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Effects of Solution Depletion and Segregation Oxidation on Morphology of Modified 310 Austenitic Stainless Steel
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ６,２ ３( ４):３ ９ ３ Ｇ ４ ０ ０
Ef f e c t so fSo l u t i onDe l e t i onandS e r e a t i onOx i da t i onon p g g Mo r l o fMod i f i e d３１０Au s t e n i t i cS t a i n l e s sS t e e l pho g yo Hong Ｇ i ngSUN１ , Qi ang HE１ , Zhang Ｇ i anZHOU２ , Man WANG２ , y j Guang Ｇmi ngZHANG２ , Shao Ｇ f uLI２
( １．KeyLabo r a t o r fKeyFunc t i ona lPa r t so fMa ch i ne,AnyangI ns t i t u t eo fTe chno l ogy,Anyang４５５００２, yo , ; , Henan Ch i na ２． Schoo lo fMa t e r i a l sSc i enc eandEng i ne e r i ng Un i ve r s i t fSc i enc eandTe chno l ogy yo Be i i ng,Be i i ng１０００８３,Ch i na) j j Ab s t r a c t:Theox i da t i onmo r l og i e so fmod i f i ed３１０s t e e le xpo s e di n９００a nd１１００ ℃ a i rwe r ei nv e s t i a t e d．Adoub l e pho g l aye rmo r l ogyc ons i s t i ngo fa ( Cr,Mn) Ｇ r i chou t e rl aye randaf i neCr Ｇ r i chi nne rl aye rwa sf o rmeda t９００ ℃． I twa s pho r e l a t edt ot heb r e akawayox i da t i oni nduc edbyt heCr Ｇ dep l e t i onandt he Mn Ｇ s eg r ega t i oni ni nne rl aye r．SomeCr Ｇ r i ch ox i de swi t hamo r t a t ewe r ef o rmeda l ongg r a i nbounda r i e s．Ands omenewf i ne rox i deg r a i ns,vo i dsandCr Ｇ phouss r i chp r e c i i t a t e swe r eobs e r vedi nspa l l a t i ona r e a sa t１１００ ℃．Co r r e spond i ng l heox i da t i onk i ne t i ccu r ved r opped p y,t wi t ht hespa l l a t i ono fs c a l eandi nc r e a s edwi t ht hef o rma t i ono fs omenewox i deg r a i ns． I twa sc aus edbys eg r ega t i on o fCrandt het r ans f o rma t i ono fox i de sf r om Cr２O３ t ot hevo l a t i l eox i de sa te l e va t edt empe r a t u r e．XRD ana l s i s y showedt ha tt hep r e c i i t a t e swe r ema i n l ompo s edo fCrO３ ．Seg r ega t i onanddep l e t i onf o rs o l u t i onswe r ea l s od i s Ｇ p yc cus s edbyox i da t i ond i f f us i onme chan i sms． Ke r d s:aus t en i t i cs t a i n l e s ss t e e l;SEM;mo r l ogy;ox i da t i on;s eg r ega t i on;e l emen t pho ywo
Aus t en i t i cs t a i n l e s ss t e e l shaved i ve r s eapp l i c a Ｇ t i onsduet ot he i rc omb i na t i ono fgoodh i Ｇ t empe r a Ｇ gh [ ] t u r ec r e eps t r eng t handox i da t i onr e s i s t anc e１Ｇ３ ．The r e a c t i vee l emen t so fCr,AlandS ic on t r i bu t es i i f i Ｇ gn c an t l oenhanc i ngt heox i da t i onr e s i s t anc eo faus t e Ｇ yt n i t i cs t a i n l e s ss t e e l s．Al t hought he s es t e e l shaveex Ｇ c e l l en tgene r a lox i da t i onr e s i s t anc e,t heya r esus c ep Ｇ t i b l et o“ br e akaway”ox i da t i oni ns omes t r i ngen t c ond i t i ons．Asoneo ft hemo s tc ommons e r v i c ef a i l Ｇ u r e s,“ b r e ak awa i d a t i onc a u s e sun a c c e t a b l el o s s y”ox p f o rme t a l l i cma t e r i a l s．Th i sl o c a l i z eda c c e l e r a t edox i Ｇ da t i ono f t ent ake sp l a c ei nt hespe c i f i cagg r e s s i veen Ｇ v i r onmen t s,sucha sh i empe r a t u r eandnuc l e a r ght “ ” , r ad i a t i on．The b r e akaway p r o c e s si sspo r ad i cr an Ｇ domands t ocha s t i c． Soi ti sd i f f i cu l tt op r ed i c a t et he [] t imeand t hel o c a t i on o f even t s４ ．Al t hough t he , me chan i smo fb r e akawayox i da t i oni sunc l e a rt he r e i snodoub tt ha ti ti sr e l a t edt ot hemi c r o s t ruc t u r eo f s t e e l s．Theg r owt ho fox i de si sba s edond i f f us i on
r oc e s s,wh i chr e l a t e st ot hecha r a c t e r i s t i c so fsubＧ p s t r a t e( c hemi c a lc ompo s i t i on,g r a i ns i z e,g r a i nbound a Ｇ ) r i e scha r a c t e rd i s t r i bu t i onandso l u t es eg r ega t i on i n add i t i ont ot heox i d i z i ngenv i r onmen t s( med i umand [ ,] t empe r a t ur e)３ ５ ． Seve r a lbr e akawayox i da t i onst ha t [ ４] , l i nkt og r a i nbounda r i e s chemi c a lf a i l ur e o r me Ｇ [] chan i c a lf a i l ur e６ havebe enobs e r ved,wh i l et hespe Ｇ c i f i cp r oc e s si ss t i l lunc l e a r． Thed i f f us i ono f mi no ra l l oy add i t i onsa f f e c t s t hee s t ab l i shmen tandg r owt ho ft hep r o t e c t i veox i de s c a l e s,some t ime sevenp l aysas i i f i c an tr o l ei nt he gn [ [ [ ] ７] ８] ７, ox i da t i on p r oc e s s ．Wang and Paú le ta l ９ s t ud i edt hed i f f us i onme chan i smso ft her e a c t i vee l e Ｇ men t sandt her e su l t sshowedt ha td i f f us i onpa t hso f bene f i c i a le l emen t smi tbechangedbe c aus eo ft he gh chr omi umdep l e t i oni nsubs t r a t eandt hes eg r ega t i on ong r a i nbounda r i e s．Re a c t i vee l emen t sa r ep r og r e s Ｇ s i ve l i ngox i da t i onp r oc e ed i ng,wh i ch yconsumeddur i nduc e st heso l u t i ondep l e t i oni n Cr, Mo,Nb,Zr
Founda t i onI t em: I t em Spons o r edbyKeyPr o e c t sFundedPr og r amo fHenanPr ov i nc eEduc a t i onDepa r tmen to fCh i na ( I １５A４３００１２) j : , , ; : ; : , B i o r a h H o n Ｇ i n UN D o c t o r L e c t u r e s h i E Ｇ m a i l s h s u n ０ ２ ９＠１ ６ ３ c o m R e c e i v e dD a t e J a n u a r １ ２ ０ １ ５ gy gS p y y１ g py Co r r e s i ngAu t ho r s:Qi angHE,Do c t o r,As s o c i a t ePr o f e s s o r; E Ｇma i l:ays t a r＠１６３ c om pond Zhang Ｇ i anZHOU,Do c t o r,Pr o f e s s o r; E Ｇma i l:zhouzh t e r us t b edu cn j j＠ma
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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 ２３
andS i Ｇ con t a i neds t a i n l e s ss t e e l． I n manyc a s e s,t he s o l u t ep r e c i i t a t i oni sdemons t r a t edbyt hechange s p , o fc ompos i t i on s t ruc t u r eo ft he mu l t i Ｇ l aye rs c a l e s [ ] andt heevapo r a t i ono fs omel owＧme l t i ngox i de s１０ ． Fo rexamp l e,evapo r ab l eox i de so fCrl e adt oCr Ｇ de Ｇ , l e t i oni nma t r i x wh i chi nduc e sat r ans f o rma t i ono f p ox i de sl aye rf r om Cr Ｇ r i chox i de st ot hel e s sp r o t e c Ｇ t i veCr,Feo rMnsp i ne l． I nt hepa s ts eve r a lde c ade s,many wo rkshave be enc a r r i edou tandc ons i de r ab l ep r og r e s sha sbe en a ch i evedi nunde r s t and i ngt he me chan i c a lf a i l u r eo f [ ４] , ox i des c a l e s ．Howeve r chemi c a lf a i l u r eo ft he r o t e c t i veox i des c a l e,wh i chr e l a t edt os o l u t e Ｇ dep l e Ｇ p , t i onands eg r ega t i on wa sr epo r t edi nani nc omp r e Ｇ [,, , ] hens i ve way４ ８ １０ １１ ．The a im o ft h i s wo rki st o s t udyt heox i da t i onbehav i o ro famod i f i ed３１０aus t e Ｇ n i t i cs t a i n l e s ss t e e lbyi nve s t i t i ngt hesu r f a c emo r Ｇ ga l og i e so fox i des c a l e s．The me chan i sm o fs l ow pho b r e akawayox i da t i ona t９００ ℃ i l l us t r a t edby me ans o fs o l u t i ond i f f us i on．Thei n f l uenc e so fs o l u t ep r e c i Ｇ p i t a t i onands eg r ega t i onont hespa l l a t i onandf o rma Ｇ t i ono fne two rkox i da t i onf o rmeda t１１００ ℃ we r e a l s od i s cus s ed．
ox i d i z edspe c imens we r ecu tf r om t her o l l ed p l a t e wi t has i z eo f１ ５mm×１５ mm×２５ mm ( t h i c kn e s s× wi d t h×l eng t h)．Spe c imens we r e po l i shedt o２０００ r i t．Then,t hey we r et ho r ough l r e a s ed wi t h g y deg anhyd r ouse t hano lbyu l t r a son i cc l e an i ngf o r２０mi n． Subs equen t l c imens we r ed r i edi n a va cuum y,spe boxa t１７５ ℃ f o r４h．Af t e rspe c imenswe r ecoo l ed t or oom t empe r a t ur e,t he i rs i z e sand ma s s e s we r e me a sur ed．Ox i da t i ont e s twa sc a r r i edou ti namu f f l e f urna c ewi t hf r e ef l owi nga i ra t９００and１１００ ℃ f o r ５,１０,２５,５０and１００h,r e spe c t i ve l ． A f t e r f i n i s h Ｇ y i ngt heox i da t i on p r oc e s s,s amp l e s we r ecoo l edt o amb i e n tt emp e r a t u r ei nav e n t i l a t e dp l a c e．The ma s s change so fspe c imenswe r eme a sur eda f t e rt heox i da Ｇ t i ont e s t s． Subs t r a t e mi c r os t ruc t ur e swe r ei nve s t i t edby ga ( , op t i c a lmi c r os cope OM ZEISS Obs e r ve r．A１m)． Ox i de mo r l og i e s we r e exami ned us i ng a Leo pho １５３０VPs c ann i nge l e c t r on mi c r os cope ( SEM)．The coup l edene r i spe r s i vespe c t r os cope( EDS)de t e c Ｇ gyd t o rwa sapp l i edf o rchemi c a lcompos i t i onana l i s． ys Theox i depha s e swe r eana l z edbyXＧ r ayd i f f r a c t i on y ( , / ) XRD D MAXＧRB ．
