edpha s e yp p i n NF７０９s t e e l( ２２Cr ２５NiMoNbN)．A compa r i son o fs t e e lagedf o r６０００and１００hshowst ha tt hes i z e o ft h i sf i nep r e c i i t a t ed i dno tchanges i i f i c an t l p gn y wi t hag i ngt ime,andi twa sa lwaysa r ound４０nmi n d i ame t e r,bu ti t samoun ti nc r e a s eds i i f i c an t l gn y． , Asshowni nF i ６ asma l lamoun to f M２３C６ g c a rb i dewa sa l sof oundwi t h i nt heg r a i n．Ac c o r d i ngt o
( a)Ag i ngf o r１００h; ( b)Ag i ngf o r３０００h; ( c)Di f f r a c t i onpa t t e r ns．
F i ５ Mo rpho l o fi n t r a r anu l a r l r e c i i t a t e dZ Ｇpha s ei nHR３Cs t e e la e da t７００ ℃ g g yo g yp p g
( a)TEM mo r l ogy; ( b),( c)Di f f r a c t i onpa t t e r ns． pho
F i ６ Mo rpho l o fi n t r a r anu l a r l r e c i i t a t e d M２３C６i nHR３Cs t e e la e da t７００ ℃ f o r３０００h g g yo g yp p g
i t sd i f f r a c t i onpa t t e rns,t hei n t r ag r anu l a rM２３C６c a r Ｇ b i de sa l s or e t a i nedac ohe r en tr e l a t i onsh i t ht he p wi ma t r i xandhadano r i en t a t i onr e l a t i onsh i t ht he p wi
ma t r i xa s( ２２０)M２３C６ ∥ ( ２２０) nd [ ２３３]M２３C６ ∥ γ a [ Al t hought he M２３C６ c a rb i de swe r ef oundi n ２３３] γ． , t heg r a i nt heamoun to fM２３C６c a rb i de swa sf a rl e s s
t hant ha ta tt heg r a i nbounda r t ss i z ewa sr e l Ｇ y,andi a t i ve l t ab l ea t３００－５００nm． ys ２ ２ E f f e c to fa i n emp e r a t u r eo np r e c i i t a t e dpha s e g gt p ２ ２ １ Typeofpr e c ipi t a t edpha s e XRDpa t t e rnso ft heex t r a c t edpowde ra f t e rag Ｇ
I s sue８ Mi c r o s t r uc t u r eEvo l u t i onand Me chan i c a lPr ope r t i e so fHR３CS t e e ldu r i ngLong Ｇ t e rm Ag i ng
i nga t６５０and７５０ ℃ we r es imi l a rt ot ha ta t７００ ℃ , and no o t he rp r e c i i t a t ed pha s e s we r ef ound．As p showni nF i ７,on l h ed i f f r a c t i oni n t e n s i t i e sd i f f e r e d g yt
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s l i t l i nga t７５０ ℃ f o rapp r ox ima t e l gh y;ag y１００h, t hes t r onge s tpe aksi nt heXRDspe c t r awe r e M２３C６ c a rb i de s,wh i l et hes t r onge s tpeaksbe l ongedt othe
F i ７ XRDpa t t e rn so fs e c ondpha s epa r t i c l e se x t r a c t e di ns t e e la e da t６５０ ℃ ( a)and７５０ ℃ ( b)f o rd i f f e r en tt ime g g
Z Ｇ s ed i f f r a c t i ona t６５０and７００ ℃． pha ２ ２ ２ Mo rpho l ogyofpr e c ipi t a t edpha s e F i ８showsSEM mi c r og r aphso ft hep r e c i i Ｇ g p t a t e sa tt heg r a i nbounda r t６５０and７５０ ℃ wi t h ya d i f f e r en tag i ngs t a t e s．Thec ompa r i s onshowedt ha t, agedf o rt hes amet ime,t hep r e c i i t a t edpha s es i z e p a tt heg r a i nbounda r nc r e a s eds i i f i c an t l t he l Ｇ yi gn ywi eva t i ngag i ngt empe r a t u r e．The mo r l ogy o ft he pho e c i i t a t edpha s ea tt heg r a i nbounda r Ｇ pr p ychangedno , t i c e ab l w h e na i n a t７ ５ ０ ℃ f o r１ ０ ０ ０h a n d a r y g g pt
o ft hep r e c i i t a t ed pha s ef o rmedsphe r i c a lpa r t i c l e s p ( ( ) ) wi t hd i s con t i nuous d i s t r i bu t i on F i ８ d ．Th i s g s mo r e ev i den tf o r ６０００ h ag i ng phenomenon wa ( F i ８ ( f))．S imi l a r phenomenon wa sa l sof ound g ( whenag i nga t７００ ℃ f o r３０００and６０００h F i ３ gs ( e)and３( f))．Ag i nga t６５０ ℃f o r６０００h,t h i sphe Ｇ nomenond i dno tex i s tandt hep r e c i i t a t edpha s ea t p t heg r a i n bounda r e t a i nedane l onga t edd i s t r i bu Ｇ yr t i on．Th i sr e su l ti nd i c a t e st ha tt heevo l u t i ono ft he r e c i i t a t edpha s ea tt heg r a i nbounda r sa c c e l e r Ｇ p p ywa
( a)６５０ ℃ ,１００h; ( b)７５０ ℃ ,１００h; ( c)６５０ ℃ ,１０００h; ( d)７５０ ℃ ,１０００h; ( e)６５０ ℃ ,６０００h; ( f)７５０ ℃ ,６０００h．
F i ８ SEMima e so fp r e c i i t a t e dpha s e sa tt h eg r a i nbounda r o rd i f f e r en ta i ngs t a t e s g g p yf g
a t edwi t hi nc r e a s i ngag i ngt empe r a t u r e． Th eTEM mo r l og i e so ft h ep r e c i i t a t e dpha s e s pho p a tt heg r a i nbounda r i nt h ea i n s t a t ea t６ ５ ０a n d y g g ７５０ ℃ a r eshowni nF i ９．Thewi d t ho ft he M２３C６ g c a rb i de sa tt heg r a i nbound a r fs t e e la e da t７５０ ℃ yo g
f o r１００hwa ss l i t l a r rt hant ha ta t６５０ ℃ f o r gh yl ge ３０００h ( F i ９( a)and９( b))．TheM２３C６c a rb i de sa t gs t heg r a i nbound a r f o r t h e ６ ０ ０ ０ha i n s t a t ea t ７ ５ ０ ℃ y gg we r ecoa r s eneds i i f i c an t l t hani nc r e a s ei nove r gn ywi １μmi nt heho r i z on t a ld i r e c t i on．
７７０
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 ２１
( a)７５０ ℃ ,１００h; ( b)６５０ ℃ ,３０００h; ( c)７５０ ℃ ,６０００h．
F i ９ Ev o l u t i ono fp r e c i i t a t e d M２３C６ c a r b i d e sa tg r a i nbounda r f t e ra i ng g p ya g
S imi l a rt ot heag i ngs t a t ea t７００ ℃ ,t hef i nei n Ｇ t r ag r anu l a r l r e c i i t a t e d h a s e s w e r eZ Ｇ h a s e sf o r yp p p p ( ) t he６０００hag i ngs t a t ea t６５０and７５０ ℃ F i １０ ． g Thed i f f e r enc ei nd imens i onand dens i t ft heZ Ｇ yo
s e swa ssma l lf o rt he６０００hag i ngs t a t e sa t６５０ pha and７５０ ℃．The s er e su l t ssugge s t edt ha tt heag i ng t empe r a t ur ehadar e l a t i ve l l le f f e c tont heZ Ｇ ysma s ep r e c i i t a t i onbehav i o r． pha p
( a)６５０ ℃ ,６０００h; ( b)７５０ ℃ ,６０００h．
F i １０ Mo rpho l o i e so fi n t r a r anu l a r l r e c i i t a t e dZ Ｇpha s e si nHR３Cs t e e lf o rd i f f e r en ta i ngs t a t e s g g g yp p g
２ ３ Re l a r i t ns i z echang eo fpr e c i i t a t e dpha s e gu yi p S t a t i s t i c so ft he p r e c i i t a t ed pha s es i z e we r e p conduc t ed ba s ed on TEM obs e r va t i on．Unde rt he emi s et ha ti t scha r a c t e rwa sc on f i rmedbye l e c t r on pr , d i f f r a c t i on t he max imum t r ans ve r s ed imens i on o f t hepr e c i i t a t ed pha s e wa s me a su r eda si t ss i z e Ｇ de Ｇ p
t e rmi n i ngpa r ame t e r．The we i t edave r ageo ft he gh me a sur eds i z ewa su s e da st hea v e r a es i z eo ft heme a s Ｇ g u r e dpha s e,andt henumbe ro ft hes e condpha s epa r Ｇ t i c l e sme a sur edwa smo r et han５０i ne a chs t a t e．As , showni nF i １１ t hes i z eo ft he M２３C６ c a rb i de si n Ｇ g c r e a s eds i i f i c an t l t hi n c r e a s i nga i ngt ime,wh i l e gn y wi g
( a)M２３C６c a r b i de s; ( b)Z Ｇ s e． pha
