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Effects of Austenizing Temperature on Reprecipitation of BN
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ３,２ ０( ９):９ ９ Ｇ １ ０ ４
Ef f e c t so fAu s t e n i z i ngTempe r a t u r eonRepr e c i i t a t i ono fBN p YINSh i Ｇ ke１ , A Rong１ , Mi t suruTan i no２
( １．Ch i naI r onandS t e e lRe s e a r chI ns t i t u t eGr oup,Be i i ng１０００８１,Ch i na; ２．Fundamen t a lRe s e a r ch j , , , ) t e e lCo Kawa s ak i２１１ J apan Labo r a t o r pponS y Ni Ab s t r a c t:Mo s to fBN wa sp r e c i i t a t eda r oundt hesphe r i c a lMnSandf o rmedt hec ompoundo fMnSandBNdu r i ng p t hei s o t he rma lt r e a tmen ta t８５０ ℃ a f t e raus t en i z i nga t９５０－１０５０ ℃．Mo s to f MnS wa st r ans f o rmedi n t opo l ygon whenaus t en i z eda t１１５０ ℃ o rabove,wh i chc ou l dno tbet henuc l e io fBNanymo r e．Du r i ngt hei nsu l a t i onp r o c e s sa t , ８５０ ℃ MnSkep tt hes t a t eo fmonome r．Thec ompoundo fMnSandBNa te a r l i e rt imewa so ff i nepo l c r s t a l l i nei n y y sphe r a l i t sf o rmeda sap l a t e Ｇ l i kemono c r s t a lonac e r t a i npa r to ft hepo l c r s t a l l i newheni t sd imens i on yandBN wa y y y r e a ched０ ６μm． Ke r d s:aus t en i z i ngt empe r a t u r e;BN;r ep r e c i i t a t i on;i s o t he rma lt r e a tmen t p ywo
Ti nyamoun to fbo r oni ns t e e lha sanappa r en t e f f e c tonimp r ovemen to fha r denab i l i t r on wa s y．Bo o f t enaddedf o rimpr ov i ng t oughne s so ft he h i gh s t r eng t hs t e e landi t she a ta f f e c t edz one s．Ac e r t a i n amoun to fbo r oni sa l s of o ri nc r e a s i ngt hewe a rr e Ｇ s i s t i ng p r ope r t fs t e e l s．Fo rt he he a tr e s i s t i ng yo s t e e l s,t hec r e epr e s i s t anc eandt hes t r eng t ho fg r a i n bounda r r eenhanc edbysma l lamoun to fbo r on． ywe I nadd i t i on,t he g r a i n bounda r e r r i t e (GBF)i n yf we l dswa sev i den t l c r e a s edand we l dt oughne s s y de wa simp r ovedby bo r onadd i t i on．Howeve r,bo r on c on t en ti nt hes t e e landwe l dme t a lshou l dbes t r i c t l y c on t r o l l edbe c aus eo ft hede c r e a s eo fha r denab i l i t y
andde t e r i o r a t i ono ft heme chan i c a lp r ope r t i e sdur i ng [] he a tt r e a tmen t１ ．Thusi ti simpo r t an tt oi nve s t i t e ga t hebehav i o r so fbo r i de sp r e c i i t a t i oni no rde rt owe l l p u t i l i z ei t se f f e c t s．
１ Ma t e r i a l sandExp e r imen t s
Chemi c a lcompos i t i ono ft het e s t eds t e e li sl i s Ｇ t edi n Tab l e１．Thes t e e lwa sp r epa r edbyva cuum me l t i ngandt hes r espe c imenswi t hs e c t i ona ls i z e qua o f１２ mm×１２ mm we r e ma ch i nedf r om t hes t e e l． No rma l i z i ngt r e a tmen twa she l di nt hecond i t i ono f ９００ ℃ ×３０ mi nf o rhomogen i z a t i ono f mi c r os t ruc Ｇ t ur e．
Tab l e１ Compo s i t i ono ft e s t e ds t e e l (ma s spe r c en t,％ ) C
０ １０
Mn
１ ００
S i
０ ２０
P
０ ００２
S
０ ００４
Fo l l owi ng me t hodswe r eapp l i edf o rhe a tt r e a t Ｇ men ti nt heexpe r imen t:１)t hespe c imenswe r et r e a Ｇ t eda tf o l l owi ngaus t en i t i z i ngt empe r a t ur e so f９５０, １０５０,１１５０and１２５０ ℃ r e spe c t i ve l l df o r y,andhe , ６０ mi n t hen wa t e rc oo l edt or oomt empe r a t u r ef o r i nve s t i t i ngt hei n f l uenc eo ft empe r a t u r eonBNd i s Ｇ ga t r i bu t i on;２)a f t e rbe i nghe a t edt o９５０－１２５０ ℃ f o r , ６０ mi n t hespe c imenswe r ec oo l eddownt o８５０ ℃ immed i a t e l l df o r３０,６０and１２０ mi nr e Ｇ y,andhe
Al
０ ０１０
N
０ ００１９
O
０ ００１１
B
０ ００１８
spe c t i ve l henwa t e rcoo l edt or oomt empe r a Ｇ y,andt t ur ef o ri nve s t i t i ngt hebehav i o ro fBNr ep r e c i i t a Ｇ ga p t i ona t８５０ ℃．Theα Ｇ r t i c l eau t o r ad i og r aphme t hod pa [] wa sapp l i edf o rt r a c i ngt hebo r ond i s t r i bu t i on２ ．Be Ｇ , f o r ee t ch i ng t hespe c imenswe r ei r r ad i a t eda c co rd Ｇ i ngt ot hef o l l owi ng me t hod．Ther e a c t i onbe twe en bo r onandneu t r onwa sa sf o l l ows ０ １ ７ １ i＋４ e＋α ５ B＋０n→３L ２H α Ｇ r ay dur i ngr e a c t i ons wa st r a c ed by n i t r oc e l l u l os e
B i o r aphy: YINSh i Ｇke( １９４１—),Ma l e,Ba che l o r,Pr o f e s s o r; E Ｇma i l:y i nsh i ke＠a tmcn c om; Re c e i v e dDa t e:Novembe r１５,２０１１ g
１００
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２０
membr ane sandshown by c o r r o s i on．The de t a i l ed t e s t i ngp r oc e s s e swe r ea sf o l l ows:１)Thespe c imen wi t hs i z eo f１２mm×１２mm×１mm wa spo l i shedon ones i de,andsma l lamoun to f me t hano landa c e t i c a c i dwe r eapp l i edont hepo l i shedsu r f a c ef o rs t i ck i ng t hen i t r oc e l l u l o s e memb r ane sandt hena i rd r i ed． ２) Thespe c imenswe r ei r r ad i a t edi nana t omi cr e a c t o r wi t ht heneu t r onf l uxo f９ ６×１０１０cm－２f o r１２hand f o l l owedbya t t enua t i onf o rmo r et han２４h． ３)The /L NaOH s spe c imenswe r ec o r r odedi n２ ５ mo l o l u Ｇ ) t i ona t２５ ℃f o r２－３h． ４ Thememb r ane swe r ea i r d r i edandt henva cuumc oa t ed． Thee x t r a c t i onr e l i c awa sma d ef o rt h equ a n t i t a t i v e p a n a l s i sby me anso fnon Ｇ aqueouse l e c t r o l t e Ｇ t en Ｇ y y po [] t i o s t a t i ce t ch i ng me t hod ( SPEED)３ ,who s ee f f e c t wa smo r eobv i oust hant hep i c r i ca c i dand１％ hyd r o Ｇ ch l o r i ca c i ds o l u t i on,be c aus es omep r e c i i t a t e swi t h p sma l ls i z ewe r ee a s i l i s s o l vedawaybyt hea c i dand yd l e f tsma l lho l e sa tg r a i nbounda r i e s．Obs e r va t i onand t og r aph i ngo fmi c r o s t ruc t u r ewe r emadeonbo t h pho op t i c a lmi c r o s c opeandt r ansmi s s i one l e c t r on mi c r o Ｇ s c ope ( TEM ),andt hec r t a ls t ruc t u r e so fbo r on ys r e c i i t a t e swe r ede t e rmi ned by s e l e c t eda r e ae l e c Ｇ p p t r ond i f f r a c t i onpa t t e rns ( SADPs)．