Subs t r a t ema t e r i a lwa samod i f i ed３１０aus t en i t i c s t e e ldeve l opedi nt hel abo r a t o r c a lc omＧ y．Thechemi s i t i ons (ma s s％ ) we r e de s i s:Cr２５, Ni po gned a , , , , ２０ S i０ ６５ C０ １ Mo２ ０ Ti０ ２,Zr０ ２, W ０ １５andV０ １５． Thea l l oy wa sf ab r i c a t edt oas t e e lp l a t ewi t ha t h i ckne s so f６mmv i ame t a l l u r r o c e s s e so fva cu Ｇ gyp umＧme l t i ng,mo l d Ｇ c a s t i ng,f o r i nga ndr o l l i ng．Sma l l g
２ １ Mi c r o s t r u c t u r a le vo l u t i ona t９００ ℃ Thet i c a lmi c r os t ruc t ur eo ft hesubs t r a t ema Ｇ yp ( ) t e r i a li sshowni nF i １ a ． I t c o n s i s t so f h o m o e n e Ｇ g g ousequ i axedaus t en i t eg r a i nsandsomef i ne g r a i n bound a r r e c i i t a t e s．Thea v e r a eg r a i ns i z ei sabou t yp p g １０ ４μm wh i chi sme a sur edbyt heme t hodo fi n t e r Ｇ rup t i onl i ne s． I nF i １( b),t he５hox i d i z edspe c i Ｇ g menexh i b i t stwol aye r s．Theou t e rox i de sa r el a r ge,
１ Exp e r imen t a lPr o c e du r e s
２ Re s u l t sandDi s c u s s i on
( a)Subs t r a t emi c r o s t r uc t ur e; ( b)５h; ( c)１０h; ( d)２５h; ( e)５０h; ( f)１００h．
F i １ Op t i c a lmi c r o r aph so ft h es ub s t r a t emi c r o s t r u c t u r eandox i d emo rpho l o f t e rd i f f e r en tt imea t９００ ℃ g g g ya
I s sue４ Ef f e c t so fSo l u t i onDep l e t i onandSeg r ega t i onOx i da t i onon Mod i f i ed３１０Aus t en i t i cS t a i n l e s sS t e e l
wh i l et hei nne rone sa r ef i ne．TheEDSr e su l t si nd i Ｇ c a t et ha tt hec oa r s eox i de sa r e( Cr,Mn) Ｇ r i chox i de s c on t a i n i ngasma l lqu a n t i t fFe,wh i l et h ef i n e ron e s yo a r ema i n l Ｇ r i chox i de s．Theou t e rl aye r sp r og r e s Ｇ yCr s i ve l rt hei nne rl aye r swi t ht heox i da t i onde Ｇ ycove ve l opmen t．Nos i i f i c an tchange so fox i de sshape gn a r eobs e r vedi nF i １( d)and１( e)．Theox i de son gs t hesur f a c ed i s t r i bu t emo r ehomogeneous l a n dt he i r y s i z eg r adua l l c ome sl a r rwi t hi nc r e a s i ngt ime． y be ge Howeve r,t he r ei sanobv i ousd i f f e r enc ei nt heox i de ( ) ( ) ( ) mo r h o l o i e sb e t w e e nF i s １ c －１ e a n d１ f ． At p g g , f o r e a r tt e rmo fox i d a t i on un i f o rme i a x e dg r a i nsa r e p qu f o rmed,wh i l et heya r ema i n l l t i Ｇ angu l a rando c Ｇ y mu ( ) , t ahed r a lg r a i nsi nF i １f i nd i c a t i ngt ha tachange g i ns t ruc t ur eo fsu r f a c eox i de st ake sp l a c ewi t h i nt he exami nedox i da t i onpe r i od． I ti si n t e r e s t i ngandimpo r t an tt os t udyt hed i s Ｇ t r i bu t i ono fa l l oy i nge l emen t si nt heox i demo r l Ｇ pho ogys howni nF i s １( b)－１( f)．Th ec ompo s i t i ona nd g mi c r os t ruc t u r eo fpha s e swe r echa r a c t e r i z edbyEDS andXRD,r e spe c t i ve l i cha r eshowni nF i ２ y,wh gs and３．F i ２i l l us t r a t e st her e l a t i vei n t ens i t i e so fO, g
F i ２ Chang e si nc ompo s i t i on so f g t h eox i d e sbyEDSana l s i s y
F i ３ XRDs e c t r umo ft h es c a l e sf o r１００hand g p １０hox i da t i ona t９００ ℃
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Cr,MnandFea saf unc t i ono ft heox i da t i ont ime． Thecon t en t so fCrand O de c r e a s eobv i ous l t h y wi , , i nc r e a s i ngt heox i da t i ont ime whe r e a st hecon t en t s o f MnandFei nc r e a s edur i ngt hes amecour s e．At t heox i da t i ont imebe twe en５０and１００h,Mncon Ｇ , t en ti nt heox i de si smo r et hant ha to fCr wh i chr e Ｇ su l t si ng r a i ng r owt handas l i tbr e akawayox i da Ｇ gh t i onbe c aus eo ft hef o rma t i ono fmang an e s e Ｇ c h r omi um [ １２, １３] o ri r on Ｇ chr omi um sp i ne lox i de ．Co r r e spond i ng Ｇ l hechangeo fox i de si sobs e r veda c co rd i ngt ot he y,t XRD r e su l t, wh i c hi sa s c r i b e dt ot he Cr Ｇ d e l e t i on p ( ) F i ３ ．Thed i f f r a c t i oni n t ens i t fCr２O３i swe akＧ g yo enedandt hos eo f( Cr,Mn) Ｇ sp i ne la r eenhanc edi n t heox i d i z eds amp l ef o r１００h．Th i sr e su l tc anbei n Ｇ t e r r e t edbyt hed i f f e r en td i f f us i onr a t e so fchr omi Ｇ p umi nt he ma t r i xandox i des c a l e s．Tobespe c i f i c, t hed i f f us i onr a t eo fCri sh i ri nma t r i x,sod i f f u Ｇ ghe s i onma i n l cur si nt hesubs t r a t e１４ ．Ast het h i ckＧ yoc ne s so fs c a l ei nc r e a s e swi t hp r o l ong i ngt heox i da t i on , t ime i ti s mo r eand mo r ed i f f i cu l tf o rCri onst o r e a cht heou t e rl aye r．Howeve r,Mni onsc and i f f us e [] a tah i a t eeveni nt heox i des c a l e s８ ． ghr [ ]
２ ２ Mi c r o s t r u c t u r a le vo l u t i ona t１１００ ℃ Wi t hp r o l ong i ngox i da t i ont imea t９００ ℃ ,t he mo r l ogyappe a r eda she t e r ogeneous．The r ea r ea pho f ew Cr Ｇ r i chi s l andsr andoml i s t r i bu t i ng ove rt he yd ( ) ) homogeneousox i de s( F i ４ a ． S o m eb u c k l i n s g gi , obs e r vedduet ot he rma ls t r e s s．Whe r e a sf o rt hespe c i Ｇ menexpos eda t１１００ ℃ ,t he r e we r e mo r eCr Ｇ r i ch i s l andsevenon l f t e rexpos i ngf o r５h．Thei s l ands ya coa r s ened and ex t ended ahe ad dur i ng ox i da t i on, wh i chi nduc ed mo r ecomp l ex mo r l og i e s．Be s i de s pho Cr Ｇ r i chox i de,t he r ea r e br i h t Ｇ w h i t el a r e ro x i d e g g r a i nsandun i f o rmf i ne rg r a i ns,wh i cha r ede s i t Ｇ g gna edwi t ha r r owsi nF i ４( c)．Theya r ei den t i f i edt obe g Ti Ｇ r i chr a t i l eand ( Cr,Mn) Ｇ r i chsp i ne l,r e spe c t i ve l y． , Af t e rox i d i z edf o r１００h t he s eox i dei s l andss l owl y conne c t edt oe a cho t he randappe a r edt obene two rk． Then,t heg r a i nbounda r i e s we r ep r e s en t edbyt he de co r a t i ono fthe s ecomp l i c a t edox i de s,wh i cha r e adu l t e r a t edwi t hsomel a r rs e condpha s e s．Th i sr e Ｇ ge [ １５] su l ti scons i s t en twi t ht hewo rko fGou t i e re ta l , whof oundt ha tchr omi aobv i ous l r ewa l ongg r a i n yg bounda r i e sunde rCO２ a tmosphe r ea tt het empe r a Ｇ t ur eo f９２０－１０２０ ℃． De t a i l edexami na t i ono ft hecomp l exCr Ｇ r i chox Ｇ i des c a l e sshowst ha tt he i rsur f a c ei sspa l l i ng o r , c r a ck i ng wh i chc aus e st hei n t e r f a c ebe twe enCr Ｇ r i ch ox i d es c a l eandhomogeneousox i del aye rbe comes t Ｇ eppedandl owe r ed ( a sde s i n a t e dw i t hb l a c ka r r o w s g
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l ２３ 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
( a)９００ ℃ ,２５h; ( b)１１００ ℃ ,５h; ( c)１１００ ℃ ,２５h; ( d)１１００ ℃ ,１００h．
F i ４ Amo rphou sd i s t r i bu t i ono fox i d e sund e rd i f f e r en tc ond i t i on s g