F i １１ S i z echang eo fM２３C６ c a r b i d e sandZ Ｇpha s ei nHR３Cs t e e lwi t hi nc r e a s i nga i ngt ime g g
I s sue８ Mi c r o s t r uc t u r eEvo l u t i onand Me chan i c a lPr ope r t i e so fHR３CS t e e ldu r i ngLong Ｇ t e rm Ag i ng
t hes i z eo ft heZ Ｇ s e wa sr e l a t i ve l t ab l e．Wi t h pha ys , t hei nc r e a s ei nag i ngt empe r a t u r e awi den i ngo ft he M２３C６ c a rb i de swa simp r oveds i i f i c an t l i l ei t s gn y wh e f f e c tont heZ Ｇ s ewa sr e l a t i ve l l i t． pha ys gh ２ ４ Va r i a t i oni nc on t e n to fpr e c i i t a t e dpha s e p , Thr ough chemi c a l pha s e ana l i s cur ve so f ys ma s sf r a c t i onaga i ns tag i ngt imef o rt he M２３C６ c a r Ｇ b i de sandZ Ｇ a s e( c on t a i n i ngt r a c e so ft h eNb( C, N) ph ) s e we r eob t a i nedf o rt het hr e et empe r a t ur eag Ｇ pha
７７１
i ngp r oc e s s e s( F i １２)．Dur i ngt heag i ngp r oc e s s, g t het o t a lamoun to fp r e c i i t a t edpha s ei nc r e a s edr ap Ｇ p i d l t hi nc r e a s i ngag i ngt ime wi t h i n１０００ hand y wi showedas i i f i c an t l l owe rr a t eo fi nc r e a s et he r e Ｇ gn ys a f t e r．Thee f f e c to fag i ngt empe r a t ur eont heamoun t o fM２３C６c a rb i de sp r e c i i t a t edwa sr e l a t i ve l i i f i Ｇ p ys gn c an t,wh i l ei t simpa c tont heZ Ｇ s ewa sr e l a t i ve l pha y sma l l．Fo rt he６０００hag i ngs t a t e,t hema s sf r a c t i on o fM２３C６ c a rb i de si nt hes amp l eageda t７５０ ℃ wa s , , １ １５７％ wh i c hwa s１ ４１t ime st ha ta t６５０ ℃ wh i l e
( a)M２３C６c a r b i de s; ( b)Z Ｇ s e． pha
F i １２ Chang ei nc on t en t so fp r e c i i t a t e dpha s e si na i ngs t a t eo fHR３Cs t e e la a i n s ta i ngt ime g p g g g
t hec o r r e spond i ngr a t i oo ft heZ Ｇ s ewa s１ ０７６． pha ２ ５ Me chan i c a lpr ope r t i e sa f t e rl ong Ｇ t e rm a i nga t g h i empe r a t u r e ght Sho r t Ｇ t e rm t ens i l et e s t sf o rt he６５０,７００and ７５０ ℃ ag i ngs t a t ewe r ec onduc t eda t７００ ℃ wi t hr e Ｇ su l t sshowni nF i １３．Thed i f f e r enc ei nh i emＧ g ght r a t u r ey i e l ds t r eng t hi nt hec a s eo fag i ng a tt he pe t hr e et empe r a t u r e sf o r１０h wa si ns i i f i c an t．Wi t h gn anex t ens i oni n ag i ng t ime,t he h i empe r a t ur e ght i e l ds t r e n t ho ft h es t e e lf i r s ti n c r e a s e da n dt h e n y g d e c r e a s e dwh e nt h es t e e lwa sa e da t７５０℃． Anov e r a Ｇ g g i ngphenomenon o c cu r r ed,wi t hava l ueo fa r ound ２６０ MPaa ta bou t３００h．Fo rt h ea i nga t７００ ℃ ,t he g h i emp e r a t u r ey i e l ds t r e ng t hi nc r e a s edr ap i d l r om ght yf
F i １３ Hi emp e r a t u r ey i e l dp e r f o rmanc eo fHR３C g ght s t e e lf o rd i f f e r en ta i ngs t a t e sa t７００ ℃ g
１０t o１０００hwi t hani nc r e a s ef r om１９０t o２４５ MPa, wh i ch wa ss l i t l l eva t edf r om １０００ h andr e Ｇ gh ye ma i neds t ab l ea ta r ox ima t e l f t e r３０００h． pp y２５５ MPaa Fo rt heag i nga t６５０ ℃ ,t heh i empe r a t ur ey i e l d ght s t r eng t hi nc r e a s edf r om１０t o６０００h,andt heva l ue f r om１８５MPar e a ched２５５MPa．Wi t hi nc r e a s i ngt he ag i ngt empe r a t ur e,t hepe akso ft heh i empe r a Ｇ ght t ur ey i e l ds t r eng t hsh i f t edt ot hel e f t． Fo rt he１０hag i ngs t a t e,t heimpa c tene r Ｇ gyde c r e a s eds i i f i c an t l t hi n c r e a s i nga i ngt emp e r a t u r e, gn ywi g a sshowni nF i １４．Fo rt he１０－３００ha i ngp r oc e s s g g
F i １４ Impa c ten e r fHR３Cs t e e lf o rd i f f e r en t g g yo a i n s t a t e sa t r o o mt e m e r a t u r e gg p
７７２
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 ２１
a teve r empe r a t u r e,t heimpa c tene r c r e a s ed yt gy de , r ap i d l t e rag i nga t７５０ ℃ f o r３００h t heimpa c t y．Af ene r nc r e a s eds l i t l twa se s s en t i a l l he gyi gh y．Andi yt s amef o rt heag i nga t６５０and７００ ℃．Whent heag Ｇ i ngt imeo f６０００hwa sr e a ched,wi t hi nc r e a s i ngag Ｇ i ngt empe r a t u r e,t heimpa c tene r nc r e a s eds l i t Ｇ gyi gh l nimpa c tene r sr e l a t edt ot he y．Thechangei gy wa mo r l ogyandd i s t r i bu t i ono ft heM２３C６c a rb i de sa t pho t heg r a i nbounda r y．
M２３C６ c a rb i de sandt heenhanc emen tc aus edbyt he cons t an tp r e c i i t a t i ono ft hef i neZ Ｇ s ea ch i eveda p pha r e l a t i ve l l anc eds t a t e,c aus i ngl eve l i ng Ｇ o f fo ft he yba i e l ds t r eng t ha f t e rag i nga t７００ ℃ f o r３０００h．Fo r y t he１０－６０００hag i ngp r oc e s sa t６５０ ℃ ,p r e c i i t a t i Ｇ p onr a t e so ft heM２３C６c a rb i de sandZ Ｇ s ede c r e a s ed pha , aga i n a ndt h eM２３C６c a r b i d eg r owt hs l owe dd owna a i n． g Howeve r,t hep r e c i i t a t i ons t r eng t hen i nge f f e c twa s p enhanc ed, c aus i ng t he h i empe r a t ur e y i e l d gh t s t r eng t ht oi nc r e a s e． ３ E f f e c to fP r e c i i t a t e so nS t r e n t ha n dT o u hn e s s p g g Thechangei nimpa c tt oughne s swa sma i n l Ｇ ybe aus eo ft heevo l u t i ono fM２３C６c a rb i de sa tt heg r a i n Du r i ngt heag i ngo ft he HR３Cs t e e l,t he ma i n c r o ra i ngt imef r om１０t o３００h,l a r e e c i i t a t edph a s e swe r e M２３C６ c a r b i d e sa ndZ Ｇ s e． bounda y,andf g g pr p pha t so f M２３C６ c a rb i de s we r ep r e c i i t a t eda l ong Change si nt he s etwo pha s e s de t e rmi nedt he pe r Ｇ amoun p t heg r a i nbounda r c t edi n t oacon t i nuous f o rmanc eva r i a t i ono ft hes t e e lag i ngs t a t e． yandconne ( ) ( ) , i na sshowni nF i ４ b and９ b ．Thecon t i nu Ｇ I ti swe l lknownt ha ti ft hes i z eo ft hep r e c i i Ｇ cha gs p r a i nbounda r cup i edbyt he M２３C６ c a rb i de s t a t edpha s ei ssma l l e randi t snumbe ri sg r e a t e r,t he ousg yoc sconduc i vet oc r a ck p r opaga t i onandr e su l t edi n e c i i t a t i onha r den i ng e f f e c t wi l lbe mo r es i i f i Ｇ wa pr p gn [ １４, １５] i t t l ene s so ft hes t e e landas i i f i c an tr educ t i oni n c an t ．The changei nh i empe r a t ur ey i e l d br gn gh t t i l i t fs t e e l．Af t e r１０００ho fag i nga t７５０ ℃ , s t r eng t hi sc aus edp r e c i s e l hechangei ns i z eand duc yo ybyt M２３C６c a r b i d e sa tt heg r a i nbound a r hang e dg r adua l l numbe ro ft he M２３ C６ c a rb i de sand Z Ｇ s ei nt he yc y pha , r om a con t i nuous cha i n Ｇ t oad i s con t i nuous s t e e l．