２ Exp e r imen t a lRe s u l t s ２ １ Ef f e c to fau s t en i t i z i ngt empe r a t u r eonBNd i s t r i Ｇ bu t i on Thespe c imenwa she a t eda td i f f e r en taus t en i t i z Ｇ , , i ngt emp e r a t u r e so f９５０ １０５０and１１５０ ℃ andhe l d f o r６０ mi nr e spe c t i ve l hen wa t e rcoo l ed．The yandt FTE ( f i eo ft r a c ee t ch i ng)s t ruc t ur ei sshowni n gur F i １． I tc anbef oundf r omt hef i et ha tt hebo Ｇ g gur r i de sex i s t edi npa r t i c l e sa l ongt hep r ima r t en i t e yaus bounda r i e s．Me anwh i l ebo r ona c cumu l a t eda l ongt he newaus t en i t ebounda r i e s[ F i １ ( a)],andapa r to f g bo r i de swou l dbeso l veddur i nghe a t i ngandho l d i ng a t９５０ ℃．Af t e rhe a t i ng and ho l d i ng a t１０５０ ℃ , mos to fbo r i de s wh i ch p r e c i i t a t eda tt he p r ima r p y aus t en i t ebounda r i e s we r ed i s so l vedandt hes i z eo f t hel e f tbe c ameobv i ous l l l．Thebo r onconc en Ｇ ysma t r a t i ona tt henewaus t en i t ebounda r i e swa ss imi l a r t ot ha to fcoo l i nga t９５０ ℃ [ F i １ ( b)]．Af t e rhe a t Ｇ g i ngandho l d i nga t１１５０ ℃ ,t hebo r i de sa tt hep r ima Ｇ r t en i t ebounda r i e sa lmos td i s appe a r ed,andt he yaus bo r onconc en t r a t i ona tt henewaus t en i t ebounda r i e s wa sb a s i c a l l hes amea st hetwoc a s e sme n t i on e dabov e yt [ F i １ ( c)]． g
( a)９５０ ℃×６０ mi n,WQ; ( b)１０５０ ℃×６０ mi n,WQ; ( c)１１５０ ℃×６０ mi n,WQ．
F i １ FTEa td i f f e r en tau s t en i t i z i ngt emp e r a t u r e s g
Ther e su l tobs e r vedby TEMi nd i c a t edt ha tt he bo r i de sp r e c i i t a t eda tt henewaus t en i t ebounda r i e s p we r eFe２３( C, B) h i chhadnor e l a t i ont ot heaus Ｇ ６ ,w t en i t i z i ngt empe r a t u r e．I tc ou l d bec ons i de r edt ha t a l lt hebo r i de swe r ep r e c i i t a t eddu r i ng wa t e rc oo l Ｇ p i ng．Thep r e c i i t a t i ono ft hebo r i de swi t h i naus t en i t e p r a i nsi sshowni nF i ２．Theo r d i na t ei nt hef i r e g g gu r e s en t st henumbe ro fp r e c i i t a t e sobs e r vedf r om p p oneho l ewi t hana r e ao f０ ０４mm２ont hec oppe rne t o fex t r a c t i onr ep l i c a．MnSp r e s en t edi nt hef o rm o f s i ng l eMnSandc ompoundo fMnSandBN． Fo l l owi ngi n f o rma t i on wa sob t a i n e df r om F i ２． g ( ) Mo s to fBN a bou t８０％ wa sp r e c i i t a t eda r oundt he p
F i ２ Ef f e c to fau s t en i t i z i ngt emp e r a t u r eonp r e c i i t a t el e v e l g p
I s sue９ Ef f e c t so fAus t en i z i ngTempe r a t u r eonRep r e c i i t a t i ono fBN p
MnSpa r t i c l e st of o rmt hec ompoundo fMnSandBN [ ( ) ] , F i ３ a a n ds m a l l a m o u n to f s i n l ec r t a lBN g g ys ( ) [ ( ) ] abou t２０％ kep t monome r F i ３ b ．Af t e r g he a t i nga t１０５０ ℃f o r６０mi n,t hequan t i t i e so fbo t h
c ompoundo fMnSandBNandt he monome ro fBN we r er educ ed by abou tt he ha l f．Af t e r he a t i ng a t １１５０ ℃ f o r６０ mi n,BNf o rmedt hec ompoundand t hemonome rwa sa lmo s td i s s o l ved．Af t e rh e a t i nga nd , ho l d i nga t９５０－１１５０ ℃ t hequan t i t fMnSva r i ed yo s l i t l twa st her e su l to fBN d i s s o l u t i onon gh y．Tha t heou t e rshe l lo ft he MnSand BN c ompoundand monome ro fMnSwa sno td i s s o l veda tt het empe r a Ｇ t u r e．Af t e rhe a t i ngandho l d i nga t９５０and１０５０ ℃ ,
１０１
MnSwa ss t i l lsphe r i c a l[ F i ４ ( a)],bu ta f t e rhe a t Ｇ g i ngandho l d i nga t１１５０ ℃ MnSbe c amepo l h e d r a l y [ ( ) ] F i ４ b ．Af t e rhe a t i ngandho l d i nga t１２５０ ℃ g f o r６０ mi nt hequan t i t f MnS wa sr e du c e dt ol e s s yo t hanaha l f,bu ta f t e rhe a t i nga t１３５０℃ MnSc omp l e t e Ｇ l i s a e a r e d．Whe nhe a t i nga tt heabov et emp e r a t u r e, yd pp t hequ an t i t fMnSwa sr e du c e dandi t ss ha ewa sa l s o yo p [ ( ) ] c hang e df r oms h e r i c a l t o o l h e d r a l F i ４ c ． A f t e r p py g he a t i ngandho l d i nga t１２５０ ℃f o r６０mi npo l l ygona MnS wou l dke ept heo r i i na ls t a t eo ft he monome r g MnSand BN wa sno tf o rmeda r oundevent hough t hespe c imenwa si nsu l a t eda t８５０ ℃ f o r６０ mi n,a s showni nF i ４ ( d)． g
( a)Compoundo fMnSandBN; ( b)S i ng l eBN．
F i ３ Mo rpho l o i e so fBN g g
( a)９５０ ℃×１ mi n; ( b)１１５０ ℃×６０ mi n; ( c)１２５０ ℃×６０ mi n; ( d)１２５０ ℃→８５０ ℃．
F i ４ Mo rpho l o i e so fMnS g g
２ ２ Re e c i i t a t i ono fBNdu r i ngho l d i nga t８５０ ℃ pr p Thes e c ime n wa si s o t h e rma l l r e a t e da t８５０ ℃ p yt f o r６０ mi nandt h e nc o o l e dt or o omt emp e r a t u r ea f t e r , , h e a t e da t１０５０ １１５０a nd１２５０℃ he l df o r６０mi nr e Ｇ spe c t i ve l r ond i s t r i bu t i onunde rt heabove y．Thebo c ond i t i oni sshowni nF i ５．Compa r i ng F i ５ ( a) g g ( ) wi t hF i １ b i tc anbef oundt ha tt hequan t i t f g yo BN p r e c i i t a t e dw i t h i ng r a i n s wa sobv i ou s l n c r e a s e d p yi andt hes i z eo f pr e c i i t a t e s b e c a m e b i e r d u r i n p gg g