i nF i ５( a))．Theex t e rna ll a e ri sf r a c t u r e d．Howe v Ｇ g y e r,F i ５( b)showss ome ( Cr,Mn) Ｇ sp i ne lg r a i ns g su r r oundedby Cr Ｇ r i chf l ake s wh i chs t i l lke epi n t e Ｇ r a t ed．Ac au l i f l owe r Ｇ l i kepa r t i cu l a t es e emsat owe r g anda r r ange st i t l rt hem． Fu r t he r,s omesma l l gh yove de eppo r e sa r ev i s i b l e．Theb r i tf i ne rp r e c i i t a t e s gh p a r ec l e a r l e r vedi n Cr Ｇ r i chox i de s( F i ５( c))． y obs g Th i spo r ouss t ruc t u r ei nt hes c a l ep r ov i de sasho r t Ｇ cu tf o rt r anspo r t a t i ono fi onsandc ons equen t l c Ｇ ya c e l e r a t e sox i da t i onr e a c t i on．TheEDSr e su l tshows t ha tt hea t omi cr a t i oo fCrt o Of o rb r i tp r e c i i Ｇ gh p , t a t e si s１∶３ i nd i c a t i ngt ha tt he s ep r e c i i t a t e sa r e p CrO３ wi t hl ow me l t i ngpo i n t．They maybef o rmed byf r e e z i ngdu r i ngc oo l i ngf r om h i empe r a t u r et o ght r oomt empe r a t u r e．Ther a t i oo fCrt o Oa tg r eyr e Ｇ i onsi s２ １－２ ３,wh i chi nd i c a t e st ha tt heg r eyr e Ｇ g i onsa r ecompo s edo fva r i ousox i de so fCr．Co l l e c Ｇ g , t i ve l he s er e su l t ssugge s tt ha tno ton l hep r e Ｇ yt yt c i i t a t e sbu ta l s ot heg r eyox i de sa r eCr Ｇ r i chox i de s． p Henc e,t hene two rko fCr Ｇ r i chox i de si sp r obab l e Ｇ yr l a t ed t ot he s eg r ega t i on o f chr omi um on g r a i n bounda r i e sandt hedep l e t i oni ns i deg r a i n． Tof ur t he rc on f i rmt hep r e s enc eo fva r i ousox Ｇ , i de so fCr t hepha s e si nox i des c a l e swe r eana l z ed． y F i ６( a)showst he XRD pa t t e rnso fs amp l e sex Ｇ g , o s e df o r１ ０a n d１ ０ ０ha t１ １ ０ ０ ℃ r e s e c t i v e l ． I p p y t
c anbes e enf r omF i ６( a)t ha tt hed i f f r a c t i oni n t en Ｇ g s i t fCr２O３ d r opssha r l s t i ngt ha tCr２O３ yo p y,sugge s c a l ebe come st h i n be c aus eo ft r ans f o rma t i oni n t o o t he rCrox i de s．I no rde rt ot e s t i f hep r e s enc eo f yt vo l a t i l eox i de si nt hes c a l e s,t hed i f f r a c t i onpe akso f θf r om ３６ °t o３８ ２８ °,whe r et heCrO３ pha s e sa r e ２ l oc a t ed,we r ez oomedanda r eshowni nF i ６( b)． I t g c anbes e ent ha tt hed i f f r a c t i oni n t ens i t fnon Ｇ o Ｇ yo pr t e c t i veCrO３ b e c ome ss t r ong e r( a ss howni nF i ６( b) g byb l a cka r r ows)． I ti sr e a sonab l et ha tt he s eCrO３ a r ef o rmedv i af ur t he rr e a c t i ngo fsomeCr２O３ wi t h oxygen．I ti s no tc l e a r whent h i sappa r en t pha s e t r ans f o rma t i onoc cur s,bu tt he i rg r owt hl i nkst ot he t h i ckne s so fCr２O３l aye rf o rmedont heg r a i nbound Ｇ a r i e s． [ ] Ga r ime l l ae ta l １６ r epo r t edt ha th i ＧCrs t a i n Ｇ gh l e s ss t e e lpos s e s s e sanab i l i t fs e l f Ｇ r epa i ra tt hede Ｇ yo , nudedz one s be c aus espa l l a t i oncond i t i onf avo r sf o r i ng r e s so fex t e rna la i r,wh i chi ss imi l a rt ot hecond i Ｇ t i onsa ti n i t i a ls t age． F i ７( a)showsap r a c t i c a lev i Ｇ g denc eo ft he pr oduc t i on o fnew g r a i nsi n denuded z one s． I ti sp r ed i c t edt ha tt h i sp r oc e s scou l dr epe a t owi ngt ot hepr e s enc eo fc a t i onsandan i ons,wh i ch con t r i bu t e st ot hef o rma t i on o fsuc c e s s i ve banded s c a l es t ruc t ur ea th i empe r a t ur e．Mo r eove r,t he ght ma s sga i ncur veo fspe c imenss howsar i s ef o rO２p e n Ｇ
I s sue４ Ef f e c t so fSo l u t i onDep l e t i onandSeg r ega t i onOx i da t i onon Mod i f i ed３１０Aus t en i t i cS t a i n l e s sS t e e l
３９７
( a)I n t e r f a c e sbe twe ennon Ｇ spa l l a t i onandspa l l a t i ona r e a s; ( b)Spe c i f i cmo r l ogyo fspa l l a t i ona r e a s; pho ( c)Somea r e a swi t hde epvo i dsandsma l ldepo s i tox i de s; ( d)EDSspe c t r umo ft hedepo s i tox i de s．
F i ５ Sp e c i f i cmo rpho l o fs l l a t i ona r e a sandEDSr e s u l to ft h ep r e c i i t a t e dox i d e s g g yo pa p
( a)XRDpa t t e r ns; ( b)Lo c a lamp l i f i c a t i ono fF i ６ ( a)． g
F i ６ XRDpa t t e rn so fox i d ef i lmsf o rme dont e s t e ds t e e le xpo s e dt o１１００ ℃ f o r１００h g
e t r a t i on,f o l l owed by ad r op be c aus eo fspa l l a t i on ( a sshowni nF i ７( b))．Fo rc ompa r i s on,t het ime Ｇ g dependen tma s sga i na t９００ ℃ i sp l o t t edi nF i ７ g ( b)． I tshowst ha tt hema s sga i ni sunusua l l i r yh ghe t hant ha ta t１１００ ℃． I nt h i sc a s e,ox i da t i onk i ne t i c cu r ve ha rd l eve a l st he a c t ua l ox i da t i on r e s i s t Ｇ yr [] anc e１ ．Thema s s Ｇ i nda t ac omp r ehens i ve l e f l e c t s ga yr t hed i f f e r enc ebe twe enup Ｇ t ak i ngoxygent of o rmox Ｇ
i de sandt hema s sl os sduet ospa l l a t i ono rvo l a t i l i z a Ｇ t i ono fl ow me l t i ngpo i n tox i de s．Ther e su l t sco r r ob Ｇ o r a t et ha tt hei nve s t i a t i o no f s u r f a c em o r h o l o o g p gy f ox i des c a l ei smo r ene c e s s a r r t an tf o rde Ｇ yandimpo t e rmi n i ngt heox i da t i onr e s i s t anc ei nt h i swo rk． ２ ３ Ox i da t i onme chan i sm Ox i da t i onr e a c t i oni sdomi n a t e dbya c t i v ec a t i ons
３９８
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 ２３
( a)Ev i denc eo ff o rma t i ono fnewox i deg r a i na tspa l l a t i ona r e a; ( b)Ma s schangecur ve sa t９００and１１００ ℃．
F i ７ Fo rma t i ono ft h en ewg r a i n sandt h eunu s ua lk i n e t i cox i da t i onc u r v e s g
andt he i rchemi c a la f f i n i t t hoxygen．Ox i da t i on y wi r e a c t i on i sf i n i shed t hr ough i ons t r anspo r t a t i on, [ , ] wh i chr e su l t si nac on t i nuousox i da t i on１７ １８ ．Ba s ed ont heana l i s,t heox i da t i onp r o c e s s e swe r ei l l us Ｇ ys t r a t eda sf o l l ows:Att hebeg i nn i ng,i ti se a s o r yf t heme t a li onst oc on t a c td i s s o l vedoxygenandf o rm /s ox i des c a l e t e e li n t e r f a c ebyox i da t i onr e a c t i on．The r o c e s si scon t r o l l edbyc onc en t r a t i onso fme t a li ons p , andan i ons a s we l la st heox i da t i ont empe r a t u r e． Whenox i des c a l e sc ove rt hewho l esu r f a c e s,t heox i Ｇ da t i onp r oc e s s e so ft hemod i f i ed３１０s t e e lwe r er e l a t Ｇ ( ) edt o １ t hei ng r e s sandd i f f us i ono f O２ i nox i de s c a l e;( ２)t hepr i o r i t i f f us i ono fox i dee l emen t s yd t hr oughox i des c a l eandt hesubs t r a t e;( ３)t heox i Ｇ da t i ono fFe,S iandCra t oms．Wi t hox i da t i ongo i ng on,i onson l i f f us et hr ought hei nne rox i del aye r yd t of u r t he rox i da t i onr e a c t i on．Att hes amet ime,t he /s c onc en t r a t i ono f me t a li onsa tox i des c a l e t e e li n Ｇ t e r f a c eb e c ome sl owe rt h a nt h a ta ti n i t i a lp e r i od,t hu s,
me t a li onsmus td i f f us et hr ought hesubs t r a t e．Con Ｇ , s equen t l i da t i on pr o c e s si s domi nan t l on Ｇ y ox yc t r o l l ed by t he d i f f us i on r a t e so f me t a li ons．As known,t hed i f f us i onr a t e so fCr,Fe,MnandTia r e , r e a t l i f f e r en t． Henc e t he i r ox i de sc ompo s e g yd mu l t i Ｇ l aye r ox i de s．The ox i de so ft he e l emen t s who s ed i f f us i onr a t e sa r eh i rd i s t r i bu t ei nt he ghe ou t e rl aye r．Ont hec on t r a r nne rl aye r sa r ec omＧ y,i s edo ft heox i de so fl owe rd i f f us i onr a t ee l emen t s． po Ac c o rd i ngt ot h i s me chan i sm,i nne rs c a l er e t a i ns mo r ep r o t e c t i vee l emen t sbe c aus eo ft he i rl owd i f f u Ｇ s i onr a t e si nox i de ssucha sCr．Howeve r,t hed i f f u Ｇ s i onr a t e so fFe,MnandTia r eh i rt hant ha to f ghe [ １９] , Cr sot hec on t en to fMni nc r e a s e s．Thec oa r s en TiO２ i sobs e r vedi nt heou t e rl aye r．Th i sana l i s ys imp l i e st ha tox i da t i ondependsh i l hed i f f u Ｇ gh yont s i on me chan i smo fe l emen t s．Ther e a s onwhynoFe Ｇ