Du r i ngag i nga t７５０ ℃ t hey i e l ds t r eng t hi n Ｇ f ype t r anu l a r Ｇ t i s t r i bu t i on ( F i ８( d)and８( f))． c r e a s edr ap i d l r om １０t o３００hbe c aus et henumＧ g yped gs yf , W i t hi m a c tf r a c t u r i n t h ec r a c ks r e a da l o n he be r so f M２３ C６ c a rb i de sandt he Z Ｇ h a s ei n c r e a s e d p g p gt p , , r a i nbounda r r eene r sr equ i r edwhen r ap i d l h i spe r i od t ho s ep r e c i i t a t e swe r ed i s Ｇ g y andmo gywa y．Att p hed i s con t i nuousd i s t r i bu t i ono fM２３C６c a rb i de swa s t r i bu t edd i s c on t i nuous l i chc anho l dd i s l oc a t i on t y,wh t e r ed．Th i si nc r e a s ed t he impa c t duc t i l i t mo t i onandt he r e f o r es t r eng t hent hes t e e l．Af t e r３００ encoun y l i t l t e rl ong Ｇ t e rm ag i ng,t h i sd i s con t i nuous h,t heM２３C６c a rb i de swi deneds i i f i c an t l he s gh y．Af gn y,andt i s t r i bu t i on phenomenoni nc r e a s ed wi t hi nc r e a s i ng s t r eng t hen i nge f f e c t wa s we akened．Ani nc r e a s ei n d i ngt empe r a t ur e．Bu tt hei nc r e a s e wa si ns i i f i Ｇ s t r eng t hc aus edbyt hei nc r e a s edamoun to ft heZ Ｇ ag gn an t;t he r e f o r e,t hee f f e c to ft h i sphenomenonon s e wa s sma l l e rt han t he de c r e a s ei ns t r eng t h c pha heimp a c tdu c t i l i t t６５０and７００ ℃ wa sno ts hown c aus edbyt hewi den i ngo ft he M２３C６ c a rb i de s．The t ya l e a r l i １５showst hemo r l og i e so ft heimpa c t h i empe r a t u r ey i e l ds t r eng t ht he r e f o r ede c r e a s ed c y．F g pho ght r a c t ur e sa f t e rag i nga tt hr e eag i ngt empe r a t ur e sf o r s l owl ndt h ec h a ng ei ns t r e ng t ha t７５０℃ wa sat Ｇ f y,a yp r a c t ur ea t６５０ ℃i sat i c a lb r i t t l er o c k i c a love r ag i ngphenomenon．Du r i ngag i nga t７００ ℃ , ６０００h．Thef yp , andy Ｇ l i kef r a c t u r e wh i l ea l lf r a c t u r esur f a c e sa t７００ e c i i t a t i onr a t e so ft heM２３C６c a rb i de sandZ Ｇ s e c pr p pha e r t a i namoun to fd imp l e st ha ti n Ｇ we r es l owe rt hant ho s ea t７５０ ℃ ,andt hei nc r e a s e and７５０ ℃ haveac r e a s eds i i f i c an t l t７５０ ℃．Th i sr e su l ti scons i s t Ｇ i ny i e l ds t r eng t hs l owl c r e a s ed．Af t e rag i ngf or c gn ya yde , twi t hp r ev i ousexp l ana t i ons． ３０００h t he we aken i ngc aus edby wi den i ng o ft he en
( a)６５０ ℃ ; ( b)７００ ℃ ; ( c)７５０ ℃．
F i １５ Mo rpho l o i e so fimpa c tf r a c t u r ef o rt h e６０００ha i ngs t a t e g g g
I s sue８ Mi c r o s t r uc t u r eEvo l u t i onand Me chan i c a lPr ope r t i e so fHR３CS t e e ldu r i ngLong Ｇ t e rm Ag i ng
４ Conc l u s i on s ( １)Du r i ngt heag i ngp r o c e s sa t６５０,７００and , ７５０ ℃ t he ma i np r e c i i t a t ed pha s e so ft he HR３C p s t e e li n c l ud e dt h eM２３C６ c a r b i d e s,Z Ｇ s eandat r a c e pha amoun to f Nb( C,N)．M２３ C６ c a rb i de sp r e c i i t a t ed p ma i n l tt heg r a i nbounda r l ew we r e ya yandon yaf e c i i t a t ed wi t h i nt he g r a i n．Z Ｇ s ep r e c i i t a t ed pr p pha p ma i n l t h i nt heg r a i n． y wi ( ) ２ Wi t ha ne x t e n s i ono fa i ngt ime,t h eamoun t g o fM２３C６c a rb i de si nt hes t e e li nc r e a s edc on t i nuous l y． Andt henumbe rands i z eo fM２３C６c a rb i de si nc r e a s ed s i i f i c an t l t hani nc r e a s ei nag i ngt empe r a t ur e． gn y wi Shapeandd i s t r i bu t i ono fM２３C６c a rb i de sa tt heg r a i n bounda r rwen tt hr e ed i f f e r en ts t age s．Atf i r s t, yunde
t hesma l lpa r t i c l e s we r e unc onne c t ed a tt he g r a i n bounda r he pa r t i c l e sg r ew i n t os t r i Ｇ l i ke y．Then t p shapeandc onne c t edwi t he a cho t he rt of o rmcon t i n Ｇ , uouscha i nsa l ongt heg r a i nbounda r a s t when y．Atl t hec a r b i d e sc o a r s e n e di n t os e r i c a ls h a e,t he r e ph p y we unc onne c t edaga i n．Wi t hani nc r e a s ei nag i ngt emＧ r a t u r e,t heevo l u t i onl awbe c amemo r es i i f i c an t． pe gn ( ３)Themo r l ogyandd imens i onso ft hei n Ｇ pho t r ag r anu l a rZ Ｇ h a s ed i dn o t c h a n e s i n i f i c a n t l w i t h p g g y ag i ngt imeand t empe r a t u r e, wh i ch had a s t e ady s t r eng t hen i nge f f e c t． ( ４)Wi d e n i ngo ft h eM２３C６c a r b i d e swa st hema i n r e a s onf o rade c r e a s ei nt heh i Ｇ t empe r a t ur ey i e l d gh s t r eng t h wi t hag i nga t７５０ ℃．I nc r e a s i ngl eve l so f M２３C６c a rb i de sf o rag i nga t６５０and７００ ℃ we r er e l Ｇ a t i ve l owe r,andt hes t e adys t r eng t hen i nge f f e c to f yl
７７３
t heZ Ｇ s e ma d et heh i emp e r a t u r ey i e l ds t r e ng t h pha ght i nc r e a s econs t an t l t i l i t sc aus ed y．Theduc ychangewa ma i n l hechangei nmo r l ogyandd i s t r i bu t i on ybyt pho o ft heM２３C６c a rb i de sa tt heg r a i nbounda r y． Re f e r enc e s: [ １] F．Ma suyama,I S I JI n t． ４１ ( ２００１)６１２ Ｇ ６２５． [ ２] J Z．Wang,Z D．L i u,S C．Cheng,HS．Bao,J． I r onS t e e l Re s． I n t． １８ ( ２０１１)No １０,５４ Ｇ ５８． [ ３] A．Na t o r i,S t a i n l e s sS t e e lEur ope４ ( １９９２)No． １６,２０ Ｇ ２５． [ ４] J Z．Wa ng,Z D．L i u,HS．Ba o,S C．Ch e ng,B．Wa ng,J． I r on S t e e lRe s． I n t． ２０ ( ２０１３)５４ Ｇ ５８． [ ５] T． Sourma i l,Ma t e r． Sc i．Te chno l． １７ ( ２００１)１ Ｇ １４． [ ６] M．Va ch,T．Kun í ková,M．Dománková,P．Šev c,L．Cap l ov Ｇ i c,P．Gogo l a,J．J anove c, Ma t e r．Cha r a c t．５９ ( ２００８)１７９２ Ｇ
１７９８． [ ７] I．Pa rk,F．Ma suyama,T．Endo,Key Eng．Ma t e r．１７１ Ｇ １７４ ( ２０００)４４５ Ｇ ４５２． [ ８] A． I s eda,H．Okada,H． Semba,M． I r a sh i,Ene r t e r． ２ ga gyMa ( ２００７)１９９ Ｇ ２０６． [ ９] J．L i u,C．Lu,Y．Yao,Phys i c a lChemi s t r s eAna l i so f yPha ys i Sc i en t i f i c & S t e e land I r on, Ni cke l Ｇ ba s ed Al l oy,Shangha Te chn i c a lPub l i she r s,Shangha i,１９８４． [ c i a lS t e e l D．L i u,S C．Cheng,HS．Bao,Spe １０] J Z．Wang,Z ３２ ( ２０１１)No ３,６１ Ｇ ６４． [ N．L i,Ac t a Me t a l l．S i n． ４６ ( ２０１０) １１] YY．Fang,J．Zhao,X
８４４ Ｇ ８４９． [ Q．Gao,HQ．Zhang, Zhang,J．Hong,J １２] B C．Peng,HX． t e r．Sc i．Eng．A ５２７ ( ２０１０)４４２４ Ｇ J F．L i,QJ．Wang,Ma ４４３０． [ １３] T． Sourma i l,HKD H． Bhade sh i a,Me t a l l．Ma t e r．Tr ans．A ３６ ( ２００５)２３ Ｇ ３４． [ １４] K．Ma r uyama,K． Sawada,J．Ko i ke,I S I JI n t． ４１ ( ２００１)６４１ Ｇ ６５３． [ D．L i u,S P．Tan,J． I r onS t e e l １５] HS．Bao,S C．Cheng,Z Re s． I n t． １７ ( ２０１０)No ２,６７ Ｇ ７３．