ho l d i nga t８５０ ℃．Thequan t i t fBNp r e c i i t a t eda t yo p t heg r a i nbounda r i e swa ssma l lbu twi t hl a r rs i z e． ge I na dd i t i ondu r i ngt hei s o t he rma lt r e a tme n ta t８５０ ℃ f o r６０ mi nj us tapa r to fbo r on wa sp r e c i i t a t edi n p BNf o rm,andt hebo r onwh i chhadno tbe enp r e c i i Ｇ p t a t ed ye t wa sa c cumu l a t ed a l ong aus t en i t eg r a i n bounda r i e sandwa sf o rmedi n t oFe２３( C, B) ６． I nt hei s o t he rma lt r e a tme n ta t８５０ ℃ a f t e rhe a t i ng a t１１５０℃ ,t her e r e c i i t a t e dB N u a n t i t w a s r e d u c e d p p q y
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２０
１０２
( a)１０５０ ℃→８５０ ℃ ,WQ; ( b)１１５０ ℃→８５０ ℃ ,WQ; ( c)１２５０ ℃→８５０ ℃ ,WQ．
F i ５ Ef f e c to fau s t en i t i z i ngt emp e r a t u r eond i s t r i bu t i ono fbo r i d ea f t e ri s o t h e rma lt r e a tmen ta t８５０ ℃ f o r６０mi n g
d i s t i nc t l oabou t１０％ o ft het o t a lquan t i t fBN, yt yo wh i chwa si n s u l a t e da t８５０ ℃ a f t e rh e a t i nga t１０５０ ℃． Thes i z eo ft he p r e c i i t a t e sbo t hi ng r a i nsanda t p [ ( ) ] bounda r i e swa sobv i ous l l a r i ５ b ． yen ged F g Dur i ngt hei s o t he rma lt r e a tmen ta t８５０ ℃ a f t e r he a t i nga t１２５０ ℃ ,t hes amephenomenonwa smo r e r ema rkab l e．Asshowni nF i ５ ( c)t hep r e c i i t a t e s g p wi t h i ng r a i ns we r ef u r t he rr educ ed,andt he i rs i z e be c ameevenb i r．Be s i de st hei nd i v i dua l l r own gge yg , BNa tt heg r a i nbounda r i e st he r ewe r es omec oa r s e r BNf o rme dbyt h ec omb i n a t i ono faf ewBNp a r t i c l e s． Wi t hd i f f e r en ti n i t i a laus t en i z i ngt empe r a t u r e s t hequan t i t i z eo fBNr ep r e c i i t a t eddu r i ngt he yands p i s o t he rma lt r e a tmen ta t８５０ ℃ we r equ i t ed i f f e r en t duet ot hechange so ft hequan t i t fMnS yandshapeo du r i nghe a t i nga th i empe r a t u r e．Whenhe a t i nga t ght ９５０－１０５０ ℃ ,MnSwa ss t i l lsphe r i c a landt hed i s Ｇ s o l u t i onands o l i ds o l u t i ond i dno thappen． Be c aus ea r e a tnumbe ro fsphe r i c a lMnS wou l dbet henuc l e i g
o fBN c r t a l l i z a t i on,t he quan t i t fp r e c i i t a t ed ys yo p BN be c ame b i r,bu t wi t h sma l l e rs i z e．When gge he a t i nga t１１５０ ℃ mos to ft hesphe r i c a l MnSbe Ｇ , c amepo l r a l wh i ch wou l dno tbet henuc l e io f yhed BN c r t a l l i z a t i on．Be c aus eo ft hede c r e a s eo ft he ys nuc l e ir a t et hequan t i t fp r e c i i t a t edBN wa sa l so yo p , r educ ed bu tt hes i z eo ft hep r e c i i t a t e sbe c ameb i Ｇ p g r．Whenhe a t i nga t１２５０ ℃ mo r et hanaha l fo f ge MnS we r ed i s so l vedi n add i t i ont ot hechange o f MnSshape．The r e f o r et he quan t i t fp r e c i i t a t ed yo p BNbe c amesma l l e r,andt hes i z eo ft hep r e c i i t a t e s p be c ameb i e r ．W i t hi n c r e a s e o ft h e B N s i z et h e gg mo r l ogyo fBN wa schanged,t oo．Usua l l he pho yt compoundo fMnSandBN wa sne a r l r i c a l,and ysphe BN wa sp r e c i i t a t edi nar ad i a t i onf o rma r oundMnS． p AsBNs i z er e a chedac r i t i c a lva l uei twa sp r e c i i t a Ｇ p t edaga i na sap l a t e Ｇ l i ke monoc r t a l．Theshapeo f ys t hecompoundbe c amei r r egu l a ra sshowni nF i ６． g Someo ft hep l a t e Ｇ l i keBNwe r ewi t hc o r n e rang l e,and
( a),( b),( c)８５０ ℃×３０ mi n; ( d)８５０ ℃×１２０ mi n．
F i ６ MnSandBNc ompoundandp l a t e Ｇ l i k eBNo fs t e e lt r e a t e dby１１５０ ℃×６０mi n＋WQ→８５０ ℃× ( ３０－１２０)mi n＋WQ g
s omewe r eo fa r c．
３ Di s c u s s i on
３ １ Ef f e c to fi n t e r f a c eb e twe e n MnSandma t r i x I twa sobs e r vedi nt heexpe r imen tt ha ta r ound t heMnSpa r t i c l e si ng r a i nst hep r e c i i t a t i o nr a t eo f p BN wa sve r i twa sp r e c i i t a t edi ng r a i ns yh ghandi p e a r l i e rt hana tg r a i nbounda r i e s．Duet ot ha tt heav Ｇ e r aged i s t anc ebe twe en MnS wa ssma l l e rt hant ha t
be twe eng r a i nbounda r i e s,bo r ona t omst ooksho r t e r t imet od i f f us et owa rdsMnS．Anobs e r vedimpo r t an t t h i ng wa st ha tbo r ona t omsa r ound MnSwe r ea c cu Ｇ mu l a t ed mo r ee a s i l r ed wi t ht ha ta tg r a i n y compa bound a r i e s．F i ７ wa st ake na sa mod e lt os howt he g d i f f e r enc eo ft hea c cumu l a t i on o fbo r on a t omsa t / r a i nbounda r i e sandont hei n t e r f a c eo f MnS ma Ｇ g t r i x． Fo rt heconven i enc et heg r a i nbounda r sa s Ｇ ywa , / sumedt obeap l ane andt hei n t e r f a c eo fMnS ma t r i x
I s sue９ Ef f e c t so fAus t en i z i ngTempe r a t u r eonRep r e c i i t a t i ono fBN p
( a)Gr a i nbounda r b)MnSbounda r f a c e． y; ( ysur
F i ７ Mod e lo fg r a i nbounda r r u r f a c e g yandbounda ys
wa st obeasphe r e． I twa ssuppo s edt ha tt her ad i us o fMnSsphe r ewa sr,t hed i f f us i ond i s t anc eo fbo r on a t omsa tag i vent imewa sl,anda l lt hebo r ona t oms wi t h i nt he d i s t anc el we r ea c cumu l a t ed a tg r a i n bounda r i e sandont hei n t e r f a c e．Thec onc en t r a t i on o fbo r ona t oms wi t h i nan un i t evo l umeo f ma t r i x wa s[ B]M ,andt hes i t ua t i ono fbo r ona c cumu l a t i on a t omst owa r dsg r a i nbounda r i e sf r omtwos i de swa s , , c ons i de r ed． So f o rg r a i nbounda r i e st hequan t i t f yo nanun i tbounda r r e awa sc a l Ｇ bo r ona t oms [ B] ya GBi cu l a t eda sf o l l ows [ ] ( B GB ＝２ l[ B]M １) Fo rt hei n t e r f a c eo fMnS/ma t r i x,i ns i deo ft he r＋l)andi sphe r ewi t hanou t e rd i ame t e ro f( nne r , d i ame t e ro fr a l lbo r ona t omswe r ea c cumu l a t edon t hei n t e r f a c e wi t h asu r f a c ea r e ao f４π r２ ,sot he [ ] u a n t i t o fb o r o na t o m s B i nt h eu n i tb o u n d a r q y y MnS a r e awa s ìï üï ï４ ï ３ ( [ B]MnS＝ íïï π[( B]M ２) r＋l) －r３]÷４π r３ ýïï [ î３ þ As sumi ng [ B]MnS＞ [ B] t hen GB , ïìï４ ïüï ３ ( [ B]MnS＝ íïï π[( l ３) －r３]÷４π r＋l) r２ ýïï ＞２ î３ þ Tos imp l i f ha t yt ( l２ ＋３ r l－３ r３ ＞０ ４) a srandla r epo s i t i ve,s oEqn ( ４)wou l dbe
