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Effect of Cr on Characteristic of Rust Layer Formed on Low Alloy Steel in Flow-accelerated Corrosion Environment
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ６,２ ３( ６):６ ０ ２ Ｇ ６ ０ ７
Ef f e c to fCronCha r a c t e r i s t i co fRu s tLay e rFo rme donLowAl l o y S t e e li nF l owＧ a c c e l e r a t e dCo r r o s i onEnv i r onme n t FengCHAI, ShanJ IANG, Ca i Ｇ f uYANG
( Depa r tmen to fEng i ne e r i ngS t e e l s,Cen t r a lI r onandS t e e lRe s e a r chI ns i t i t u t e,Be i i ng１０００８１,Ch i na) j Ab s t r a c t:Thef l owＧ a c c e l e r a t edc o r r o s i onexpe r imen t swe r ec a r r i edou tt or e s e a r cht hee f f e c to fCront her us tl aye r s f o rmedont hec a r bons t e e la ndCr Ｇ c on t a i n i ngs t e e l,a swe l la st h es t r u c t u r eo fr u s tl a e ro ft h etwoe xp e r ime n t a ls t e e l s． y Thei n f l uenc eo fCront hef l owＧ a c c e l e r a t edc o r r o s i onr e s i s t anc eandt hec o r r o s i on mo r l ogyo fi nne rr us tl aye r pho f o rmedont heCr Ｇ c on t a i n i ngs t e e lwe r es t ud i e dbyt h e me t hod so fpo l a r i z a t i onc u r v e s,s c a nn i nge l e c t r on mi c r o s c op e, t r a n smi s s i one l e c t r onmi c r o s c op e,a ndX Ｇ r a t o e l e c t r ons e c t r o s c op e． Th ed i s t r i bu t i ono fCrandi t sf o rmo fex i s t enc ei n ypho p
t hei nne rr us tl aye rwe r eana l z ed．Ther e su l t sshowt ha tc o r r odedma s sl o s so fCr Ｇ c on t a i n i ngs t e e li sl owe rt hant ha t y o fc a r bons t e e landi t si nne rr us tl aye ri sc ompa c t．Crex i s t si nt hef o rmo fFe２CrO４ andi sen r i chedi nt hei nne rr us t l aye r．Th i sc onc en t r a t i onc ou l dmaket hei nne rr us tl aye rexh i b i tt het endencyo famo r i sphenomenoni sr e Ｇ phous．Th l a t edt of i neFe２CrO４ ．Thei nne rr us tl aye rbe c ome smo r ec ompa c tbe c aus eo ft hef o rma t i ono ff i neFe２CrO４ ,andt he r o t e c t i vene s so fi nne rr us tl aye rc ou l dbeimp r ovedr ema r kab l p y． Ke r d s:Cr Ｇ c on t a i n i ngs t e e l;f l owＧ a c c e l e r a t edc o r r o s i on;i nne rr us tl aye r;amo r phous ywo
Me t a l se r odedbyf l u i dc ommon l akep l a c ei n yt , a l lk i ndso fi ndus t r i a lf a c i l i t i e s and wi l lc aus es e r i Ｇ ousde s t ruc t i vee f f e c twh i chc ou l dl e adt oasudden f a i l ur eo f equ i ti ns e r v i c e．Me t a lc o r r os i on pmen c aus edbyf l u i di se s s en t i a l l of l owＧ a c c e l e r a t ed yduet co r r os i on ( FAC),wh i ch s i i f i c an t l educ e st he gn yr t h i ckne s so f ma t e r i a l whe r ef l u i d pa s s e st hr ough,
andhenc ee r ode st hec omponen t１Ｇ５ ．I n t ens i ver e Ｇ s e a r chha sbe endoneont hebehav i o ro ff l owＧ a c c e l Ｇ [] [] e r a t edc o r r o s i on． Cops on６ andCr agno l i no７ po i n t ed ou tt ha ti nc r e a s i ngf l owr a t ewou l df a c i l i t a t ec o r r o Ｇ [] s i onr a t eo fme t a l．Re s e a r che sby Chene ta l ８ and [] Ne s i ce ta l ９ sugge s t edt ha tt hei nc r e a s eo fc o r r o Ｇ s i onr a t ewa se s s en t i a l l t t r i bu t edt ot h i sphenome Ｇ ya nonwhe r ef l owf avo r edt hed i f f us i ono fdepo l a r i z a Ｇ t i ont owa r ds me t a lsu r f a c e,c ons equen t l c c e l e r a Ｇ ya t i ngt hee l e c t r o chemi c a lr e a c t i on． Lowa l l oyeds t e e l sbe i ngl ongt e rmexpo su r et o co r r os i onenv i r onmen ta r ep r onet orus tl aye rf o rma Ｇ t i on ont hes t e e lsu r f a c e s．I t ha s be en c onc l uded f r omt her e su l t so fex t ens i vei nve s t i t i ononrus t ga l aye r sonwe a t he r i ngs t e e l st h a tr u s tl a e r l a sas i Ｇ y py g n i f i c an tr o l ei nimp r o v i ngt h ec o r r o s i onr e s i s t a n c eo fl ow [ , ] a l l oyeds t e e l s１０ １１ ．Th er u s tl a e rf o rme dont h es t e e l y [
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sur f a c ei senr i chmen to fa l l oy i nge l emen t s．Among [ , ] , t hem Cri sac r u c i a le l eme n t． Pub l i s he dr e r t s１２ １３ i n Ｇ po d i c a t edt ha tCrenr i chedi nt hei nne rrus tl aye rena Ｇ b l edi tt or ep l a c eFea t omo fα ＧFeOOHandt husr e Ｇ ( , ) su l t edi nt hef o rma t i ono ff i ne rα Ｇ Fe１－x Crx OOH (mos to ft hem wi t hs i z el e s st han８nm),wh i chimＧ r ovedt hec omp a c t n e s so fi nn e rr u s tl a e ronwe a t he Ｇ p y r i ngs t e e l s． Add i ngasma l lamoun to fCri nc a rbons t e e lc an imp r ovet hes e r v i c el i f eo fp i l i nesot ha t mak i ng pe t hes e r v i c el i f eo fp i l i nei sequa lt ot ha to fve s s e l． pe Howeve r,f ewpub l i c a t i onsr eve a l edhowCrp l aysi t s r o l ei nrus tl aye runde rt heimpa c to fs a l twa t e r． I n t h i spape r,t hecomponen t sandpha s e si nrus tl aye r have be en i nve s t i t ed．Th i s pape ra l so demon Ｇ ga s t r a t e st hee f f e c to fCront herus tl aye randme cha Ｇ n i sm o fhow Crc animp r ovet he p r o t e c t i vene s so f rus tl aye runde rt heimpa c to fs a l twa t e r．
１ Exp e r imen t a l
１ １ Ma t e r i a l spr e r a t i on pa Twos t e e l sus edi nt h i ss t udywe r esme l t edi na va cuumi nduc t i onf urna c e．Af t e rf o r i ngt hei ngo t s g t ob l ocks,t he b l ocks we r e ho tr o l l edi n t op l a t e s
B i o r aphy: FengCHAI,Do c t o r,Sen i o rEng i ne e r; E Ｇma i l: cha i f eng＠c i s r i c omcn; Re c e i v e dDa t e: May１４,２０１５ g
I s sue６ Ef f e c to fCronCha r a c t e r i s t i co fRus tLaye rFo rmedonLow Al l oyS t e e l