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ４,２ １( ８):７ ６ ５ Ｇ ７ ７ ３
Mi c r o s t r u c t u r eEv o l u t i onand Me chan i c a lPr ope r t i e so fHR３C S t e e ldu r i ngLong Ｇ t e rm Ag i nga tHi r a t u r e ghTempe B i n WANG１ ２, Zh e ng Ｇ dongL IU１, Sh i Ｇ c hangCHENG１, Chun Ｇmi ngL IU１, J i ng Ｇ z hong WANG１ ,
( １． I ns t i t u t eo fS t r uc t u r a lMa t e r i a l s,Ch i naI r onandS t e e lRe s e a r chI ns t i t u t eGr oup,Be i i ng１０００８１,Ch i na; j , , , , ) ２． Schoo lo fMa t e r i a l sand Me t a l l u r r t he a s t e r nUn i ve r s i t i aon i ng Ch i na gy No y Shenyang１１０００４ L
Ab s t r a c t:Mi c r o s t r uc t u r ee vo l u t i onandt hechange si nme chan i c a lp r ope r t i e so fHR３Cs t e e ldu r i ngl ong Ｇ t e rmag i nga t , ６５０ ７００and７５０ ℃ we r ei nve s t i t ed．Thep r e c i i t a t edpha s e so ft heag i ngs t e e li nc l uded M２３C６ c a r b i de s,Z Ｇpha s e ga p andat r a c eamoun to fNb( C, N)．TheM２３C６ c a r b i de swe r ed i s t r i bu t edma i n l tt heg r a i nbounda r i l eZ Ｇpha s e ya y,wh wa sma i n l ns i det heg r a i ns．Amoun t so fbo t h M２３C６ c a r b i de sandZ Ｇpha s edu r i ngt heag i ngp r o c e s si nc r e a s edwi t h yi i nc r e a s i ngag i ngpe r i odandt empe r a t u r e． Coa r s en i ngo fM２３C６c a r b i de swa si n f l uenc eds i i f i c an t l i ngt imeand gn ybyag t empe r a t u r e,wh i l et hes i z eo ft heZ Ｇpha s ewa sr e l a t i ve l e s sa f f e c t edbyt heag i ngt imeandt empe r a t u r e,wh i chhad yl as t e adys t r eng t hen i nge f f e c t．Coa r s en i ngo ft heM２３C６c a r b i de swa st hema i nr e a s onf o rt hede c l i nei nh i empe r a Ｇ ght t u r ey i e l ds t r eng t hdu r i ngl ong Ｇ t e rmag i nga t７５０ ℃．The M２３C６ c a r b i de swe r el i nkedi n t oac on t i nuouscha i na l ong t heg r a i nbounda r i cha c c oun t edf o rt hede c r e a s eo ft oughne s sdu r i ngag i ng． ywh Ke r d s:HR３Cs t e e l;mi c r o s t r uc t u r ee vo l u t i on;me chan i c a lp r ope r t i ng y;ag ywo DOI:１０ １３２２８/ boyuan i s sn１００６ Ｇ ７０６x ２０１３００８９ j
HR３Cs t e e l,a２５Cr Ｇ ２０Ni Ｇ t t en i t i che a t Ｇ ypeaus r e s i s t an ts t e e lwi t hexc e l l en tr e s i s t anc et os t e amco r Ｇ r o s i onandar e l a t i ve l i t u r es t r eng t h,i san yh ghrup exc e l l en tma t e r i a lf o rus ei nsupe rhe a t e randr ehe a Ｇ [ ] t e ro fUSCun i t s１－５ ．Pr ev i ouss t ud i e shavef ocus ed ma i n l heimpa c to ft hec omponen t sandsome yont [] i nd i v i dua lpr e c i i t a t edpha s e s６ ．Fo rexamp l e,Pa rk p [] e ta l ７ d i s cus s edt heimpo r t an tr o l eo fn i t r ogeni n s t e e lt hr ough t he c r e ep behav i o rc ompa r i son o f HR３Cs t e e landSUS３１０Ss t e e l( ２５Cr Ｇ ２０Ni)wi t hou t [] t ud i edt hemi Ｇ n i ob i umandn i t r ogen． I s edae ta l ８ s c r o s t ruc t u r a ls t ab i l i t ft h i ss t e e ldu r i ngl ong Ｇ t e rm yo ag i nga t５００－７５０ ℃．Howeve r,r e l a t i ve l imi t ed yl , s t ud i e shavebe enc onduc t edont henumbe r mo r Ｇ l ogyand g r owt hl aw o ft hep r e c i i t a t ed pha s e s pho p andt her e l a t i onsh i twe ent hep r e c i i t a t edpha s e p be p andt heme chan i c a lp r ope r t i e so ft hes t e e ldur i ngt he h i Ｇ t empe r a t u r el ong Ｇ t e rm ag i ng o f HR３C s t e e l． gh Th e r e f o r e,f u r t h e rs t ud i e sont h emi c r o s t r u c t u r ee vo l u Ｇ t i onandpr ope r t so ft h i ss t e e ldu r i ngl ong Ｇ ychange t e rmag i nga r es t i l lr equ i r ed． I nt h i ss t udy,bychemＧ
[] i c a lpha s eana l i s９ ,s c ann i nge l e c t r on mi c r os copy ys ( SEM),t r ansmi s s i one l e c t r on mi c r os copy (TEM ) ando t he rt e chno l og i e s,t het s,t opog r aphy,p r e Ｇ ype c i i t a t i onl oc a t i on,p r e c i i t a t i onamoun tandevo l u Ｇ p p t i onp r oc e s so ft hep r e c i i t a t e d h a s ed u r i n t h ea Ｇ p p g g i ng o f HR３Cs t e e lwe r eobs e r vedandana l ed．I n yz add i t i on,t hee f f e c t so ft hep r e c i i t a t edpha s eevo l u Ｇ p t i onont hepe r f o rmanc eo ft hes t e e lwe r ed i s cus s ed．
１ Exp e r imen t a lPr o c e du r e s
２５kgt e s ts t e e lwa ssme l t edi nava cuumi nduc Ｇ t i onf urna c eandf o r n t oaba rwi t ht hed i ame t e r gedi o f１６mm．Thechemi c a lcompos i t i onswe r eana l ed yz t obe C ０ ０５１,S i０ ２８, Mn１ ３０,Ni２０ ６０,Cr ２４ ０１,Nb０ ３７andN０ ２４ ( ma s s％ )．Af t e rt heso Ｇ l u t i ont r e a tmen ta t１２３０ ℃ f o r３０ mi n,t he mi c r o Ｇ s t ruc t ur eo fs t e e li sshowni nF i １,i nwh i cht he r e g wa sani r r egu l a rshapedp r imepha s ei ns i det heg r a i n wi t has i z eo f１００－８００nm．Ene r Ｇ d i spe r s i veXＧ r ay gy ( ) spe c t r os copy EDS ana l i sshowst ha tt hecon Ｇ ys t en t so fn i ob i umandchr omi um we r er e l a t i ve l i yh gh
Founda t i onI t em: I t em Spons o r edbyNa t i ona lHi ＧTe chRe s e a r chandDeve l opmen tPr og r am ( ８６３Pr og r am)o fCh i na ( ２０１２AA０３A５０１); gh I n t e r na t i ona lSc i enc eandTe chno l ogyCoope r a t i onPr og r amo fCh i na ( ２０１２DFG５１６７０) B i o r aphy: B i n WANG,Do c t o r; E Ｇma i l: b i nk i ng２００９＠f oxma i l c om; Re c e i v e dDa t e:Ma r ch２８,２０１３ g
７６６
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 ２１
F i １ Op t i c a lmi c r o s c opyima e( a)andEDSpa t t e rn ( b)o fs t e e la f t e rs o l u t i ont r e a tmen t g g
i nt h i spr imepha s e．Ac c o r d i ngt or e su l t sf r om p r ev i Ｇ [ １０] , ouss t udy t hep r imepha s eshou l dbet heund i s Ｇ so l vedZ Ｇ s e．Nop r e c i i t a t edpha s ewa sf ounda t pha p t heg r a i nbounda r i e s．Af t e rs o l u t i ont r e a tmen t,t he spe c imenswe r eageda t６５０,７００and７５０ ℃f o r１０, １００,３００,１０００,３０００and６０００h,r e spe c t i ve l y． , Ch a r a c tt e s ta tr o omt emp e r a t u r e as ho r t Ｇ pyimp t e rmh i Ｇ t emp e r a t u r et e n s i l et e s ta t７００ ℃ a ndc hemi Ｇ gh c a lph a s eana l i so ft heageds amp l e s we r ec a r r i ed ys ou t．Theimpa c t eds amp l e swe r eus eda sme t a l l ur i Ｇ g c a ls amp l e sande t chedi nCuCl２ ＋HCl＋H２Oso l u Ｇ t i on．Ana l i so ft hemi c r o s t ruc t u r eandimpa c tf r a c Ｇ ys t u r e mo r l ogy wa sc onduc t ed unde r an S Ｇ ４３００ pho s c ann i nge l e c t r on mi c r o s c ope．Thes amp l ef o rt r ans Ｇ mi s s i one l e c t r on mi c r o s c opy wa spo l i shed me chan i Ｇ , c a l l l e Ｇ e t t ede l e c t r o l t i c a l l e r vedun Ｇ y doub j y yandobs de ran HＧ ８００t r ansmi s s i one l e c t r on mi c r o s c ope．
