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Effect of vanadium on dynamic continuous cooling transformation behavior of medium-carbon forging steels
J our na lo fI r onandS t e e lRe s e a r ch, I n t e r na t i ona l２４ (２０１７) ６４１－６４８
Ef f e c to fvanad i umondynami cc on t i nuousc oo l i ngt r ans f o rma t i on behav i o ro fmed i umＧ c a r bonf o r i ngs t e e l s g We i Ｇ un Hu i１ ∗ , NaXi ao１ , Xi ao Ｇ l iZhao１ , Yong Ｇ i anZhang１ , Yu Ｇ f eng Wu２ j j ,
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Schoo lo fMe chan i c a l, El e c t r on i candCon t r o lEng i ne e r i ng, Be i i ngJ i ao t ongUn i ve r s i t i i ng１０００４４, Ch i na j y, Be j Fa cu l t fMa t e r i a l sSc i enc eandEng i ne e r i ng, Kunmi ngUn i ve r s i t fSc i enc eandTe chno l ogy, Kunmi ng６５００９３, Yunnan, yo yo Ch i na ARTICLEINFO
ABSTRACT
Keywo rds: Dynami cCCTd i ag r am Vanad i um Mi c r oa l l oyeds t e e l Mi c r o s t r uc t ur e Ha r dne s s
Dynami cc on t i nuousc oo l i ngt r ans f o rma t i on ( CCT) behav i o ro f med i umＧ c a r bonf o r i ng g s t e e l s mi c r oa l l oyed wi t hd i f f e r en tVc on t en t supt o０ ２９％ wa si nve s t i t edby me anso f ga d i l a t ome t r i cme a sur emen t, mi c r o s t r uc t ur a lobs e r va t i onandha r dne s sme a sur emen t．Ther e Ｇ su l t sshowedt ha tt hedynami cCCTd i ag r amswe r es imi l a randt hema i nd i f f e r enc ewa st ha t t hef i e l dso ft het r ans f o rma t i onp r oduc t swe r esh i f t edt ot her i ts i deo ft hed i ag r amswi t h gh t hei nc r e a s eo fVc on t en t, andt h i se f f e c twa smo r eno t i c e ab l ewi t hanadd i t i ono f０ ２９％ V． TheAc１andAc３t empe r a t ur e sshowedi nc r e a s i ngt r endswi t hi nc r e a s i ng Vc on t en t, wh i l e t hec r i t i c a lc oo l i ngr a t e sde c r e a s edwi t hi nc r e a s i ngVc on t en t．Thei nc r e a s eo fVc on t en tr e Ｇ su l t edi ns i i f i c an ti nc r e a s eo fha r dne s sandt h i st endenc senhanc ed wi t hi nc r e a s i ng gn y wa c oo l i ngr a t eun t i lt hef o rma t i ono fa c i cu l a rf e r r i t e (AF) ．Ap r omi s i ngapp r oa cho fr ema rk Ｇ ab l r ov i ngt het oughne s so ff e r r i t i c Ｇ a r l i t i c med i umＧ c a r bonf o r i ngs t e e l swi t hsu i t Ｇ yimp pe g ab l eVadd i t i onandt hei n t r oduc t i ono fAF wi t hou tno t ab l epena l t t ss t r eng t hl eve l yoni wa ssugge s t ed．
１． I n t r odu c t i on Re c en t l he r ehavebe eni nc r e a s i ngapp l i c a t i ons y, t o fmi c r oa l l oyed ( MA) med i umＧ c a rbonf o r i ngs t e e l s g a ssubs t i t u t e sf o rt r ad i t i ona lquenchedandt empe r ed (Q&T) f o r i ngs t e e l st o manu f a c t u r eava r i e t f g yo au t omob i l ec omponen t s．El imi na t i ng t he c o s to f t Ｇ f o r i ng he a tt r e a tmen t (quench i ng and h i pos g gh t empe r a t u r et empe r i ng) i st he ma i nt a r tf o rt he ge [ , ] i n t r oduc t i on o ft h i sk i nd o fs t e e l１ ２ ．Thede s i r ed me chan i c a lpr ope r t i e so ff o r omponen t sc ou l d gedc beob t a i nedt hr oughc on t r o l l edc oo l i ngf r omf o r i ng g t empe r a t u r e．The r e f o r e, f a c t o r ssuch a schemi c a l c ompos i t i ons, c oo l i ngs t r a t eg i e sandf o r i ngpa r amＧ g e t e r shaves t r ongi n f l uenc e sont he mi c r o s t ruc t u r a l cha r a c t e r i s t i c s, and t hus on t hef i na l me chan i c a l [ ] r ope r t i e so ff o r i ngsmadeo ft h i sk i ndo fs t e e l３Ｇ８ ． p g I ti swe l lknownt ha tc on t i nuousc oo l i ngt r ans f o r Ｇ ma t i on (CCT) d i ag r ami sanexc e l l en tt oo lt os t udy t hei n f l uenc eo fchemi c a lc ompo s i t i on andc oo l i ng r a t eonpha s et r ans f o rma t i onp r oduc t s, wh i chu l t i Ｇ ma t e l n f l uenc et heme chan i c a lp r ope r t i e s, a si ta l Ｇ yi , Ph． ∗ Co r r e spond i ngau t ho r．Pr o f． D． EＧma i laddr e s s: wjhu i＠b t ue ．duc ． n (WJ．Hu i) ． j
l owst oi den t i f hedoma i nandbounda r fe a ch yt yo / ( , , s eand o rcons t i t uen t f e r r i t e pe a r l i t e ba i n i t e pha [ ] andma r t ens i t e) a saf unc t i ono fcoo l i ngr a t e９ ．The cons t ruc t i ono fa CCT d i ag r am i sba s edf i r s t l y on d i l a t ome t r i cana l i scomp l emen t edbybo t h mi c r o Ｇ ys s t ruc t ur eandha rdne s ss t ud i e s．Theshapeo faCCT d i ag r ami sve r ens i t i vet ot hechemi c a lcompos i Ｇ ys t i onso ft het e s t eds t e e landt hecoo l i ngr a t e sus ed [ , ] dur i ngp r oc e s s i ng１０ １１ ． I nt hec a s eo fMA med i umＧ c a rbonf o r i ng s t e e l s, Mn and mi c r oa l l oy i ng e l e Ｇ g men t sa r e gene r a l l r e s en t．Theadd i t i on o f Mn yp sh i f t st heeu t e c t o i dpo i n tt owa rdsl owe rc a rboncon Ｇ c en t r a t i on, l owe r st he pha s et r ans f o rma t i ont emＧ r a t ur e s, andt husp r omo t e spe a r l i t ef o rma t i onand pe de c r e a s e st het r ans f o rma t i onspe edo faus t en i t et o [ ] a r l i t e１２ ．Mna l so make st hep r oeu t e c t o i df e r r i t e pe cur veo f CCT d i ag r ams movet ot he r i t, and gh r e a t l r omo t e st he f o rma t i on o fi n t e rmed i a t e g yp [ ] t r ans f o rma t i onp r oduc t ssucha sba i n i t e１３ ． Fur t he r Ｇ mo r e,i ti swe l lknownt ha tt heMnadd i t i oni nc r e a Ｇ s e st heso l ub i l i t fVCand VNi naus t en i t e, and yo [ ] t hu se nhan c e sp r e c i i t a t i onha r d e n i nge f f e c t１２ ．The r e Ｇ p
Re c e i ved９Oc t obe r２０１６; Re c e i vedi nr ev i s edf o rm２４De c embe r２０１６; Ac c ep t ed２５De c embe r２０１６ Ava i l ab l eon l i ne１５June２０１７ １００６ Ｇ ７０６X/Copy r i tⓒ２０１７, Th ee d i t o r i a lo f f i c eo fJ ou r n a lo fI r ona ndS t e e lRe s e a r c h, I n t e r n a t i on a l． Pub l i s h e dbyE l s e v i e rL imi t e d．Al lr i t sr e s e r v e d． gh gh
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
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f o r e, f o r MA f e r r i t e Ｇ a r l i t et o r i ng s t e e l s, pe ypef g t he i r Mn c on t en t sa r e usua l l owe rt han １ ５％ , yl whe r e a sf o r MA ba i n i t i cf o r i ng s t e e l s, t ho s ea r e g enhanc edt oh i rt han１ ５％． ghe Thema i n mi c r oa l l oy i nge l emen ti n MA med i umＧ c a rbonf o r i ngs t e e l si sVduet oi t ss t r ongande a s i Ｇ g , l c o n t r o l l a b l e r e c i i t a t i o nh a r d e n i n e f f e c t w h i c h y p p g i sp r ima r i l ot her e l a t i ve l a r o l ub i l i t f yduet yl ges yo i t sc a rbon i t r i deV(C,N) i naus t en i t ea tc onven i en t [ , , ] he a t i ngt empe r a t u r e１ １１ １２ ．F i ne V(C, N) pa r t i c l e s c ou l dp r e c i i t a t ei n bo t hp r oeu t e c t o i df e r r i t e and p a r l i t i cf e r r i t eonc on t i nuousc oo l i ngdu r i ngand/o r pe [２,５] a f t e raus t en i t e Ｇ f e r r i t et r ans f o rma t i on ．The r ei s s t i l lsomed i s ag r e emen ti nl i t e r a t u r er ega r d i ngt he e f f e c to fV ont het r ans f o rma t i onbehav i o ro f MA s t e e l s． I ti sgene r a l l l i evedt ha tV a t omss eg r e Ｇ ybe t et oaus t en i t eg r a i n bounda r i e sr ende r i ngt hem ga l e s se f f e c t i vea sf e r r i t e nuc l e a t i on s i t e s, t husi n Ｇ c r e a s i ngha r denab i l i t r e s s i ngf e r r i t e Ｇ a r l i t e ybysupp pe [ ] f o rma t i on５ ．Howeve r,i ti sa l s obe l i evedt ha tVa c Ｇ t ua l l sno tsupp r e s sg r a i nbounda r e a c t i onand ydoe yr [１,１４] even de c r e a s e s ha r denab i l i t ．Re c en ts t udy o f y t heau t ho r sha sshownt ha tf e r r i t ef r a c t i oni nc r e a s e s wi t hi nc r e a s i ng V c on t en ti na s Ｇ f o r iVS ged３７MnS [ ] s t e e l１５ , andf u r t he ri nve s t i a t i o na l s or e v e a l e dt ha t g i nc r e a s i ng Vc on t en ts i n i f i c a n t l e n h a n c e st h ef o r Ｇ g y ma t i ono fa c i cu l a rf e r r i t e (AF) s t ruc t u r ea ta mod Ｇ [１６] e r a t ecoo l i ngr a t e ．Ther e su l t so ft hei n f l uenc eo f r ehe a t i ngt empe r a t u r eand V c on t en tont het r ans Ｇ f o rma t i onbehav i o ro fmed i umＧ c a rbonf o r i ngs t e e l s g sugge s tt ha tVi ns o l i ds o l u t i onp r omo t e st hef o rma Ｇ [ ] t i ono fba i n i t e５ ．I tha sa l s of oundt ha t V (C, N) r t i c l e sc ana c ta sp r e f e r en t i a lnuc l e a t i ons i t e sf o r pa ba i n i t ei nVＧMA me d i umＧ c a r bons t e e l s, wh i c ht hu sf a Ｇ Tab l e１ Chemi c a lc ompo s i t i onso ft e s t eds t e e l s (ma s s％ ) S t e e l D１ D２ D３
C
０ ４１ ０ ４０ ０ ４０
S i
０ ４２ ０ ４４ ０ ４４
Mn
１ ２５ １ ２２ １ ２６
P
０ ０１５ ０ ０１５ ０ ０１７
S
０ ０４１ ０ ０３９ ０ ０４２
Cr
０ １６ ０ １７ ０ １８