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wi t ht h i ckne s so f１３ mm．Th ec h emi c a lc ompo s i t i on s me a sur emen t swe r er i ns edwi t ha c e t oneandd r i edby o ft heexpe r imen t a ls t e e l sa r eshowni n Tab l e１． a i r,t he nwe i dbyami c r ob a l an c e．Af t e re a c ht imeo f ghe , The s etwos t e e l shaves ameba s echemi s t r e x c e t e x o s u r e t h es e c i m e n s w e r ed e s c a l e db i mm e r Ｇ y p p p y f o rCradd i t i on． s i oni nHClso l u t i on,andt henr i ns edi nd i s t i l l edwa Ｇ t e rand a c e t one suc c e s s i ve l t e ra i r Ｇ d r i ed,t he y．Af Tab l e１ Ch emi c a lc ompo s i t i on so fe xp e r imen t a ls t e e l s spe c imenswe r er ewe i no rde rt oc a l cu l a t et he ghedi ma s s％ ma s sl os sduet oco r r os i on． S t e e l C Mn S i P S Cr Po t en t i odynami c po l a r i z a t i oncur ve s we r eob Ｇ Ca r bons t e e l ０ ０８２ ０ ６３ ０ ２４ ０ ０１２ ０ ００３６ － t a i nedus i ngaPr i nc e t on２７３Ae l e c t r ochemi c a lwo rkＧ Cr Ｇ c on t a i n i ng s t a t i onwi t hvo l t ages c anr a t eo f３０ mV/mi n． ０ ０７８ ０ ６０ ０ ２１ ０ ０１８ ０ ００２０ ２ s t e e l
１ ２ Sa l twa t e rf l owＧ a c c e l e r a t e dc o r r o s i ons imu l a t i on １ ２ １ Expe r imen t a ls e t up Fo r c e d Ｇ c onv e c t i v er o t a t i ng Ｇ c l i nd e re l e c t r od eme t hＧ y od wa s wi de l edf o ri nve s t i t i ngt hec o r r os i on y us ga [ , ] behav i o ro fme t a le xpo s u r et of l u i d me d i a１４ １５ ．Ba s e d , on p r ev i ous s t ud i e s af l owＧ a c c e l e r a t ed c o r r os i on s imu l a t i ondev i c ewa sde s i o rt h i spu r s e．The gnedf po s chema t i cs e t upi si l l us t r a t edi nF i １． g
F i １ S ch ema t i ci l l u s t r a t i ono ft h eequ i tu s e df o r g pmen f l owＧ a c c e l e r a t e dc o r r o s i one xp e r imen t
１ ２ ２ Co r r o s i onparame t e r s A ７ Ｇ day du r a t i onc o r r o s i ont e s tha sbe en pe r Ｇ f o rmedi na３ ５ma s s％ NaCls o l u t i onwi t hf l owve Ｇ l oc i t f１ ５ m/sandt empe r a t u r eo f２０ ℃． yo １ ２ ３ Sampl e s Th ed ime n s i ono fs amp l e su s e df o rc o r r o s i ont e s ti s ２０mm ( l e ng t h)×２０ mm ( w i d t h)×２ mm ( d e t h)．A p ho l ewi t hd i ame t e ro f２mmi spunchedonbo t hends f o rt hepu r s eo fhang i ngs amp l e．Be f o r et e s t,t he po sur f a c esub e c t edt oexpo su r ewa sg r adua l l l i shed j ypo t o１０００g r i tbyab r a s i vepape randt henc l e anedby e t hano l． １ ３ Di r e c tma s sl o s sme a s u r eme n t sandpo t e n t i ody Ｇ nami cpo l a r i z a t i onme a s u r eme n t s Pr i o rt oexpo su r e,t hespe c imensf o rma s sl os s
１ ４ Ru s tl a e rana l s i s y y Rus tl aye rc an bed i v i dedi n t otwoi nd i v i dua l r t s:al oos eou t e rrus tl aye randacompa c ti nne r pa [ ] rus tl a e r１３ ．Thel oo s eou t e rrus tl aye rwa sr emoved y andco l l e c t edbyaha i rbrush,andt hent her e s i dua l compa c ti nne rrus tl aye rwa sbr okeno f fandco l l e c t Ｇ ed by a shove l．Pha s e ana l i s wa s done wi t ha ys PHILIPSAPDＧ １０XＧ r ayd i f f r a c t ome t e r( wi t hCoa s t a r t)ont heco l l e c t edpowde r s．Mo r l ogyobs e r Ｇ ge pho va t i onswe r emadeont heappe a r anc e so fbo t hou t e r andi nne rrus tl aye r swi t haco l df i e l demi s s i ons c an Ｇ n i nge l e c t r onmi c r os cope ( SEM,HITACHIS Ｇ ４００)． Thes amp l ewi t hi nne rrus tl aye rr ema i neda l one wa ssub e c t edt ou l t r a s on i cv i br a t i oni ne t hano ls o l u Ｇ j t i onf o r１hi no rde rt os epa r a t ep r oduc t sf r om t he i nne rrus tl aye r．Then,t her e su l t i ng so l u t i on wa s d r i a rbonf i lm．Af t e rt hea l coho lvo l a t i l ed, ppedonac appe a r anc e obs e r va t i on and pha s e ana l i s we r e ys madebyaFEIFECNAIG２F２０t r ansmi s s i one l e c Ｇ t r onmi c r os cope (TEM )．I no rde rt ode t e rmi neCr va l enc es t a t eand pha s e sf o rmedont hei nne rrus t , l aye r aPHIQuan t e r aSXM X Ｇ r a t o e l e c t r ons e c Ｇ ypho p t r o s c op e( XPS)wi t ht hee n e r e s o l u t i ono f０ ５eV gyr ( Ala sanod i ct a r t)ope r a t eda tah i cuum o f ge ghva －８ ６ ７×１０ Pawa sus ed．
２ Re s u l t sandDi s c u s s i on
２ １ Di r e c tma s sl o s sme a s u r emen t s F i ２showst he ma s sl os so ft hetwoexpe r i Ｇ g men t a ls t e e l s wi t h exposur et imef o rt her o t a t i ng c l i nde rs t em．F i r s to fa l l,t he ma s sl os so fCr Ｇ y ys con t a i n i ngs t e e li sl owe rt hant ha to fc a rbons t e e li n e a chco r r os i on pe r i od．Se cond l he ma s sl os so f y,t c a rbons t e e li nc r e a s e sa sapowe rf unc t i ono ft heco r Ｇ r os i ont ime,wh i l et he ma s sl os so fCr Ｇ con t a i n i ng , s t e e lr i s e sl i ne a r l nadd i t i on t hed i f f e r enc ebe Ｇ y．I twe en ma s sl os so ft he two expe r imen t a ls t e e l s s e emsve r l li nt hee a r l r r os i onpe r i od,bu t ysma yco suchd i f f e r enc ei sg r adua l l i s t i nc twi t ht heco r r o Ｇ yd s i ont ime．
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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
２ ２ Po t en t i odynami cpo l a r i z a t i onme a s u r emen t s Fo rbo t hs t e e l s,po t en t i odynami c po l a r i z a t i on me a sur emen t swe r ec a r r i edou tont hes amp l e swi t hＧ ou trus tl aye rf o rma t i onr i ta f t e ri n i t i a lco r r os i on gh and s amp l e s wi t h ex i s t i ng rus tl aye ra f t e r７ Ｇ day f l owＧ a c c e l e r a t edco r r os i on exposur e．Ther e su l t i ng l a r i z a t i oncur ve sa r eshowni nF i ３．I tc an be po g s e ent ha twhennorus tl aye rf o rmsont hesur f a c e,