１０３
ont hei n t e r f a c eo f MnS/ma t r i x wa s much h i r ghe t hant ha ta tg r a i nbounda r i e s．Asbo r onconc en t r a Ｇ t i onr e a chedac e r t a i nc r i t i c a lva l ue,BNj us ts t a r t ed t obep r e c i i t a t ed． SowhenMnSex i s t ed,t hep r e c i Ｇ p p i t a t i ono fBNi ng r a i nswa se a r l i e rt hant ha ta tg r a i n bounda r i e s． Be s i de s,n i t r ogenwa sa l soe a s i l eg r ega t edt o Ｇ ys wa rdst heg r a i nbounda r i e swi t hh i he n e r a sb o Ｇ g gy r ond i d． I twa sbe c aus en i t r ogend i f f us i on wa ss l o Ｇ we rt hanbo r oni naus t en i t e,sot heg r owt ho fBN wa sde t e rmi nedbyn i t r ogend i f f us i on,andBNi nt he s t e e lwi t hh i i t r ogenwa spr e c i i t a t ede a s i l ghn p y． ３ ２ Ef f e c to fMnSmo r l o e c i i t a t i on pho gyonBNpr p I twa sf oundi nt heexpe r imen tt ha twi t ht hei n Ｇ c r e a s eo fhe a t i ngt empe r a t ur et he MnS mo r l ogy pho wa schanged,wh i cha l sochangedt hef unc t i ono fnu Ｇ c l e io fc r t a l l i z a t i on．Almos ta l lo fMnSwe r ene a r l ys y sphe r i c a land BN wa sp r e c i i t a t eda r ound MnSi n p t hef o rmo fcompoundo fMnSandBNunde rf o r i ng g o rno rma l i z i ng．Att hehe a t i ngt emp e r a t u r el owe rt han １０５０ ℃ ,mos to fMnSwh i chhadno tbe eni nso l i d so l u t i on wa schangedf r om sphe r i c a lt o po l r a l． yhed Th i st e nd e n c e c amemo r es i i f i c an twi t ht her a i s eo f yb gn t hehe a t i ngt empe r a t ur e． I twa sf oundf r omal o to f obs e r va t i onst ha tnoBN wa sp r e c i i t a t eda r oundt he p l r a l MnS．Tha t me an tt ha tt he po l r a l po yhed yhed MnSwa snol onge ra st henuc l e io fBNc r s t a l l i z a Ｇ y t i on．By me anso fe l e c t r ond i f f r a c t i onandcompos i Ｇ t i onana l i si n mi c r o Ｇ z one,i t wa si nd i c a t edt ha t ys bo t ht hes t ruc t ur eandcons t i t uen to f MnShadno change sa td i f f e r en tt empe r a t ur e sbe f o r ei t sso l u t i on． The r e f o r et hechangeo f MnS mo r l ogy a th i pho gh t empe r a t ur e wou l d ber e l a t edt ot hes emi Ｇ eu t e c t i c r e l a t i onbe twe en MnSand ma t r i x．I nt h i sc a s et he shapeo fMnSbounda r i i f i c an td i f f e r enc e yhadnos gn compa r i ng wi t hg r a i nbounda r c aus eo ft hel owＧ y．Be e rsur f a c eene r ns emi Ｇ eu t e c t i cr e l a t i on,MnSl os t gyi t he ab i l i t o be nuc l e io fc r t a l l i z a t i on a st he yt ys sphe r i c a lMnS．
－３＋ ２１ ( r≈０ ７９１ r ５) ２ The r e f o r e,a sl onga sl＞０ ８ r,t hebo r onc on Ｇ c en t r a t i onont hei n t e r f a c eo fMnS/ma t r i xi sh i r ghe ３ Shapeo fBN t hant ha ta tg r a i nbounda r i e s．Al t houghi nt her e a l ３ I twa scon f i rmedbyt hep r ev i ouswo rkt ha tBN c r t a l l i z a t i ont heg r a i nbounda r sno tt her e a l ys y wa ns t e e lex i s t edi npo l r t a lf o rma l ong [ ０００１]ax i s l ane,t hei n t e r f a c eo fMnS/ma t r i xwa sno tt her e a l i yc ys p [ ４] a n d l i k et h es h e r i c a l r a h i t ei nr a d i a ld i r e c t i o n ． sphe r e,bu twi t ht hes amet endenc ． p g p y Add i t i ona l l twa sa l sof oundt ha tt heg r owt ho ft he I t wa sknownf r om t heobs e r va t i on by TEM yi a r l r i c a lBN wa sl imi t edt oac e r t a i ns i z ei n t ha tt her ad i uso fMnSi nt hec ompoundo fMnSand ne ysphe i chBN g r ewa sap l a t e Ｇ l i kemonoc r s t a l ． A c c o r d Ｇ BN wa si nt her angeo f０ ０７－０ １５μm,t hed i f f u Ｇ wh y / , ngt oobs e r va t i onst hec r i t i c a ls i z e wa sabou t０ ６ s i onr a t eo fbo r oni naus t en i t ewa s４ ０４μm s and i S i ng l ec r t a lBNg r ewupa l ongapa r to fsphe r Ｇ t hed i f f u s i ont imewou l db e１ ９×１０－４ －８８×１０－４ s, μm． ys c a lBNandhadt hes ameo r i en t a t i ono fc r s t a l l i z a Ｇ wh i ch me e t sEqn ( ５)．Sot hebo r onc onc en t r a t i on i y l＞
１０４
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２０
monome r． ４)Att hee a r l t a et hep r e c i i t a t e dBNwa spo l Ｇ ys g p y c r s t a l l i n eandt he na r e a t e di ns r i c a lf o rm．The i r y gg g phe ４ Conc l u s i on s mo r l og i e s we r es imi l a rt ot ha to f sphe r i c a l pho r a h i t e ． T h e r o w t ho f t h es h e r i c a lB N w a s l i m i t Ｇ １)Unde rf o r i n o rn o r m a l i z i n c o n d i t i o nB N g p g p g g g oac e r t a i ns i z ei nwh i chBN wa sp r e c i i t a t eda sa r e c i i t a t edi nt hef o rm o fMnSandBNc ompound． edt p p p l a t e Ｇ l i ke monoc r t a lona pa r to fpo l r t a l l i ne． Ashe a t i nga t１０５０ ℃ BN wa sd i s s o l ved． I fi twa s p ys yc ys twa si na c co rdanc e wi t ht hes t a t i s t i c a lr e su l t s t heni so t he rma l l r e a t eda t８５０ ℃ BNr ep r e c i i t a t Ｇ Tha yt p r om obs e r va t i ons wh i chi nd i c a t edt ha tt hec r i t i c a l edf r omt her e s i dua lc ompoundo fMnSandBN．The f i z eo fBNi npo l r t a l l i newa sabou t０ ６μm． r e c i i t a t i ngr a t eo fBNa tg r a i nbounda r i e so faus Ｇ s yc ys p p t en i t ewa smuchs l owe rt hant ha tont hei n t e r f a c eo f Re f e r enc e s: MnS/ma t r i x． [ １] Hi t o sh iH,Take sh iN,Take sh iS,e ta l．Ef f e c to fTiandBon ２)Whenhe a t edove r１１５０ ℃ mo s to fMnSwa s M i c r o s t r u c t u r eo f７ ８ ０ MP a C l a s s H i h S t r e n t h We l d Me t a l g g changedf r omsphe r i c a lt opo l r a l．