２ Exp e r imen t a lRe s u l t s
f o rt het imepe r i odo fbo t h１００and６０００h,p r oba Ｇ ( , ) , b l c aus et heNb C N pha s ewa sr a r e andt he ybe d i f f r a c t i onpe ako ft he M２３C６ c a rb i de swa sh i ghand cove r edt ha to ft heNb( C, N)pha s e．
F i ２ XRDpa t t e rn so fe x t r a c t e ds e c ondpha s epa r t i c l e si n g s t e e la f t e ra i nga t７００ ℃ f o r１０,１００and６０００h g
２ １ Mi c r o s t r u c t u r ee v o l u t i ondu r i ngl ong Ｇ t e rma i ng ２ １ ２ Evo l u t i onof pr e c ipi t a t ed pha s ea tgra i n g ２ １ １ Type sofs e c ondpha s ei ns t e e lwi t hdi e r Ｇ b oundary f f en tagi ngt ime Af t e ra i nga t７００ ℃ ,p r e c i i t a t e dpha s ea e a r e d g p pp , TheXRD pa t t e rnso ft heex t r a c t ed powde ro f a l ongt heg r a i nbounda r ． A i n f o r１ ０－１ ０ ０ ０h t h e y g g , HR３Cs t e e lageda t７００ ℃ f o r１０ １００and６０００h amoun tands i z eo ft hepha s epr e c i i t a t eda tg r a i n p a r eshowni nF i ２．Thema i np r e c i i t a t edpha s e si n bounda r nc r e a s eds i i f i c an t l n i t i a lpa r t i cuＧ g p yi gn y．Thei t hes t e e lwe r e M２３ C６ c a rb i de s,Z Ｇ s e (NbCrN) l a t e s( F i s ３( a)and３( b))we r ec onn e c t e dandg r a du a l Ｇ pha g ( , ) ( , andat r a c eamoun to fNb C N pha s e on l nt he l r ewi n t os t r i i chwe r ed i s t r i bu t eda l ongt he yi yg ps wh s amp l ea e df o r１０h)． Fu r t h e rmo r e,f o rt h e１０hs t a t e, g r a i nbounda r i e scon t i nuous l rs emi Ｇ con t i nuous l g yo y ( ( ) ( ) ) , t hed i f f r a c t i oni n t ens i t o ft h eZ Ｇ h a s e w a ss i n i f i Ｇ F i ３ c and３ d ．Fr om １０００t o６０００h t he y p g gs c an t l t r ong e rt h a nt h a to ft h e M２３C６ c a r b i d e s,wh i l e coa r s en i ng o ft he p r e c i i t a t ed pha s ea tt he g r a i n ys p f o rt he１００and６０００hag i ngs t a t e s,t hed i f f r a c t i on bounda r nc r e a s eds l i t l F i ３( d)t o３( f))． yi gh y( gs i n t ens i t ft he M２３C６ c a rb i de si nt hes t e e lwa se l e Ｇ Thes t e e l mo r l ogy changeds l i t l r a i n yo pho gh y．The g va t eds i i f i c a n t l Th i si nd i c a t e st h a tal a r eamoun to f bounda r r e c i i t a t ewa sd i s t r i bu t edi nacon t i nuous gn y． g yp p M２３C６c a rb i de shadp r e c i i t a t eddu r i ngt he s etwoag Ｇ s t r i o rmf o rag i ngo f１０００handd i s t r i bu t edd i s Ｇ p pf ( , ) i ngp r o c e s s e s．The Nb C N pha s e wa sno tf ound con t i nuous l o rag i ngo f３０００－６０００hwi t hasphe Ｇ yf
I s sue８ Mi c r o s t r uc t u r eEvo l u t i onand Me chan i c a lPr ope r t i e so fHR３CS t e e ldu r i ngLong Ｇ t e rm Ag i ng
７６７
( a)１０h; ( b)１００h; ( c)３００h; ( d)１０００h; ( e)３０００h; ( f)６０００h．
F i ３ SEMima e so fp r e c i i t a t e dpha s ea tg r a i nbounda r i e sa e da t７００ ℃ f o rd i f f e r en tt ime g g p g
r o i d i z i ngt r end ( F i ３( e)and３( f))． gs Ca l i b r a t i on o ft he TEM d i f f r a c t i on pa t t e rns showed t ha tt he p r e c i i t a t ed pha s ea tt he g r a i n p bounda r sM２３C６c a rb i de,wi t hc omp l i c a t edcub i c ywa , c r s t a ls t r u c t u r e w h i c h r e t a i n e d ac o h e r e n tr e l a Ｇ y
t i onsh i t ht he ma t r i x( γ)．Theo r i en t a t i onr e l a Ｇ p wi t i onsh i twe ent he M２３C６ c a rb i deandt he ma t r i x pbe wa s[ ０１０]M２３C６ ∥ [ ０１０] sshowni nF i ４( d)．Th i s g γa r e su l twa scons i s t en tr e spe c t i ve l t ht ha tr epo r t ed y wi [ ] [ ] byFange ta l １１ andPenge ta l１２ ．Thel a t t i c econ Ｇ
F i ４ M２３C６ c a r b i d emo rpho l o tg r a i nbounda r fs t e e la e da t７００ ℃ f o r１００h ( a),１０００h ( b)and g g ya yo g ６０００h ( c)andc a l i b r a t i ono fTEM d i f f r a c t i onpa t t e rn s( d)
７６８
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 ２１
s t an to ft he M２３C６ c a rb i de swa st hr e et ime st ha to f , t hema t r i x t husi t sd i f f r a c t i onspo tl eng t hwa sone t h i r dt ha to ft hema t r i x,wh i chwa sat i c a lcha r a c Ｇ yp t e r i s t i co fM２３C６c a rb i de s． S imi l a rt ot heevo l u t i ono f t hepr e c i i t a t ed pha s ea tt heg r a i nbounda r r p y unde SEM,t he mo r l ogyevo l u t i ono ft he M２３C６ c a r Ｇ pho b i de sa tt heg r a i nbounda r rTEM wa sa sf o l Ｇ yunde l ows．Fr om app r ox ima t e l o３００ha tt hee a r l y１０t y ag i ngs t age,M２３C６c a rb i de sl e s st han２００nmi ns i z e we r ep r e c i i t a t ed and d i spe r s ed a l ong t he g r a i n p bounda r sshowni nF i ４( a)．Wi t hex t end i ngag Ｇ ya g i ngt ime,t he M２３ C６ c a rb i de sg r ew g r adua l l y and conne c t edt oge t he rt of o rm a s emi Ｇ c on t i nuous o r con t i nuouscha i no f２００－３００nmi nwi d t ha l ongt he r a i nbounda r r om３００t o１０００h,a ss howni nF i ４ g yf g ( ) , b ．Af t e r１０００h t her e l a t i ves i z eo ft heM２３C６c a r Ｇ b i de sc on t i nuedt oi nc r e a s ebu tt heg r owi ngr a t ewa s , r e l a t i ve l s l o w a n dt h e M C c a r b i d e s w e r es h e Ｇ y p ２３ ６ r o i d i z e dg r adua l l t h ex t end i ng ag i ng t ime and y wi f o rmedd i s c on t i nuousp a r t i c l e sa l ongt h eg r a i nbound a Ｇ
r ss howni nF i ４( c)． ya g ２ １ ３ Ev o l u t i o nofi n t r agr anu l a rpr e c i i t a t edpha s e p Asshowni nF i ５,asho r tr od Ｇ l i kef i nepr e c i Ｇ g p , i t a t ed pha s e wi t h ad i s t r i bu t i on wi t h i nt he g r a i n andasma l ls i z eo fapp r ox ima t e l sf ound y４０nm,wa common l nt heag i ngs t a t e so ft hes amp l e．Ac co rd Ｇ yi , i ngt ot hed i f f r a c t i onpa t t e rns t h i ssma l lpr e c i i t a Ｇ p t ed pha s ecou l d bei den t i f i eda st he Z Ｇ s e,and pha compa r edwi t ht hebu l kyZ Ｇ s ei nF i １,t hes i z e pha g o ft h i sZ Ｇ s ei nt heag i ngs t a t e so ft hes amp l ei s pha sma l l e rt hant hebu l kyon e．TheZ Ｇ s ec r s t a ls t r u c Ｇ pha y [ ] t u r ewa st e t r agona l．Sourma i landBhade sh i a１３ a l so r epo r t edt h i sf i nei n t r ag r anu l a r l r e c i i t a t edpha s e yp p i n NF７０９s t e e l( ２２Cr ２５NiMoNbN)．A compa r i son o fs t e e lagedf o r６０００and１００hshowst ha tt hes i z e o ft h i sf i nep r e c i i t a t ed i dno tchanges i i f i c an t l p gn y wi t hag i ngt ime,andi twa sa lwaysa r ound４０nmi n d i ame t e r,bu ti t samoun ti nc r e a s eds i i f i c an t l gn y． , Asshowni nF i ６ asma l lamoun to f M２３C６ g c a rb i dewa sa l sof oundwi t h i nt heg r a i n．Ac c o r d i ngt o