r i chox i dei sobs e r vedi nt heou t e rl aye rwi l lbeex Ｇ l a i n e d i nt h en e x t s e c t i o n ． p ２ ４ Ef f e c t so ft hes o l u t i onde l e t i onands e r e a t i on p g g Atp r e s en t,t hee f f e c t so ft heso l u t i ondep l e t i on ands eg r ega t i ononox i da t i on mo r l ogy haveno t pho be enex t ens i ve l epo r t ed,e spe c i a l l o r３１０t yr yf ype s t a i n l e s ss t e e l s．Thef o rma t i ono fnon Ｇ r o t e c t i veCr Ｇ p r i chox i dea l ongg r a i nbounda r i e sandt heabs enc eo f Fe,S iox i de sa tsur f a c e may be add i t i ona l l Ｇ y ex l a i nedbyde t a i l edana l i s． F i ８showst hema c r o Ｇ p ys g． , s cop i cmo r l ogyo fs c a l ei nt hespe c imen wh i ch pho wa sf o rmeda t１１００ ℃ f o r１００h,wi t hsomed i s t r i Ｇ bu t i onmapso fe l emen t sf o rO,Cr,S i,C,Mn,Ti andFe．TheEDS mapsr eve a lt ha tt hed i f f e r en td i s Ｇ t r i bu t i on pa t t e rnso fcons t i t uen te l emen t s．Be s i de s t hechr omi umＧ r i chz one sont heg r a i nbounda r i e s,S i , i sa l soa ti n t e r r anu l a ra r e a wh i l eo t he re l emen t s g a r ei ni n t r ag r anu l a rr eg i ons．Thed i s t r i bu t i ono fFei s comp l i c a t ed:abundan tFed i s t r i bu t e si n t r a r anu l a r l g y, andsma l lamoun ta r ea ti n t e r r anu l a ra r e a．I ti s g wo r t hno t i ngt ha tt hed i s t r i bu t i onso fS iandFea r e ve r imi l a r．Att hes amet ime,Fe Ｇ dep l e t i oni sob Ｇ ys s e r vedong r a i nbounda r i e s． I nt h i ss t e e l,s i l i coni saddedt oenhanc eox i da Ｇ t i onr e s i s t anc e,be c aus ei tha sh i f f i n i t ghoxygena y andc anr e a c twi t hoxygena tme t a l Ｇ s c a l ei n t e r f a c eo r [ ２０] oni n t e rna lg r a i nbounda r i e s ． I ti st hei n t e rna ls i l Ｇ i c ap r e c i i t a t e st ha tchangedt heme chan i smo fso l u Ｇ p t i ond i f f us i onby b l ock i ngt heou twa rdt r anspo r t a Ｇ t i onchanne l,pa r t i cu l a r l het r anspo r t a t i onchanne l yt o fi r on．The r e f o r e,a sa d i f f us i on ba r r i e r,s i l i c a i nnedi r ona tt he me t a l Ｇ s c a l ei n t e r f a c e．Some Mn p andCri onsgot ot heex t e rna lsur f a c edur i ngox i da Ｇ t i on,whe r e a st hos een t r appeddono tr e a cht hei n Ｇ t e r f a c eduet ot hel a t ch i ngbyt heS iO２． Con s e e n t l qu y,
I s sue４ Ef f e c t so fSo l u t i onDep l e t i onandSeg r ega t i onOx i da t i onon Mod i f i ed３１０Aus t en i t i cS t a i n l e s sS t e e l
３９９
F i ８ E l e c t r onmi c r o r aph so fb r e akawa i d enodu l eont h eg r ounds u r f a c ea f t e r１００hox i da t i ona t１１００ ℃ g g yox
Fe Ｇ i onsf a i lt or e a cht heou t e rs c a l eandFe Ｇ dep l e t i on i sobs e r vedong r a i nbounda r i e s．Th i sc ons equenc eo f Feen t r appedi ssuppo r t edbyt heXRDda t ai nF i ６． g The r e su l t sa r ei n ag r e emen t wi t hs ome r e s e a r Ｇ [ ８, ２０, ２１] ,wh che s i chr epo r t edt ha ts i l i c ons eg r ega t eda t t hea l l oy Ｇ ox i dei n t e r f a c eandde c r e a s edi r onc a t i ons a c t i v i t y． Asknown,d i s l o c a t i on s,c r s t a ll a t t i c ea ndg r a i n y bounda r i e spr ov i despe c i a ld i f f us i onpa t hsf o rva c an Ｇ , c i e sandso l u t e．Ac c o r d i ngt oana l i si ti sbe l i eved ys t ha tt hed i f f e r enc eo ft heox i de si sl i nkedt ot hed i f Ｇ , f us i onpa t hso fs o l u t i onsi nt hea l l oy e spe c i a l l yCr． Att empe r a t u r ebe twe en９００and９５０ ℃ ,t hed i f f u Ｇ s i ono fCri onsi s ma i n l hr ought hec r t a ll a t Ｇ yt ys [] t i c e４ ,whos er a t ei sl owe rt hant ha to fg r a i n Ｇ bound Ｇ [ ] a r i f f us i on２０ ．Fu r t he rmo r e,i nt h i sr angeo ft emＧ yd r a t ur e,S iO２ ont heg r a i nbounda r anb l o ckt he pe yc t r anspo r to fCri ons．The r e f o r e,t he s etwof a c t o r s makei nne rCr２O３ s c a l et h i nne rand mo r eun i f o rm． Howeve r,g r a i n Ｇ bounda r i f f us i onmayp l ayadomＧ yd i nan tr o l ea t１１００ ℃．Andt hes i l i c aong r a i nbound Ｇ a r come si ne f f i c i en tt oc ap t u r e Cri onsa th i y be gh [ ,] [ ] t empe r a t ur e７ ８ ． S imi l a r l a i ae ta l ２２ a l s ono t Ｇ y,Ts edt ha tt hes eg r ega t i ono fe l emen t so rt he i rox i de s ont he g r a i nbounda r i e sf a i l edt oc omp l e t e l l o ck yb t he g r a i n Ｇbounda r i f f us i ons．Henc e,t he g r a i n yd bounda r i e sa c ta ss i t e sf o rt hep r e f e r en t i a lf o rma t i on o fCr２O３ ．I nadd i t i on,t hei nne rS iO２ r educ e st he spa l l a t i onr e s i s t anc e,wh i chi sdependen tont hec on Ｇ , t en to fS ii nt hea l l oy t hec on t i nu i t swe l la st he ya [ ] t h i ckne s so fS iO２ ２３ ．Ano t he rc aus eo ft hes eg r ega Ｇ
t i on o fchr omi um t ot hei n t e r r anu l a rr eg i onsi s g somechr omi umＧ r i ch c a rb i de p r e f e r en t i a l l i s t ed y ex l e ad i ngt oal oc a l i z edi nc r e a s eo fchr omi um conc en Ｇ t r a t i on．Thedep l e t i on ands eg r ega t i on o f Cr,t he e f f e c to fd i s so l u t i ono fc a rb i deonox i da t i ona th i gh t empe r a t ur e swi l lb ei nv e s t i a t e di nf u r t he rwo r k． g
３ Conc l u s i on s
( １)At９００ ℃ ,ox i da t i on wa sh i l n f l u Ｇ gh yi enc edby d i f f us i ono fa l l oy i nge l emen t s．Theox i de mo r l ogy changed f r om equ i axed t o oc t ahed r a l pho r a i nswi t hi nc r e a s i ngox i da t i ont imeduet ot heCr Ｇ g dep l e t i on and t he f o rma t i on o f Mn Ｇ r i ch ox i de s, wh i chr e su l ti nas l owbr e akawayox i da t i ona tp r ev i Ｇ ouss t age s． ( ２)Cr t a lox i de s,ne two rkox i de sands eve r Ｇ ys a ll a r rs i z eg r a i nso fTiO２ comp r i s edt heou tmos t ge l aye ra t１１００ ℃．The Cr Ｇ r i ch ox i de s ne two rki s mo r esus c ep t i b l et ospa l l a t i onbe c aus eo ft hei ns t a Ｇ b i l i t f Cr２O３ ．Some Cr Ｇ r i ch ox i de s havet r ans Ｇ yo f o rmedi n t ovo l a t i l eox i de ssucha sCrO３ ． ( ３)Di f f us i onr a t eo ft he Cra t１１００ ℃ be Ｇ come sf a s t e rbe c aus et hepa t hschangef r om c r t a l ys l a t t i c et og r a i nbounda r i e s．Thecomp l exCr Ｇ r i chox Ｇ i demo r l ogyi sr e l a t edt os eg r ega t i onso fCr,t he pho Fe Ｇ c ap t ur eby S iand Mnandt he Fe Ｇ dep l e t i on on , r a i nbounda r s we l la st hena t ur es t ruc t ur eo f g y a r a i nbounda r i e s． g Re f e r enc e s:
[ １] Y．Yamamo t o,MP．Br a dy,Z P．Lu,P J．Ma z i a s z,C T．L i u, B A． P i n t,K L．Mo r e,HM．Meye r,E A．Pay z an t,Sc i enc e．
４００
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 ２３
３１６ ( ２００７)４３３ Ｇ ４３６． [ ２] M．Wang,Z J． Zhou,HY． Sun,HH．Hu,S F． L i,J．Nuc l． Ma t e r． ４３０ ( ２０１２)２５９ Ｇ ２６３． [ ３] R L．Hi i n s on,MA E． J e s on,G D．We s t,Ma t e r． Sc i．Te ch Ｇ gg p no l ２２ ( ２００６)１３２５ Ｇ １３３２． [ ４] S．Cr uch l eya,HE．Evans a,MP．Tay l o r a,MC．Ha r dyb,S． S t ekov i c,Co r r o s． Sc i． ７５ ( ２０１３)５８ Ｇ ６６． [ ５] L． Sánche z,MP．Hi e r r o,F J．Pé r e z,Ox i d．Me t． ７１ ( ２００９)
１７３ Ｇ １８６． [ ６] R L．Hi i ns on,G．Gr e en,Co r r o s． Sc i． ５３ ( ２０１１)１６９０ Ｇ １６９３． gg [ ７] A．Pa ú l,R． Sán c h e z,O M．Mon t e s,J A．Od r i o z o l a,Ox i d．Me t． ６７ ( ２００７)８７ Ｇ １０５． [ ８] X．Wang,A．At k i ns on,Ac t a Me t a l l． ５９ ( ２０１１)２５１４ Ｇ ２５２５． [ ９] A． Pa ú l,J A．Od r i o z o l a,MA． S a nMi e l,J． Fe r nánd e zS a n z,L． gu J．Ál v a r e z,Ac t a Ma t e r． ４８ ( ２０００)２９５１ Ｇ ２９５８． [ １０] VA．Lav r enko,VB．Vo i t ov i ch,VM．Ade ev,Adv．Ma t e r． j ９３ ( １９９４)２９１ Ｇ ２９６． [ １１] F H． S t o t t,GC．Wood,J．S t r i nge r,Ox i d．Me t． ４４ ( １９９５)
１１３ Ｇ １４５． [ J． I r onS t e e lRe s． I n t． １９ ( ２０１２) １２] Z T．Zhang,YY．Zhang． No ８,６７ Ｇ ７４．
[ １３] J H．Ramí r e z ＧRamí r e z,R． Co l á s,N F．Ga r z a ＧMon t e s Ｇ d e ＧOc a,J． I r onS t e e lRe s． I n t． ２０ ( ２０１３)No １０,１２２ Ｇ １２９． [ １４] C．Os twa l d,H．Gr abke,Co r r o s． Sc i． ４６ ( ２００４)１１１３ Ｇ １１２７． [ １５] F．Gou t i e r,S．Va l e t t e,A．Va r de l l e,P．Le f o r t,Co r r o s．Sc i． ５２ ( ２０１０)２４０３ Ｇ ２４１２． [ １６] N．Ga r ime l l a,MP．Br ady,Y．Sohn,J．Pha s eEqu i l i b．Di f f． ２７ ( ２００６)６６５ Ｇ ６７０． [ １７] HL．Hu,Z J．Zhou,M．L i,L F．Zhang,M．Wang,S F． L i,C C．Ge,Co r r o s． Sc i． ６５ ( ２０１２)２０９ Ｇ ２１３． [ １８] M．Sun,X．Wu,Z．Zh a ng,E H．Ha n,Co r r o s．S c i． ５１ ( ２００９) １０６９ Ｇ １０７２． [ １９] X Y．Yu a n,Y T．Ya o,L Q． Ch e n,Ac t aMe t a l l． S i n． ２７ ( ２０１４) ４０１ Ｇ ４０６． [ ２０] H．Bus c a i l,S．ElMe s sk i,F．Ri f f a r d,S． Pe r r i e r,R．Cue f f,E． Caud r on,C． I s s a r t e l,Ma t e r．Chem．Phys．１１１ ( ２００８)４９１ Ｇ ４９６． [ ２１] AM．Hun t z,Ma t e r． Sc i．Eng．A２０１ ( １９９５)２１１ Ｇ ２２８． [ ２２] S C．Ts a i a,AM．Hun t z,C．Do l i n,Ma t e r．Sc i．Eng．A２１２ ( １９９６)６ Ｇ １３． [ ２３] X J．L i u,YQ．He,GM． Cao,T． J i a,T Z．Wu,Z Y． L i u, J． I r onS t e e lRe s． I n t． ２２ ( ２０１５)No ３,２３８ Ｇ ２４４．