F i ２ Ma s sl o s sv s． t imec u r v eo fe xp e r imen t a ls t e e l s g
bo t hs t e e l sshow as imi l a rc a t hod i ccur r en tdens i t y , l eve l．Howeve r a f t e raso l i drus tl aye rf o rmedon t hes t e e lsur f a c e,Cr Ｇ con t a i n i ng s t e e lshowsar e Ｇ ma rkab l owe rc a t hod i ccur r en tdens i t r ed yl y compa wi t hp l a i nc a rbons t e e l． I nadd i t i on,f o rbo t hs t e e l s, c a t hod i ccur r en tdens i t i e sr e s u l t i ngf r oms amp l e swi t h
( a)Po l a r i z a t i oncur ve so ft hetwoexpe r imen t a lba r es t e e l s; ( b)Po l a r i z a t i oncur ve so ft hetwoexpe r imen t a ls t e e l sc o r r odedf o r７d．
F i ３ Po l a r i z a t i onc u r v e so ft h etwoe xp e r imen t a ls t e e l si nt h ef l owi ng３ ５ma s s％ NaC ls o l u t i on g
as o l i dr u s tl a e ra r el owe rt h a nt ho s eo fs amp l e swi t h Ｇ y , ou tr u s tl a e r w h i c h i n d i c a t e s t h a t r u s t l a e r s u r e s s e s y y pp c a t hod i cr e a c t i on and Cr Ｇ c on t a i n i ng s t e e l de l i ve r s h i ri nh i b i t i one f f e c tt hanp l a i nc a rbons t e e l．Th i s ghe r e su l ta l s odemons t r a t e st ha tf l owＧ a c c e l e r a t edc o r r o Ｇ s i onpr o c e s si sc on t r o l l edbyd i f f us i onve l o c i t fde Ｇ yo [ ,] l a r i z e r( O２)t owa r dst hec a t hod i csu r f a c e８ ９ ． po ２ ３ Crd i s t r i bu t i oni nr u s tl a e r y SEM wa sus edt oobs e r vep r o f i l eo frus tl aye r andde t e rmi net hed i s t r i bu t i ono fa l l oy i nge l emen t s i nt herus tl aye r,a sshowni nF i ４． I ti sc l e a rf r om g F i ４t ha tt herus tl aye ri sc ompo s edo fi nne rand g ou t e rrus tl aye r sf o rbo t h Cr Ｇ c on t a i n i ng and p l a i n c a rbons t e e l s,andt hei nne rl aye ri s mo r ec ompa c t t hant hel oo s eou t e rl aye r． Ene r c t rumana l i s gyspe ys r e su l t sshowt ha tCri sma i n l i s t r i bu t edi nt hei n Ｇ yd ne rrus tl aye r．Th i sphenomenonha sbe enr epo r t ed i np r ev i ous pub l i c a t i onandc a l l edc onc en t r a t i on o f [ １２, １３] Cri nt hei nne rrus tl a e r ．Du et ot h eCre n r i c he d y i nt hei nn e rrus tl aye r,t hef o cuswi l lbemadeont he
i nve s t i t i ono fi nne rrus tl aye rande f f e c to fCron ga t hei nne rrus tl aye rf o rma t i oni nt hef o l l owi ngpa r t s o ft h i spape r． ２ ４ Mo r l o fi nne rr u s tl a e r pho gyo y Theappe a r anc eo fi nne rrus tl aye r son bo t h s t e e l si sg i veni nF i ５． I ti sc l e a r l e ent ha tcomＧ g ys c t ne s so fi nne rrus tl aye ronCr Ｇ con t a i n i ngs t e e li s pa much h i rt hant ha to fp l a i nc a rbon s t e e l．Fo r ghe l a i nc a rbons t e e l,t hei nne rrus tl aye rp r e s en t sa p l a r ro fc r a cksandhenc ei nc r e a s e spe rme a Ｇ genumbe b i l i t equen t l os i ngi t sp r o t e c t i vene s supon y,cons yl subs t r a t e．Compa r ed wi t hp l a i nc a rbon s t e e l,Cr Ｇ con t a i n i ngs t e e lp r oduc e sa much mo r ecompa c ti n Ｇ ne rrus tl aye ri ns i de whe r et hec r a cksappe a ri na sma l lamoun tanda r ef i ne r． ２ ５ TEMob s e r va t i ononi nne rr u s tl a e r y TEMimage so ft hei nne rrus tl aye r sf o rmedon t hetwoexpe r imen t a ls t e e l sa r eshowni nF i ６． I ti s g ev i den tt ha tr ema rkab l ed i f f e r enc ei ss e e ni nbo t hmo Ｇ
I s sue６ Ef f e c to fCronCha r a c t e r i s t i co fRus tLaye rFo rmedonLow Al l oyS t e e l
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F i ４ Di s t r i bu t i ono fCri nt h ei nn e rr u s tl a e rf o rme donc a r bons t e e l( a,c)andCr Ｇ c on t a i n i ngs t e e l( b,d) g y
F i ５ SEM mi c r o r a so fi nn e rr u s tl a e r sf o rme donc a r bons t e e l( a)andCr Ｇ c on t a i n i ngs t e e l( b) g g gh y
r l ogyo frus tpr oduc t sandi t sc r t a l l i n i t l i v Ｇ pho ys yde e r edbytwok i ndso fs t e e l s．Fo rp l a i nc a rbons t e e l, ma s sf l o c cu l en tpr oduc t sa r eobs e r vedi nt hei nne r rus tl aye randi t sd i f f r a c t i on pa t t e rni ssha r a n d p c l e a r． Bu tf o rt heCr Ｇ c on t a i n i ngs t e e l,t herus tp r od Ｇ uc t ss e emt obepowde r i v i ngac l e a r l l un td i f Ｇ y,g yb f r a c t i onpa t t e rn,wh i chsugge s t st ha trus tp r oduc t r eve a l st het endenc fbe c omi ngamo r Ｇ yo phous．Fur t he r EDS ana l i so fd i f f e r en tc o r r o s i on p r oduc t s ys con f i rmst heen r i chmen to fCri nt h ei nn e rr u s tl a e r, y a sshowni nF i ７． g
２ ６ XPSana l s i s y I no rde rt ode t e rmi net hef o rm o fCre l emen t ex i s t i ngi nt hei nne rrus tl aye r,XPSana l i s wa s ys madeont hei nne rrus tl aye rf o rmedont heCr Ｇ con Ｇ , t a i n i ngs t e e l a sshowni nF i ８．Ther e su l tsug Ｇ g s t st ha tCrenr i che si nt hei nne rrus tl aye ri nf o rm ge i c h ha st hes ames t r u c t u r et ea s o fFe２CrO４ , wh yp Fe３O４,andbo t ho ft hema r esp i ne lox i de s． ２ ７ Di s cu s s i on Theenr i chmen to fCri nt hei nne rrus tl aye ri sa
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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
F i ６ TEMima e sandd i f f r a c t i onpa t t e rn so fi nn e rr u s tl a e r sf o rme donc a r bons t e e l( a,c)andCr Ｇ c on t a i n i ngs t e e l( b,d) g g y
F i ７ EDSana l s i so fd i f f e r en tc o r r o s i onp r odu c t sf o rme donc a r bons t e e l( a)andCr Ｇ c on t a i n i ngs t e e l( b) g y