c i l i t a t e sba i n i t ef o rma t i ona tf a s t e rcoo l i ngr a t e s１７ ． I tshou l dbeno t edt ha tde f o rma t i ona l soha sas i Ｇ g n i f i c an ti n f l uenc e on t he pha s et r ans f o rma t i on o f [ , ] s t e e l s１３ １８ ．The r e f o r e, i ti s no t enough on l o yt knowt hes t a t i cCCT d i ag r ams wh i chde s c r i bet he t r ans f o rma t i oni nnon Ｇ de f o rmedaus t en i t eo ff o r i ng g s t e e l s．Mo r eove r, ma i n l oi t se f f i c i en tp r e c i i Ｇ yduet p t a t i onha rden i nge f f e c tands i n i f i c a n t i m r o v e m e n t g p o ff a t i u e r o e r t i e s o f m e d i u m Ｇ c a r b o n f o r i n g p p g g [ ] s t e e l s１５ , t he r eha sbe enat endenc of ur t he ri n Ｇ yt [ , ] c r e a s eV con t en tupt oabou t０ ３０％ １９ ２０ ．The r e Ｇ f o r e, t hea im o ft hep r e s en ts t udyi st os t ema t i Ｇ ys c a l l nve s t i t et hei n f l uenc eo f V con t en tup t o yi ga ０ ３０％ ont hedynami cCCTcha r a c t e r i s t i c so fmed i Ｇ umＧ c a rbonf o r i ngs t e e l s．Theha rdne s schangeand g mi c r os t ruc t ur a levo l u t i onwi t hcoo l i ngr a t e shavea l Ｇ sobe enana l z ed．Ther e su l t s wi l lbebene f i c i a lt o y t he p r a c t i c a lapp l i c a t i on o fcon t r o l l edf o r i ng and g coo l i ngt ot hep r oduc t i ono fh i r f o rmanc ef o r Ｇ ghpe g i ngcomponen t smadeo fMA med i umＧ c a rbons t e e l s． [
]
２．Ma t e r i a l sandExp e r imen t a lPr o c e du r e
Med i umＧ c a rbonf o r i ngs t e e l swi t hd i f f e r en tcon Ｇ g t en t so fV (０％ , ０ １０％ and０ ２９％ ), wh i ch we r e de s i t eda sD１, D２andD３, we r eu s e di nt hep r e s e n t gna s t udy．The s es t e e l swe r eme l t edi nal abo r a t o r v a c Ｇ y uumi nduc t i onf urna c eandc a s ti n t o１１０kgi ngo t s． Tab l e １ showst hechemi c a lcompos i t i ons o ft he t e s t eds t e e l s．The s ea s Ｇ c a s ti ngo t swe r er ehe a t edt o abou t１２５０° C, he l df o ra tl e a s t１ h, andf i na l l y r e s sf o r oba r s (４５ mmi nd i ame t e r) f o l l owed p gedt bys t i l la i rcoo l i ng．Cy l i nd r i c a lspe c imens (６ mmi n d i ame t e rand８０ mmi nhe i t) we r ecu tf r om ha l f gh r ad i uso ft hea s Ｇ f o r r sandha dt hel ongax i sp a Ｇ gedba
V
－ ０ １０ ０ ２９
r a l l e lt ot heba rax i s． Thedynami c ( wi t h ho tde f o rma t i on) CCT d i a Ｇ r amswe r ec onduc t edonaGl e eb l e Ｇ ３８００t he rmome Ｇ g chan i c a ls imu l a t o r．Th e rmo c oup l e sw i t had i ame t e ro f ０ ２mm we r espo twe l dedt ot hesu r f a c eo ft hespe c i Ｇ mensa tt he i r mi dd l el eng t ht or e c o r dt het empe r a Ｇ t u r e． Spe c imenswe r ef i r s t l ehe a t edt o１２２０° Ca ta yr c ons t an the a t i ngr a t eo f１０° C/sandhe l df o r１２０s, / andt hent hey we r ec oo l eda t５° C st ode f o rma t i on t empe r a t u r e１１００° C．To mi n imi z et empe r a t u r eg r a Ｇ d i en t, t hespe c imenswe r ekep ta t１１００° Cf o r５s． Then, t he spe c imens we r ec omp r e s s ed t o at rue s t r a i no f０ ３６ (r educ t i oni n he i to f３０％ ) a ta gh nomi na ls t r a i nr a t eo f１ s－１ andf i na l l oo l edt o yc
Ti
０ ０１７ ０ ０２２ ０ ０２７
Al
０ ０２９ ０ ０３１ ０ ０３１
N
０ ０２２ ０ ０１６ ０ ０１７
Fe
Ba l anc e Ba l anc e Ba l anc e
r oomt empe r a t ur ea td i f f e r en tl i n e a rc oo l i ngr a t e si n t her ang eo f０ ０３－４１ ５０° C/s．The s ecoo l i ngr a t e s we r echos ena si nd i c a t edbyt hes t a t i cCCTd i ag r am o fmed i umＧ c a rbonf o r i ngs t e e lwi t hs imi l a rchemi Ｇ g [ ] c a lcompos i t i on１２ , wh i ch we r et hencon t r o l l edby t hede s i l i ngpa t t e rno ft hes imu l a t o rs t em． gnedcoo ys Seve r a lspe c imens we r ed i r e c t l r om de Ｇ yquenchedf f o rma t i ont empe r a t ur ei no rde rt ode t e rmi net hei n i Ｇ t i a laus t en i t eg r a i ns i z e．Thedynami cCCTd i ag r ams we r ec on s t r u c t e da f t e rd e t e rmi n i ngt hec r i t i c a lt r an s f o r Ｇ ma t i ont emp e r a t u r e sc omp l eme n t e dby mi c r o s t r u c t u r a l ob s e r v a t i on sandVi cke r sha rdne s sme a sur emen t s． Spe c imensf o rop t i c a lmi c r os copy (OM) we r eme Ｇ chan i c a l l r oundandpo l i shed, andt hene t chedwi t h yg
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
３vo l ％ n i t a l．Thequenchedspe c imenswe r ee t ched i ns a t ur a t edaqueousp i c r i cs o l u t i onwi t hs omed r ops o fsur f a c t an tt or eve a laus t en i t eg r a i n．Theave r age aus t en i t eg r a i ns i z ewa sme a su r edt hr ought hel i ne a r i n t e r c ep tme t hod．Spe c imensf o rt r ansmi s s i one l e c Ｇ t r onmi c r o s c opy (TEM) we r ef i r s t l l i c e di n t o０ ５mm ys t h i ck p l a t eandsubs equen t l r o u n dd o w nt of o i l s yg wi t hat h i ckne s so fa r ound５０μm．The s ef o i l swe r e f i na l l l e c t r opo l i shedi natwi n Ｇ e te l e c t r opo l i sh i ng ye j appa r a t usus i ngas t anda r dchr omi umt r i ox i de Ｇ a c e t i c a c i dso l u t i on．Th i nf o i l swe r eexami nedi na Hi t a ch i HＧ ８００t r ansmi s s i one l e c t r onmi c r o s c opea tanop e r a t Ｇ i ngvo l t a eo f２００kV．Vi c k e r sh a r dn e s so ft hes amp l e s g wa sme a su r edwi t ha４９Nl oadandt heha r dne s sr e Ｇ su l t sa r et heave r ageo fa tl e a s t１０me a su r emen t sf o r e a chs amp l e．
３．Re s u l t sandDi s c u s s i on ３ １．Mi c r o s t ruc t ur e s
F i １showst hec a l cu l a t edequ i l i b r i umf r a c t i ono f g V(C,N) p r e c i i t a t e sandt hes i t ef r a c t i onso fCand p Ni nV(C,N) a saf unc t i ono ft empe r a t u r e． I tr eve a l s t ha tt heV(C,N) p r e c i i t a t e sa r et he rmodynami c a l l p y s t ab l eove rar a ng eo ft emp e r a t u r e sf o rbo t ht h eVＧMA s t e e l s, andt heexpe c t edf r a c t i ono fV(C,N) a tl ow t empe r a t u r eandf e r r i t ef i e l do ft heD３s t e e li sabou t twot ime sh i rt hant ha to ft heD２s t e e l． I ta l s or e Ｇ ghe ve a l st ha tt hec a l cu l a t edd i s s o l u t i ont empe r a t u r e so f V(C,N) p r e c i i t a t e so ft heD２andD３s t e e l sa r e９７７ p and１１４８° C, r e spe c t i ve l i chi nd i c a t e st ha tt he y, wh d i s so l u t i on t empe r a t u r ei ss i i f i c an t l nc r e a s ed gn yi whenVc on t en ti si nc r e a s edf r om０ １０％ t o０ ２９％． Mo r eove r, t hesha r c r e a s eo ft hema s sf r a c t i ono f pde V(C,N)i sma i n l s c r i bedt ot heno t ab l ep r e c i i t a t i Ｇ ya p ono fpe a r l i t i cc emen t i t e．Theave r agep r i o raus t en i t e r a i ns i z e so ft hede f o rmedspe c imenso fD１, D２and g D３s t e e l swe r ede t e rmi neda s(６３±１２), (５３±８) and (４９±７) μm, r e spe c t i ve l headd i t i ono fV y．Thus, t exh i b i t sapo s i t i vee f f e c tonde c r e a s i ngt heaus t en i t e r a i ns i z e, wh i c hi sc on s i s t e n tw i t ht h ef a c tt h a tVt e nd s g
F i １． Ca l cu l a t ede i l i b r i umo fV(C,N) f r a c t i ono fVＧMA qu g s t e e l sD２andD３us i ngThe rmo ＧCa l cs o f twa r e．
６４３
t or e f i net hedynami c a l l e c r t a l l i z edg r a i ns i z eo f yr ys [ ] ３７MnS iVSs t e e l２１ ．The r e f o r e, ahe a t i ngt empe r a t ur e o f１２２０° C wa schos enno ton l o rt hecomp l e t ed i s Ｇ yf so l u t i ono fVi nau s t e n i t eandt hu smak i ngt hemo s to f t hep r e c i i t a t i onha rden i nge f f e c to fV(C,N), bu ta l Ｇ p sobe c aus ei ti sve r l os et ot hei ndus t r i a lhe a t i ng yc t empe r a t ur e su s u a l l u s e d f o r a u t o m o t i v e c o m o n e n t s ． y p Thet i c a lo t i c a l m i c r o r a h so ft h ed e f o r m e d yp p g p s e c ime n sa td i f f e r e n tc oo l i ngr a t e sa r eg i v e ni nF i s ２－ p g , ４．Asexpe c t ed a l lt hede f o rmedspe c imensexh i b i ta mi x t ur e mi c r os t ruc t ur eo fp r oeu t e c t o i df e r r i t eand a r l i t ewhencoo l eda tl owe rcoo l i ngr a t e s．Thep r o Ｇ pe eu t e c t o i df e r r i t e ma i n l l i ne a t eda tp r i o raus t en i t e yde r a i nbounda r i e swi t haf ewde co r a t edwi t h i naus t en Ｇ g i t eg r a i ns．Thef r a c t i ono ff e r r i t ede c r e a s e swi t hi n Ｇ c r e a s i ngcoo l i ngr a t eandt hust hepe a r l i t epha s ebe Ｇ come s mo r edomi nan t．Thei nc r e a s eo f V con t en t r omo t e st hef o rma t i on o ff e r r i t ee spe c i a l l n t r a Ｇ p yi r anu l a rf e r r i t e (IGF) ．Fur t he ri nc r e a s i ng coo l i ng g r a t el e adst oevenl e s sf e r r i t eandp r omo t e st hef o r Ｇ ma t i ono f AF p r ima r i l tt heexpens eo fpe a r l i t e． ya L i ket ha to fIGF, t hef o rma t i ono fAFwa sa l sos i Ｇ g n i f i c an t l r omo t edwi t ht hei nc r e a s eo fVcon t en t． yp F i ５(a,b) p r e s en t st heda rkf i e l d TEM mi c r o Ｇ g r a h ss h o w i n f i n e r e c i i t a t e sd i s t r i b u t e d w i t h i n g p g p p bo t ht hep r oeu t e c t o i df e r r i t eandpe a r l i t i cf e r r i t er e Ｇ i o n so f t h eD ３s t e e l c o r r e s o n d i n t oac o o l i n r a t e g p g g o f０ ８３° C/s．