Th i spo l Ｇ yhed yhed [ J]．KobeS t e e lEng i ne e r i ngRepo r t s,２００８,５８:１８． r a lMnScou l dno tbet henuc l e io fBN c r t a l l i z a Ｇ ys [ ２] Hi t ox iK．Cu r r e n tS t a t eAn a l s i so fI r ona ndS t e e l [M]．T okyo: y t i on．Thena f t e rt hei s o t he rma lt r e a tmen ta t８５０ ℃ AGUNAII ndus t r e s s,１９７９ ( i nJ apane s e)． yPr [ ３] Fumi oK,I s amuT,RyuTa r o M．Obs e r va t i ono fPr e c i i t a t e s t hes i ng l epo l r a lMnSwa sp r e s en t edandnoBN p yhed a n d M e t a l l o r aph i cGr a i n Or i en t a t i oni nS t e e lbyaNon ＧAque Ｇ g wa sp r e c i i t a t e da r oundt h epo l e d r a lMnS．Anumb e r p yh ousEl e c t r o l t e ＧPo t en t i o s t a t i cEt ch i ng Me t hod [ J]．J our na lo f y o fBN we r ep r e c i i t a t eda r oundt hesma l lamoun to f p t heJ apanI ns t i t u t eo fMe t a l,１９７９,４３:１０６８． sphe r i c a lMnSandg r ewi n t oc oa r s eBN p r e c i i t a t e s． [ p ４] Wa t anabeS,Oh t an iH． Pr e c i i t a t i onBehav i o ro fBo r oni nHi p gh ３)Mo s to fBNe x i s t e di nt h ef o rmo fMnSa ndBN S t r eng t hS t e e l[ J]． J our na lo ft heI r onandS t e e lI ns t i t u t eo fJ a Ｇ pan,１９７６,６２:１８５１． c ompoundand a sma l lamoun to f BN ex i s t edi n t i onl i ket heo r i i na lBN．Thef a c t o r sde t e rmi n i ng g t hec r i t i c a ls i z eo ft h es h e r i c a lB N w e r en o t c l e a r e p yt．
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ３,２ ０( ９):９ ９ Ｇ １ ０ ４
Ef f e c t so fAu s t e n i z i ngTempe r a t u r eonRepr e c i i t a t i ono fBN p YINSh i Ｇ ke１ , A Rong１ , Mi t suruTan i no２
( １．Ch i naI r onandS t e e lRe s e a r chI ns t i t u t eGr oup,Be i i ng１０００８１,Ch i na; ２．Fundamen t a lRe s e a r ch j , , , ) t e e lCo Kawa s ak i２１１ J apan Labo r a t o r pponS y Ni Ab s t r a c t:Mo s to fBN wa sp r e c i i t a t eda r oundt hesphe r i c a lMnSandf o rmedt hec ompoundo fMnSandBNdu r i ng p t hei s o t he rma lt r e a tmen ta t８５０ ℃ a f t e raus t en i z i nga t９５０－１０５０ ℃．Mo s to f MnS wa st r ans f o rmedi n t opo l ygon whenaus t en i z eda t１１５０ ℃ o rabove,wh i chc ou l dno tbet henuc l e io fBNanymo r e．Du r i ngt hei nsu l a t i onp r o c e s sa t , ８５０ ℃ MnSkep tt hes t a t eo fmonome r．Thec ompoundo fMnSandBNa te a r l i e rt imewa so ff i nepo l c r s t a l l i nei n y y sphe r a l i t sf o rmeda sap l a t e Ｇ l i kemono c r s t a lonac e r t a i npa r to ft hepo l c r s t a l l i newheni t sd imens i on yandBN wa y y y r e a ched０ ６μm． Ke r d s:aus t en i z i ngt empe r a t u r e;BN;r ep r e c i i t a t i on;i s o t he rma lt r e a tmen t p ywo
Ti nyamoun to fbo r oni ns t e e lha sanappa r en t e f f e c tonimp r ovemen to fha r denab i l i t r on wa s y．Bo o f t enaddedf o rimpr ov i ng t oughne s so ft he h i gh s t r eng t hs t e e landi t she a ta f f e c t edz one s．Ac e r t a i n amoun to fbo r oni sa l s of o ri nc r e a s i ngt hewe a rr e Ｇ s i s t i ng p r ope r t fs t e e l s．Fo rt he he a tr e s i s t i ng yo s t e e l s,t hec r e epr e s i s t anc eandt hes t r eng t ho fg r a i n bounda r r eenhanc edbysma l lamoun to fbo r on． ywe I nadd i t i on,t he g r a i n bounda r e r r i t e (GBF)i n yf we l dswa sev i den t l c r e a s edand we l dt oughne s s y de wa simp r ovedby bo r onadd i t i on．Howeve r,bo r on c on t en ti nt hes t e e landwe l dme t a lshou l dbes t r i c t l y c on t r o l l edbe c aus eo ft hede c r e a s eo fha r denab i l i t y
andde t e r i o r a t i ono ft heme chan i c a lp r ope r t i e sdur i ng [] he a tt r e a tmen t１ ．Thusi ti simpo r t an tt oi nve s t i t e ga t hebehav i o r so fbo r i de sp r e c i i t a t i oni no rde rt owe l l p u t i l i z ei t se f f e c t s．
１ Ma t e r i a l sandExp e r imen t s
Chemi c a lcompos i t i ono ft het e s t eds t e e li sl i s Ｇ t edi n Tab l e１．Thes t e e lwa sp r epa r edbyva cuum me l t i ngandt hes r espe c imenswi t hs e c t i ona ls i z e qua o f１２ mm×１２ mm we r e ma ch i nedf r om t hes t e e l． No rma l i z i ngt r e a tmen twa she l di nt hecond i t i ono f ９００ ℃ ×３０ mi nf o rhomogen i z a t i ono f mi c r os t ruc Ｇ t ur e．
Tab l e１ Compo s i t i ono ft e s t e ds t e e l (ma s spe r c en t,％ ) C
０ １０
Mn
１ ００
S i
０ ２０
P
０ ００２
S
０ ００４
Fo l l owi ng me t hodswe r eapp l i edf o rhe a tt r e a t Ｇ men ti nt heexpe r imen t:１)t hespe c imenswe r et r e a Ｇ t eda tf o l l owi ngaus t en i t i z i ngt empe r a t ur e so f９５０, １０５０,１１５０and１２５０ ℃ r e spe c t i ve l l df o r y,andhe , ６０ mi n t hen wa t e rc oo l edt or oomt empe r a t u r ef o r i nve s t i t i ngt hei n f l uenc eo ft empe r a t u r eonBNd i s Ｇ ga t r i bu t i on;２)a f t e rbe i nghe a t edt o９５０－１２５０ ℃ f o r , ６０ mi n t hespe c imenswe r ec oo l eddownt o８５０ ℃ immed i a t e l l df o r３０,６０and１２０ mi nr e Ｇ y,andhe
Al
０ ０１０
N
０ ００１９
O
０ ００１１
B
０ ００１８
spe c t i ve l henwa t e rcoo l edt or oomt empe r a Ｇ y,andt t ur ef o ri nve s t i t i ngt hebehav i o ro fBNr ep r e c i i t a Ｇ ga p t i ona t８５０ ℃．Theα Ｇ r t i c l eau t o r ad i og r aphme t hod pa [] wa sapp l i edf o rt r a c i ngt hebo r ond i s t r i bu t i on２ ．Be Ｇ , f o r ee t ch i ng t hespe c imenswe r ei r r ad i a t eda c co rd Ｇ i ngt ot hef o l l owi ng me t hod．Ther e a c t i onbe twe en bo r onandneu t r onwa sa sf o l l ows ０ １ ７ １ i＋４ e＋α ５ B＋０n→３L ２H α Ｇ r ay dur i ngr e a c t i ons wa st r a c ed by n i t r oc e l l u l os e
B i o r aphy: YINSh i Ｇke( １９４１—),Ma l e,Ba che l o r,Pr o f e s s o r; E Ｇma i l:y i nsh i ke＠a tmcn c om; Re c e i v e dDa t e:Novembe r１５,２０１１ g