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ６,２ ３( ４):３ ９ ３ Ｇ ４ ０ ０
Ef f e c t so fSo l u t i onDe l e t i onandS e r e a t i onOx i da t i onon p g g Mo r l o fMod i f i e d３１０Au s t e n i t i cS t a i n l e s sS t e e l pho g yo Hong Ｇ i ngSUN１ , Qi ang HE１ , Zhang Ｇ i anZHOU２ , Man WANG２ , y j Guang Ｇmi ngZHANG２ , Shao Ｇ f uLI２
( １．KeyLabo r a t o r fKeyFunc t i ona lPa r t so fMa ch i ne,AnyangI ns t i t u t eo fTe chno l ogy,Anyang４５５００２, yo , ; , Henan Ch i na ２． Schoo lo fMa t e r i a l sSc i enc eandEng i ne e r i ng Un i ve r s i t fSc i enc eandTe chno l ogy yo Be i i ng,Be i i ng１０００８３,Ch i na) j j Ab s t r a c t:Theox i da t i onmo r l og i e so fmod i f i ed３１０s t e e le xpo s e di n９００a nd１１００ ℃ a i rwe r ei nv e s t i a t e d．Adoub l e pho g l aye rmo r l ogyc ons i s t i ngo fa ( Cr,Mn) Ｇ r i chou t e rl aye randaf i neCr Ｇ r i chi nne rl aye rwa sf o rmeda t９００ ℃． I twa s pho r e l a t edt ot heb r e akawayox i da t i oni nduc edbyt heCr Ｇ dep l e t i onandt he Mn Ｇ s eg r ega t i oni ni nne rl aye r．SomeCr Ｇ r i ch ox i de swi t hamo r t a t ewe r ef o rmeda l ongg r a i nbounda r i e s．Ands omenewf i ne rox i deg r a i ns,vo i dsandCr Ｇ phouss r i chp r e c i i t a t e swe r eobs e r vedi nspa l l a t i ona r e a sa t１１００ ℃．Co r r e spond i ng l heox i da t i onk i ne t i ccu r ved r opped p y,t wi t ht hespa l l a t i ono fs c a l eandi nc r e a s edwi t ht hef o rma t i ono fs omenewox i deg r a i ns． I twa sc aus edbys eg r ega t i on o fCrandt het r ans f o rma t i ono fox i de sf r om Cr２O３ t ot hevo l a t i l eox i de sa te l e va t edt empe r a t u r e．XRD ana l s i s y showedt ha tt hep r e c i i t a t e swe r ema i n l ompo s edo fCrO３ ．Seg r ega t i onanddep l e t i onf o rs o l u t i onswe r ea l s od i s Ｇ p yc cus s edbyox i da t i ond i f f us i onme chan i sms． Ke r d s:aus t en i t i cs t a i n l e s ss t e e l;SEM;mo r l ogy;ox i da t i on;s eg r ega t i on;e l emen t pho ywo
Aus t en i t i cs t a i n l e s ss t e e l shaved i ve r s eapp l i c a Ｇ t i onsduet ot he i rc omb i na t i ono fgoodh i Ｇ t empe r a Ｇ gh [ ] t u r ec r e eps t r eng t handox i da t i onr e s i s t anc e１Ｇ３ ．The r e a c t i vee l emen t so fCr,AlandS ic on t r i bu t es i i f i Ｇ gn c an t l oenhanc i ngt heox i da t i onr e s i s t anc eo faus t e Ｇ yt n i t i cs t a i n l e s ss t e e l s．Al t hought he s es t e e l shaveex Ｇ c e l l en tgene r a lox i da t i onr e s i s t anc e,t heya r esus c ep Ｇ t i b l et o“ br e akaway”ox i da t i oni ns omes t r i ngen t c ond i t i ons．Asoneo ft hemo s tc ommons e r v i c ef a i l Ｇ u r e s,“ b r e ak awa i d a t i onc a u s e sun a c c e t a b l el o s s y”ox p f o rme t a l l i cma t e r i a l s．Th i sl o c a l i z eda c c e l e r a t edox i Ｇ da t i ono f t ent ake sp l a c ei nt hespe c i f i cagg r e s s i veen Ｇ v i r onmen t s,sucha sh i empe r a t u r eandnuc l e a r ght “ ” , r ad i a t i on．The b r e akaway p r o c e s si sspo r ad i cr an Ｇ domands t ocha s t i c． Soi ti sd i f f i cu l tt op r ed i c a t et he [] t imeand t hel o c a t i on o f even t s４ ．Al t hough t he , me chan i smo fb r e akawayox i da t i oni sunc l e a rt he r e i snodoub tt ha ti ti sr e l a t edt ot hemi c r o s t ruc t u r eo f s t e e l s．Theg r owt ho fox i de si sba s edond i f f us i on
r oc e s s,wh i chr e l a t e st ot hecha r a c t e r i s t i c so fsubＧ p s t r a t e( c hemi c a lc ompo s i t i on,g r a i ns i z e,g r a i nbound a Ｇ ) r i e scha r a c t e rd i s t r i bu t i onandso l u t es eg r ega t i on i n add i t i ont ot heox i d i z i ngenv i r onmen t s( med i umand [ ,] t empe r a t ur e)３ ５ ． Seve r a lbr e akawayox i da t i onst ha t [ ４] , l i nkt og r a i nbounda r i e s chemi c a lf a i l ur e o r me Ｇ [] chan i c a lf a i l ur e６ havebe enobs e r ved,wh i l et hespe Ｇ c i f i cp r oc e s si ss t i l lunc l e a r． Thed i f f us i ono f mi no ra l l oy add i t i onsa f f e c t s t hee s t ab l i shmen tandg r owt ho ft hep r o t e c t i veox i de s c a l e s,some t ime sevenp l aysas i i f i c an tr o l ei nt he gn [ [ [ ] ７] ８] ７, ox i da t i on p r oc e s s ．Wang and Paú le ta l ９ s t ud i edt hed i f f us i onme chan i smso ft her e a c t i vee l e Ｇ men t sandt her e su l t sshowedt ha td i f f us i onpa t hso f bene f i c i a le l emen t smi tbechangedbe c aus eo ft he gh chr omi umdep l e t i oni nsubs t r a t eandt hes eg r ega t i on ong r a i nbounda r i e s．Re a c t i vee l emen t sa r ep r og r e s Ｇ s i ve l i ngox i da t i onp r oc e ed i ng,wh i ch yconsumeddur i nduc e st heso l u t i ondep l e t i oni n Cr, Mo,Nb,Zr
Founda t i onI t em: I t em Spons o r edbyKeyPr o e c t sFundedPr og r amo fHenanPr ov i nc eEduc a t i onDepa r tmen to fCh i na ( I １５A４３００１２) j : , , ; : ; : , B i o r a h H o n Ｇ i n UN D o c t o r L e c t u r e s h i E Ｇ m a i l s h s u n ０ ２ ９＠１ ６ ３ c o m R e c e i v e dD a t e J a n u a r １ ２ ０ １ ５ gy gS p y y１ g py Co r r e s i ngAu t ho r s:Qi angHE,Do c t o r,As s o c i a t ePr o f e s s o r; E Ｇma i l:ays t a r＠１６３ c om pond Zhang Ｇ i anZHOU,Do c t o r,Pr o f e s s o r; E Ｇma i l:zhouzh t e r us t b edu cn j j＠ma
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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 ２３
andS i Ｇ con t a i neds t a i n l e s ss t e e l． I n manyc a s e s,t he s o l u t ep r e c i i t a t i oni sdemons t r a t edbyt hechange s p , o fc ompos i t i on s t ruc t u r eo ft he mu l t i Ｇ l aye rs c a l e s [ ] andt heevapo r a t i ono fs omel owＧme l t i ngox i de s１０ ． Fo rexamp l e,evapo r ab l eox i de so fCrl e adt oCr Ｇ de Ｇ , l e t i oni nma t r i x wh i chi nduc e sat r ans f o rma t i ono f p ox i de sl aye rf r om Cr Ｇ r i chox i de st ot hel e s sp r o t e c Ｇ t i veCr,Feo rMnsp i ne l． I nt hepa s ts eve r a lde c ade s,many wo rkshave be enc a r r i edou tandc ons i de r ab l ep r og r e s sha sbe en a ch i evedi nunde r s t and i ngt he me chan i c a lf a i l u r eo f [ ４] , ox i des c a l e s ．Howeve r chemi c a lf a i l u r eo ft he r o t e c t i veox i des c a l e,wh i chr e l a t edt os o l u t e Ｇ dep l e Ｇ p , t i onands eg r ega t i on wa sr epo r t edi nani nc omp r e Ｇ [,, , ] hens i ve way４ ８ １０ １１ ．The a im o ft h i s wo rki st o s t udyt heox i da t i onbehav i o ro famod i f i ed３１０aus t e Ｇ n i t i cs t a i n l e s ss t e e lbyi nve s t i t i ngt hesu r f a c emo r Ｇ ga l og i e so fox i des c a l e s．The me chan i sm o fs l ow pho b r e akawayox i da t i ona t９００ ℃ i l l us t r a t edby me ans o fs o l u t i ond i f f us i on．Thei n f l uenc e so fs o l u t ep r e c i Ｇ p i t a t i onands eg r ega t i onont hespa l l a t i onandf o rma Ｇ t i ono fne two rkox i da t i onf o rmeda t１１００ ℃ we r e a l s od i s cus s ed．
ox i d i z edspe c imens we r ecu tf r om t her o l l ed p l a t e wi t has i z eo f１ ５mm×１５ mm×２５ mm ( t h i c kn e s s× wi d t h×l eng t h)．Spe c imens we r e po l i shedt o２０００ r i t．Then,t hey we r et ho r ough l r e a s ed wi t h g y deg anhyd r ouse t hano lbyu l t r a son i cc l e an i ngf o r２０mi n． Subs equen t l c imens we r ed r i edi n a va cuum y,spe boxa t１７５ ℃ f o r４h．Af t e rspe c imenswe r ecoo l ed t or oom t empe r a t ur e,t he i rs i z e sand ma s s e s we r e me a sur ed．Ox i da t i ont e s twa sc a r r i edou ti namu f f l e f urna c ewi t hf r e ef l owi nga i ra t９００and１１００ ℃ f o r ５,１０,２５,５０and１００h,r e spe c t i ve l ． A f t e r f i n i s h Ｇ y i ngt heox i da t i on p r oc e s s,s amp l e s we r ecoo l edt o amb i e n tt emp e r a t u r ei nav e n t i l a t e dp l a c e．The ma s s change so fspe c imenswe r eme a sur eda f t e rt heox i da Ｇ t i ont e s t s． Subs t r a t e mi c r os t ruc t ur e swe r ei nve s t i t edby ga ( , op t i c a lmi c r os cope OM ZEISS Obs e r ve r．A１m)． Ox i de mo r l og i e s we r e exami ned us i ng a Leo pho １５３０VPs c ann i nge l e c t r on mi c r os cope ( SEM)．The coup l edene r i spe r s i vespe c t r os cope( EDS)de t e c Ｇ gyd t o rwa sapp l i edf o rchemi c a lcompos i t i onana l i s． ys Theox i depha s e swe r eana l z edbyXＧ r ayd i f f r a c t i on y ( , / ) XRD D MAXＧRB ．