c ruc i a lf a c t o rc on t r i bu t i ngt oimp r ovec o r r o s i onr e Ｇ s i s t anc eo fexpe r imen t a ls t e e l．Unde rt hec ond i t i on o ff l owi ng NaCls o l u t i on,c o r r o s i onr a t eo fme t a li s e s s en t i a l l on t r o l l edbyt hed i f f us i onr a t eo fO２t o Ｇ yc
wa rdsme t a lsur f a c e,andi nt hecour s eo fco r r os i on, i ti sde t e rmi nedbyf l owr a t eandi ndependen to fma Ｇ [ ８, ９] , t e r i a lna t ur e ．Ast heco r r os i on p r oc e eds arus t l aye rf o rmedont heme t a lsur f a c esupp r e s s e st hed i f Ｇ
I s sue６ Ef f e c to fCronCha r a c t e r i s t i co fRus tLaye rFo rmedonLow Al l oyS t e e l
６０７
t hef o rma t i ono ff i ne rFe２CrO４ pa r t i c l e sc ans i i f i Ｇ gn c an t l t r i bu t et ot hecompa c t ne s so frus tl aye r y con andhenc er ema rkab l i m r o v et h ei n n e rr u s tl a e y p yr r o t e c t i ono fsubs t r a t ef r omco r r os i on． p
３ Conc l u s i on s
F i ８ Sp e c t r umo fCr２p f r omt h ei nn e rr u s to f g e xp e r imen t a ls t e e l sob t a i n e dbyXPS
f us i ono fdepo l a r i z e rt owa r dst hec a t hodeandhenc e r educ e st hee l e c t r o chemi c a lr e a c t i onr a t e．Asar e su l t , o ft h i si nh i b i t i one f f e c tt hec o r r o s i onr a t eha sbe en r educ ed． I nt h i sc on t ex t,pe r f o rmanc eo frus tl aye r i sakeyf a c t o rt ode t e rmi net hec o r r o s i onr e s i s t anc e o fme t a l．Ther e su l t sshowni nF i ２i nd i c a t et ha t g f o rmedc o r r o s i onp r oduc t sc anhe l ode c r e a s et he pt d i s so l u t i onr a t eo fanodet oac e r t a i nex t en t,andt h i s con t r i bu t i ont o Cr Ｇ c on t a i n i ngs t e e li s much g r e a t e r t hant op l a i nc a rbons t e e l．Bu tt her e a c t i onr a t eon c a t hodes i dei sneve r t he l e s sl owe rt hant ha to fanode s i de．Ac c o r d i ng l hee l e c t r o chemi c a lc o r r o s i onr e Ｇ y,t a c t i oni ss t i l ldomi na t edbyc a t hod i cr e a c t i oneve ra f Ｇ t e ras o l i drus tl aye rf o rmedont he me t a lsu r f a c e． Thef a c tt ha tc a t hod i ccu r r en tdens i t o rCr Ｇ c on t a i Ｇ yf n i ngs t e e li sr ema rkab l owe rt hant ha to fp l a i nc a r Ｇ yl bons t e e lsugge s t st ha trus tl aye rf o rmedonCr Ｇ con Ｇ t a i n i ngs t e e limpo s e ss t r onge rsupp r e s s i one f f e c to f depo l a r i z e rd i f f us i ont owa r dsme t a lsu r f a c eandf e a Ｇ t ur e sbe t t e rpr o t e c t i vene s so fc o r r o s i onf o rs ub s t r a t e． Compa r ed wi t hp l a i nc a rbons t e e l,Cr Ｇ c on t a i Ｇ n i ngs t e e lde l i ve r sa mo r ec ompa c ti nne rrus tl aye r andh i rc o r r o s i onr e s i s t anc et of l owi ngs a l twa t e r． ghe Te s tr e su l t sshowt ha tf i nepowde r r oduc tappe a r s yp i nt hei nne rrus tl aye rf o rmedonCr Ｇ c on t a i n i ngs t e e l． Pr ev i ousr e s e a r chpo i n t edou tt ha tFe ＧCrox i de sa r e [ , ] ve r i ne,wi t h mo s to ft heml e s st han８nm １２ １３ ． yf Rega r d i ngt heXRDandd i f f r a c t i onpa t t e rnana l i s, ys t hef i neg r a i npa r t i c l e wi l lc aus eab l un td i f f r a c t i on t t e rnandgene r a t eamorphouse f f e c t．Mor eove r, pa
( １)Co r r os i onma s sl os so fCr Ｇ con t a i n i ngs t e e l i sl owe rt hant ha to fc a rbons t e e l,be c aus eCr Ｇ con Ｇ t a i n i ngs t e e lde l i ve r samo r ecompa c ti nne rrus tl aye r wh i chh i nde r st hed i f f us i ono fdepo l a r i z e rt owa rds t he me t a lsur f a c e and henc er educ e st he e l e c t r o Ｇ chemi c a lr e a c t i onr a t e．Th i si sma o rcon t r i bu t i ont o j t heg r e a timp r ovemen ti nt her e s i s t anc et of l owＧ a c Ｇ c e l e r a t edco r r os i on． ( ２)Crenr i che si nt hei nne rrus tl aye ri nf o rm o fFe２CrO４．Cre n r i c hme n tr e s u l t si namo r st e nd Ｇ phou , e n c cur r i ngi nt hei nne rrus tl aye r wh i chi swe l l yoc a s soc i a t edwi t hf i neg r a i ns i z eo fFe２CrO４ ．Thef o r Ｇ ma t i ono ff i ne rFe２CrO４ pa r t i c l e sc ans i i f i c an t l gn y con t r i bu t et ot hec omp a c t n e s so fr u s tl a e randhe n c e y r ema rkab l ovet hei nne rrus tl aye rp r o t e c t i on yimpr o fsubs t r a t ef r omco r r os i on． Re f e r enc e s:
[ １] KD． Ef i r d,E J．Wr i t,J A． Bo r o s,T G．Ha i l ey,Co r r o s i on gh ４９ ( １９９３)９９２ Ｇ １００３． [ ２] E．He i t z．Chemo ＧMe chan i c a l,Co r r o s i on４７ ( １９９１)１３５ Ｇ １４５． [ ３] WH．Ahmed,Anna l so fNuc l e a rEne r ７ ２０１０)５９８ Ｇ ６０５． gy３ ( [ ４] V．Ka i n,S．Ro c howdhu r d a b a d i,D K．Ba r u a,Eng． y y,P．Ahme Fa i l．Ana l． １８ ( ２０１１)２０２８ Ｇ ２０４１． [ ５] S．Na s r a z adan i,R K．Nakka,D．Hopk i ns,J．S t evens,I n t． J． Pr e s s．Ve s s e l sP i ８６ ( ２００９)８４５ Ｇ ８５２． p． [ ６] HR．Cops on,Co r r o s i on１６ ( １９６０)８６ Ｇ ９２． [ ７] G．Cr agno l i no,Co r r o s i on ′ ８７,１９８７,８６/１ Ｇ ８６/１１． [ ８] T Y． Ch e n,A A．Mo c c a r i,D D．Ma c don a l d,Co r r o s i on４８ ( １９９２) ２３９ Ｇ ２５５． [ r r o s i on５１ ( １９９５)７７３ Ｇ ９] S．Ne s i c,GT． So l v i,J．Ene rhaug,Co ７８７． [ １０] NK．Ni sh imur a,T．Ma suda,J． I ns t．Me t a l s６３ ( １９９９)１１３３ Ｇ １１４２． [ １１] I． Suzuk i,N．Ma suko,Y．Hi s ama t su,Co r r o s． Sc i． １９ ( １９７９) ５２１ Ｇ ５３５． [ １２] M．Yama sh i t a,T． Sh imi zu,H．Kon i sh i,J．Mi zuk i,H．Uch i Ｇ da,Co r r o s． Sc i． ４５ ( ２００３)３８１ Ｇ ３９４． [ １３] M．Yama s h i t a,H．Mi i,Y．Ma t s ud a,Co r r o s． S c i． ３６ ( １９９４) yuk ２８３ Ｇ ２９９． [ W．Chapman,J．El e c t r o chem． So c． １４] S C．Yen,J S．Wang,T １３９ ( １９９２)２２３１ Ｇ ２２３８． [ １５] HP．Ha c k,HW．P i c k e r i ng,J．E l e c t r o c h em．So c． １３８ ( １９９１) ６９０ Ｇ ６９５．