１００
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２０
membr ane sandshown by c o r r o s i on．The de t a i l ed t e s t i ngp r oc e s s e swe r ea sf o l l ows:１)Thespe c imen wi t hs i z eo f１２mm×１２mm×１mm wa spo l i shedon ones i de,andsma l lamoun to f me t hano landa c e t i c a c i dwe r eapp l i edont hepo l i shedsu r f a c ef o rs t i ck i ng t hen i t r oc e l l u l o s e memb r ane sandt hena i rd r i ed． ２) Thespe c imenswe r ei r r ad i a t edi nana t omi cr e a c t o r wi t ht heneu t r onf l uxo f９ ６×１０１０cm－２f o r１２hand f o l l owedbya t t enua t i onf o rmo r et han２４h． ３)The /L NaOH s spe c imenswe r ec o r r odedi n２ ５ mo l o l u Ｇ ) t i ona t２５ ℃f o r２－３h． ４ Thememb r ane swe r ea i r d r i edandt henva cuumc oa t ed． Thee x t r a c t i onr e l i c awa sma d ef o rt h equ a n t i t a t i v e p a n a l s i sby me anso fnon Ｇ aqueouse l e c t r o l t e Ｇ t en Ｇ y y po [] t i o s t a t i ce t ch i ng me t hod ( SPEED)３ ,who s ee f f e c t wa smo r eobv i oust hant hep i c r i ca c i dand１％ hyd r o Ｇ ch l o r i ca c i ds o l u t i on,be c aus es omep r e c i i t a t e swi t h p sma l ls i z ewe r ee a s i l i s s o l vedawaybyt hea c i dand yd l e f tsma l lho l e sa tg r a i nbounda r i e s．Obs e r va t i onand t og r aph i ngo fmi c r o s t ruc t u r ewe r emadeonbo t h pho op t i c a lmi c r o s c opeandt r ansmi s s i one l e c t r on mi c r o Ｇ s c ope ( TEM ),andt hec r t a ls t ruc t u r e so fbo r on ys r e c i i t a t e swe r ede t e rmi ned by s e l e c t eda r e ae l e c Ｇ p p t r ond i f f r a c t i onpa t t e rns ( SADPs)．
２ Exp e r imen t a lRe s u l t s ２ １ Ef f e c to fau s t en i t i z i ngt empe r a t u r eonBNd i s t r i Ｇ bu t i on Thespe c imenwa she a t eda td i f f e r en taus t en i t i z Ｇ , , i ngt emp e r a t u r e so f９５０ １０５０and１１５０ ℃ andhe l d f o r６０ mi nr e spe c t i ve l hen wa t e rcoo l ed．The yandt FTE ( f i eo ft r a c ee t ch i ng)s t ruc t ur ei sshowni n gur F i １． I tc anbef oundf r omt hef i et ha tt hebo Ｇ g gur r i de sex i s t edi npa r t i c l e sa l ongt hep r ima r t en i t e yaus bounda r i e s．Me anwh i l ebo r ona c cumu l a t eda l ongt he newaus t en i t ebounda r i e s[ F i １ ( a)],andapa r to f g bo r i de swou l dbeso l veddur i nghe a t i ngandho l d i ng a t９５０ ℃．Af t e rhe a t i ng and ho l d i ng a t１０５０ ℃ , mos to fbo r i de s wh i ch p r e c i i t a t eda tt he p r ima r p y aus t en i t ebounda r i e s we r ed i s so l vedandt hes i z eo f t hel e f tbe c ameobv i ous l l l．Thebo r onconc en Ｇ ysma t r a t i ona tt henewaus t en i t ebounda r i e swa ss imi l a r t ot ha to fcoo l i nga t９５０ ℃ [ F i １ ( b)]．Af t e rhe a t Ｇ g i ngandho l d i nga t１１５０ ℃ ,t hebo r i de sa tt hep r ima Ｇ r t en i t ebounda r i e sa lmos td i s appe a r ed,andt he yaus bo r onconc en t r a t i ona tt henewaus t en i t ebounda r i e s wa sb a s i c a l l hes amea st hetwoc a s e sme n t i on e dabov e yt [ F i １ ( c)]． g
( a)９５０ ℃×６０ mi n,WQ; ( b)１０５０ ℃×６０ mi n,WQ; ( c)１１５０ ℃×６０ mi n,WQ．
F i １ FTEa td i f f e r en tau s t en i t i z i ngt emp e r a t u r e s g
Ther e su l tobs e r vedby TEMi nd i c a t edt ha tt he bo r i de sp r e c i i t a t eda tt henewaus t en i t ebounda r i e s p we r eFe２３( C, B) h i chhadnor e l a t i ont ot heaus Ｇ ６ ,w t en i t i z i ngt empe r a t u r e．I tc ou l d bec ons i de r edt ha t a l lt hebo r i de swe r ep r e c i i t a t eddu r i ng wa t e rc oo l Ｇ p i ng．Thep r e c i i t a t i ono ft hebo r i de swi t h i naus t en i t e p r a i nsi sshowni nF i ２．Theo r d i na t ei nt hef i r e g g gu r e s en t st henumbe ro fp r e c i i t a t e sobs e r vedf r om p p oneho l ewi t hana r e ao f０ ０４mm２ont hec oppe rne t o fex t r a c t i onr ep l i c a．MnSp r e s en t edi nt hef o rm o f s i ng l eMnSandc ompoundo fMnSandBN． Fo l l owi ngi n f o rma t i on wa sob t a i n e df r om F i ２． g ( ) Mo s to fBN a bou t８０％ wa sp r e c i i t a t eda r oundt he p
F i ２ Ef f e c to fau s t en i t i z i ngt emp e r a t u r eonp r e c i i t a t el e v e l g p
I s sue９ Ef f e c t so fAus t en i z i ngTempe r a t u r eonRep r e c i i t a t i ono fBN p
MnSpa r t i c l e st of o rmt hec ompoundo fMnSandBN [ ( ) ] , F i ３ a a n ds m a l l a m o u n to f s i n l ec r t a lBN g g ys ( ) [ ( ) ] abou t２０％ kep t monome r F i ３ b ．Af t e r g he a t i nga t１０５０ ℃f o r６０mi n,t hequan t i t i e so fbo t h
c ompoundo fMnSandBNandt he monome ro fBN we r er educ ed by abou tt he ha l f．Af t e r he a t i ng a t １１５０ ℃ f o r６０ mi n,BNf o rmedt hec ompoundand t hemonome rwa sa lmo s td i s s o l ved．Af t e rh e a t i nga nd , ho l d i nga t９５０－１１５０ ℃ t hequan t i t fMnSva r i ed yo s l i t l twa st her e su l to fBN d i s s o l u t i onon gh y．Tha t heou t e rshe l lo ft he MnSand BN c ompoundand monome ro fMnSwa sno td i s s o l veda tt het empe r a Ｇ t u r e．Af t e rhe a t i ngandho l d i nga t９５０and１０５０ ℃ ,
１０１
MnSwa ss t i l lsphe r i c a l[ F i ４ ( a)],bu ta f t e rhe a t Ｇ g i ngandho l d i nga t１１５０ ℃ MnSbe c amepo l h e d r a l y [ ( ) ] F i ４ b ．Af t e rhe a t i ngandho l d i nga t１２５０ ℃ g f o r６０ mi nt hequan t i t f MnS wa sr e du c e dt ol e s s yo t hanaha l f,bu ta f t e rhe a t i nga t１３５０℃ MnSc omp l e t e Ｇ l i s a e a r e d．Whe nhe a t i nga tt heabov et emp e r a t u r e, yd pp t hequ an t i t fMnSwa sr e du c e dandi t ss ha ewa sa l s o yo p [ ( ) ] c hang e df r oms h e r i c a l t o o l h e d r a l F i ４ c ． A f t e r p py g he a t i ngandho l d i nga t１２５０ ℃f o r６０mi npo l l ygona MnS wou l dke ept heo r i i na ls t a t eo ft he monome r g MnSand BN wa sno tf o rmeda r oundevent hough t hespe c imenwa si nsu l a t eda t８５０ ℃ f o r６０ mi n,a s showni nF i ４ ( d)． g