Thep r e c i i t a t ewa si d e n t i f i e da sV(C,N) p t hr oughs e l e c t ed a r e ad i f f r a c t i on pa t t e rn and EDS ana l e s (F i ５ (c,d)) ． I ti swo r t hno t i ngt ha tt he r e ys g exh i b i t saf ewamoun to fl a r es i z ep r e c i i t a t e s (abou t g p １０－２０ nm), wh i chi scons i de r edt obenuc l e a t ed dur i ng t he he a tp r e s e r va t i on and ho t de f o rma t i on [ ] r oc e s s１１ ． p Vi nt het e s t eds t e e l sc ana f f e c tt het r ans f o rma t i on behav i o rand mi c r os t ruc t ur a lcha r a c t e r i s t i c si ntwo ,p s t a t e s,i e． r e c i i t a t e sandso l i dso l u t i on． I ti sr e Ｇ p rdedt ha tV p r e c i i t a t e s V (C, N) a r ep r ima r i l ga p y f o rmedi nt he pha s et r ans f o rma t i on p r oc e s so rt he [ ] he a tp r e s e r va t i on p r oc e s sa f t e rt r ans f o rma t i on２２ ． Howeve r, V(C,N) cou l da l sobef o rmedi naus t en i t e a f t e raus t en i t i z i ngt r e a tmen to rdur i ngpos t Ｇho tde Ｇ f o rma t i oncoo l i ng whent he C o r N con t en t s we r e [２３,２４] h i ．Bo t ht he N andScon t en t so ft het e s t ed gh s t e e l sa r econs i de r ab l i o rt he p r e c i i t a t e so f yh ghf p VN, o rNＧ r i chV(C,N) on MnSi nc l us i onsmi ta l Ｇ gh [ ] r e adyex i s ti nt hede f o rmedaus t en i t econd i t i on２４ ． Thef o rma t i ono ft he s ep r e c i i t a t e sno ton l owe r s p yl t hec a rbonso l u t i oncon t en ti nt heaus t en i t ebu ta l so r omo t e st hef o rma t i ono fIGFi d i omo r tl owe r p phsa coo l i ngr a t e so rt hei n t r ag r anu l a rnuc l e a t i ono fAFa t [ , , ] mode r a t ecoo l i ngr a t e s５ １７ ２４ ．Theh i rt heVcon Ｇ ghe t en ti s, t hel a r rt heamoun to fp r e c i i t a t e si naus Ｇ ge p t en i t er eg i ont he r ewi l lbe, t houghi ti sa l sosugge s Ｇ t edt ha tVi nso l i dso l u t i onp r omo t edt hef o rma t i on [ ] o fba i n i t e５ o rVa t omc l us t e r i ngf a c i l i t a t e dana l t e r n Ｇ
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WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
(a) ０ ８３° C/s; (b) １ ６６° C/s; (c) ４ １５° C/s; (d) １６ ６０° C/s．
F i ２． Op t i c a lmi c r o s t r uc t u r e so fho tde f o rmedspe c imenso fD１s t e e lc on t i nuous l oo l edt or oomt empe r a t u r ea td i f f e r en t yc g c oo l i ngr a t e s．
(a) ０ ８３° C/s; (b) １ ６６° C/s; (c) ４ １５° C/s; (d) １６ ６０° C/s．
F i ３． Op t i c a lmi c r o s t r uc t u r e so fho tde f o rmedspe c imenso fD２s t e e lc on t i nuous l oo l edt or oomt empe r a t u r ea td i f f e r en t yc g c oo l i ngr a t e s．
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
６４５
(a) ０ ８３° C/s; (b) １ ６６° C/s; (c) ４ １５° C/s; (d) １６ ６０° C/s．
F i ４． Op t i c a lmi c r os t ruc t ur e so fho tde f ormedspe c imenso fD３s t e e lcon t i nuous l l edt or oomt empe r a t ur ea td i f f e r en t ycoo g c oo l i ngr a t e s．
F i ５． TEM mi c r og r aphso fho tde f o rmedspe c imeno fD３s t e e lc oo l eda t０ ８３° C/s, s how i ngf i n eV(C,N) pa r t i c l e sd i s t r i bu t ed g wi t h i np r oeu t e c t o i df e r r i t e (a, c) andpe a r l i t i cf e r r i t e (b), andEDSo fpa r t i c l e si n (c) (d) ．
６４６
ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８ WJ．Hu
a t i ve AF nuc l e a t i on１４ ．The r e f o r e, t hef e r r i t eand AFt r ans f o rma t i onswou l dbef u r t he rp r omo t ed． [
]
３ ２．Hardne s s
Thee f f e c t so fVc on t en tand po s t Ｇ de f o rma t i on c oo l i ngr a t e sonha r dne s sa r eshowni nF i ６(a) ． I t g i sc l e a rt ha tt he r ei sas t r ongdependenc eo fHVva l Ｇ ue sonVc on t en tandc oo l i ngr a t e．The r ei sane a r l y l i ne a rr e l a t i onsh i b e t w e e nt h eh a r d n e s so f t h et e s t Ｇ p eds t e e l sandc oo l i ngr a t ebe f o r et hef o rma t i on o f AF．Th i si s ma i n l ot hef o rma t i on o f mo r e y duet a r l i t e, t hede c r e a s eo fpe a r l i t el a t hst h i ckne s sand pe spa c i ng wi t ht hei nc r e a s eo fc oo l i ngr a t e．Asf o rt he VＧMAs t e e l sD２and D３, t hep r e c i i t a t i ono f mo r e p f i ned i s e r s e dV(C,N) p a r t i c l e sw i t hi n c r e a s i ngc oo l i ng p [ ] r a t ea l sor ema rkab l edt he ha r dne s s１６ ．I t y enhanc
shou l dbeno t edt ha tt oos l owcoo l i ng mayc aus et he coa r s en i ngo ft hei n i t i a lf i ne V (C, N) p r e c i i t a t e s p t hr oughOs twa l dr i e n i ngme c han i sma th i emp e r a Ｇ p ght t u r e s, whe r e a st oof a s tc oo l i ng ma tg i v eenough y no t imef o rt hecomp l e t ep r e c i i t a t i ono f V (C, N) i n p f e r r i t ewh i chc aus e sl owe rf r a c t i ono fp r e c i i t a t e sa l Ｇ p t houghf i ne rp r e c i i t a t e sc o u l db eo b t a i n e d ． T h a t i s p t os ay, anop t imumcoo l i ngr a t eex i s t st oob t a i nan app r op r i a t ef r a c t i on o ff i ne p r e c i i t a t e st o ge tt he p h i s tp r e c i i t a t i onha rden i nge f f e c tf o rt het e s t ed ghe p s t e e l swi t hf e r r i t e Ｇ a r l i t emi c r os t ruc t ur e．Fr omt he pe heop t imum coo l i ng r a t ei sabou t r e s en ts t udy, t p ３ ０° C/sf o rD２s t e e l, wh i chi si na c co rdanc e wi t h [ ] conven t i ona lVＧMA me d i umＧ c a r bonf o r i ngs t e e l s１２ , g anda r ound１ ５° C/sf o rD３s t e e l(F i ６(b)) ． g ( ), Ass e enf r omF i ６ a t heha rdne s so ft het e s t ed g
F i ６． Va r i a t i onso fha r dne s s (a) andha r dne s sd i f f e r enc e (b) wi t hc oo l i ngr a t ea f t e rho td e f o rma t i on (ΔHV５r e f e r st oh a r dn e s s g HV５ d i f f e r enc ebe twe ent heVＧMAs t e e l s (D２, D３) andba s es t e e l(D１) a ts amec oo l i ngr a t e) ．
s t e e l sshowsasha r nc r e a s eaboveac r i t i c a lc oo l i ng pi r a t e, wh i chc o r r e spondst ot hef o rma t i ono fAF．As t heD１s t e e lc on t a i nsnoV,i ti sr e a s onab l et or ega r d t h i ssha r nc r e a s ea st hef o rma t i ono fha r de rpha s e s pi o fba i n i t e, AFand ma r t ens i t e．Asa l s oi nd i c a t edi n F i ６(a), t hei nc r e a s eo fVc on t en tr e su l t si ns i i f Ｇ g gn i c an ti n c r e a s eo fh a r dn e s s, a ndt h i st e nd e n c e n h a n c e s y w i t hi n c r e a s i ngc oo l i ngr a t eun t i lt hef o rma t i ono fAF (F i ６(b)) ．Th i sha r den i ngi sp r ima r i l ot he g yduet r e c i i t a t i onha r den i ngby mo r ef i ne V(C, N) p r e Ｇ p p c i i t a t e si nf e r r i t ewi t ht hei nc r e a s eo fVc on t en tand p [ , ] c oo l i ngr a t e３ ５ , wh i l et hel e s se f f e c t i ve V (C, N) r e c i i t a t i on ha r den i ng o ff o rmi ng i n t e rmed i a t e p p t r ans f o rma t i onp r oduc t ssucha sAFandba i n i t ec au Ｇ s e st heha r dne s sd i f f e r enc eΔHV５ de c r e a s ewi t hf u r Ｇ [ , ] t he ri nc r e a s i ngc oo l i ngr a t e５ １９ ．Fo rt hef o rma t i on o f ma r t ens i t ea tac ons i de r ab l i oo l i ng r a t e, yh gh c ΔHV５i sne a r l e r obe c aus et heha r dne s so f ma r Ｇ yz t ens i t eba s i c a l l t sc a rbonc on t en to t he r ydependsoni t hanVcon t en t．
３ ３． CCTdi agrams
F i ７showst hedynami c CCT d i ag r amso ft he g t e s t eds t e e l s．Repr e s en t a t i vec oo l i ngcu r ve s, c oo l i ng
r a t e s, t r an s f o rma t i onr ang e s, t hena t ur eo ft het r ans Ｇ f o rma t i onp r oduc t sandt heva l ue so fVi cke r sha rd Ｇ ne s s (HV５) a r es howni nt hed i a r ams．Ac１ andAc３ , g wh i ch we r eob t a i nedonaFo rma s t o r ＧFI Id i l a t ome Ｇ t e r, a r ea l sog i veni nt hed i ag r ams．Al lt hed i ag r ams show mu l t i Ｇ t r ans f o rma t i on cur ve s, r eve a l i ng t ha t comp l exmi c r os t ruc t ur e sex i s twhent hecoo l i ngr a t e i si nc r e a s edf r om０ ０３t o４１ ５０° C/s． I nt het empe r Ｇ , a t ur er angeo ft hema o rt r ans f o rma t i oncur ve st he j f o rmed mi c r os t ruc t ur e s mayi nc l udef e r r i t e, pe a r l i Ｇ t e, AF, ba i n i t eandma r t ens i t e． Fo rt heba s es t e e lD１, a sshowni nF i ７(a), g / coo l i ngr a t e sl owe rt hanabou t４° C swou l dp r omo t e t hef o rma t i ono fami x t ur eo ff u l lf e r r i t eandpe a r l i t e mi c r os t ruc t ur e, wh i chi st hede s i r ed mi c r os t ruc t ur e f o r conven t i ona lf e r r i t i c Ｇ a r l i t i c med i umＧ c a rbon pe f o r i ngs t e e l s． I ti sc l e a rt ha tf e r r i t eandpe a r l i t ee s Ｇ g c i a l l hef o rme rcou l d be ob t a i nedt hr oughou t pe yt wi decoo l i ngr a t er angef r om０ ０３t o１７° C/s, wh i l e AFi spr oduc edunde rt hecoo l i ngr a t er angef r om４ t o１７° C/s, andba i n i t ebeg i nst obepr oduc ed when t hecoo l i ngr a t ei si nc r e a s edt oh i rt han１７° C/s． ghe Howeve r, ne i t he rt hef u l lAF mi c r os t ruc t ur eno rt he f u l lba i n i t i cmi c r os t ruc t ur ecou l dbeobt a i ned．Ma r Ｇ