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ６,２ ３( ６):６ ０ ２ Ｇ ６ ０ ７
Ef f e c to fCronCha r a c t e r i s t i co fRu s tLay e rFo rme donLowAl l o y S t e e li nF l owＧ a c c e l e r a t e dCo r r o s i onEnv i r onme n t FengCHAI, ShanJ IANG, Ca i Ｇ f uYANG
( Depa r tmen to fEng i ne e r i ngS t e e l s,Cen t r a lI r onandS t e e lRe s e a r chI ns i t i t u t e,Be i i ng１０００８１,Ch i na) j Ab s t r a c t:Thef l owＧ a c c e l e r a t edc o r r o s i onexpe r imen t swe r ec a r r i edou tt or e s e a r cht hee f f e c to fCront her us tl aye r s f o rmedont hec a r bons t e e la ndCr Ｇ c on t a i n i ngs t e e l,a swe l la st h es t r u c t u r eo fr u s tl a e ro ft h etwoe xp e r ime n t a ls t e e l s． y Thei n f l uenc eo fCront hef l owＧ a c c e l e r a t edc o r r o s i onr e s i s t anc eandt hec o r r o s i on mo r l ogyo fi nne rr us tl aye r pho f o rmedont heCr Ｇ c on t a i n i ngs t e e lwe r es t ud i e dbyt h e me t hod so fpo l a r i z a t i onc u r v e s,s c a nn i nge l e c t r on mi c r o s c op e, t r a n smi s s i one l e c t r onmi c r o s c op e,a ndX Ｇ r a t o e l e c t r ons e c t r o s c op e． Th ed i s t r i bu t i ono fCrandi t sf o rmo fex i s t enc ei n ypho p
t hei nne rr us tl aye rwe r eana l z ed．Ther e su l t sshowt ha tc o r r odedma s sl o s so fCr Ｇ c on t a i n i ngs t e e li sl owe rt hant ha t y o fc a r bons t e e landi t si nne rr us tl aye ri sc ompa c t．Crex i s t si nt hef o rmo fFe２CrO４ andi sen r i chedi nt hei nne rr us t l aye r．Th i sc onc en t r a t i onc ou l dmaket hei nne rr us tl aye rexh i b i tt het endencyo famo r i sphenomenoni sr e Ｇ phous．Th l a t edt of i neFe２CrO４ ．Thei nne rr us tl aye rbe c ome smo r ec ompa c tbe c aus eo ft hef o rma t i ono ff i neFe２CrO４ ,andt he r o t e c t i vene s so fi nne rr us tl aye rc ou l dbeimp r ovedr ema r kab l p y． Ke r d s:Cr Ｇ c on t a i n i ngs t e e l;f l owＧ a c c e l e r a t edc o r r o s i on;i nne rr us tl aye r;amo r phous ywo
Me t a l se r odedbyf l u i dc ommon l akep l a c ei n yt , a l lk i ndso fi ndus t r i a lf a c i l i t i e s and wi l lc aus es e r i Ｇ ousde s t ruc t i vee f f e c twh i chc ou l dl e adt oasudden f a i l ur eo f equ i ti ns e r v i c e．Me t a lc o r r os i on pmen c aus edbyf l u i di se s s en t i a l l of l owＧ a c c e l e r a t ed yduet co r r os i on ( FAC),wh i ch s i i f i c an t l educ e st he gn yr t h i ckne s so f ma t e r i a l whe r ef l u i d pa s s e st hr ough,
andhenc ee r ode st hec omponen t１Ｇ５ ．I n t ens i ver e Ｇ s e a r chha sbe endoneont hebehav i o ro ff l owＧ a c c e l Ｇ [] [] e r a t edc o r r o s i on． Cops on６ andCr agno l i no７ po i n t ed ou tt ha ti nc r e a s i ngf l owr a t ewou l df a c i l i t a t ec o r r o Ｇ [] s i onr a t eo fme t a l．Re s e a r che sby Chene ta l ８ and [] Ne s i ce ta l ９ sugge s t edt ha tt hei nc r e a s eo fc o r r o Ｇ s i onr a t ewa se s s en t i a l l t t r i bu t edt ot h i sphenome Ｇ ya nonwhe r ef l owf avo r edt hed i f f us i ono fdepo l a r i z a Ｇ t i ont owa r ds me t a lsu r f a c e,c ons equen t l c c e l e r a Ｇ ya t i ngt hee l e c t r o chemi c a lr e a c t i on． Lowa l l oyeds t e e l sbe i ngl ongt e rmexpo su r et o co r r os i onenv i r onmen ta r ep r onet orus tl aye rf o rma Ｇ t i on ont hes t e e lsu r f a c e s．I t ha s be en c onc l uded f r omt her e su l t so fex t ens i vei nve s t i t i ononrus t ga l aye r sonwe a t he r i ngs t e e l st h a tr u s tl a e r l a sas i Ｇ y py g n i f i c an tr o l ei nimp r o v i ngt h ec o r r o s i onr e s i s t a n c eo fl ow [ , ] a l l oyeds t e e l s１０ １１ ．Th er u s tl a e rf o rme dont h es t e e l y [
]
sur f a c ei senr i chmen to fa l l oy i nge l emen t s．Among [ , ] , t hem Cri sac r u c i a le l eme n t． Pub l i s he dr e r t s１２ １３ i n Ｇ po d i c a t edt ha tCrenr i chedi nt hei nne rrus tl aye rena Ｇ b l edi tt or ep l a c eFea t omo fα ＧFeOOHandt husr e Ｇ ( , ) su l t edi nt hef o rma t i ono ff i ne rα Ｇ Fe１－x Crx OOH (mos to ft hem wi t hs i z el e s st han８nm),wh i chimＧ r ovedt hec omp a c t n e s so fi nn e rr u s tl a e ronwe a t he Ｇ p y r i ngs t e e l s． Add i ngasma l lamoun to fCri nc a rbons t e e lc an imp r ovet hes e r v i c el i f eo fp i l i nesot ha t mak i ng pe t hes e r v i c el i f eo fp i l i nei sequa lt ot ha to fve s s e l． pe Howeve r,f ewpub l i c a t i onsr eve a l edhowCrp l aysi t s r o l ei nrus tl aye runde rt heimpa c to fs a l twa t e r． I n t h i spape r,t hecomponen t sandpha s e si nrus tl aye r have be en i nve s t i t ed．Th i s pape ra l so demon Ｇ ga s t r a t e st hee f f e c to fCront herus tl aye randme cha Ｇ n i sm o fhow Crc animp r ovet he p r o t e c t i vene s so f rus tl aye runde rt heimpa c to fs a l twa t e r．
１ Exp e r imen t a l
１ １ Ma t e r i a l spr e r a t i on pa Twos t e e l sus edi nt h i ss t udywe r esme l t edi na va cuumi nduc t i onf urna c e．Af t e rf o r i ngt hei ngo t s g t ob l ocks,t he b l ocks we r e ho tr o l l edi n t op l a t e s
B i o r aphy: FengCHAI,Do c t o r,Sen i o rEng i ne e r; E Ｇma i l: cha i f eng＠c i s r i c omcn; Re c e i v e dDa t e: May１４,２０１５ g
I s sue６ Ef f e c to fCronCha r a c t e r i s t i co fRus tLaye rFo rmedonLow Al l oyS t e e l