( a)Compoundo fMnSandBN; ( b)S i ng l eBN．
F i ３ Mo rpho l o i e so fBN g g
( a)９５０ ℃×１ mi n; ( b)１１５０ ℃×６０ mi n; ( c)１２５０ ℃×６０ mi n; ( d)１２５０ ℃→８５０ ℃．
F i ４ Mo rpho l o i e so fMnS g g
２ ２ Re e c i i t a t i ono fBNdu r i ngho l d i nga t８５０ ℃ pr p Thes e c ime n wa si s o t h e rma l l r e a t e da t８５０ ℃ p yt f o r６０ mi nandt h e nc o o l e dt or o omt emp e r a t u r ea f t e r , , h e a t e da t１０５０ １１５０a nd１２５０℃ he l df o r６０mi nr e Ｇ spe c t i ve l r ond i s t r i bu t i onunde rt heabove y．Thebo c ond i t i oni sshowni nF i ５．Compa r i ng F i ５ ( a) g g ( ) wi t hF i １ b i tc anbef oundt ha tt hequan t i t f g yo BN p r e c i i t a t e dw i t h i ng r a i n s wa sobv i ou s l n c r e a s e d p yi andt hes i z eo f pr e c i i t a t e s b e c a m e b i e r d u r i n p gg g
ho l d i nga t８５０ ℃．Thequan t i t fBNp r e c i i t a t eda t yo p t heg r a i nbounda r i e swa ssma l lbu twi t hl a r rs i z e． ge I na dd i t i ondu r i ngt hei s o t he rma lt r e a tme n ta t８５０ ℃ f o r６０ mi nj us tapa r to fbo r on wa sp r e c i i t a t edi n p BNf o rm,andt hebo r onwh i chhadno tbe enp r e c i i Ｇ p t a t ed ye t wa sa c cumu l a t ed a l ong aus t en i t eg r a i n bounda r i e sandwa sf o rmedi n t oFe２３( C, B) ６． I nt hei s o t he rma lt r e a tme n ta t８５０ ℃ a f t e rhe a t i ng a t１１５０℃ ,t her e r e c i i t a t e dB N u a n t i t w a s r e d u c e d p p q y
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２０
１０２
( a)１０５０ ℃→８５０ ℃ ,WQ; ( b)１１５０ ℃→８５０ ℃ ,WQ; ( c)１２５０ ℃→８５０ ℃ ,WQ．
F i ５ Ef f e c to fau s t en i t i z i ngt emp e r a t u r eond i s t r i bu t i ono fbo r i d ea f t e ri s o t h e rma lt r e a tmen ta t８５０ ℃ f o r６０mi n g
d i s t i nc t l oabou t１０％ o ft het o t a lquan t i t fBN, yt yo wh i chwa si n s u l a t e da t８５０ ℃ a f t e rh e a t i nga t１０５０ ℃． Thes i z eo ft he p r e c i i t a t e sbo t hi ng r a i nsanda t p [ ( ) ] bounda r i e swa sobv i ous l l a r i ５ b ． yen ged F g Dur i ngt hei s o t he rma lt r e a tmen ta t８５０ ℃ a f t e r he a t i nga t１２５０ ℃ ,t hes amephenomenonwa smo r e r ema rkab l e．Asshowni nF i ５ ( c)t hep r e c i i t a t e s g p wi t h i ng r a i ns we r ef u r t he rr educ ed,andt he i rs i z e be c ameevenb i r．Be s i de st hei nd i v i dua l l r own gge yg , BNa tt heg r a i nbounda r i e st he r ewe r es omec oa r s e r BNf o rme dbyt h ec omb i n a t i ono faf ewBNp a r t i c l e s． Wi t hd i f f e r en ti n i t i a laus t en i z i ngt empe r a t u r e s t hequan t i t i z eo fBNr ep r e c i i t a t eddu r i ngt he yands p i s o t he rma lt r e a tmen ta t８５０ ℃ we r equ i t ed i f f e r en t duet ot hechange so ft hequan t i t fMnS yandshapeo du r i nghe a t i nga th i empe r a t u r e．Whenhe a t i nga t ght ９５０－１０５０ ℃ ,MnSwa ss t i l lsphe r i c a landt hed i s Ｇ s o l u t i onands o l i ds o l u t i ond i dno thappen． Be c aus ea r e a tnumbe ro fsphe r i c a lMnS wou l dbet henuc l e i g
o fBN c r t a l l i z a t i on,t he quan t i t fp r e c i i t a t ed ys yo p BN be c ame b i r,bu t wi t h sma l l e rs i z e．When gge he a t i nga t１１５０ ℃ mos to ft hesphe r i c a l MnSbe Ｇ , c amepo l r a l wh i ch wou l dno tbet henuc l e io f yhed BN c r t a l l i z a t i on．Be c aus eo ft hede c r e a s eo ft he ys nuc l e ir a t et hequan t i t fp r e c i i t a t edBN wa sa l so yo p , r educ ed bu tt hes i z eo ft hep r e c i i t a t e sbe c ameb i Ｇ p g r．Whenhe a t i nga t１２５０ ℃ mo r et hanaha l fo f ge MnS we r ed i s so l vedi n add i t i ont ot hechange o f MnSshape．The r e f o r et he quan t i t fp r e c i i t a t ed yo p BNbe c amesma l l e r,andt hes i z eo ft hep r e c i i t a t e s p be c ameb i e r ．W i t hi n c r e a s e o ft h e B N s i z et h e gg mo r l ogyo fBN wa schanged,t oo．Usua l l he pho yt compoundo fMnSandBN wa sne a r l r i c a l,and ysphe BN wa sp r e c i i t a t edi nar ad i a t i onf o rma r oundMnS． p AsBNs i z er e a chedac r i t i c a lva l uei twa sp r e c i i t a Ｇ p t edaga i na sap l a t e Ｇ l i ke monoc r t a l．Theshapeo f ys t hecompoundbe c amei r r egu l a ra sshowni nF i ６． g Someo ft hep l a t e Ｇ l i keBNwe r ewi t hc o r n e rang l e,and
( a),( b),( c)８５０ ℃×３０ mi n; ( d)８５０ ℃×１２０ mi n．
F i ６ MnSandBNc ompoundandp l a t e Ｇ l i k eBNo fs t e e lt r e a t e dby１１５０ ℃×６０mi n＋WQ→８５０ ℃× ( ３０－１２０)mi n＋WQ g
s omewe r eo fa r c．
３ Di s c u s s i on
３ １ Ef f e c to fi n t e r f a c eb e twe e n MnSandma t r i x I twa sobs e r vedi nt heexpe r imen tt ha ta r ound t heMnSpa r t i c l e si ng r a i nst hep r e c i i t a t i o nr a t eo f p BN wa sve r i twa sp r e c i i t a t edi ng r a i ns yh ghandi p e a r l i e rt hana tg r a i nbounda r i e s．Duet ot ha tt heav Ｇ e r aged i s t anc ebe twe en MnS wa ssma l l e rt hant ha t
be twe eng r a i nbounda r i e s,bo r ona t omst ooksho r t e r t imet od i f f us et owa rdsMnS．Anobs e r vedimpo r t an t t h i ng wa st ha tbo r ona t omsa r ound MnSwe r ea c cu Ｇ mu l a t ed mo r ee a s i l r ed wi t ht ha ta tg r a i n y compa bound a r i e s．F i ７ wa st ake na sa mod e lt os howt he g d i f f e r enc eo ft hea c cumu l a t i on o fbo r on a t omsa t / r a i nbounda r i e sandont hei n t e r f a c eo f MnS ma Ｇ g t r i x． Fo rt heconven i enc et heg r a i nbounda r sa s Ｇ ywa , / sumedt obeap l ane andt hei n t e r f a c eo fMnS ma t r i x