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
６４７
(a) D１; (b) D２; (c) D３． F—Fe r r i t e; P—Pe a r l i t e; AF—Ac i cu l a rf e r r i t e; B—Ba i n i t e; M— Ma r t ens i t e．
F i ７． Dynami cCCTd i ag r amso ft e s t eds t e e l s． g
t ens i t ewa sobs e r veda tt hec oo l i ngr a t eh i rt han ghe a r ound１５° C/s, wh i l ef u l lma r t ens i t emi c r o s t ruc t u r e c ou l dbeob t a i neda te v e nh i e rc o o l i ngr a t eo fa r ound gh ２０° C/s． Theshape so ft hedynami cCCTd i ag r amsf o rt he VＧMAs t e e l sD２and D３a r es imi l a rt ot ha tf o rt he ba s es t e e l D１, a sshowni nF i ７ (b, c), wh i ch g me anst ha tt he i rt r ans f o rma t i onbehav i o ri ss imi l a r． The ma i nd i f f e r enc ei st ha tt hef e r r i t e, pe a r l i t e, AF, ba i n i t eand ma r t ens i t et r ans f o rma t i onf i e l dsi n t heD２andD３s t e e l sa r esh i f t edt ol onge rt imes i de (t ot her i ts i de) a sc ompa r edwi t ht ho s eo ft heD１ gh s t e e l, andt hed i f f e r enc ei smo r es i i f i c an ti nt heD３ gn s t e e l．Tha ti st os ay, t he s e pha s et r ans f o rma t i on sh i f t si nc r e a s ewi t ht hei nc r e a s eo fVc on t en t．Mo r e Ｇ ove r, t he AFt r ans f o rma t i onf i e l di sa l s oexpanded wi t hi nc r e a s i ng Vc on t en t． The me a su r ed Ac１ and Ac３ t empe r a t u r e sf o rt he t e s t eds t e e l sa r eg i veni nTab l e２． I ti sc l e a rt ha tt he add i t i ono fVi nduc e si nc r e a s edAc１andAc３t empe r a Ｇ , t u r e s．Asas t r ongf e r r i t ef o rme r Ve f f e c t i ve l t a Ｇ ys b i l i z e sf e r r i t ebyr a i s i ngt hef e r r i t e→aus t en i t et emＧ r a t ur e s．Thef e r r i t ef i e l dwi l lbeexpandeda sVi s pe added．The r e f o r e,t heAc１andAc３t empe r a t u r e sdu r Ｇ i nghe a t i ngshowi nc r e a s i ngt r endswi t hi nc r e a s i ngV c on t en t．The va l ue so f ma r t ens i t et r ans f o rma t i on s t a r tt empe r a t u r e (Ms) f o rt het e s t eds t e e l sa r ea l s o i veni nTab l e２． I ti sobv i oust ha tVshowsapo s i Ｇ g t i vee f f e c ton de c r e a s i ng Ms．Thec r i t i c a lc oo l i ng r a t e sf o rt hes t a r t i ngo fAFandma r t ens i t et r ans f o r Ｇ ma t i ons, a ndf o rob t a i n i ngc omp l e t ef e r r i t ea ndpe a r l i t e mi c r os t ruc t u r ea r ea l s osumma r i z edi nTab l e２． I ti s c l e a rt os e et ha tt headd i t i ono fVi nduc e sde c r e a s ed c r i t i c a lcoo l i ngr a t e s, andt h i sde c r e a s ei smo r es i Ｇ g n i f i c an twhent heVc on t en ti si nc r e a s edt o０ ２９％． Thec r i t i c a lc oo l i ngr a t ef o rob t a i n i ngc omp l e t ef e r Ｇ r i t eandpe a r l i t e mi c r o s t r u c t u r ed e c r e a s e sf r oma r ound ４° C/sf o rt heba s es t e e lD１t oa r ound１ ５° C/sf o r , t he０ ２９％Vs t e e lD３．Tha ti st os ay t headd i t i ono f V pr omo t e st hef o rma t i on o fha r d pha s e ssucha s AF, ba i n i t e and ma r t ens i t e, t husi nc r e a s i ng t he [ ] ha rdenab i l i t ft het e s t eds t e e l s５ ． yo
Tab l e２ Ac１ andAc３t empe r a t u r e sandc r i t i c a lc oo l i ngr a t e sf o rpha s e t r ans f orma t i onandobt a i n i ngcomp l e t ef e r r i t e Ｇpe a r l i t e mi c r o s t r uc t u r e S t e e l
Ac１/ Ac３/ t a r t i ng/ ° C ° C AFs (° Cs－１)
Coo l i ngr a t e Ms t a r t i ng/ (° Cs－１)
D１
７４０
７９５
~４
~１６
D３
７７７
８３２
~１ ５
~８
D２
７６２
８１７
~３
~１６
Comp l e t e F＋P/ (° Cs－１) ~４ ~３
~１ ５
I ti swo r t hno t i ngt ha tduet ot hei nhe r en tc l e av Ｇ agef r a c t ur e modeo fpe a r l i t e pha s eandt hede t r i Ｇ men t a li n f l uenc eo fp r e c i i t a t i on ha rden i ng ont he p t oughne s so ff e r r i t i c Ｇ a r l i t i cmed i umＧ c a rbonf o r i ng pe g s t e e l s, mo r ea t t en t i onha sbe en pa i dt o mod i f he yt f e r r i t e Ｇ a r l i t e mi c r os t ruc t ur e wi t hh i oughne s s pe ght s esucha sAFbyapp l i ngamode r a t epos t Ｇ f o r Ｇ pha y g [ , ] i ngcoo l i ngr a t e４ ６ ．Fo rt he D３s t e e l mi c r oa l l oyed wi t h０ ２９％V, acons i de r ab l ef r a c t i ono fAFcou l d beobt a i nedunde rcoo l i ngr a t esasl ow asaround [１２] ２° C/s, wh i chi sapp l i c ab l ei ni ndus t r r e Ｇ y ．The f o r e,i ti sr e a sonab l et oan t i c i t et ha tt hei n t r oduc Ｇ pa t i ono fcons i de r ab l ef r a c t i ono fAFa tt heexpens eo f a r l i t ei nf e r r i t i c Ｇ a r l i t i cs t e e lcou l dimp r ovei t s pe pe t oughn e s swi t hou tno t ab l ep e n a l t t ss t r eng t hl eve l． yoni Howeve r, f ur t he rt ho r oughwo rkne edst obedone．
４．Conc l u s i on s
(１) Thep r i o raus t en i t eg r a i nsa r er e f i neda f t e r t headd i t i ono fV．Themi c r os t ruc t ur e sf o rmedi nde Ｇ f o rmedandcon t i nuous l l eds t e e l scons i s to ff e r Ｇ ycoo r i t e, pe a r l i t e, AF, ba i n i t eand ma r t ens i t e, depen Ｇ d i ngonVcon t en tandcoo l i ngr a t e．Thef r a c t i ono f f e r r i t ee spe c i a l l nc r e a s e s wi t hi nc r e a s i ng V y IGFi con t en t, andt hef o rma t i on o f AFi ss i i f i c an t l gn y r omo t edwi t hi nc r e a s i ng Vcon t en t． p (２) Thedynami cCCTd i ag r amswe r ee s t ab l i shed wh i c he xh i b i t e ds imi l a rs ha ef o rt het h r e et e s t e ds t e e l s． p Thema i nd i f f e r enc ei st ha tt hef i e l dso ft r ans f o rma Ｇ t i onp r oduc t sa r esh i f t edt ot her i ts i deo ft hed i a Ｇ gh
６４８
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
r am wi t ht hei nc r e a s eo fV c on t en t．Thec r i t i c a l g c oo l i ngr a t ef o rpha s et r ans f o rma t i onsandf o rob t a i Ｇ n i ngcomp l e t ef e r r i t eandpe a r l i t emi c r o s t ruc t u r ede Ｇ c r e a s e swi t ht hei nc r e a s eo fVc on t en t．TheAc１ and Ac３t empe r a t u r e sdu r i nghe a t i ngshowani nc r e a s i ng t r endwi t hi nc r e a s i ng Vc on t en t． (３) Th ei n c r e a s eo fVc on t e n tr e s u l t si ns i i f i c a n t gn i nc r e a s eo fha r dne s sandt h i st endenc e n h a n c e sw i t h y i n c r e a s i ngc o o l i ngr a t eun t i lt h ef o rma t i ono fAF．An op t imumc oo l i ngr a t eex i s t st oob t a i nanapp r op r i a t e f r a c t i ono ff i nepr e c i i t a t e st oge tt heh i s tp r e c i Ｇ p ghe p i t a t i onha r den i nge f f e c tf o rt het e s t eds t e e l swi t hf e r Ｇ r i t e Ｇ a r l i t emi c r o s t ruc t u r e．F r omt h ep r e s e n ts t udy, pe t heop t imumc oo l i ngr a t ei sa r ound３ ０° C/sf o rt he , ０ １０％ VＧMA s t e e l anda r ound１ ５° C/sf o rt he ０ ２９％ VＧMAs t e e l．
Acknowl e dgmen t
The wo rk wa sf i nanc i a l l o r edby Na t i ona l yspons Key Re s e a r ch & Deve l opmen t Pr og r am o f Ch i na (２０１６YFB０３００１０３) ．
Re f e r enc e s [１] S．Eng i n e e r, B．Hu c h t ema nn, V．S c hü l e r, S t e e lRe s．５８ (１９８７) ３６９ Ｇ ３７６． [２] S r on Da i, H． Dong,I L．Chen, WJ．Hu i, L H．Wang, GW． andS t e e l４９ (２０１４) No ６, １ Ｇ ７ (i nCh i ne s e) ． [３] V．Ol l i l a i n e n, W．Ka s r z ak, L．Ho l a a, J．Ma t e r． Pr o c e s s．Te ch Ｇ p pp no l． １３４ (２００３) ４０５ Ｇ ４１２． [４] AR．Khodabandeh, M． J aha z i, S．Yue, S T．Aghda sh i, Ma Ｇ t e r．Manu f．Pr o c e s s． ２１ (２００６) １０５ Ｇ １１０．
[５] D．Gl i š i c, N．Radov i c, A．Kop r i v i c a, A．Fade l, D．Dr obn ak, j I S I JI n t． ５０ (２０１０) ６０１ Ｇ ６０６． [６] A．Ba b akh a n i, A R．Ki a n i ＧRa s h i d, S MR．Z i a e i, Ma t e r．Ma nu f． Pr o c e s s． ２７ (２０１２) １３５ Ｇ １３９． [７] M．Ha i s a f a r i, S．Na t egh, H．Yoo z ba sh i z adeh, A．Ekr am, J． j I r onS t e e lRe s． I n t． ２０ (２０１３) No ５, ６６ Ｇ ７３． [８] WJ．Hu i, YJ．Zhang, C W．Shao, S L．Chen, X L．Zhao, H．Dong, Ma t e r．Manu f．Pr o c e s s． ３１ (２０１６) ７７０ Ｇ ７７５． [９] S M． Ch e n t ou f, M． J ah a z i, L P． La i e r r e ＧBo i r e, Me t a l l o r．Mi c r o Ｇ p g s t r u c t．Ana l． ３ (２０１４) ２８１ Ｇ ２９７． [１０] F Y．Xu, YW．Wang, B Z．Ba i, HS．Fang, J． I r onS t e e l Re s． I n t． １７ (２０１０) No ３, ４６ Ｇ ５０． [１１] K ) S．Kim, L X．Du, C R．Ga o, Ac t aMe t a l l． S i n．(Eng l．Le t t． ２８ (２０１５) ６９２ Ｇ ６９８． [１２] C R．Dong, HP．Ren, T Z． J i n, Mi c r oa l l oyed Med i umＧCa r Ｇ bonS t e e l s, Me t a l l ur i c a lI ndus t r e s s, Be i i ng, ２０００． g yPr j [１３] MC．Zhao, K．Yang, F R．Xi ao, YY．Shan, Ma t e r．Sc i． Eng．A３５５ (２００３) １２６ Ｇ １３６． [１４] K．He, D V．Edmonds, Ma t e r． Sc i．Te chno l． １８ (２００２) ２８９ Ｇ ２９６． [１５] WJ．Hu i, S L．Chen, YJ．Zhang, C W．Shao, H．Dong, Ma t e r．De s． ６６ (２０１５) ２２７ Ｇ ２３４． [１６] WJ．Hu i, YJ． Zhang, C W． Shao, S L．Chen, X L． Zhao, H．Dong, J．Ma t e r． Sc i．Te chno l． ３２ (２０１６) ５４５ Ｇ ５５１． [１７] M．Gome z, L．Ranc e l, E．Es cude r o, S F．Med i na, J．Ma t e r． Sc i．Te chno l． ３０ (２０１４) ５１１ Ｇ ５１６． [１８] R． Pe t r o v, L．Ke s t e n s, Y．Houb a e r t, Ma t e r．Ch a r a c t． ５３ (２００４) ５１ Ｇ ６１． [１９] G．Mi t o, R．Ho r i, B．Poo r i, T．Fur uha r a, I S I JI n t． yamo gan j ５１ (２０１１) １７３３ Ｇ １７３９． [２０] X Z． Zhang, QZ． Ca i, GF． Zhou, QF． Chen, YZ．Xi ong, J．Ma t e r． Sc i． ４６ (２０１１) １７８９ Ｇ １７９５． [２１] WJ．Hu i, S L． Chen, C W． Shao, YJ． Zhang, H．Dong, J． I r onS t e e lRe s． I n t． ２２ (２０１５) ６１５ Ｇ ６２１． [２２] R．Lagnebo S iwe ck i, S． Za a c, B．Hu t ch i ns on, Sc an． J． r j g, T． Me t a l l． ２８ (１９９９) １８６ Ｇ ２４２． [２３] T N．Bake r, Ma t e r． Sc i．Te chno l． ２５ (２００９) １０８３ Ｇ １１０７． [２４] F． I sh i kawa, T．Takaha sh i, I S I JI n t． ３５ (１９９５) １１２８ Ｇ １１３３．