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wi t ht h i ckne s so f１３ mm．Th ec h emi c a lc ompo s i t i on s me a sur emen t swe r er i ns edwi t ha c e t oneandd r i edby o ft heexpe r imen t a ls t e e l sa r eshowni n Tab l e１． a i r,t he nwe i dbyami c r ob a l an c e．Af t e re a c ht imeo f ghe , The s etwos t e e l shaves ameba s echemi s t r e x c e t e x o s u r e t h es e c i m e n s w e r ed e s c a l e db i mm e r Ｇ y p p p y f o rCradd i t i on． s i oni nHClso l u t i on,andt henr i ns edi nd i s t i l l edwa Ｇ t e rand a c e t one suc c e s s i ve l t e ra i r Ｇ d r i ed,t he y．Af Tab l e１ Ch emi c a lc ompo s i t i on so fe xp e r imen t a ls t e e l s spe c imenswe r er ewe i no rde rt oc a l cu l a t et he ghedi ma s s％ ma s sl os sduet oco r r os i on． S t e e l C Mn S i P S Cr Po t en t i odynami c po l a r i z a t i oncur ve s we r eob Ｇ Ca r bons t e e l ０ ０８２ ０ ６３ ０ ２４ ０ ０１２ ０ ００３６ － t a i nedus i ngaPr i nc e t on２７３Ae l e c t r ochemi c a lwo rkＧ Cr Ｇ c on t a i n i ng s t a t i onwi t hvo l t ages c anr a t eo f３０ mV/mi n． ０ ０７８ ０ ６０ ０ ２１ ０ ０１８ ０ ００２０ ２ s t e e l
１ ２ Sa l twa t e rf l owＧ a c c e l e r a t e dc o r r o s i ons imu l a t i on １ ２ １ Expe r imen t a ls e t up Fo r c e d Ｇ c onv e c t i v er o t a t i ng Ｇ c l i nd e re l e c t r od eme t hＧ y od wa s wi de l edf o ri nve s t i t i ngt hec o r r os i on y us ga [ , ] behav i o ro fme t a le xpo s u r et of l u i d me d i a１４ １５ ．Ba s e d , on p r ev i ous s t ud i e s af l owＧ a c c e l e r a t ed c o r r os i on s imu l a t i ondev i c ewa sde s i o rt h i spu r s e．The gnedf po s chema t i cs e t upi si l l us t r a t edi nF i １． g
F i １ S ch ema t i ci l l u s t r a t i ono ft h eequ i tu s e df o r g pmen f l owＧ a c c e l e r a t e dc o r r o s i one xp e r imen t
１ ２ ２ Co r r o s i onparame t e r s A ７ Ｇ day du r a t i onc o r r o s i ont e s tha sbe en pe r Ｇ f o rmedi na３ ５ma s s％ NaCls o l u t i onwi t hf l owve Ｇ l oc i t f１ ５ m/sandt empe r a t u r eo f２０ ℃． yo １ ２ ３ Sampl e s Th ed ime n s i ono fs amp l e su s e df o rc o r r o s i ont e s ti s ２０mm ( l e ng t h)×２０ mm ( w i d t h)×２ mm ( d e t h)．A p ho l ewi t hd i ame t e ro f２mmi spunchedonbo t hends f o rt hepu r s eo fhang i ngs amp l e．Be f o r et e s t,t he po sur f a c esub e c t edt oexpo su r ewa sg r adua l l l i shed j ypo t o１０００g r i tbyab r a s i vepape randt henc l e anedby e t hano l． １ ３ Di r e c tma s sl o s sme a s u r eme n t sandpo t e n t i ody Ｇ nami cpo l a r i z a t i onme a s u r eme n t s Pr i o rt oexpo su r e,t hespe c imensf o rma s sl os s
１ ４ Ru s tl a e rana l s i s y y Rus tl aye rc an bed i v i dedi n t otwoi nd i v i dua l r t s:al oos eou t e rrus tl aye randacompa c ti nne r pa [ ] rus tl a e r１３ ．Thel oo s eou t e rrus tl aye rwa sr emoved y andco l l e c t edbyaha i rbrush,andt hent her e s i dua l compa c ti nne rrus tl aye rwa sbr okeno f fandco l l e c t Ｇ ed by a shove l．Pha s e ana l i s wa s done wi t ha ys PHILIPSAPDＧ １０XＧ r ayd i f f r a c t ome t e r( wi t hCoa s t a r t)ont heco l l e c t edpowde r s．Mo r l ogyobs e r Ｇ ge pho va t i onswe r emadeont heappe a r anc e so fbo t hou t e r andi nne rrus tl aye r swi t haco l df i e l demi s s i ons c an Ｇ n i nge l e c t r onmi c r os cope ( SEM,HITACHIS Ｇ ４００)． Thes amp l ewi t hi nne rrus tl aye rr ema i neda l one wa ssub e c t edt ou l t r a s on i cv i br a t i oni ne t hano ls o l u Ｇ j t i onf o r１hi no rde rt os epa r a t ep r oduc t sf r om t he i nne rrus tl aye r．Then,t her e su l t i ng so l u t i on wa s d r i a rbonf i lm．Af t e rt hea l coho lvo l a t i l ed, ppedonac appe a r anc e obs e r va t i on and pha s e ana l i s we r e ys madebyaFEIFECNAIG２F２０t r ansmi s s i one l e c Ｇ t r onmi c r os cope (TEM )．I no rde rt ode t e rmi neCr va l enc es t a t eand pha s e sf o rmedont hei nne rrus t , l aye r aPHIQuan t e r aSXM X Ｇ r a t o e l e c t r ons e c Ｇ ypho p t r o s c op e( XPS)wi t ht hee n e r e s o l u t i ono f０ ５eV gyr ( Ala sanod i ct a r t)ope r a t eda tah i cuum o f ge ghva －８ ６ ７×１０ Pawa sus ed．
２ Re s u l t sandDi s c u s s i on
２ １ Di r e c tma s sl o s sme a s u r emen t s F i ２showst he ma s sl os so ft hetwoexpe r i Ｇ g men t a ls t e e l s wi t h exposur et imef o rt her o t a t i ng c l i nde rs t em．F i r s to fa l l,t he ma s sl os so fCr Ｇ y ys con t a i n i ngs t e e li sl owe rt hant ha to fc a rbons t e e li n e a chco r r os i on pe r i od．Se cond l he ma s sl os so f y,t c a rbons t e e li nc r e a s e sa sapowe rf unc t i ono ft heco r Ｇ r os i ont ime,wh i l et he ma s sl os so fCr Ｇ con t a i n i ng , s t e e lr i s e sl i ne a r l nadd i t i on t hed i f f e r enc ebe Ｇ y．I twe en ma s sl os so ft he two expe r imen t a ls t e e l s s e emsve r l li nt hee a r l r r os i onpe r i od,bu t ysma yco suchd i f f e r enc ei sg r adua l l i s t i nc twi t ht heco r r o Ｇ yd s i ont ime．
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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
２ ２ Po t en t i odynami cpo l a r i z a t i onme a s u r emen t s Fo rbo t hs t e e l s,po t en t i odynami c po l a r i z a t i on me a sur emen t swe r ec a r r i edou tont hes amp l e swi t hＧ ou trus tl aye rf o rma t i onr i ta f t e ri n i t i a lco r r os i on gh and s amp l e s wi t h ex i s t i ng rus tl aye ra f t e r７ Ｇ day f l owＧ a c c e l e r a t edco r r os i on exposur e．Ther e su l t i ng l a r i z a t i oncur ve sa r eshowni nF i ３．I tc an be po g s e ent ha twhennorus tl aye rf o rmsont hesur f a c e,