I s sue９ Ef f e c t so fAus t en i z i ngTempe r a t u r eonRep r e c i i t a t i ono fBN p
( a)Gr a i nbounda r b)MnSbounda r f a c e． y; ( ysur
F i ７ Mod e lo fg r a i nbounda r r u r f a c e g yandbounda ys
wa st obeasphe r e． I twa ssuppo s edt ha tt her ad i us o fMnSsphe r ewa sr,t hed i f f us i ond i s t anc eo fbo r on a t omsa tag i vent imewa sl,anda l lt hebo r ona t oms wi t h i nt he d i s t anc el we r ea c cumu l a t ed a tg r a i n bounda r i e sandont hei n t e r f a c e．Thec onc en t r a t i on o fbo r ona t oms wi t h i nan un i t evo l umeo f ma t r i x wa s[ B]M ,andt hes i t ua t i ono fbo r ona c cumu l a t i on a t omst owa r dsg r a i nbounda r i e sf r omtwos i de swa s , , c ons i de r ed． So f o rg r a i nbounda r i e st hequan t i t f yo nanun i tbounda r r e awa sc a l Ｇ bo r ona t oms [ B] ya GBi cu l a t eda sf o l l ows [ ] ( B GB ＝２ l[ B]M １) Fo rt hei n t e r f a c eo fMnS/ma t r i x,i ns i deo ft he r＋l)andi sphe r ewi t hanou t e rd i ame t e ro f( nne r , d i ame t e ro fr a l lbo r ona t omswe r ea c cumu l a t edon t hei n t e r f a c e wi t h asu r f a c ea r e ao f４π r２ ,sot he [ ] u a n t i t o fb o r o na t o m s B i nt h eu n i tb o u n d a r q y y MnS a r e awa s ìï üï ï４ ï ３ ( [ B]MnS＝ íïï π[( B]M ２) r＋l) －r３]÷４π r３ ýïï [ î３ þ As sumi ng [ B]MnS＞ [ B] t hen GB , ïìï４ ïüï ３ ( [ B]MnS＝ íïï π[( l ３) －r３]÷４π r＋l) r２ ýïï ＞２ î３ þ Tos imp l i f ha t yt ( l２ ＋３ r l－３ r３ ＞０ ４) a srandla r epo s i t i ve,s oEqn ( ４)wou l dbe
１０３
ont hei n t e r f a c eo f MnS/ma t r i x wa s much h i r ghe t hant ha ta tg r a i nbounda r i e s．Asbo r onconc en t r a Ｇ t i onr e a chedac e r t a i nc r i t i c a lva l ue,BNj us ts t a r t ed t obep r e c i i t a t ed． SowhenMnSex i s t ed,t hep r e c i Ｇ p p i t a t i ono fBNi ng r a i nswa se a r l i e rt hant ha ta tg r a i n bounda r i e s． Be s i de s,n i t r ogenwa sa l soe a s i l eg r ega t edt o Ｇ ys wa rdst heg r a i nbounda r i e swi t hh i he n e r a sb o Ｇ g gy r ond i d． I twa sbe c aus en i t r ogend i f f us i on wa ss l o Ｇ we rt hanbo r oni naus t en i t e,sot heg r owt ho fBN wa sde t e rmi nedbyn i t r ogend i f f us i on,andBNi nt he s t e e lwi t hh i i t r ogenwa spr e c i i t a t ede a s i l ghn p y． ３ ２ Ef f e c to fMnSmo r l o e c i i t a t i on pho gyonBNpr p I twa sf oundi nt heexpe r imen tt ha twi t ht hei n Ｇ c r e a s eo fhe a t i ngt empe r a t ur et he MnS mo r l ogy pho wa schanged,wh i cha l sochangedt hef unc t i ono fnu Ｇ c l e io fc r t a l l i z a t i on．Almos ta l lo fMnSwe r ene a r l ys y sphe r i c a land BN wa sp r e c i i t a t eda r ound MnSi n p t hef o rmo fcompoundo fMnSandBNunde rf o r i ng g o rno rma l i z i ng．Att hehe a t i ngt emp e r a t u r el owe rt han １０５０ ℃ ,mos to fMnSwh i chhadno tbe eni nso l i d so l u t i on wa schangedf r om sphe r i c a lt o po l r a l． yhed Th i st e nd e n c e c amemo r es i i f i c an twi t ht her a i s eo f yb gn t hehe a t i ngt empe r a t ur e． I twa sf oundf r omal o to f obs e r va t i onst ha tnoBN wa sp r e c i i t a t eda r oundt he p l r a l MnS．Tha t me an tt ha tt he po l r a l po yhed yhed MnSwa snol onge ra st henuc l e io fBNc r s t a l l i z a Ｇ y t i on．By me anso fe l e c t r ond i f f r a c t i onandcompos i Ｇ t i onana l i si n mi c r o Ｇ z one,i t wa si nd i c a t edt ha t ys bo t ht hes t ruc t ur eandcons t i t uen to f MnShadno change sa td i f f e r en tt empe r a t ur e sbe f o r ei t sso l u t i on． The r e f o r et hechangeo f MnS mo r l ogy a th i pho gh t empe r a t ur e wou l d ber e l a t edt ot hes emi Ｇ eu t e c t i c r e l a t i onbe twe en MnSand ma t r i x．I nt h i sc a s et he shapeo fMnSbounda r i i f i c an td i f f e r enc e yhadnos gn compa r i ng wi t hg r a i nbounda r c aus eo ft hel owＧ y．Be e rsur f a c eene r ns emi Ｇ eu t e c t i cr e l a t i on,MnSl os t gyi t he ab i l i t o be nuc l e io fc r t a l l i z a t i on a st he yt ys sphe r i c a lMnS．
－３＋ ２１ ( r≈０ ７９１ r ５) ２ The r e f o r e,a sl onga sl＞０ ８ r,t hebo r onc on Ｇ c en t r a t i onont hei n t e r f a c eo fMnS/ma t r i xi sh i r ghe ３ Shapeo fBN t hant ha ta tg r a i nbounda r i e s．Al t houghi nt her e a l ３ I twa scon f i rmedbyt hep r ev i ouswo rkt ha tBN c r t a l l i z a t i ont heg r a i nbounda r sno tt her e a l ys y wa ns t e e lex i s t edi npo l r t a lf o rma l ong [ ０００１]ax i s l ane,t hei n t e r f a c eo fMnS/ma t r i xwa sno tt her e a l i yc ys p [ ４] a n d l i k et h es h e r i c a l r a h i t ei nr a d i a ld i r e c t i o n ． sphe r e,bu twi t ht hes amet endenc ． p g p y Add i t i ona l l twa sa l sof oundt ha tt heg r owt ho ft he I t wa sknownf r om t heobs e r va t i on by TEM yi a r l r i c a lBN wa sl imi t edt oac e r t a i ns i z ei n t ha tt her ad i uso fMnSi nt hec ompoundo fMnSand ne ysphe i chBN g r ewa sap l a t e Ｇ l i kemonoc r s t a l ． A c c o r d Ｇ BN wa si nt her angeo f０ ０７－０ １５μm,t hed i f f u Ｇ wh y / , ngt oobs e r va t i onst hec r i t i c a ls i z e wa sabou t０ ６ s i onr a t eo fbo r oni naus t en i t ewa s４ ０４μm s and i S i ng l ec r t a lBNg r ewupa l ongapa r to fsphe r Ｇ t hed i f f u s i ont imewou l db e１ ９×１０－４ －８８×１０－４ s, μm． ys c a lBNandhadt hes ameo r i en t a t i ono fc r s t a l l i z a Ｇ wh i ch me e t sEqn ( ５)．Sot hebo r onc onc en t r a t i on i y l＞
１０４
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２０
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