Ef f e c to fvanad i umondynami cc on t i nuousc oo l i ngt r ans f o rma t i on behav i o ro fmed i umＧ c a r bonf o r i ngs t e e l s g We i Ｇ un Hu i１ ∗ , NaXi ao１ , Xi ao Ｇ l iZhao１ , Yong Ｇ i anZhang１ , Yu Ｇ f eng Wu２ j j ,
１
２
Schoo lo fMe chan i c a l, El e c t r on i candCon t r o lEng i ne e r i ng, Be i i ngJ i ao t ongUn i ve r s i t i i ng１０００４４, Ch i na j y, Be j Fa cu l t fMa t e r i a l sSc i enc eandEng i ne e r i ng, Kunmi ngUn i ve r s i t fSc i enc eandTe chno l ogy, Kunmi ng６５００９３, Yunnan, yo yo Ch i na ARTICLEINFO
ABSTRACT
Keywo rds: Dynami cCCTd i ag r am Vanad i um Mi c r oa l l oyeds t e e l Mi c r o s t r uc t ur e Ha r dne s s
Dynami cc on t i nuousc oo l i ngt r ans f o rma t i on ( CCT) behav i o ro f med i umＧ c a r bonf o r i ng g s t e e l s mi c r oa l l oyed wi t hd i f f e r en tVc on t en t supt o０ ２９％ wa si nve s t i t edby me anso f ga d i l a t ome t r i cme a sur emen t, mi c r o s t r uc t ur a lobs e r va t i onandha r dne s sme a sur emen t．Ther e Ｇ su l t sshowedt ha tt hedynami cCCTd i ag r amswe r es imi l a randt hema i nd i f f e r enc ewa st ha t t hef i e l dso ft het r ans f o rma t i onp r oduc t swe r esh i f t edt ot her i ts i deo ft hed i ag r amswi t h gh t hei nc r e a s eo fVc on t en t, andt h i se f f e c twa smo r eno t i c e ab l ewi t hanadd i t i ono f０ ２９％ V． TheAc１andAc３t empe r a t ur e sshowedi nc r e a s i ngt r endswi t hi nc r e a s i ng Vc on t en t, wh i l e t hec r i t i c a lc oo l i ngr a t e sde c r e a s edwi t hi nc r e a s i ngVc on t en t．Thei nc r e a s eo fVc on t en tr e Ｇ su l t edi ns i i f i c an ti nc r e a s eo fha r dne s sandt h i st endenc senhanc ed wi t hi nc r e a s i ng gn y wa c oo l i ngr a t eun t i lt hef o rma t i ono fa c i cu l a rf e r r i t e (AF) ．Ap r omi s i ngapp r oa cho fr ema rk Ｇ ab l r ov i ngt het oughne s so ff e r r i t i c Ｇ a r l i t i c med i umＧ c a r bonf o r i ngs t e e l swi t hsu i t Ｇ yimp pe g ab l eVadd i t i onandt hei n t r oduc t i ono fAF wi t hou tno t ab l epena l t t ss t r eng t hl eve l yoni wa ssugge s t ed．
１． I n t r odu c t i on Re c en t l he r ehavebe eni nc r e a s i ngapp l i c a t i ons y, t o fmi c r oa l l oyed ( MA) med i umＧ c a rbonf o r i ngs t e e l s g a ssubs t i t u t e sf o rt r ad i t i ona lquenchedandt empe r ed (Q&T) f o r i ngs t e e l st o manu f a c t u r eava r i e t f g yo au t omob i l ec omponen t s．El imi na t i ng t he c o s to f t Ｇ f o r i ng he a tt r e a tmen t (quench i ng and h i pos g gh t empe r a t u r et empe r i ng) i st he ma i nt a r tf o rt he ge [ , ] i n t r oduc t i on o ft h i sk i nd o fs t e e l１ ２ ．Thede s i r ed me chan i c a lpr ope r t i e so ff o r omponen t sc ou l d gedc beob t a i nedt hr oughc on t r o l l edc oo l i ngf r omf o r i ng g t empe r a t u r e．The r e f o r e, f a c t o r ssuch a schemi c a l c ompos i t i ons, c oo l i ngs t r a t eg i e sandf o r i ngpa r amＧ g e t e r shaves t r ongi n f l uenc e sont he mi c r o s t ruc t u r a l cha r a c t e r i s t i c s, and t hus on t hef i na l me chan i c a l [ ] r ope r t i e so ff o r i ngsmadeo ft h i sk i ndo fs t e e l３Ｇ８ ． p g I ti swe l lknownt ha tc on t i nuousc oo l i ngt r ans f o r Ｇ ma t i on (CCT) d i ag r ami sanexc e l l en tt oo lt os t udy t hei n f l uenc eo fchemi c a lc ompo s i t i on andc oo l i ng r a t eonpha s et r ans f o rma t i onp r oduc t s, wh i chu l t i Ｇ ma t e l n f l uenc et heme chan i c a lp r ope r t i e s, a si ta l Ｇ yi , Ph． ∗ Co r r e spond i ngau t ho r．Pr o f． D． EＧma i laddr e s s: wjhu i＠b t ue ．duc ． n (WJ．Hu i) ． j
l owst oi den t i f hedoma i nandbounda r fe a ch yt yo / ( , , s eand o rcons t i t uen t f e r r i t e pe a r l i t e ba i n i t e pha [ ] andma r t ens i t e) a saf unc t i ono fcoo l i ngr a t e９ ．The cons t ruc t i ono fa CCT d i ag r am i sba s edf i r s t l y on d i l a t ome t r i cana l i scomp l emen t edbybo t h mi c r o Ｇ ys s t ruc t ur eandha rdne s ss t ud i e s．Theshapeo faCCT d i ag r ami sve r ens i t i vet ot hechemi c a lcompos i Ｇ ys t i onso ft het e s t eds t e e landt hecoo l i ngr a t e sus ed [ , ] dur i ngp r oc e s s i ng１０ １１ ． I nt hec a s eo fMA med i umＧ c a rbonf o r i ng s t e e l s, Mn and mi c r oa l l oy i ng e l e Ｇ g men t sa r e gene r a l l r e s en t．Theadd i t i on o f Mn yp sh i f t st heeu t e c t o i dpo i n tt owa rdsl owe rc a rboncon Ｇ c en t r a t i on, l owe r st he pha s et r ans f o rma t i ont emＧ r a t ur e s, andt husp r omo t e spe a r l i t ef o rma t i onand pe de c r e a s e st het r ans f o rma t i onspe edo faus t en i t et o [ ] a r l i t e１２ ．Mna l so make st hep r oeu t e c t o i df e r r i t e pe cur veo f CCT d i ag r ams movet ot he r i t, and gh r e a t l r omo t e st he f o rma t i on o fi n t e rmed i a t e g yp [ ] t r ans f o rma t i onp r oduc t ssucha sba i n i t e１３ ． Fur t he r Ｇ mo r e,i ti swe l lknownt ha tt heMnadd i t i oni nc r e a Ｇ s e st heso l ub i l i t fVCand VNi naus t en i t e, and yo [ ] t hu se nhan c e sp r e c i i t a t i onha r d e n i nge f f e c t１２ ．The r e Ｇ p
Re c e i ved９Oc t obe r２０１６; Re c e i vedi nr ev i s edf o rm２４De c embe r２０１６; Ac c ep t ed２５De c embe r２０１６ Ava i l ab l eon l i ne１５June２０１７ １００６ Ｇ ７０６X/Copy r i tⓒ２０１７, Th ee d i t o r i a lo f f i c eo fJ ou r n a lo fI r ona ndS t e e lRe s e a r c h, I n t e r n a t i on a l． Pub l i s h e dbyE l s e v i e rL imi t e d．Al lr i t sr e s e r v e d． gh gh
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
６４２
f o r e, f o r MA f e r r i t e Ｇ a r l i t et o r i ng s t e e l s, pe ypef g t he i r Mn c on t en t sa r e usua l l owe rt han １ ５％ , yl whe r e a sf o r MA ba i n i t i cf o r i ng s t e e l s, t ho s ea r e g enhanc edt oh i rt han１ ５％． ghe Thema i n mi c r oa l l oy i nge l emen ti n MA med i umＧ c a rbonf o r i ngs t e e l si sVduet oi t ss t r ongande a s i Ｇ g , l c o n t r o l l a b l e r e c i i t a t i o nh a r d e n i n e f f e c t w h i c h y p p g i sp r ima r i l ot her e l a t i ve l a r o l ub i l i t f yduet yl ges yo i t sc a rbon i t r i deV(C,N) i naus t en i t ea tc onven i en t [ , , ] he a t i ngt empe r a t u r e１ １１ １２ ．F i ne V(C, N) pa r t i c l e s c ou l dp r e c i i t a t ei n bo t hp r oeu t e c t o i df e r r i t e and p a r l i t i cf e r r i t eonc on t i nuousc oo l i ngdu r i ngand/o r pe [２,５] a f t e raus t en i t e Ｇ f e r r i t et r ans f o rma t i on ．The r ei s s t i l lsomed i s ag r e emen ti nl i t e r a t u r er ega r d i ngt he e f f e c to fV ont het r ans f o rma t i onbehav i o ro f MA s t e e l s． I ti sgene r a l l l i evedt ha tV a t omss eg r e Ｇ ybe t et oaus t en i t eg r a i n bounda r i e sr ende r i ngt hem ga l e s se f f e c t i vea sf e r r i t e nuc l e a t i on s i t e s, t husi n Ｇ c r e a s i ngha r denab i l i t r e s s i ngf e r r i t e Ｇ a r l i t e ybysupp pe [ ] f o rma t i on５ ．Howeve r,i ti sa l s obe l i evedt ha tVa c Ｇ t ua l l sno tsupp r e s sg r a i nbounda r e a c t i onand ydoe yr [１,１４] even de c r e a s e s ha r denab i l i t ．Re c en ts t udy o f y t heau t ho r sha sshownt ha tf e r r i t ef r a c t i oni nc r e a s e s wi t hi nc r e a s i ng V c on t en ti na s Ｇ f o r iVS ged３７MnS [ ] s t e e l１５ , andf u r t he ri nve s t i a t i o na l s or e v e a l e dt ha t g i nc r e a s i ng Vc on t en ts i n i f i c a n t l e n h a n c e st h ef o r Ｇ g y ma t i ono fa c i cu l a rf e r r i t e (AF) s t ruc t u r ea ta mod Ｇ [１６] e r a t ecoo l i ngr a t e ．Ther e su l t so ft hei n f l uenc eo f r ehe a t i ngt empe r a t u r eand V c on t en tont het r ans Ｇ f o rma t i onbehav i o ro fmed i umＧ c a rbonf o r i ngs t e e l s g sugge s tt ha tVi ns o l i ds o l u t i onp r omo t e st hef o rma Ｇ [ ] t i ono fba i n i t e５ ．I tha sa l s of oundt ha t V (C, N) r t i c l e sc ana c ta sp r e f e r en t i a lnuc l e a t i ons i t e sf o r pa ba i n i t ei nVＧMA me d i umＧ c a r bons t e e l s, wh i c ht hu sf a Ｇ Tab l e１ Chemi c a lc ompo s i t i onso ft e s t eds t e e l s (ma s s％ ) S t e e l D１ D２ D３