( a)Ag i ngf o r１００h; ( b)Ag i ngf o r３０００h; ( c)Di f f r a c t i onpa t t e r ns．
F i ５ Mo rpho l o fi n t r a r anu l a r l r e c i i t a t e dZ Ｇpha s ei nHR３Cs t e e la e da t７００ ℃ g g yo g yp p g
( a)TEM mo r l ogy; ( b),( c)Di f f r a c t i onpa t t e r ns． pho
F i ６ Mo rpho l o fi n t r a r anu l a r l r e c i i t a t e d M２３C６i nHR３Cs t e e la e da t７００ ℃ f o r３０００h g g yo g yp p g
i t sd i f f r a c t i onpa t t e rns,t hei n t r ag r anu l a rM２３C６c a r Ｇ b i de sa l s or e t a i nedac ohe r en tr e l a t i onsh i t ht he p wi ma t r i xandhadano r i en t a t i onr e l a t i onsh i t ht he p wi
ma t r i xa s( ２２０)M２３C６ ∥ ( ２２０) nd [ ２３３]M２３C６ ∥ γ a [ Al t hought he M２３C６ c a rb i de swe r ef oundi n ２３３] γ． , t heg r a i nt heamoun to fM２３C６c a rb i de swa sf a rl e s s
t hant ha ta tt heg r a i nbounda r t ss i z ewa sr e l Ｇ y,andi a t i ve l t ab l ea t３００－５００nm． ys ２ ２ E f f e c to fa i n emp e r a t u r eo np r e c i i t a t e dpha s e g gt p ２ ２ １ Typeofpr e c ipi t a t edpha s e XRDpa t t e rnso ft heex t r a c t edpowde ra f t e rag Ｇ
I s sue８ Mi c r o s t r uc t u r eEvo l u t i onand Me chan i c a lPr ope r t i e so fHR３CS t e e ldu r i ngLong Ｇ t e rm Ag i ng
i nga t６５０and７５０ ℃ we r es imi l a rt ot ha ta t７００ ℃ , and no o t he rp r e c i i t a t ed pha s e s we r ef ound．As p showni nF i ７,on l h ed i f f r a c t i oni n t e n s i t i e sd i f f e r e d g yt
７６９
s l i t l i nga t７５０ ℃ f o rapp r ox ima t e l gh y;ag y１００h, t hes t r onge s tpe aksi nt heXRDspe c t r awe r e M２３C６ c a rb i de s,wh i l et hes t r onge s tpeaksbe l ongedt othe
F i ７ XRDpa t t e rn so fs e c ondpha s epa r t i c l e se x t r a c t e di ns t e e la e da t６５０ ℃ ( a)and７５０ ℃ ( b)f o rd i f f e r en tt ime g g
Z Ｇ s ed i f f r a c t i ona t６５０and７００ ℃． pha ２ ２ ２ Mo rpho l ogyofpr e c ipi t a t edpha s e F i ８showsSEM mi c r og r aphso ft hep r e c i i Ｇ g p t a t e sa tt heg r a i nbounda r t６５０and７５０ ℃ wi t h ya d i f f e r en tag i ngs t a t e s．Thec ompa r i s onshowedt ha t, agedf o rt hes amet ime,t hep r e c i i t a t edpha s es i z e p a tt heg r a i nbounda r nc r e a s eds i i f i c an t l t he l Ｇ yi gn ywi eva t i ngag i ngt empe r a t u r e．The mo r l ogy o ft he pho e c i i t a t edpha s ea tt heg r a i nbounda r Ｇ pr p ychangedno , t i c e ab l w h e na i n a t７ ５ ０ ℃ f o r１ ０ ０ ０h a n d a r y g g pt
o ft hep r e c i i t a t ed pha s ef o rmedsphe r i c a lpa r t i c l e s p ( ( ) ) wi t hd i s con t i nuous d i s t r i bu t i on F i ８ d ．Th i s g s mo r e ev i den tf o r ６０００ h ag i ng phenomenon wa ( F i ８ ( f))．S imi l a r phenomenon wa sa l sof ound g ( whenag i nga t７００ ℃ f o r３０００and６０００h F i ３ gs ( e)and３( f))．Ag i nga t６５０ ℃f o r６０００h,t h i sphe Ｇ nomenond i dno tex i s tandt hep r e c i i t a t edpha s ea t p t heg r a i n bounda r e t a i nedane l onga t edd i s t r i bu Ｇ yr t i on．Th i sr e su l ti nd i c a t e st ha tt heevo l u t i ono ft he r e c i i t a t edpha s ea tt heg r a i nbounda r sa c c e l e r Ｇ p p ywa
( a)６５０ ℃ ,１００h; ( b)７５０ ℃ ,１００h; ( c)６５０ ℃ ,１０００h; ( d)７５０ ℃ ,１０００h; ( e)６５０ ℃ ,６０００h; ( f)７５０ ℃ ,６０００h．
F i ８ SEMima e so fp r e c i i t a t e dpha s e sa tt h eg r a i nbounda r o rd i f f e r en ta i ngs t a t e s g g p yf g
a t edwi t hi nc r e a s i ngag i ngt empe r a t u r e． Th eTEM mo r l og i e so ft h ep r e c i i t a t e dpha s e s pho p a tt heg r a i nbounda r i nt h ea i n s t a t ea t６ ５ ０a n d y g g ７５０ ℃ a r eshowni nF i ９．Thewi d t ho ft he M２３C６ g c a rb i de sa tt heg r a i nbound a r fs t e e la e da t７５０ ℃ yo g
f o r１００hwa ss l i t l a r rt hant ha ta t６５０ ℃ f o r gh yl ge ３０００h ( F i ９( a)and９( b))．TheM２３C６c a rb i de sa t gs t heg r a i nbound a r f o r t h e ６ ０ ０ ０ha i n s t a t ea t ７ ５ ０ ℃ y gg we r ecoa r s eneds i i f i c an t l t hani nc r e a s ei nove r gn ywi １μmi nt heho r i z on t a ld i r e c t i on．
７７０
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 ２１
( a)７５０ ℃ ,１００h; ( b)６５０ ℃ ,３０００h; ( c)７５０ ℃ ,６０００h．
F i ９ Ev o l u t i ono fp r e c i i t a t e d M２３C６ c a r b i d e sa tg r a i nbounda r f t e ra i ng g p ya g
S imi l a rt ot heag i ngs t a t ea t７００ ℃ ,t hef i nei n Ｇ t r ag r anu l a r l r e c i i t a t e d h a s e s w e r eZ Ｇ h a s e sf o r yp p p p ( ) t he６０００hag i ngs t a t ea t６５０and７５０ ℃ F i １０ ． g Thed i f f e r enc ei nd imens i onand dens i t ft heZ Ｇ yo
s e swa ssma l lf o rt he６０００hag i ngs t a t e sa t６５０ pha and７５０ ℃．The s er e su l t ssugge s t edt ha tt heag i ng t empe r a t ur ehadar e l a t i ve l l le f f e c tont heZ Ｇ ysma s ep r e c i i t a t i onbehav i o r． pha p
( a)６５０ ℃ ,６０００h; ( b)７５０ ℃ ,６０００h．
F i １０ Mo rpho l o i e so fi n t r a r anu l a r l r e c i i t a t e dZ Ｇpha s e si nHR３Cs t e e lf o rd i f f e r en ta i ngs t a t e s g g g yp p g
２ ３ Re l a r i t ns i z echang eo fpr e c i i t a t e dpha s e gu yi p S t a t i s t i c so ft he p r e c i i t a t ed pha s es i z e we r e p conduc t ed ba s ed on TEM obs e r va t i on．Unde rt he emi s et ha ti t scha r a c t e rwa sc on f i rmedbye l e c t r on pr , d i f f r a c t i on t he max imum t r ans ve r s ed imens i on o f t hepr e c i i t a t ed pha s e wa s me a su r eda si t ss i z e Ｇ de Ｇ p
t e rmi n i ngpa r ame t e r．The we i t edave r ageo ft he gh me a sur eds i z ewa su s e da st hea v e r a es i z eo ft heme a s Ｇ g u r e dpha s e,andt henumbe ro ft hes e condpha s epa r Ｇ t i c l e sme a sur edwa smo r et han５０i ne a chs t a t e．As , showni nF i １１ t hes i z eo ft he M２３C６ c a rb i de si n Ｇ g c r e a s eds i i f i c an t l t hi n c r e a s i nga i ngt ime,wh i l e gn y wi g
( a)M２３C６c a r b i de s; ( b)Z Ｇ s e． pha
F i １１ S i z echang eo fM２３C６ c a r b i d e sandZ Ｇpha s ei nHR３Cs t e e lwi t hi nc r e a s i nga i ngt ime g g