Subs t r a t ema t e r i a lwa samod i f i ed３１０aus t en i t i c s t e e ldeve l opedi nt hel abo r a t o r c a lc omＧ y．Thechemi s i t i ons (ma s s％ ) we r e de s i s:Cr２５, Ni po gned a , , , , ２０ S i０ ６５ C０ １ Mo２ ０ Ti０ ２,Zr０ ２, W ０ １５andV０ １５． Thea l l oy wa sf ab r i c a t edt oas t e e lp l a t ewi t ha t h i ckne s so f６mmv i ame t a l l u r r o c e s s e so fva cu Ｇ gyp umＧme l t i ng,mo l d Ｇ c a s t i ng,f o r i nga ndr o l l i ng．Sma l l g
２ １ Mi c r o s t r u c t u r a le vo l u t i ona t９００ ℃ Thet i c a lmi c r os t ruc t ur eo ft hesubs t r a t ema Ｇ yp ( ) t e r i a li sshowni nF i １ a ． I t c o n s i s t so f h o m o e n e Ｇ g g ousequ i axedaus t en i t eg r a i nsandsomef i ne g r a i n bound a r r e c i i t a t e s．Thea v e r a eg r a i ns i z ei sabou t yp p g １０ ４μm wh i chi sme a sur edbyt heme t hodo fi n t e r Ｇ rup t i onl i ne s． I nF i １( b),t he５hox i d i z edspe c i Ｇ g menexh i b i t stwol aye r s．Theou t e rox i de sa r el a r ge,
１ Exp e r imen t a lPr o c e du r e s
２ Re s u l t sandDi s c u s s i on
( a)Subs t r a t emi c r o s t r uc t ur e; ( b)５h; ( c)１０h; ( d)２５h; ( e)５０h; ( f)１００h．
F i １ Op t i c a lmi c r o r aph so ft h es ub s t r a t emi c r o s t r u c t u r eandox i d emo rpho l o f t e rd i f f e r en tt imea t９００ ℃ g g g ya
I s sue４ Ef f e c t so fSo l u t i onDep l e t i onandSeg r ega t i onOx i da t i onon Mod i f i ed３１０Aus t en i t i cS t a i n l e s sS t e e l
wh i l et hei nne rone sa r ef i ne．TheEDSr e su l t si nd i Ｇ c a t et ha tt hec oa r s eox i de sa r e( Cr,Mn) Ｇ r i chox i de s c on t a i n i ngasma l lqu a n t i t fFe,wh i l et h ef i n e ron e s yo a r ema i n l Ｇ r i chox i de s．Theou t e rl aye r sp r og r e s Ｇ yCr s i ve l rt hei nne rl aye r swi t ht heox i da t i onde Ｇ ycove ve l opmen t．Nos i i f i c an tchange so fox i de sshape gn a r eobs e r vedi nF i １( d)and１( e)．Theox i de son gs t hesur f a c ed i s t r i bu t emo r ehomogeneous l a n dt he i r y s i z eg r adua l l c ome sl a r rwi t hi nc r e a s i ngt ime． y be ge Howeve r,t he r ei sanobv i ousd i f f e r enc ei nt heox i de ( ) ( ) ( ) mo r h o l o i e sb e t w e e nF i s １ c －１ e a n d１ f ． At p g g , f o r e a r tt e rmo fox i d a t i on un i f o rme i a x e dg r a i nsa r e p qu f o rmed,wh i l et heya r ema i n l l t i Ｇ angu l a rando c Ｇ y mu ( ) , t ahed r a lg r a i nsi nF i １f i nd i c a t i ngt ha tachange g i ns t ruc t ur eo fsu r f a c eox i de st ake sp l a c ewi t h i nt he exami nedox i da t i onpe r i od． I ti si n t e r e s t i ngandimpo r t an tt os t udyt hed i s Ｇ t r i bu t i ono fa l l oy i nge l emen t si nt heox i demo r l Ｇ pho ogys howni nF i s １( b)－１( f)．Th ec ompo s i t i ona nd g mi c r os t ruc t u r eo fpha s e swe r echa r a c t e r i z edbyEDS andXRD,r e spe c t i ve l i cha r eshowni nF i ２ y,wh gs and３．F i ２i l l us t r a t e st her e l a t i vei n t ens i t i e so fO, g
F i ２ Chang e si nc ompo s i t i on so f g t h eox i d e sbyEDSana l s i s y
F i ３ XRDs e c t r umo ft h es c a l e sf o r１００hand g p １０hox i da t i ona t９００ ℃
３９５
Cr,MnandFea saf unc t i ono ft heox i da t i ont ime． Thecon t en t so fCrand O de c r e a s eobv i ous l t h y wi , , i nc r e a s i ngt heox i da t i ont ime whe r e a st hecon t en t s o f MnandFei nc r e a s edur i ngt hes amecour s e．At t heox i da t i ont imebe twe en５０and１００h,Mncon Ｇ , t en ti nt heox i de si smo r et hant ha to fCr wh i chr e Ｇ su l t si ng r a i ng r owt handas l i tbr e akawayox i da Ｇ gh t i onbe c aus eo ft hef o rma t i ono fmang an e s e Ｇ c h r omi um [ １２, １３] o ri r on Ｇ chr omi um sp i ne lox i de ．Co r r e spond i ng Ｇ l hechangeo fox i de si sobs e r veda c co rd i ngt ot he y,t XRD r e su l t, wh i c hi sa s c r i b e dt ot he Cr Ｇ d e l e t i on p ( ) F i ３ ．Thed i f f r a c t i oni n t ens i t fCr２O３i swe akＧ g yo enedandt hos eo f( Cr,Mn) Ｇ sp i ne la r eenhanc edi n t heox i d i z eds amp l ef o r１００h．Th i sr e su l tc anbei n Ｇ t e r r e t edbyt hed i f f e r en td i f f us i onr a t e so fchr omi Ｇ p umi nt he ma t r i xandox i des c a l e s．Tobespe c i f i c, t hed i f f us i onr a t eo fCri sh i ri nma t r i x,sod i f f u Ｇ ghe s i onma i n l cur si nt hesubs t r a t e１４ ．Ast het h i ckＧ yoc ne s so fs c a l ei nc r e a s e swi t hp r o l ong i ngt heox i da t i on , t ime i ti s mo r eand mo r ed i f f i cu l tf o rCri onst o r e a cht heou t e rl aye r．Howeve r,Mni onsc and i f f us e [] a tah i a t eeveni nt heox i des c a l e s８ ． ghr [ ]
２ ２ Mi c r o s t r u c t u r a le vo l u t i ona t１１００ ℃ Wi t hp r o l ong i ngox i da t i ont imea t９００ ℃ ,t he mo r l ogyappe a r eda she t e r ogeneous．The r ea r ea pho f ew Cr Ｇ r i chi s l andsr andoml i s t r i bu t i ng ove rt he yd ( ) ) homogeneousox i de s( F i ４ a ． S o m eb u c k l i n s g gi , obs e r vedduet ot he rma ls t r e s s．Whe r e a sf o rt hespe c i Ｇ menexpos eda t１１００ ℃ ,t he r e we r e mo r eCr Ｇ r i ch i s l andsevenon l f t e rexpos i ngf o r５h．Thei s l ands ya coa r s ened and ex t ended ahe ad dur i ng ox i da t i on, wh i chi nduc ed mo r ecomp l ex mo r l og i e s．Be s i de s pho Cr Ｇ r i chox i de,t he r ea r e br i h t Ｇ w h i t el a r e ro x i d e g g r a i nsandun i f o rmf i ne rg r a i ns,wh i cha r ede s i t Ｇ g gna edwi t ha r r owsi nF i ４( c)．Theya r ei den t i f i edt obe g Ti Ｇ r i chr a t i l eand ( Cr,Mn) Ｇ r i chsp i ne l,r e spe c t i ve l y． , Af t e rox i d i z edf o r１００h t he s eox i dei s l andss l owl y conne c t edt oe a cho t he randappe a r edt obene two rk． Then,t heg r a i nbounda r i e s we r ep r e s en t edbyt he de co r a t i ono fthe s ecomp l i c a t edox i de s,wh i cha r e adu l t e r a t edwi t hsomel a r rs e condpha s e s．Th i sr e Ｇ ge [ １５] su l ti scons i s t en twi t ht hewo rko fGou t i e re ta l , whof oundt ha tchr omi aobv i ous l r ewa l ongg r a i n yg bounda r i e sunde rCO２ a tmosphe r ea tt het empe r a Ｇ t ur eo f９２０－１０２０ ℃． De t a i l edexami na t i ono ft hecomp l exCr Ｇ r i chox Ｇ i des c a l e sshowst ha tt he i rsur f a c ei sspa l l i ng o r , c r a ck i ng wh i chc aus e st hei n t e r f a c ebe twe enCr Ｇ r i ch ox i d es c a l eandhomogeneousox i del aye rbe comes t Ｇ eppedandl owe r ed ( a sde s i n a t e dw i t hb l a c ka r r o w s g
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l ２３ 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
( a)９００ ℃ ,２５h; ( b)１１００ ℃ ,５h; ( c)１１００ ℃ ,２５h; ( d)１１００ ℃ ,１００h．
F i ４ Amo rphou sd i s t r i bu t i ono fox i d e sund e rd i f f e r en tc ond i t i on s g