C
０ ４１ ０ ４０ ０ ４０
S i
０ ４２ ０ ４４ ０ ４４
Mn
１ ２５ １ ２２ １ ２６
P
０ ０１５ ０ ０１５ ０ ０１７
S
０ ０４１ ０ ０３９ ０ ０４２
Cr
０ １６ ０ １７ ０ １８
c i l i t a t e sba i n i t ef o rma t i ona tf a s t e rcoo l i ngr a t e s１７ ． I tshou l dbeno t edt ha tde f o rma t i ona l soha sas i Ｇ g n i f i c an ti n f l uenc e on t he pha s et r ans f o rma t i on o f [ , ] s t e e l s１３ １８ ．The r e f o r e, i ti s no t enough on l o yt knowt hes t a t i cCCT d i ag r ams wh i chde s c r i bet he t r ans f o rma t i oni nnon Ｇ de f o rmedaus t en i t eo ff o r i ng g s t e e l s．Mo r eove r, ma i n l oi t se f f i c i en tp r e c i i Ｇ yduet p t a t i onha rden i nge f f e c tands i n i f i c a n t i m r o v e m e n t g p o ff a t i u e r o e r t i e s o f m e d i u m Ｇ c a r b o n f o r i n g p p g g [ ] s t e e l s１５ , t he r eha sbe enat endenc of ur t he ri n Ｇ yt [ , ] c r e a s eV con t en tupt oabou t０ ３０％ １９ ２０ ．The r e Ｇ f o r e, t hea im o ft hep r e s en ts t udyi st os t ema t i Ｇ ys c a l l nve s t i t et hei n f l uenc eo f V con t en tup t o yi ga ０ ３０％ ont hedynami cCCTcha r a c t e r i s t i c so fmed i Ｇ umＧ c a rbonf o r i ngs t e e l s．Theha rdne s schangeand g mi c r os t ruc t ur a levo l u t i onwi t hcoo l i ngr a t e shavea l Ｇ sobe enana l z ed．Ther e su l t s wi l lbebene f i c i a lt o y t he p r a c t i c a lapp l i c a t i on o fcon t r o l l edf o r i ng and g coo l i ngt ot hep r oduc t i ono fh i r f o rmanc ef o r Ｇ ghpe g i ngcomponen t smadeo fMA med i umＧ c a rbons t e e l s． [
]
２．Ma t e r i a l sandExp e r imen t a lPr o c e du r e
Med i umＧ c a rbonf o r i ngs t e e l swi t hd i f f e r en tcon Ｇ g t en t so fV (０％ , ０ １０％ and０ ２９％ ), wh i ch we r e de s i t eda sD１, D２andD３, we r eu s e di nt hep r e s e n t gna s t udy．The s es t e e l swe r eme l t edi nal abo r a t o r v a c Ｇ y uumi nduc t i onf urna c eandc a s ti n t o１１０kgi ngo t s． Tab l e １ showst hechemi c a lcompos i t i ons o ft he t e s t eds t e e l s．The s ea s Ｇ c a s ti ngo t swe r er ehe a t edt o abou t１２５０° C, he l df o ra tl e a s t１ h, andf i na l l y r e s sf o r oba r s (４５ mmi nd i ame t e r) f o l l owed p gedt bys t i l la i rcoo l i ng．Cy l i nd r i c a lspe c imens (６ mmi n d i ame t e rand８０ mmi nhe i t) we r ecu tf r om ha l f gh r ad i uso ft hea s Ｇ f o r r sandha dt hel ongax i sp a Ｇ gedba
V
－ ０ １０ ０ ２９
r a l l e lt ot heba rax i s． Thedynami c ( wi t h ho tde f o rma t i on) CCT d i a Ｇ r amswe r ec onduc t edonaGl e eb l e Ｇ ３８００t he rmome Ｇ g chan i c a ls imu l a t o r．Th e rmo c oup l e sw i t had i ame t e ro f ０ ２mm we r espo twe l dedt ot hesu r f a c eo ft hespe c i Ｇ mensa tt he i r mi dd l el eng t ht or e c o r dt het empe r a Ｇ t u r e． Spe c imenswe r ef i r s t l ehe a t edt o１２２０° Ca ta yr c ons t an the a t i ngr a t eo f１０° C/sandhe l df o r１２０s, / andt hent hey we r ec oo l eda t５° C st ode f o rma t i on t empe r a t u r e１１００° C．To mi n imi z et empe r a t u r eg r a Ｇ d i en t, t hespe c imenswe r ekep ta t１１００° Cf o r５s． Then, t he spe c imens we r ec omp r e s s ed t o at rue s t r a i no f０ ３６ (r educ t i oni n he i to f３０％ ) a ta gh nomi na ls t r a i nr a t eo f１ s－１ andf i na l l oo l edt o yc
Ti
０ ０１７ ０ ０２２ ０ ０２７
Al
０ ０２９ ０ ０３１ ０ ０３１
N
０ ０２２ ０ ０１６ ０ ０１７
Fe
Ba l anc e Ba l anc e Ba l anc e
r oomt empe r a t ur ea td i f f e r en tl i n e a rc oo l i ngr a t e si n t her ang eo f０ ０３－４１ ５０° C/s．The s ecoo l i ngr a t e s we r echos ena si nd i c a t edbyt hes t a t i cCCTd i ag r am o fmed i umＧ c a rbonf o r i ngs t e e lwi t hs imi l a rchemi Ｇ g [ ] c a lcompos i t i on１２ , wh i ch we r et hencon t r o l l edby t hede s i l i ngpa t t e rno ft hes imu l a t o rs t em． gnedcoo ys Seve r a lspe c imens we r ed i r e c t l r om de Ｇ yquenchedf f o rma t i ont empe r a t ur ei no rde rt ode t e rmi net hei n i Ｇ t i a laus t en i t eg r a i ns i z e．Thedynami cCCTd i ag r ams we r ec on s t r u c t e da f t e rd e t e rmi n i ngt hec r i t i c a lt r an s f o r Ｇ ma t i ont emp e r a t u r e sc omp l eme n t e dby mi c r o s t r u c t u r a l ob s e r v a t i on sandVi cke r sha rdne s sme a sur emen t s． Spe c imensf o rop t i c a lmi c r os copy (OM) we r eme Ｇ chan i c a l l r oundandpo l i shed, andt hene t chedwi t h yg
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
３vo l ％ n i t a l．Thequenchedspe c imenswe r ee t ched i ns a t ur a t edaqueousp i c r i cs o l u t i onwi t hs omed r ops o fsur f a c t an tt or eve a laus t en i t eg r a i n．Theave r age aus t en i t eg r a i ns i z ewa sme a su r edt hr ought hel i ne a r i n t e r c ep tme t hod．Spe c imensf o rt r ansmi s s i one l e c Ｇ t r onmi c r o s c opy (TEM) we r ef i r s t l l i c e di n t o０ ５mm ys t h i ck p l a t eandsubs equen t l r o u n dd o w nt of o i l s yg wi t hat h i ckne s so fa r ound５０μm．The s ef o i l swe r e f i na l l l e c t r opo l i shedi natwi n Ｇ e te l e c t r opo l i sh i ng ye j appa r a t usus i ngas t anda r dchr omi umt r i ox i de Ｇ a c e t i c a c i dso l u t i on．Th i nf o i l swe r eexami nedi na Hi t a ch i HＧ ８００t r ansmi s s i one l e c t r onmi c r o s c opea tanop e r a t Ｇ i ngvo l t a eo f２００kV．Vi c k e r sh a r dn e s so ft hes amp l e s g wa sme a su r edwi t ha４９Nl oadandt heha r dne s sr e Ｇ su l t sa r et heave r ageo fa tl e a s t１０me a su r emen t sf o r e a chs amp l e．
３．Re s u l t sandDi s c u s s i on ３ １．Mi c r o s t ruc t ur e s
F i １showst hec a l cu l a t edequ i l i b r i umf r a c t i ono f g V(C,N) p r e c i i t a t e sandt hes i t ef r a c t i onso fCand p Ni nV(C,N) a saf unc t i ono ft empe r a t u r e． I tr eve a l s t ha tt heV(C,N) p r e c i i t a t e sa r et he rmodynami c a l l p y s t ab l eove rar a ng eo ft emp e r a t u r e sf o rbo t ht h eVＧMA s t e e l s, andt heexpe c t edf r a c t i ono fV(C,N) a tl ow t empe r a t u r eandf e r r i t ef i e l do ft heD３s t e e li sabou t twot ime sh i rt hant ha to ft heD２s t e e l． I ta l s or e Ｇ ghe ve a l st ha tt hec a l cu l a t edd i s s o l u t i ont empe r a t u r e so f V(C,N) p r e c i i t a t e so ft heD２andD３s t e e l sa r e９７７ p and１１４８° C, r e spe c t i ve l i chi nd i c a t e st ha tt he y, wh d i s so l u t i on t empe r a t u r ei ss i i f i c an t l nc r e a s ed gn yi whenVc on t en ti si nc r e a s edf r om０ １０％ t o０ ２９％． Mo r eove r, t hesha r c r e a s eo ft hema s sf r a c t i ono f pde V(C,N)i sma i n l s c r i bedt ot heno t ab l ep r e c i i t a t i Ｇ ya p ono fpe a r l i t i cc emen t i t e．Theave r agep r i o raus t en i t e r a i ns i z e so ft hede f o rmedspe c imenso fD１, D２and g D３s t e e l swe r ede t e rmi neda s(６３±１２), (５３±８) and (４９±７) μm, r e spe c t i ve l headd i t i ono fV y．Thus, t exh i b i t sapo s i t i vee f f e c tonde c r e a s i ngt heaus t en i t e r a i ns i z e, wh i c hi sc on s i s t e n tw i t ht h ef a c tt h a tVt e nd s g
F i １． Ca l cu l a t ede i l i b r i umo fV(C,N) f r a c t i ono fVＧMA qu g s t e e l sD２andD３us i ngThe rmo ＧCa l cs o f twa r e．
６４３
t or e f i net hedynami c a l l e c r t a l l i z edg r a i ns i z eo f yr ys [ ] ３７MnS iVSs t e e l２１ ．The r e f o r e, ahe a t i ngt empe r a t ur e o f１２２０° C wa schos enno ton l o rt hecomp l e t ed i s Ｇ yf so l u t i ono fVi nau s t e n i t eandt hu smak i ngt hemo s to f t hep r e c i i t a t i onha rden i nge f f e c to fV(C,N), bu ta l Ｇ p sobe c aus ei ti sve r l os et ot hei ndus t r i a lhe a t i ng yc t empe r a t ur e su s u a l l u s e d f o r a u t o m o t i v e c o m o n e n t s ． y p Thet i c a lo t i c a l m i c r o r a h so ft h ed e f o r m e d yp p g p s e c ime n sa td i f f e r e n tc oo l i ngr a t e sa r eg i v e ni nF i s ２－ p g , ４．Asexpe c t ed a l lt hede f o rmedspe c imensexh i b i ta mi x t ur e mi c r os t ruc t ur eo fp r oeu t e c t o i df e r r i t eand a r l i t ewhencoo l eda tl owe rcoo l i ngr a t e s．Thep r o Ｇ pe eu t e c t o i df e r r i t e ma i n l l i ne a t eda tp r i o raus t en i t e yde r a i nbounda r i e swi t haf ewde co r a t edwi t h i naus t en Ｇ g i t eg r a i ns．Thef r a c t i ono ff e r r i t ede c r e a s e swi t hi n Ｇ c r e a s i ngcoo l i ngr a t eandt hust hepe a r l i t epha s ebe Ｇ come s mo r edomi nan t．Thei nc r e a s eo f V con t en t r omo t e st hef o rma t i on o ff e r r i t ee spe c i a l l n t r a Ｇ p yi r anu l a rf e r r i t e (IGF) ．