I s sue８ Mi c r o s t r uc t u r eEvo l u t i onand Me chan i c a lPr ope r t i e so fHR３CS t e e ldu r i ngLong Ｇ t e rm Ag i ng
t hes i z eo ft heZ Ｇ s e wa sr e l a t i ve l t ab l e．Wi t h pha ys , t hei nc r e a s ei nag i ngt empe r a t u r e awi den i ngo ft he M２３C６ c a rb i de swa simp r oveds i i f i c an t l i l ei t s gn y wh e f f e c tont heZ Ｇ s ewa sr e l a t i ve l l i t． pha ys gh ２ ４ Va r i a t i oni nc on t e n to fpr e c i i t a t e dpha s e p , Thr ough chemi c a l pha s e ana l i s cur ve so f ys ma s sf r a c t i onaga i ns tag i ngt imef o rt he M２３C６ c a r Ｇ b i de sandZ Ｇ a s e( c on t a i n i ngt r a c e so ft h eNb( C, N) ph ) s e we r eob t a i nedf o rt het hr e et empe r a t ur eag Ｇ pha
７７１
i ngp r oc e s s e s( F i １２)．Dur i ngt heag i ngp r oc e s s, g t het o t a lamoun to fp r e c i i t a t edpha s ei nc r e a s edr ap Ｇ p i d l t hi nc r e a s i ngag i ngt ime wi t h i n１０００ hand y wi showedas i i f i c an t l l owe rr a t eo fi nc r e a s et he r e Ｇ gn ys a f t e r．Thee f f e c to fag i ngt empe r a t ur eont heamoun t o fM２３C６c a rb i de sp r e c i i t a t edwa sr e l a t i ve l i i f i Ｇ p ys gn c an t,wh i l ei t simpa c tont heZ Ｇ s ewa sr e l a t i ve l pha y sma l l．Fo rt he６０００hag i ngs t a t e,t hema s sf r a c t i on o fM２３C６ c a rb i de si nt hes amp l eageda t７５０ ℃ wa s , , １ １５７％ wh i c hwa s１ ４１t ime st ha ta t６５０ ℃ wh i l e
( a)M２３C６c a r b i de s; ( b)Z Ｇ s e． pha
F i １２ Chang ei nc on t en t so fp r e c i i t a t e dpha s e si na i ngs t a t eo fHR３Cs t e e la a i n s ta i ngt ime g p g g g
t hec o r r e spond i ngr a t i oo ft heZ Ｇ s ewa s１ ０７６． pha ２ ５ Me chan i c a lpr ope r t i e sa f t e rl ong Ｇ t e rm a i nga t g h i empe r a t u r e ght Sho r t Ｇ t e rm t ens i l et e s t sf o rt he６５０,７００and ７５０ ℃ ag i ngs t a t ewe r ec onduc t eda t７００ ℃ wi t hr e Ｇ su l t sshowni nF i １３．Thed i f f e r enc ei nh i emＧ g ght r a t u r ey i e l ds t r eng t hi nt hec a s eo fag i ng a tt he pe t hr e et empe r a t u r e sf o r１０h wa si ns i i f i c an t．Wi t h gn anex t ens i oni n ag i ng t ime,t he h i empe r a t ur e ght i e l ds t r e n t ho ft h es t e e lf i r s ti n c r e a s e da n dt h e n y g d e c r e a s e dwh e nt h es t e e lwa sa e da t７５０℃． Anov e r a Ｇ g g i ngphenomenon o c cu r r ed,wi t hava l ueo fa r ound ２６０ MPaa ta bou t３００h．Fo rt h ea i nga t７００ ℃ ,t he g h i emp e r a t u r ey i e l ds t r e ng t hi nc r e a s edr ap i d l r om ght yf
F i １３ Hi emp e r a t u r ey i e l dp e r f o rmanc eo fHR３C g ght s t e e lf o rd i f f e r en ta i ngs t a t e sa t７００ ℃ g
１０t o１０００hwi t hani nc r e a s ef r om１９０t o２４５ MPa, wh i ch wa ss l i t l l eva t edf r om １０００ h andr e Ｇ gh ye ma i neds t ab l ea ta r ox ima t e l f t e r３０００h． pp y２５５ MPaa Fo rt heag i nga t６５０ ℃ ,t heh i empe r a t ur ey i e l d ght s t r eng t hi nc r e a s edf r om１０t o６０００h,andt heva l ue f r om１８５MPar e a ched２５５MPa．Wi t hi nc r e a s i ngt he ag i ngt empe r a t ur e,t hepe akso ft heh i empe r a Ｇ ght t ur ey i e l ds t r eng t hsh i f t edt ot hel e f t． Fo rt he１０hag i ngs t a t e,t heimpa c tene r Ｇ gyde c r e a s eds i i f i c an t l t hi n c r e a s i nga i ngt emp e r a t u r e, gn ywi g a sshowni nF i １４．Fo rt he１０－３００ha i ngp r oc e s s g g
F i １４ Impa c ten e r fHR３Cs t e e lf o rd i f f e r en t g g yo a i n s t a t e sa t r o o mt e m e r a t u r e gg p
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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 ２１
a teve r empe r a t u r e,t heimpa c tene r c r e a s ed yt gy de , r ap i d l t e rag i nga t７５０ ℃ f o r３００h t heimpa c t y．Af ene r nc r e a s eds l i t l twa se s s en t i a l l he gyi gh y．Andi yt s amef o rt heag i nga t６５０and７００ ℃．Whent heag Ｇ i ngt imeo f６０００hwa sr e a ched,wi t hi nc r e a s i ngag Ｇ i ngt empe r a t u r e,t heimpa c tene r nc r e a s eds l i t Ｇ gyi gh l nimpa c tene r sr e l a t edt ot he y．Thechangei gy wa mo r l ogyandd i s t r i bu t i ono ft heM２３C６c a rb i de sa t pho t heg r a i nbounda r y．
M２３C６ c a rb i de sandt heenhanc emen tc aus edbyt he cons t an tp r e c i i t a t i ono ft hef i neZ Ｇ s ea ch i eveda p pha r e l a t i ve l l anc eds t a t e,c aus i ngl eve l i ng Ｇ o f fo ft he yba i e l ds t r eng t ha f t e rag i nga t７００ ℃ f o r３０００h．Fo r y t he１０－６０００hag i ngp r oc e s sa t６５０ ℃ ,p r e c i i t a t i Ｇ p onr a t e so ft heM２３C６c a rb i de sandZ Ｇ s ede c r e a s ed pha , aga i n a ndt h eM２３C６c a r b i d eg r owt hs l owe dd owna a i n． g Howeve r,t hep r e c i i t a t i ons t r eng t hen i nge f f e c twa s p enhanc ed, c aus i ng t he h i empe r a t ur e y i e l d gh t s t r eng t ht oi nc r e a s e． ３ E f f e c to fP r e c i i t a t e so nS t r e n t ha n dT o u hn e s s p g g Thechangei nimpa c tt oughne s swa sma i n l Ｇ ybe aus eo ft heevo l u t i ono fM２３C６c a rb i de sa tt heg r a i n Du r i ngt heag i ngo ft he HR３Cs t e e l,t he ma i n c r o ra i ngt imef r om１０t o３００h,l a r e e c i i t a t edph a s e swe r e M２３C６ c a r b i d e sa ndZ Ｇ s e． bounda y,andf g g pr p pha t so f M２３C６ c a rb i de s we r ep r e c i i t a t eda l ong Change si nt he s etwo pha s e s de t e rmi nedt he pe r Ｇ amoun p t heg r a i nbounda r c t edi n t oacon t i nuous f o rmanc eva r i a t i ono ft hes t e e lag i ngs t a t e． yandconne ( ) ( ) , i na sshowni nF i ４ b and９ b ．Thecon t i nu Ｇ I ti swe l lknownt ha ti ft hes i z eo ft hep r e c i i Ｇ cha gs p r a i nbounda r cup i edbyt he M２３C６ c a rb i de s t a t edpha s ei ssma l l e randi t snumbe ri sg r e a t e r,t he ousg yoc sconduc i vet oc r a ck p r opaga t i onandr e su l t edi n e c i i t a t i onha r den i ng e f f e c t wi l lbe mo r es i i f i Ｇ wa pr p gn [ １４, １５] i t t l ene s so ft hes t e e landas i i f i c an tr educ t i oni n c an t ．The changei nh i empe r a t ur ey i e l d br gn gh t t i l i t fs t e e l．Af t e r１０００ho fag i nga t７５０ ℃ , s t r eng t hi sc aus edp r e c i s e l hechangei ns i z eand duc yo ybyt M２３C６c a r b i d e sa tt heg r a i nbound a r hang e dg r adua l l numbe ro ft he M２３ C６ c a rb i de sand Z Ｇ s ei nt he yc y pha , r om a con t i nuous cha i n Ｇ t oad i s con t i nuous s t e e l．