i nF i ５( a))．Theex t e rna ll a e ri sf r a c t u r e d．Howe v Ｇ g y e r,F i ５( b)showss ome ( Cr,Mn) Ｇ sp i ne lg r a i ns g su r r oundedby Cr Ｇ r i chf l ake s wh i chs t i l lke epi n t e Ｇ r a t ed．Ac au l i f l owe r Ｇ l i kepa r t i cu l a t es e emsat owe r g anda r r ange st i t l rt hem． Fu r t he r,s omesma l l gh yove de eppo r e sa r ev i s i b l e．Theb r i tf i ne rp r e c i i t a t e s gh p a r ec l e a r l e r vedi n Cr Ｇ r i chox i de s( F i ５( c))． y obs g Th i spo r ouss t ruc t u r ei nt hes c a l ep r ov i de sasho r t Ｇ cu tf o rt r anspo r t a t i ono fi onsandc ons equen t l c Ｇ ya c e l e r a t e sox i da t i onr e a c t i on．TheEDSr e su l tshows t ha tt hea t omi cr a t i oo fCrt o Of o rb r i tp r e c i i Ｇ gh p , t a t e si s１∶３ i nd i c a t i ngt ha tt he s ep r e c i i t a t e sa r e p CrO３ wi t hl ow me l t i ngpo i n t．They maybef o rmed byf r e e z i ngdu r i ngc oo l i ngf r om h i empe r a t u r et o ght r oomt empe r a t u r e．Ther a t i oo fCrt o Oa tg r eyr e Ｇ i onsi s２ １－２ ３,wh i chi nd i c a t e st ha tt heg r eyr e Ｇ g i onsa r ecompo s edo fva r i ousox i de so fCr．Co l l e c Ｇ g , t i ve l he s er e su l t ssugge s tt ha tno ton l hep r e Ｇ yt yt c i i t a t e sbu ta l s ot heg r eyox i de sa r eCr Ｇ r i chox i de s． p Henc e,t hene two rko fCr Ｇ r i chox i de si sp r obab l e Ｇ yr l a t ed t ot he s eg r ega t i on o f chr omi um on g r a i n bounda r i e sandt hedep l e t i oni ns i deg r a i n． Tof ur t he rc on f i rmt hep r e s enc eo fva r i ousox Ｇ , i de so fCr t hepha s e si nox i des c a l e swe r eana l z ed． y F i ６( a)showst he XRD pa t t e rnso fs amp l e sex Ｇ g , o s e df o r１ ０a n d１ ０ ０ha t１ １ ０ ０ ℃ r e s e c t i v e l ． I p p y t
c anbes e enf r omF i ６( a)t ha tt hed i f f r a c t i oni n t en Ｇ g s i t fCr２O３ d r opssha r l s t i ngt ha tCr２O３ yo p y,sugge s c a l ebe come st h i n be c aus eo ft r ans f o rma t i oni n t o o t he rCrox i de s．I no rde rt ot e s t i f hep r e s enc eo f yt vo l a t i l eox i de si nt hes c a l e s,t hed i f f r a c t i onpe akso f θf r om ３６ °t o３８ ２８ °,whe r et heCrO３ pha s e sa r e ２ l oc a t ed,we r ez oomedanda r eshowni nF i ６( b)． I t g c anbes e ent ha tt hed i f f r a c t i oni n t ens i t fnon Ｇ o Ｇ yo pr t e c t i veCrO３ b e c ome ss t r ong e r( a ss howni nF i ６( b) g byb l a cka r r ows)． I ti sr e a sonab l et ha tt he s eCrO３ a r ef o rmedv i af ur t he rr e a c t i ngo fsomeCr２O３ wi t h oxygen．I ti s no tc l e a r whent h i sappa r en t pha s e t r ans f o rma t i onoc cur s,bu tt he i rg r owt hl i nkst ot he t h i ckne s so fCr２O３l aye rf o rmedont heg r a i nbound Ｇ a r i e s． [ ] Ga r ime l l ae ta l １６ r epo r t edt ha th i ＧCrs t a i n Ｇ gh l e s ss t e e lpos s e s s e sanab i l i t fs e l f Ｇ r epa i ra tt hede Ｇ yo , nudedz one s be c aus espa l l a t i oncond i t i onf avo r sf o r i ng r e s so fex t e rna la i r,wh i chi ss imi l a rt ot hecond i Ｇ t i onsa ti n i t i a ls t age． F i ７( a)showsap r a c t i c a lev i Ｇ g denc eo ft he pr oduc t i on o fnew g r a i nsi n denuded z one s． I ti sp r ed i c t edt ha tt h i sp r oc e s scou l dr epe a t owi ngt ot hepr e s enc eo fc a t i onsandan i ons,wh i ch con t r i bu t e st ot hef o rma t i on o fsuc c e s s i ve banded s c a l es t ruc t ur ea th i empe r a t ur e．Mo r eove r,t he ght ma s sga i ncur veo fspe c imenss howsar i s ef o rO２p e n Ｇ
I s sue４ Ef f e c t so fSo l u t i onDep l e t i onandSeg r ega t i onOx i da t i onon Mod i f i ed３１０Aus t en i t i cS t a i n l e s sS t e e l
３９７
( a)I n t e r f a c e sbe twe ennon Ｇ spa l l a t i onandspa l l a t i ona r e a s; ( b)Spe c i f i cmo r l ogyo fspa l l a t i ona r e a s; pho ( c)Somea r e a swi t hde epvo i dsandsma l ldepo s i tox i de s; ( d)EDSspe c t r umo ft hedepo s i tox i de s．
F i ５ Sp e c i f i cmo rpho l o fs l l a t i ona r e a sandEDSr e s u l to ft h ep r e c i i t a t e dox i d e s g g yo pa p
( a)XRDpa t t e r ns; ( b)Lo c a lamp l i f i c a t i ono fF i ６ ( a)． g
F i ６ XRDpa t t e rn so fox i d ef i lmsf o rme dont e s t e ds t e e le xpo s e dt o１１００ ℃ f o r１００h g
e t r a t i on,f o l l owed by ad r op be c aus eo fspa l l a t i on ( a sshowni nF i ７( b))．Fo rc ompa r i s on,t het ime Ｇ g dependen tma s sga i na t９００ ℃ i sp l o t t edi nF i ７ g ( b)． I tshowst ha tt hema s sga i ni sunusua l l i r yh ghe t hant ha ta t１１００ ℃． I nt h i sc a s e,ox i da t i onk i ne t i c cu r ve ha rd l eve a l st he a c t ua l ox i da t i on r e s i s t Ｇ yr [] anc e１ ．Thema s s Ｇ i nda t ac omp r ehens i ve l e f l e c t s ga yr t hed i f f e r enc ebe twe enup Ｇ t ak i ngoxygent of o rmox Ｇ
i de sandt hema s sl os sduet ospa l l a t i ono rvo l a t i l i z a Ｇ t i ono fl ow me l t i ngpo i n tox i de s．Ther e su l t sco r r ob Ｇ o r a t et ha tt hei nve s t i a t i o no f s u r f a c em o r h o l o o g p gy f ox i des c a l ei smo r ene c e s s a r r t an tf o rde Ｇ yandimpo t e rmi n i ngt heox i da t i onr e s i s t anc ei nt h i swo rk． ２ ３ Ox i da t i onme chan i sm Ox i da t i onr e a c t i oni sdomi n a t e dbya c t i v ec a t i ons
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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 ２３
( a)Ev i denc eo ff o rma t i ono fnewox i deg r a i na tspa l l a t i ona r e a; ( b)Ma s schangecur ve sa t９００and１１００ ℃．
F i ７ Fo rma t i ono ft h en ewg r a i n sandt h eunu s ua lk i n e t i cox i da t i onc u r v e s g
andt he i rchemi c a la f f i n i t t hoxygen．Ox i da t i on y wi r e a c t i on i sf i n i shed t hr ough i ons t r anspo r t a t i on, [ , ] wh i chr e su l t si nac on t i nuousox i da t i on１７ １８ ．Ba s ed ont heana l i s,t heox i da t i onp r o c e s s e swe r ei l l us Ｇ ys t r a t eda sf o l l ows:Att hebeg i nn i ng,i ti se a s o r yf t heme t a li onst oc on t a c td i s s o l vedoxygenandf o rm /s ox i des c a l e t e e li n t e r f a c ebyox i da t i onr e a c t i on．The r o c e s si scon t r o l l edbyc onc en t r a t i onso fme t a li ons p , andan i ons a s we l la st heox i da t i ont empe r a t u r e． Whenox i des c a l e sc ove rt hewho l esu r f a c e s,t heox i Ｇ da t i onp r oc e s s e so ft hemod i f i ed３１０s t e e lwe r er e l a t Ｇ ( ) edt o １ t hei ng r e s sandd i f f us i ono f O２ i nox i de s c a l e;( ２)t hepr i o r i t i f f us i ono fox i dee l emen t s yd t hr oughox i des c a l eandt hesubs t r a t e;( ３)t heox i Ｇ da t i ono fFe,S iandCra t oms．Wi t hox i da t i ongo i ng on,i onson l i f f us et hr ought hei nne rox i del aye r yd t of u r t he rox i da t i onr e a c t i on．Att hes amet ime,t he /s c onc en t r a t i ono f me t a li onsa tox i des c a l e t e e li n Ｇ t e r f a c eb e c ome sl owe rt h a nt h a ta ti n i t i a lp e r i od,t hu s,
me t a li onsmus td i f f us et hr ought hesubs t r a t e．Con Ｇ , s equen t l i da t i on pr o c e s si s domi nan t l on Ｇ y ox yc t r o l l ed by t he d i f f us i on r a t e so f me t a li ons．As known,t hed i f f us i onr a t e so fCr,Fe,MnandTia r e , r e a t l i f f e r en t． Henc e t he i r ox i de sc ompo s e g yd mu l t i Ｇ l aye r ox i de s．The ox i de so ft he e l emen t s who s ed i f f us i onr a t e sa r eh i rd i s t r i bu t ei nt he ghe ou t e rl aye r．Ont hec on t r a r nne rl aye r sa r ec omＧ y,i s edo ft heox i de so fl owe rd i f f us i onr a t ee l emen t s． po Ac c o rd i ngt ot h i s me chan i sm,i nne rs c a l er e t a i ns mo r ep r o t e c t i vee l emen t sbe c aus eo ft he i rl owd i f f u Ｇ s i onr a t e si nox i de ssucha sCr．Howeve r,t hed i f f u Ｇ s i onr a t e so fFe,MnandTia r eh i rt hant ha to f ghe [ １９] , Cr sot hec on t en to fMni nc r e a s e s．Thec oa r s en TiO２ i sobs e r vedi nt heou t e rl aye r．Th i sana l i s ys imp l i e st ha tox i da t i ondependsh i l hed i f f u Ｇ gh yont s i on me chan i smo fe l emen t s．Ther e a s onwhynoFe Ｇ