Fur t he ri nc r e a s i ng coo l i ng g r a t el e adst oevenl e s sf e r r i t eandp r omo t e st hef o r Ｇ ma t i ono f AF p r ima r i l tt heexpens eo fpe a r l i t e． ya L i ket ha to fIGF, t hef o rma t i ono fAFwa sa l sos i Ｇ g n i f i c an t l r omo t edwi t ht hei nc r e a s eo fVcon t en t． yp F i ５(a,b) p r e s en t st heda rkf i e l d TEM mi c r o Ｇ g r a h ss h o w i n f i n e r e c i i t a t e sd i s t r i b u t e d w i t h i n g p g p p bo t ht hep r oeu t e c t o i df e r r i t eandpe a r l i t i cf e r r i t er e Ｇ i o n so f t h eD ３s t e e l c o r r e s o n d i n t oac o o l i n r a t e g p g g o f０ ８３° C/s．Thep r e c i i t a t ewa si d e n t i f i e da sV(C,N) p t hr oughs e l e c t ed a r e ad i f f r a c t i on pa t t e rn and EDS ana l e s (F i ５ (c,d)) ． I ti swo r t hno t i ngt ha tt he r e ys g exh i b i t saf ewamoun to fl a r es i z ep r e c i i t a t e s (abou t g p １０－２０ nm), wh i chi scons i de r edt obenuc l e a t ed dur i ng t he he a tp r e s e r va t i on and ho t de f o rma t i on [ ] r oc e s s１１ ． p Vi nt het e s t eds t e e l sc ana f f e c tt het r ans f o rma t i on behav i o rand mi c r os t ruc t ur a lcha r a c t e r i s t i c si ntwo ,p s t a t e s,i e． r e c i i t a t e sandso l i dso l u t i on． I ti sr e Ｇ p rdedt ha tV p r e c i i t a t e s V (C, N) a r ep r ima r i l ga p y f o rmedi nt he pha s et r ans f o rma t i on p r oc e s so rt he [ ] he a tp r e s e r va t i on p r oc e s sa f t e rt r ans f o rma t i on２２ ． Howeve r, V(C,N) cou l da l sobef o rmedi naus t en i t e a f t e raus t en i t i z i ngt r e a tmen to rdur i ngpos t Ｇho tde Ｇ f o rma t i oncoo l i ng whent he C o r N con t en t s we r e [２３,２４] h i ．Bo t ht he N andScon t en t so ft het e s t ed gh s t e e l sa r econs i de r ab l i o rt he p r e c i i t a t e so f yh ghf p VN, o rNＧ r i chV(C,N) on MnSi nc l us i onsmi ta l Ｇ gh [ ] r e adyex i s ti nt hede f o rmedaus t en i t econd i t i on２４ ． Thef o rma t i ono ft he s ep r e c i i t a t e sno ton l owe r s p yl t hec a rbonso l u t i oncon t en ti nt heaus t en i t ebu ta l so r omo t e st hef o rma t i ono fIGFi d i omo r tl owe r p phsa coo l i ngr a t e so rt hei n t r ag r anu l a rnuc l e a t i ono fAFa t [ , , ] mode r a t ecoo l i ngr a t e s５ １７ ２４ ．Theh i rt heVcon Ｇ ghe t en ti s, t hel a r rt heamoun to fp r e c i i t a t e si naus Ｇ ge p t en i t er eg i ont he r ewi l lbe, t houghi ti sa l sosugge s Ｇ t edt ha tVi nso l i dso l u t i onp r omo t edt hef o rma t i on [ ] o fba i n i t e５ o rVa t omc l us t e r i ngf a c i l i t a t e dana l t e r n Ｇ
６４４
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
(a) ０ ８３° C/s; (b) １ ６６° C/s; (c) ４ １５° C/s; (d) １６ ６０° C/s．
F i ２． Op t i c a lmi c r o s t r uc t u r e so fho tde f o rmedspe c imenso fD１s t e e lc on t i nuous l oo l edt or oomt empe r a t u r ea td i f f e r en t yc g c oo l i ngr a t e s．
(a) ０ ８３° C/s; (b) １ ６６° C/s; (c) ４ １５° C/s; (d) １６ ６０° C/s．
F i ３． Op t i c a lmi c r o s t r uc t u r e so fho tde f o rmedspe c imenso fD２s t e e lc on t i nuous l oo l edt or oomt empe r a t u r ea td i f f e r en t yc g c oo l i ngr a t e s．
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
６４５
(a) ０ ８３° C/s; (b) １ ６６° C/s; (c) ４ １５° C/s; (d) １６ ６０° C/s．
F i ４． Op t i c a lmi c r os t ruc t ur e so fho tde f ormedspe c imenso fD３s t e e lcon t i nuous l l edt or oomt empe r a t ur ea td i f f e r en t ycoo g c oo l i ngr a t e s．
F i ５． TEM mi c r og r aphso fho tde f o rmedspe c imeno fD３s t e e lc oo l eda t０ ８３° C/s, s how i ngf i n eV(C,N) pa r t i c l e sd i s t r i bu t ed g wi t h i np r oeu t e c t o i df e r r i t e (a, c) andpe a r l i t i cf e r r i t e (b), andEDSo fpa r t i c l e si n (c) (d) ．
６４６
ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８ WJ．Hu
a t i ve AF nuc l e a t i on１４ ．The r e f o r e, t hef e r r i t eand AFt r ans f o rma t i onswou l dbef u r t he rp r omo t ed． [
]
３ ２．Hardne s s
Thee f f e c t so fVc on t en tand po s t Ｇ de f o rma t i on c oo l i ngr a t e sonha r dne s sa r eshowni nF i ６(a) ． I t g i sc l e a rt ha tt he r ei sas t r ongdependenc eo fHVva l Ｇ ue sonVc on t en tandc oo l i ngr a t e．The r ei sane a r l y l i ne a rr e l a t i onsh i b e t w e e nt h eh a r d n e s so f t h et e s t Ｇ p eds t e e l sandc oo l i ngr a t ebe f o r et hef o rma t i on o f AF．Th i si s ma i n l ot hef o rma t i on o f mo r e y duet a r l i t e, t hede c r e a s eo fpe a r l i t el a t hst h i ckne s sand pe spa c i ng wi t ht hei nc r e a s eo fc oo l i ngr a t e．Asf o rt he VＧMAs t e e l sD２and D３, t hep r e c i i t a t i ono f mo r e p f i ned i s e r s e dV(C,N) p a r t i c l e sw i t hi n c r e a s i ngc oo l i ng p [ ] r a t ea l sor ema rkab l edt he ha r dne s s１６ ．I t y enhanc
shou l dbeno t edt ha tt oos l owcoo l i ng mayc aus et he coa r s en i ngo ft hei n i t i a lf i ne V (C, N) p r e c i i t a t e s p t hr oughOs twa l dr i e n i ngme c han i sma th i emp e r a Ｇ p ght t u r e s, whe r e a st oof a s tc oo l i ng ma tg i v eenough y no t imef o rt hecomp l e t ep r e c i i t a t i ono f V (C, N) i n p f e r r i t ewh i chc aus e sl owe rf r a c t i ono fp r e c i i t a t e sa l Ｇ p t houghf i ne rp r e c i i t a t e sc o u l db eo b t a i n e d ． T h a t i s p t os ay, anop t imumcoo l i ngr a t eex i s t st oob t a i nan app r op r i a t ef r a c t i on o ff i ne p r e c i i t a t e st o ge tt he p h i s tp r e c i i t a t i onha rden i nge f f e c tf o rt het e s t ed ghe p s t e e l swi t hf e r r i t e Ｇ a r l i t emi c r os t ruc t ur e．Fr omt he pe heop t imum coo l i ng r a t ei sabou t r e s en ts t udy, t p ３ ０° C/sf o rD２s t e e l, wh i chi si na c co rdanc e wi t h [ ] conven t i ona lVＧMA me d i umＧ c a r bonf o r i ngs t e e l s１２ , g anda r ound１ ５° C/sf o rD３s t e e l(F i ６(b)) ． g ( ), Ass e enf r omF i ６ a t heha rdne s so ft het e s t ed g
F i ６． Va r i a t i onso fha r dne s s (a) andha r dne s sd i f f e r enc e (b) wi t hc oo l i ngr a t ea f t e rho td e f o rma t i on (ΔHV５r e f e r st oh a r dn e s s g HV５ d i f f e r enc ebe twe ent heVＧMAs t e e l s (D２, D３) andba s es t e e l(D１) a ts amec oo l i ngr a t e) ．
s t e e l sshowsasha r nc r e a s eaboveac r i t i c a lc oo l i ng pi r a t e, wh i chc o r r e spondst ot hef o rma t i ono fAF．As t heD１s t e e lc on t a i nsnoV,i ti sr e a s onab l et or ega r d t h i ssha r nc r e a s ea st hef o rma t i ono fha r de rpha s e s pi o fba i n i t e, AFand ma r t ens i t e．Asa l s oi nd i c a t edi n F i ６(a), t hei nc r e a s eo fVc on t en tr e su l t si ns i i f Ｇ g gn i c an ti n c r e a s eo fh a r dn e s s, a ndt h i st e nd e n c e n h a n c e s y w i t hi n c r e a s i ngc oo l i ngr a t eun t i lt hef o rma t i ono fAF (F i ６(b)) ．Th i sha r den i ngi sp r ima r i l ot he g yduet r e c i i t a t i onha r den i ngby mo r ef i ne V(C, N) p r e Ｇ p p c i i t a t e si nf e r r i t ewi t ht hei nc r e a s eo fVc on t en tand p [ , ] c oo l i ngr a t e３ ５ , wh i l et hel e s se f f e c t i ve V (C, N) r e c i i t a t i on ha r den i ng o ff o rmi ng i n t e rmed i a t e p p t r ans f o rma t i onp r oduc t ssucha sAFandba i n i t ec au Ｇ s e st heha r dne s sd i f f e r enc eΔHV５ de c r e a s ewi t hf u r Ｇ [ , ] t he ri nc r e a s i ngc oo l i ngr a t e５ １９ ．Fo rt hef o rma t i on o f ma r t ens i t ea tac ons i de r ab l i oo l i ng r a t e, yh gh c ΔHV５i sne a r l e r obe c aus et heha r dne s so f ma r Ｇ yz t ens i t eba s i c a l l t sc a rbonc on t en to t he r ydependsoni t hanVcon t en t．
３ ３． CCTdi agrams
F i ７showst hedynami c CCT d i ag r amso ft he g t e s t eds t e e l s．Repr e s en t a t i vec oo l i ngcu r ve s, c oo l i ng
r a t e s, t r an s f o rma t i onr ang e s, t hena t ur eo ft het r ans Ｇ f o rma t i onp r oduc t sandt heva l ue so fVi cke r sha rd Ｇ ne s s (HV５) a r es howni nt hed i a r ams．Ac１ andAc３ , g wh i ch we r eob t a i nedonaFo rma s t o r ＧFI Id i l a t ome Ｇ t e r, a r ea l sog i veni nt hed i ag r ams．Al lt hed i ag r ams show mu l t i Ｇ t r ans f o rma t i on cur ve s, r eve a l i ng t ha t comp l exmi c r os t ruc t ur e sex i s twhent hecoo l i ngr a t e i si nc r e a s edf r om０ ０３t o４１ ５０° C/s． I nt het empe r Ｇ , a t ur er angeo ft hema o rt r ans f o rma t i oncur ve st he j f o rmed mi c r os t ruc t ur e s mayi nc l udef e r r i t e, pe a r l i Ｇ t e, AF, ba i n i t eandma r t ens i t e． Fo rt heba s es t e e lD１, a sshowni nF i ７(a), g / coo l i ngr a t e sl owe rt hanabou t４° C swou l dp r omo t e t hef o rma t i ono fami x t ur eo ff u l lf e r r i t eandpe a r l i t e mi c r os t ruc t ur e, wh i chi st hede s i r ed mi c r os t ruc t ur e f o r conven t i ona lf e r r i t i c Ｇ a r l i t i c med i umＧ c a rbon pe f o r i ngs t e e l s． I ti sc l e a rt ha tf e r r i t eandpe a r l i t ee s Ｇ g c i a l l hef o rme rcou l d be ob t a i nedt hr oughou t pe yt wi decoo l i ngr a t er angef r om０ ０３t o１７° C/s, wh i l e AFi spr oduc edunde rt hecoo l i ngr a t er angef r om４ t o１７° C/s, andba i n i t ebeg i nst obepr oduc ed when t hecoo l i ngr a t ei si nc r e a s edt oh i rt han１７° C/s． ghe Howeve r, ne i t he rt hef u l lAF mi c r os t ruc t ur eno rt he f u l lba i n i t i cmi c r os t ruc t ur ecou l dbeobt a i ned．Ma r Ｇ