Du r i ngag i nga t７５０ ℃ t hey i e l ds t r eng t hi n Ｇ f ype t r anu l a r Ｇ t i s t r i bu t i on ( F i ８( d)and８( f))． c r e a s edr ap i d l r om １０t o３００hbe c aus et henumＧ g yped gs yf , W i t hi m a c tf r a c t u r i n t h ec r a c ks r e a da l o n he be r so f M２３ C６ c a rb i de sandt he Z Ｇ h a s ei n c r e a s e d p g p gt p , , r a i nbounda r r eene r sr equ i r edwhen r ap i d l h i spe r i od t ho s ep r e c i i t a t e swe r ed i s Ｇ g y andmo gywa y．Att p hed i s con t i nuousd i s t r i bu t i ono fM２３C６c a rb i de swa s t r i bu t edd i s c on t i nuous l i chc anho l dd i s l oc a t i on t y,wh t e r ed．Th i si nc r e a s ed t he impa c t duc t i l i t mo t i onandt he r e f o r es t r eng t hent hes t e e l．Af t e r３００ encoun y l i t l t e rl ong Ｇ t e rm ag i ng,t h i sd i s con t i nuous h,t heM２３C６c a rb i de swi deneds i i f i c an t l he s gh y．Af gn y,andt i s t r i bu t i on phenomenoni nc r e a s ed wi t hi nc r e a s i ng s t r eng t hen i nge f f e c t wa s we akened．Ani nc r e a s ei n d i ngt empe r a t ur e．Bu tt hei nc r e a s e wa si ns i i f i Ｇ s t r eng t hc aus edbyt hei nc r e a s edamoun to ft heZ Ｇ ag gn an t;t he r e f o r e,t hee f f e c to ft h i sphenomenonon s e wa s sma l l e rt han t he de c r e a s ei ns t r eng t h c pha heimp a c tdu c t i l i t t６５０and７００ ℃ wa sno ts hown c aus edbyt hewi den i ngo ft he M２３C６ c a rb i de s．The t ya l e a r l i １５showst hemo r l og i e so ft heimpa c t h i empe r a t u r ey i e l ds t r eng t ht he r e f o r ede c r e a s ed c y．F g pho ght r a c t ur e sa f t e rag i nga tt hr e eag i ngt empe r a t ur e sf o r s l owl ndt h ec h a ng ei ns t r e ng t ha t７５０℃ wa sat Ｇ f y,a yp r a c t ur ea t６５０ ℃i sat i c a lb r i t t l er o c k i c a love r ag i ngphenomenon．Du r i ngag i nga t７００ ℃ , ６０００h．Thef yp , andy Ｇ l i kef r a c t u r e wh i l ea l lf r a c t u r esur f a c e sa t７００ e c i i t a t i onr a t e so ft heM２３C６c a rb i de sandZ Ｇ s e c pr p pha e r t a i namoun to fd imp l e st ha ti n Ｇ we r es l owe rt hant ho s ea t７５０ ℃ ,andt hei nc r e a s e and７５０ ℃ haveac r e a s eds i i f i c an t l t７５０ ℃．Th i sr e su l ti scons i s t Ｇ i ny i e l ds t r eng t hs l owl c r e a s ed．Af t e rag i ngf or c gn ya yde , twi t hp r ev i ousexp l ana t i ons． ３０００h t he we aken i ngc aus edby wi den i ng o ft he en
( a)６５０ ℃ ; ( b)７００ ℃ ; ( c)７５０ ℃．
F i １５ Mo rpho l o i e so fimpa c tf r a c t u r ef o rt h e６０００ha i ngs t a t e g g g
I s sue８ Mi c r o s t r uc t u r eEvo l u t i onand Me chan i c a lPr ope r t i e so fHR３CS t e e ldu r i ngLong Ｇ t e rm Ag i ng
４ Conc l u s i on s ( １)Du r i ngt heag i ngp r o c e s sa t６５０,７００and , ７５０ ℃ t he ma i np r e c i i t a t ed pha s e so ft he HR３C p s t e e li n c l ud e dt h eM２３C６ c a r b i d e s,Z Ｇ s eandat r a c e pha amoun to f Nb( C,N)．M２３ C６ c a rb i de sp r e c i i t a t ed p ma i n l tt heg r a i nbounda r l ew we r e ya yandon yaf e c i i t a t ed wi t h i nt he g r a i n．Z Ｇ s ep r e c i i t a t ed pr p pha p ma i n l t h i nt heg r a i n． y wi ( ) ２ Wi t ha ne x t e n s i ono fa i ngt ime,t h eamoun t g o fM２３C６c a rb i de si nt hes t e e li nc r e a s edc on t i nuous l y． Andt henumbe rands i z eo fM２３C６c a rb i de si nc r e a s ed s i i f i c an t l t hani nc r e a s ei nag i ngt empe r a t ur e． gn y wi Shapeandd i s t r i bu t i ono fM２３C６c a rb i de sa tt heg r a i n bounda r rwen tt hr e ed i f f e r en ts t age s．Atf i r s t, yunde
t hesma l lpa r t i c l e s we r e unc onne c t ed a tt he g r a i n bounda r he pa r t i c l e sg r ew i n t os t r i Ｇ l i ke y．Then t p shapeandc onne c t edwi t he a cho t he rt of o rmcon t i n Ｇ , uouscha i nsa l ongt heg r a i nbounda r a s t when y．Atl t hec a r b i d e sc o a r s e n e di n t os e r i c a ls h a e,t he r e ph p y we unc onne c t edaga i n．Wi t hani nc r e a s ei nag i ngt emＧ r a t u r e,t heevo l u t i onl awbe c amemo r es i i f i c an t． pe gn ( ３)Themo r l ogyandd imens i onso ft hei n Ｇ pho t r ag r anu l a rZ Ｇ h a s ed i dn o t c h a n e s i n i f i c a n t l w i t h p g g y ag i ngt imeand t empe r a t u r e, wh i ch had a s t e ady s t r eng t hen i nge f f e c t． ( ４)Wi d e n i ngo ft h eM２３C６c a r b i d e swa st hema i n r e a s onf o rade c r e a s ei nt heh i Ｇ t empe r a t ur ey i e l d gh s t r eng t h wi t hag i nga t７５０ ℃．I nc r e a s i ngl eve l so f M２３C６c a rb i de sf o rag i nga t６５０and７００ ℃ we r er e l Ｇ a t i ve l owe r,andt hes t e adys t r eng t hen i nge f f e c to f yl
７７３
t heZ Ｇ s e ma d et heh i emp e r a t u r ey i e l ds t r e ng t h pha ght i nc r e a s econs t an t l t i l i t sc aus ed y．Theduc ychangewa ma i n l hechangei nmo r l ogyandd i s t r i bu t i on ybyt pho o ft heM２３C６c a rb i de sa tt heg r a i nbounda r y． Re f e r enc e s: [ １] F．Ma suyama,I S I JI n t． ４１ ( ２００１)６１２ Ｇ ６２５． [ ２] J Z．Wang,Z D．L i u,S C．Cheng,HS．Bao,J． I r onS t e e l Re s． I n t． １８ ( ２０１１)No １０,５４ Ｇ ５８． [ ３] A．Na t o r i,S t a i n l e s sS t e e lEur ope４ ( １９９２)No． １６,２０ Ｇ ２５． [ ４] J Z．Wa ng,Z D．L i u,HS．Ba o,S C．Ch e ng,B．Wa ng,J． I r on S t e e lRe s． I n t． ２０ ( ２０１３)５４ Ｇ ５８． [ ５] T． Sourma i l,Ma t e r． Sc i．Te chno l． １７ ( ２００１)１ Ｇ １４． [ ６] M．Va ch,T．Kun í ková,M．Dománková,P．Šev c,L．Cap l ov Ｇ i c,P．Gogo l a,J．J anove c, Ma t e r．Cha r a c t．５９ ( ２００８)１７９２ Ｇ
１７９８． [ ７] I．Pa rk,F．Ma suyama,T．Endo,Key Eng．Ma t e r．１７１ Ｇ １７４ ( ２０００)４４５ Ｇ ４５２． [ ８] A． I s eda,H．Okada,H． Semba,M． I r a sh i,Ene r t e r． ２ ga gyMa ( ２００７)１９９ Ｇ ２０６． [ ９] J．L i u,C．Lu,Y．Yao,Phys i c a lChemi s t r s eAna l i so f yPha ys i Sc i en t i f i c & S t e e land I r on, Ni cke l Ｇ ba s ed Al l oy,Shangha Te chn i c a lPub l i she r s,Shangha i,１９８４． [ c i a lS t e e l D．L i u,S C．Cheng,HS．Bao,Spe １０] J Z．Wang,Z ３２ ( ２０１１)No ３,６１ Ｇ ６４． [ N．L i,Ac t a Me t a l l．S i n． ４６ ( ２０１０) １１] YY．Fang,J．Zhao,X
８４４ Ｇ ８４９． [ Q．Gao,HQ．Zhang, Zhang,J．Hong,J １２] B C．Peng,HX． t e r．Sc i．Eng．A ５２７ ( ２０１０)４４２４ Ｇ J F．L i,QJ．Wang,Ma ４４３０． [ １３] T． Sourma i l,HKD H． Bhade sh i a,Me t a l l．Ma t e r．Tr ans．A ３６ ( ２００５)２３ Ｇ ３４． [ １４] K．Ma r uyama,K． Sawada,J．Ko i ke,I S I JI n t． ４１ ( ２００１)６４１ Ｇ ６５３． [ D．L i u,S P．Tan,J． I r onS t e e l １５] HS．Bao,S C．Cheng,Z Re s． I n t． １７ ( ２０１０)No ２,６７ Ｇ ７３．