r i chox i dei sobs e r vedi nt heou t e rl aye rwi l lbeex Ｇ l a i n e d i nt h en e x t s e c t i o n ． p ２ ４ Ef f e c t so ft hes o l u t i onde l e t i onands e r e a t i on p g g Atp r e s en t,t hee f f e c t so ft heso l u t i ondep l e t i on ands eg r ega t i ononox i da t i on mo r l ogy haveno t pho be enex t ens i ve l epo r t ed,e spe c i a l l o r３１０t yr yf ype s t a i n l e s ss t e e l s．Thef o rma t i ono fnon Ｇ r o t e c t i veCr Ｇ p r i chox i dea l ongg r a i nbounda r i e sandt heabs enc eo f Fe,S iox i de sa tsur f a c e may be add i t i ona l l Ｇ y ex l a i nedbyde t a i l edana l i s． F i ８showst hema c r o Ｇ p ys g． , s cop i cmo r l ogyo fs c a l ei nt hespe c imen wh i ch pho wa sf o rmeda t１１００ ℃ f o r１００h,wi t hsomed i s t r i Ｇ bu t i onmapso fe l emen t sf o rO,Cr,S i,C,Mn,Ti andFe．TheEDS mapsr eve a lt ha tt hed i f f e r en td i s Ｇ t r i bu t i on pa t t e rnso fcons t i t uen te l emen t s．Be s i de s t hechr omi umＧ r i chz one sont heg r a i nbounda r i e s,S i , i sa l soa ti n t e r r anu l a ra r e a wh i l eo t he re l emen t s g a r ei ni n t r ag r anu l a rr eg i ons．Thed i s t r i bu t i ono fFei s comp l i c a t ed:abundan tFed i s t r i bu t e si n t r a r anu l a r l g y, andsma l lamoun ta r ea ti n t e r r anu l a ra r e a．I ti s g wo r t hno t i ngt ha tt hed i s t r i bu t i onso fS iandFea r e ve r imi l a r．Att hes amet ime,Fe Ｇ dep l e t i oni sob Ｇ ys s e r vedong r a i nbounda r i e s． I nt h i ss t e e l,s i l i coni saddedt oenhanc eox i da Ｇ t i onr e s i s t anc e,be c aus ei tha sh i f f i n i t ghoxygena y andc anr e a c twi t hoxygena tme t a l Ｇ s c a l ei n t e r f a c eo r [ ２０] oni n t e rna lg r a i nbounda r i e s ． I ti st hei n t e rna ls i l Ｇ i c ap r e c i i t a t e st ha tchangedt heme chan i smo fso l u Ｇ p t i ond i f f us i onby b l ock i ngt heou twa rdt r anspo r t a Ｇ t i onchanne l,pa r t i cu l a r l het r anspo r t a t i onchanne l yt o fi r on．The r e f o r e,a sa d i f f us i on ba r r i e r,s i l i c a i nnedi r ona tt he me t a l Ｇ s c a l ei n t e r f a c e．Some Mn p andCri onsgot ot heex t e rna lsur f a c edur i ngox i da Ｇ t i on,whe r e a st hos een t r appeddono tr e a cht hei n Ｇ t e r f a c eduet ot hel a t ch i ngbyt heS iO２． Con s e e n t l qu y,
I s sue４ Ef f e c t so fSo l u t i onDep l e t i onandSeg r ega t i onOx i da t i onon Mod i f i ed３１０Aus t en i t i cS t a i n l e s sS t e e l
３９９
F i ８ E l e c t r onmi c r o r aph so fb r e akawa i d enodu l eont h eg r ounds u r f a c ea f t e r１００hox i da t i ona t１１００ ℃ g g yox
Fe Ｇ i onsf a i lt or e a cht heou t e rs c a l eandFe Ｇ dep l e t i on i sobs e r vedong r a i nbounda r i e s．Th i sc ons equenc eo f Feen t r appedi ssuppo r t edbyt heXRDda t ai nF i ６． g The r e su l t sa r ei n ag r e emen t wi t hs ome r e s e a r Ｇ [ ８, ２０, ２１] ,wh che s i chr epo r t edt ha ts i l i c ons eg r ega t eda t t hea l l oy Ｇ ox i dei n t e r f a c eandde c r e a s edi r onc a t i ons a c t i v i t y． Asknown,d i s l o c a t i on s,c r s t a ll a t t i c ea ndg r a i n y bounda r i e spr ov i despe c i a ld i f f us i onpa t hsf o rva c an Ｇ , c i e sandso l u t e．Ac c o r d i ngt oana l i si ti sbe l i eved ys t ha tt hed i f f e r enc eo ft heox i de si sl i nkedt ot hed i f Ｇ , f us i onpa t hso fs o l u t i onsi nt hea l l oy e spe c i a l l yCr． Att empe r a t u r ebe twe en９００and９５０ ℃ ,t hed i f f u Ｇ s i ono fCri onsi s ma i n l hr ought hec r t a ll a t Ｇ yt ys [] t i c e４ ,whos er a t ei sl owe rt hant ha to fg r a i n Ｇ bound Ｇ [ ] a r i f f us i on２０ ．Fu r t he rmo r e,i nt h i sr angeo ft emＧ yd r a t ur e,S iO２ ont heg r a i nbounda r anb l o ckt he pe yc t r anspo r to fCri ons．The r e f o r e,t he s etwof a c t o r s makei nne rCr２O３ s c a l et h i nne rand mo r eun i f o rm． Howeve r,g r a i n Ｇ bounda r i f f us i onmayp l ayadomＧ yd i nan tr o l ea t１１００ ℃．Andt hes i l i c aong r a i nbound Ｇ a r come si ne f f i c i en tt oc ap t u r e Cri onsa th i y be gh [ ,] [ ] t empe r a t ur e７ ８ ． S imi l a r l a i ae ta l ２２ a l s ono t Ｇ y,Ts edt ha tt hes eg r ega t i ono fe l emen t so rt he i rox i de s ont he g r a i nbounda r i e sf a i l edt oc omp l e t e l l o ck yb t he g r a i n Ｇbounda r i f f us i ons．Henc e,t he g r a i n yd bounda r i e sa c ta ss i t e sf o rt hep r e f e r en t i a lf o rma t i on o fCr２O３ ．I nadd i t i on,t hei nne rS iO２ r educ e st he spa l l a t i onr e s i s t anc e,wh i chi sdependen tont hec on Ｇ , t en to fS ii nt hea l l oy t hec on t i nu i t swe l la st he ya [ ] t h i ckne s so fS iO２ ２３ ．Ano t he rc aus eo ft hes eg r ega Ｇ
t i on o fchr omi um t ot hei n t e r r anu l a rr eg i onsi s g somechr omi umＧ r i ch c a rb i de p r e f e r en t i a l l i s t ed y ex l e ad i ngt oal oc a l i z edi nc r e a s eo fchr omi um conc en Ｇ t r a t i on．Thedep l e t i on ands eg r ega t i on o f Cr,t he e f f e c to fd i s so l u t i ono fc a rb i deonox i da t i ona th i gh t empe r a t ur e swi l lb ei nv e s t i a t e di nf u r t he rwo r k． g
３ Conc l u s i on s
( １)At９００ ℃ ,ox i da t i on wa sh i l n f l u Ｇ gh yi enc edby d i f f us i ono fa l l oy i nge l emen t s．Theox i de mo r l ogy changed f r om equ i axed t o oc t ahed r a l pho r a i nswi t hi nc r e a s i ngox i da t i ont imeduet ot heCr Ｇ g dep l e t i on and t he f o rma t i on o f Mn Ｇ r i ch ox i de s, wh i chr e su l ti nas l owbr e akawayox i da t i ona tp r ev i Ｇ ouss t age s． ( ２)Cr t a lox i de s,ne two rkox i de sands eve r Ｇ ys a ll a r rs i z eg r a i nso fTiO２ comp r i s edt heou tmos t ge l aye ra t１１００ ℃．The Cr Ｇ r i ch ox i de s ne two rki s mo r esus c ep t i b l et ospa l l a t i onbe c aus eo ft hei ns t a Ｇ b i l i t f Cr２O３ ．Some Cr Ｇ r i ch ox i de s havet r ans Ｇ yo f o rmedi n t ovo l a t i l eox i de ssucha sCrO３ ． ( ３)Di f f us i onr a t eo ft he Cra t１１００ ℃ be Ｇ come sf a s t e rbe c aus et hepa t hschangef r om c r t a l ys l a t t i c et og r a i nbounda r i e s．Thecomp l exCr Ｇ r i chox Ｇ i demo r l ogyi sr e l a t edt os eg r ega t i onso fCr,t he pho Fe Ｇ c ap t ur eby S iand Mnandt he Fe Ｇ dep l e t i on on , r a i nbounda r s we l la st hena t ur es t ruc t ur eo f g y a r a i nbounda r i e s． g Re f e r enc e s:
[ １] Y．Yamamo t o,MP．Br a dy,Z P．Lu,P J．Ma z i a s z,C T．L i u, B A． P i n t,K L．Mo r e,HM．Meye r,E A．Pay z an t,Sc i enc e．
４００
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 ２３
３１６ ( ２００７)４３３ Ｇ ４３６． [ ２] M．Wang,Z J． Zhou,HY． Sun,HH．Hu,S F． L i,J．Nuc l． Ma t e r． ４３０ ( ２０１２)２５９ Ｇ ２６３． [ ３] R L．Hi i n s on,MA E． J e s on,G D．We s t,Ma t e r． Sc i．Te ch Ｇ gg p no l ２２ ( ２００６)１３２５ Ｇ １３３２． [ ４] S．Cr uch l eya,HE．Evans a,MP．Tay l o r a,MC．Ha r dyb,S． S t ekov i c,Co r r o s． Sc i． ７５ ( ２０１３)５８ Ｇ ６６． [ ５] L． Sánche z,MP．Hi e r r o,F J．Pé r e z,Ox i d．Me t． ７１ ( ２００９)
１７３ Ｇ １８６． [ ６] R L．Hi i ns on,G．Gr e en,Co r r o s． Sc i． ５３ ( ２０１１)１６９０ Ｇ １６９３． gg [ ７] A．Pa ú l,R． Sán c h e z,O M．Mon t e s,J A．Od r i o z o l a,Ox i d．Me t． ６７ ( ２００７)８７ Ｇ １０５． [ ８] X．Wang,A．At k i ns on,Ac t a Me t a l l． ５９ ( ２０１１)２５１４ Ｇ ２５２５． [ ９] A． Pa ú l,J A．Od r i o z o l a,MA． S a nMi e l,J． Fe r nánd e zS a n z,L． gu J．Ál v a r e z,Ac t a Ma t e r． ４８ ( ２０００)２９５１ Ｇ ２９５８． [ １０] VA．Lav r enko,VB．Vo i t ov i ch,VM．Ade ev,Adv．Ma t e r． j ９３ ( １９９４)２９１ Ｇ ２９６． [ １１] F H． S t o t t,GC．Wood,J．S t r i nge r,Ox i d．Me t． ４４ ( １９９５)
１１３ Ｇ １４５． [ J． I r onS t e e lRe s． I n t． １９ ( ２０１２) １２] Z T．Zhang,YY．Zhang． No ８,６７ Ｇ ７４．
[ １３] J H．Ramí r e z ＧRamí r e z,R． Co l á s,N F．Ga r z a ＧMon t e s Ｇ d e ＧOc a,J． I r onS t e e lRe s． I n t． ２０ ( ２０１３)No １０,１２２ Ｇ １２９． [ １４] C．Os twa l d,H．Gr abke,Co r r o s． Sc i． ４６ ( ２００４)１１１３ Ｇ １１２７． [ １５] F．Gou t i e r,S．Va l e t t e,A．Va r de l l e,P．Le f o r t,Co r r o s．Sc i． ５２ ( ２０１０)２４０３ Ｇ ２４１２． [ １６] N．Ga r ime l l a,MP．Br ady,Y．Sohn,J．Pha s eEqu i l i b．Di f f． ２７ ( ２００６)６６５ Ｇ ６７０． [ １７] HL．Hu,Z J．Zhou,M．L i,L F．Zhang,M．Wang,S F． L i,C C．Ge,Co r r o s． Sc i． ６５ ( ２０１２)２０９ Ｇ ２１３． [ １８] M．Sun,X．Wu,Z．Zh a ng,E H．Ha n,Co r r o s．S c i． ５１ ( ２００９) １０６９ Ｇ １０７２． [ １９] X Y．Yu a n,Y T．Ya o,L Q． Ch e n,Ac t aMe t a l l． S i n． ２７ ( ２０１４) ４０１ Ｇ ４０６． [ ２０] H．Bus c a i l,S．ElMe s sk i,F．Ri f f a r d,S． Pe r r i e r,R．Cue f f,E． Caud r on,C． I s s a r t e l,Ma t e r．Chem．Phys．１１１ ( ２００８)４９１ Ｇ ４９６． [ ２１] AM．Hun t z,Ma t e r． Sc i．Eng．A２０１ ( １９９５)２１１ Ｇ ２２８． [ ２２] S C．Ts a i a,AM．Hun t z,C．Do l i n,Ma t e r．Sc i．Eng．A２１２ ( １９９６)６ Ｇ １３． [ ２３] X J．L i u,YQ．He,GM． Cao,T． J i a,T Z．Wu,Z Y． L i u, J． I r onS t e e lRe s． I n t． ２２ ( ２０１５)No ３,２３８ Ｇ ２４４．