F i ２ Ma s sl o s sv s． t imec u r v eo fe xp e r imen t a ls t e e l s g
bo t hs t e e l sshow as imi l a rc a t hod i ccur r en tdens i t y , l eve l．Howeve r a f t e raso l i drus tl aye rf o rmedon t hes t e e lsur f a c e,Cr Ｇ con t a i n i ng s t e e lshowsar e Ｇ ma rkab l owe rc a t hod i ccur r en tdens i t r ed yl y compa wi t hp l a i nc a rbons t e e l． I nadd i t i on,f o rbo t hs t e e l s, c a t hod i ccur r en tdens i t i e sr e s u l t i ngf r oms amp l e swi t h
( a)Po l a r i z a t i oncur ve so ft hetwoexpe r imen t a lba r es t e e l s; ( b)Po l a r i z a t i oncur ve so ft hetwoexpe r imen t a ls t e e l sc o r r odedf o r７d．
F i ３ Po l a r i z a t i onc u r v e so ft h etwoe xp e r imen t a ls t e e l si nt h ef l owi ng３ ５ma s s％ NaC ls o l u t i on g
as o l i dr u s tl a e ra r el owe rt h a nt ho s eo fs amp l e swi t h Ｇ y , ou tr u s tl a e r w h i c h i n d i c a t e s t h a t r u s t l a e r s u r e s s e s y y pp c a t hod i cr e a c t i on and Cr Ｇ c on t a i n i ng s t e e l de l i ve r s h i ri nh i b i t i one f f e c tt hanp l a i nc a rbons t e e l．Th i s ghe r e su l ta l s odemons t r a t e st ha tf l owＧ a c c e l e r a t edc o r r o Ｇ s i onpr o c e s si sc on t r o l l edbyd i f f us i onve l o c i t fde Ｇ yo [ ,] l a r i z e r( O２)t owa r dst hec a t hod i csu r f a c e８ ９ ． po ２ ３ Crd i s t r i bu t i oni nr u s tl a e r y SEM wa sus edt oobs e r vep r o f i l eo frus tl aye r andde t e rmi net hed i s t r i bu t i ono fa l l oy i nge l emen t s i nt herus tl aye r,a sshowni nF i ４． I ti sc l e a rf r om g F i ４t ha tt herus tl aye ri sc ompo s edo fi nne rand g ou t e rrus tl aye r sf o rbo t h Cr Ｇ c on t a i n i ng and p l a i n c a rbons t e e l s,andt hei nne rl aye ri s mo r ec ompa c t t hant hel oo s eou t e rl aye r． Ene r c t rumana l i s gyspe ys r e su l t sshowt ha tCri sma i n l i s t r i bu t edi nt hei n Ｇ yd ne rrus tl aye r．Th i sphenomenonha sbe enr epo r t ed i np r ev i ous pub l i c a t i onandc a l l edc onc en t r a t i on o f [ １２, １３] Cri nt hei nne rrus tl a e r ．Du et ot h eCre n r i c he d y i nt hei nn e rrus tl aye r,t hef o cuswi l lbemadeont he
i nve s t i t i ono fi nne rrus tl aye rande f f e c to fCron ga t hei nne rrus tl aye rf o rma t i oni nt hef o l l owi ngpa r t s o ft h i spape r． ２ ４ Mo r l o fi nne rr u s tl a e r pho gyo y Theappe a r anc eo fi nne rrus tl aye r son bo t h s t e e l si sg i veni nF i ５． I ti sc l e a r l e ent ha tcomＧ g ys c t ne s so fi nne rrus tl aye ronCr Ｇ con t a i n i ngs t e e li s pa much h i rt hant ha to fp l a i nc a rbon s t e e l．Fo r ghe l a i nc a rbons t e e l,t hei nne rrus tl aye rp r e s en t sa p l a r ro fc r a cksandhenc ei nc r e a s e spe rme a Ｇ genumbe b i l i t equen t l os i ngi t sp r o t e c t i vene s supon y,cons yl subs t r a t e．Compa r ed wi t hp l a i nc a rbon s t e e l,Cr Ｇ con t a i n i ngs t e e lp r oduc e sa much mo r ecompa c ti n Ｇ ne rrus tl aye ri ns i de whe r et hec r a cksappe a ri na sma l lamoun tanda r ef i ne r． ２ ５ TEMob s e r va t i ononi nne rr u s tl a e r y TEMimage so ft hei nne rrus tl aye r sf o rmedon t hetwoexpe r imen t a ls t e e l sa r eshowni nF i ６． I ti s g ev i den tt ha tr ema rkab l ed i f f e r enc ei ss e e ni nbo t hmo Ｇ
I s sue６ Ef f e c to fCronCha r a c t e r i s t i co fRus tLaye rFo rmedonLow Al l oyS t e e l
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F i ４ Di s t r i bu t i ono fCri nt h ei nn e rr u s tl a e rf o rme donc a r bons t e e l( a,c)andCr Ｇ c on t a i n i ngs t e e l( b,d) g y
F i ５ SEM mi c r o r a so fi nn e rr u s tl a e r sf o rme donc a r bons t e e l( a)andCr Ｇ c on t a i n i ngs t e e l( b) g g gh y
r l ogyo frus tpr oduc t sandi t sc r t a l l i n i t l i v Ｇ pho ys yde e r edbytwok i ndso fs t e e l s．Fo rp l a i nc a rbons t e e l, ma s sf l o c cu l en tpr oduc t sa r eobs e r vedi nt hei nne r rus tl aye randi t sd i f f r a c t i on pa t t e rni ssha r a n d p c l e a r． Bu tf o rt heCr Ｇ c on t a i n i ngs t e e l,t herus tp r od Ｇ uc t ss e emt obepowde r i v i ngac l e a r l l un td i f Ｇ y,g yb f r a c t i onpa t t e rn,wh i chsugge s t st ha trus tp r oduc t r eve a l st het endenc fbe c omi ngamo r Ｇ yo phous．Fur t he r EDS ana l i so fd i f f e r en tc o r r o s i on p r oduc t s ys con f i rmst heen r i chmen to fCri nt h ei nn e rr u s tl a e r, y a sshowni nF i ７． g
２ ６ XPSana l s i s y I no rde rt ode t e rmi net hef o rm o fCre l emen t ex i s t i ngi nt hei nne rrus tl aye r,XPSana l i s wa s ys madeont hei nne rrus tl aye rf o rmedont heCr Ｇ con Ｇ , t a i n i ngs t e e l a sshowni nF i ８．Ther e su l tsug Ｇ g s t st ha tCrenr i che si nt hei nne rrus tl aye ri nf o rm ge i c h ha st hes ames t r u c t u r et ea s o fFe２CrO４ , wh yp Fe３O４,andbo t ho ft hema r esp i ne lox i de s． ２ ７ Di s cu s s i on Theenr i chmen to fCri nt hei nne rrus tl aye ri sa
６０６
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
F i ６ TEMima e sandd i f f r a c t i onpa t t e rn so fi nn e rr u s tl a e r sf o rme donc a r bons t e e l( a,c)andCr Ｇ c on t a i n i ngs t e e l( b,d) g g y
F i ７ EDSana l s i so fd i f f e r en tc o r r o s i onp r odu c t sf o rme donc a r bons t e e l( a)andCr Ｇ c on t a i n i ngs t e e l( b) g y
c ruc i a lf a c t o rc on t r i bu t i ngt oimp r ovec o r r o s i onr e Ｇ s i s t anc eo fexpe r imen t a ls t e e l．Unde rt hec ond i t i on o ff l owi ng NaCls o l u t i on,c o r r o s i onr a t eo fme t a li s e s s en t i a l l on t r o l l edbyt hed i f f us i onr a t eo fO２t o Ｇ yc
wa rdsme t a lsur f a c e,andi nt hecour s eo fco r r os i on, i ti sde t e rmi nedbyf l owr a t eandi ndependen to fma Ｇ [ ８, ９] , t e r i a lna t ur e ．Ast heco r r os i on p r oc e eds arus t l aye rf o rmedont heme t a lsur f a c esupp r e s s e st hed i f Ｇ
I s sue６ Ef f e c to fCronCha r a c t e r i s t i co fRus tLaye rFo rmedonLow Al l oyS t e e l
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t hef o rma t i ono ff i ne rFe２CrO４ pa r t i c l e sc ans i i f i Ｇ gn c an t l t r i bu t et ot hecompa c t ne s so frus tl aye r y con andhenc er ema rkab l i m r o v et h ei n n e rr u s tl a e y p yr r o t e c t i ono fsubs t r a t ef r omco r r os i on． p
３ Conc l u s i on s
F i ８ Sp e c t r umo fCr２p f r omt h ei nn e rr u s to f g e xp e r imen t a ls t e e l sob t a i n e dbyXPS
f us i ono fdepo l a r i z e rt owa r dst hec a t hodeandhenc e r educ e st hee l e c t r o chemi c a lr e a c t i onr a t e．Asar e su l t , o ft h i si nh i b i t i one f f e c tt hec o r r o s i onr a t eha sbe en r educ ed． I nt h i sc on t ex t,pe r f o rmanc eo frus tl aye r i sakeyf a c t o rt ode t e rmi net hec o r r o s i onr e s i s t anc e o fme t a l．Ther e su l t sshowni nF i ２i nd i c a t et ha t g f o rmedc o r r o s i onp r oduc t sc anhe l ode c r e a s et he pt d i s so l u t i onr a t eo fanodet oac e r t a i nex t en t,andt h i s con t r i bu t i ont o Cr Ｇ c on t a i n i ngs t e e li s much g r e a t e r t hant op l a i nc a rbons t e e l．Bu tt her e a c t i onr a t eon c a t hodes i dei sneve r t he l e s sl owe rt hant ha to fanode s i de．Ac c o r d i ng l hee l e c t r o chemi c a lc o r r o s i onr e Ｇ y,t a c t i oni ss t i l ldomi na t edbyc a t hod i cr e a c t i oneve ra f Ｇ t e ras o l i drus tl aye rf o rmedont he me t a lsu r f a c e． Thef a c tt ha tc a t hod i ccu r r en tdens i t o rCr Ｇ c on t a i Ｇ yf n i ngs t e e li sr ema rkab l owe rt hant ha to fp l a i nc a r Ｇ yl bons t e e lsugge s t st ha trus tl aye rf o rmedonCr Ｇ con Ｇ t a i n i ngs t e e limpo s e ss t r onge rsupp r e s s i one f f e c to f depo l a r i z e rd i f f us i ont owa r dsme t a lsu r f a c eandf e a Ｇ t ur e sbe t t e rpr o t e c t i vene s so fc o r r o s i onf o rs ub s t r a t e． Compa r ed wi t hp l a i nc a rbons t e e l,Cr Ｇ c on t a i Ｇ n i ngs t e e lde l i ve r sa mo r ec ompa c ti nne rrus tl aye r andh i rc o r r o s i onr e s i s t anc et of l owi ngs a l twa t e r． ghe Te s tr e su l t sshowt ha tf i nepowde r r oduc tappe a r s yp i nt hei nne rrus tl aye rf o rmedonCr Ｇ c on t a i n i ngs t e e l． Pr ev i ousr e s e a r chpo i n t edou tt ha tFe ＧCrox i de sa r e [ , ] ve r i ne,wi t h mo s to ft heml e s st han８nm １２ １３ ． yf Rega r d i ngt heXRDandd i f f r a c t i onpa t t e rnana l i s, ys t hef i neg r a i npa r t i c l e wi l lc aus eab l un td i f f r a c t i on t t e rnandgene r a t eamorphouse f f e c t．Mor eove r, pa
( １)Co r r os i onma s sl os so fCr Ｇ con t a i n i ngs t e e l i sl owe rt hant ha to fc a rbons t e e l,be c aus eCr Ｇ con Ｇ t a i n i ngs t e e lde l i ve r samo r ecompa c ti nne rrus tl aye r wh i chh i nde r st hed i f f us i ono fdepo l a r i z e rt owa rds t he me t a lsur f a c e and henc er educ e st he e l e c t r o Ｇ chemi c a lr e a c t i onr a t e．Th i si sma o rcon t r i bu t i ont o j t heg r e a timp r ovemen ti nt her e s i s t anc et of l owＧ a c Ｇ c e l e r a t edco r r os i on． ( ２)Crenr i che si nt hei nne rrus tl aye ri nf o rm o fFe２CrO４．Cre n r i c hme n tr e s u l t si namo r st e nd Ｇ phou , e n c cur r i ngi nt hei nne rrus tl aye r wh i chi swe l l yoc a s soc i a t edwi t hf i neg r a i ns i z eo fFe２CrO４ ．Thef o r Ｇ ma t i ono ff i ne rFe２CrO４ pa r t i c l e sc ans i i f i c an t l gn y con t r i bu t et ot hec omp a c t n e s so fr u s tl a e randhe n c e y r ema rkab l ovet hei nne rrus tl aye rp r o t e c t i on yimpr o fsubs t r a t ef r omco r r os i on． Re f e r enc e s:
[ １] KD． Ef i r d,E J．Wr i t,J A． Bo r o s,T G．Ha i l ey,Co r r o s i on gh ４９ ( １９９３)９９２ Ｇ １００３． [ ２] E．He i t z．Chemo ＧMe chan i c a l,Co r r o s i on４７ ( １９９１)１３５ Ｇ １４５． [ ３] WH．Ahmed,Anna l so fNuc l e a rEne r ７ ２０１０)５９８ Ｇ ６０５． gy３ ( [ ４] V．Ka i n,S．Ro c howdhu r d a b a d i,D K．Ba r u a,Eng． y y,P．Ahme Fa i l．Ana l． １８ ( ２０１１)２０２８ Ｇ ２０４１． [ ５] S．Na s r a z adan i,R K．Nakka,D．Hopk i ns,J．S t evens,I n t． J． Pr e s s．Ve s s e l sP i ８６ ( ２００９)８４５ Ｇ ８５２． p． [ ６] HR．Cops on,Co r r o s i on１６ ( １９６０)８６ Ｇ ９２． [ ７] G．Cr agno l i no,Co r r o s i on ′ ８７,１９８７,８６/１ Ｇ ８６/１１． [ ８] T Y． Ch e n,A A．Mo c c a r i,D D．Ma c don a l d,Co r r o s i on４８ ( １９９２) ２３９ Ｇ ２５５． [ r r o s i on５１ ( １９９５)７７３ Ｇ ９] S．Ne s i c,GT． So l v i,J．Ene rhaug,Co ７８７． [ １０] NK．Ni sh imur a,T．Ma suda,J． I ns t．Me t a l s６３ ( １９９９)１１３３ Ｇ １１４２． [ １１] I． Suzuk i,N．Ma suko,Y．Hi s ama t su,Co r r o s． Sc i． １９ ( １９７９) ５２１ Ｇ ５３５． [ １２] M．Yama sh i t a,T． Sh imi zu,H．Kon i sh i,J．Mi zuk i,H．Uch i Ｇ da,Co r r o s． Sc i． ４５ ( ２００３)３８１ Ｇ ３９４． [ １３] M．Yama s h i t a,H．Mi i,Y．Ma t s ud a,Co r r o s． S c i． ３６ ( １９９４) yuk ２８３ Ｇ ２９９． [ W．Chapman,J．El e c t r o chem． So c． １４] S C．Yen,J S．Wang,T １３９ ( １９９２)２２３１ Ｇ ２２３８． [ １５] HP．Ha c k,HW．P i c k e r i ng,J．E l e c t r o c h em．So c． １３８ ( １９９１) ６９０ Ｇ ６９５．