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
６４７
(a) D１; (b) D２; (c) D３． F—Fe r r i t e; P—Pe a r l i t e; AF—Ac i cu l a rf e r r i t e; B—Ba i n i t e; M— Ma r t ens i t e．
F i ７． Dynami cCCTd i ag r amso ft e s t eds t e e l s． g
t ens i t ewa sobs e r veda tt hec oo l i ngr a t eh i rt han ghe a r ound１５° C/s, wh i l ef u l lma r t ens i t emi c r o s t ruc t u r e c ou l dbeob t a i neda te v e nh i e rc o o l i ngr a t eo fa r ound gh ２０° C/s． Theshape so ft hedynami cCCTd i ag r amsf o rt he VＧMAs t e e l sD２and D３a r es imi l a rt ot ha tf o rt he ba s es t e e l D１, a sshowni nF i ７ (b, c), wh i ch g me anst ha tt he i rt r ans f o rma t i onbehav i o ri ss imi l a r． The ma i nd i f f e r enc ei st ha tt hef e r r i t e, pe a r l i t e, AF, ba i n i t eand ma r t ens i t et r ans f o rma t i onf i e l dsi n t heD２andD３s t e e l sa r esh i f t edt ol onge rt imes i de (t ot her i ts i de) a sc ompa r edwi t ht ho s eo ft heD１ gh s t e e l, andt hed i f f e r enc ei smo r es i i f i c an ti nt heD３ gn s t e e l．Tha ti st os ay, t he s e pha s et r ans f o rma t i on sh i f t si nc r e a s ewi t ht hei nc r e a s eo fVc on t en t．Mo r e Ｇ ove r, t he AFt r ans f o rma t i onf i e l di sa l s oexpanded wi t hi nc r e a s i ng Vc on t en t． The me a su r ed Ac１ and Ac３ t empe r a t u r e sf o rt he t e s t eds t e e l sa r eg i veni nTab l e２． I ti sc l e a rt ha tt he add i t i ono fVi nduc e si nc r e a s edAc１andAc３t empe r a Ｇ , t u r e s．Asas t r ongf e r r i t ef o rme r Ve f f e c t i ve l t a Ｇ ys b i l i z e sf e r r i t ebyr a i s i ngt hef e r r i t e→aus t en i t et emＧ r a t ur e s．Thef e r r i t ef i e l dwi l lbeexpandeda sVi s pe added．The r e f o r e,t heAc１andAc３t empe r a t u r e sdu r Ｇ i nghe a t i ngshowi nc r e a s i ngt r endswi t hi nc r e a s i ngV c on t en t．The va l ue so f ma r t ens i t et r ans f o rma t i on s t a r tt empe r a t u r e (Ms) f o rt het e s t eds t e e l sa r ea l s o i veni nTab l e２． I ti sobv i oust ha tVshowsapo s i Ｇ g t i vee f f e c ton de c r e a s i ng Ms．Thec r i t i c a lc oo l i ng r a t e sf o rt hes t a r t i ngo fAFandma r t ens i t et r ans f o r Ｇ ma t i ons, a ndf o rob t a i n i ngc omp l e t ef e r r i t ea ndpe a r l i t e mi c r os t ruc t u r ea r ea l s osumma r i z edi nTab l e２． I ti s c l e a rt os e et ha tt headd i t i ono fVi nduc e sde c r e a s ed c r i t i c a lcoo l i ngr a t e s, andt h i sde c r e a s ei smo r es i Ｇ g n i f i c an twhent heVc on t en ti si nc r e a s edt o０ ２９％． Thec r i t i c a lc oo l i ngr a t ef o rob t a i n i ngc omp l e t ef e r Ｇ r i t eandpe a r l i t e mi c r o s t r u c t u r ed e c r e a s e sf r oma r ound ４° C/sf o rt heba s es t e e lD１t oa r ound１ ５° C/sf o r , t he０ ２９％Vs t e e lD３．Tha ti st os ay t headd i t i ono f V pr omo t e st hef o rma t i on o fha r d pha s e ssucha s AF, ba i n i t e and ma r t ens i t e, t husi nc r e a s i ng t he [ ] ha rdenab i l i t ft het e s t eds t e e l s５ ． yo
Tab l e２ Ac１ andAc３t empe r a t u r e sandc r i t i c a lc oo l i ngr a t e sf o rpha s e t r ans f orma t i onandobt a i n i ngcomp l e t ef e r r i t e Ｇpe a r l i t e mi c r o s t r uc t u r e S t e e l
Ac１/ Ac３/ t a r t i ng/ ° C ° C AFs (° Cs－１)
Coo l i ngr a t e Ms t a r t i ng/ (° Cs－１)
D１
７４０
７９５
~４
~１６
D３
７７７
８３２
~１ ５
~８
D２
７６２
８１７
~３
~１６
Comp l e t e F＋P/ (° Cs－１) ~４ ~３
~１ ５
I ti swo r t hno t i ngt ha tduet ot hei nhe r en tc l e av Ｇ agef r a c t ur e modeo fpe a r l i t e pha s eandt hede t r i Ｇ men t a li n f l uenc eo fp r e c i i t a t i on ha rden i ng ont he p t oughne s so ff e r r i t i c Ｇ a r l i t i cmed i umＧ c a rbonf o r i ng pe g s t e e l s, mo r ea t t en t i onha sbe en pa i dt o mod i f he yt f e r r i t e Ｇ a r l i t e mi c r os t ruc t ur e wi t hh i oughne s s pe ght s esucha sAFbyapp l i ngamode r a t epos t Ｇ f o r Ｇ pha y g [ , ] i ngcoo l i ngr a t e４ ６ ．Fo rt he D３s t e e l mi c r oa l l oyed wi t h０ ２９％V, acons i de r ab l ef r a c t i ono fAFcou l d beobt a i nedunde rcoo l i ngr a t esasl ow asaround [１２] ２° C/s, wh i chi sapp l i c ab l ei ni ndus t r r e Ｇ y ．The f o r e,i ti sr e a sonab l et oan t i c i t et ha tt hei n t r oduc Ｇ pa t i ono fcons i de r ab l ef r a c t i ono fAFa tt heexpens eo f a r l i t ei nf e r r i t i c Ｇ a r l i t i cs t e e lcou l dimp r ovei t s pe pe t oughn e s swi t hou tno t ab l ep e n a l t t ss t r eng t hl eve l． yoni Howeve r, f ur t he rt ho r oughwo rkne edst obedone．
４．Conc l u s i on s
(１) Thep r i o raus t en i t eg r a i nsa r er e f i neda f t e r t headd i t i ono fV．Themi c r os t ruc t ur e sf o rmedi nde Ｇ f o rmedandcon t i nuous l l eds t e e l scons i s to ff e r Ｇ ycoo r i t e, pe a r l i t e, AF, ba i n i t eand ma r t ens i t e, depen Ｇ d i ngonVcon t en tandcoo l i ngr a t e．Thef r a c t i ono f f e r r i t ee spe c i a l l nc r e a s e s wi t hi nc r e a s i ng V y IGFi con t en t, andt hef o rma t i on o f AFi ss i i f i c an t l gn y r omo t edwi t hi nc r e a s i ng Vcon t en t． p (２) Thedynami cCCTd i ag r amswe r ee s t ab l i shed wh i c he xh i b i t e ds imi l a rs ha ef o rt het h r e et e s t e ds t e e l s． p Thema i nd i f f e r enc ei st ha tt hef i e l dso ft r ans f o rma Ｇ t i onp r oduc t sa r esh i f t edt ot her i ts i deo ft hed i a Ｇ gh
６４８
WJ．Hu ie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ６４１－６４８
r am wi t ht hei nc r e a s eo fV c on t en t．Thec r i t i c a l g c oo l i ngr a t ef o rpha s et r ans f o rma t i onsandf o rob t a i Ｇ n i ngcomp l e t ef e r r i t eandpe a r l i t emi c r o s t ruc t u r ede Ｇ c r e a s e swi t ht hei nc r e a s eo fVc on t en t．TheAc１ and Ac３t empe r a t u r e sdu r i nghe a t i ngshowani nc r e a s i ng t r endwi t hi nc r e a s i ng Vc on t en t． (３) Th ei n c r e a s eo fVc on t e n tr e s u l t si ns i i f i c a n t gn i nc r e a s eo fha r dne s sandt h i st endenc e n h a n c e sw i t h y i n c r e a s i ngc o o l i ngr a t eun t i lt h ef o rma t i ono fAF．An op t imumc oo l i ngr a t eex i s t st oob t a i nanapp r op r i a t e f r a c t i ono ff i nepr e c i i t a t e st oge tt heh i s tp r e c i Ｇ p ghe p i t a t i onha r den i nge f f e c tf o rt het e s t eds t e e l swi t hf e r Ｇ r i t e Ｇ a r l i t emi c r o s t ruc t u r e．F r omt h ep r e s e n ts t udy, pe t heop t imumc oo l i ngr a t ei sa r ound３ ０° C/sf o rt he , ０ １０％ VＧMA s t e e l anda r ound１ ５° C/sf o rt he ０ ２９％ VＧMAs t e e l．
Acknowl e dgmen t
The wo rk wa sf i nanc i a l l o r edby Na t i ona l yspons Key Re s e a r ch & Deve l opmen t Pr og r am o f Ch i na (２０１６YFB０３００１０３) ．
Re f e r enc e s [１] S．Eng i n e e r, B．Hu c h t ema nn, V．S c hü l e r, S t e e lRe s．５８ (１９８７) ３６９ Ｇ ３７６． [２] S r on Da i, H． Dong,I L．Chen, WJ．Hu i, L H．Wang, GW． andS t e e l４９ (２０１４) No ６, １ Ｇ ７ (i nCh i ne s e) ． [３] V．Ol l i l a i n e n, W．Ka s r z ak, L．Ho l a a, J．Ma t e r． Pr o c e s s．Te ch Ｇ p pp no l． １３４ (２００３) ４０５ Ｇ ４１２． [４] AR．Khodabandeh, M． J aha z i, S．Yue, S T．Aghda sh i, Ma Ｇ t e r．Manu f．Pr o c e s s． ２１ (２００６) １０５ Ｇ １１０．
[５] D．Gl i š i c, N．Radov i c, A．Kop r i v i c a, A．Fade l, D．Dr obn ak, j I S I JI n t． ５０ (２０１０) ６０１ Ｇ ６０６． [６] A．Ba b akh a n i, A R．Ki a n i ＧRa s h i d, S MR．Z i a e i, Ma t e r．Ma nu f． Pr o c e s s． ２７ (２０１２) １３５ Ｇ １３９． [７] M．Ha i s a f a r i, S．Na t egh, H．Yoo z ba sh i z adeh, A．Ekr am, J． j I r onS t e e lRe s． I n t． ２０ (２０１３) No ５, ６６ Ｇ ７３． [８] WJ．Hu i, YJ．Zhang, C W．Shao, S L．Chen, X L．Zhao, H．Dong, Ma t e r．Manu f．Pr o c e s s． ３１ (２０１６) ７７０ Ｇ ７７５． [９] S M． Ch e n t ou f, M． J ah a z i, L P． La i e r r e ＧBo i r e, Me t a l l o r．Mi c r o Ｇ p g s t r u c t．Ana l． ３ (２０１４) ２８１ Ｇ ２９７． [１０] F Y．Xu, YW．Wang, B Z．Ba i, HS．Fang, J． I r onS t e e l Re s． I n t． １７ (２０１０) No ３, ４６ Ｇ ５０． [１１] K ) S．Kim, L X．Du, C R．Ga o, Ac t aMe t a l l． S i n．(Eng l．Le t t． ２８ (２０１５) ６９２ Ｇ ６９８． [１２] C R．Dong, HP．Ren, T Z． J i n, Mi c r oa l l oyed Med i umＧCa r Ｇ bonS t e e l s, Me t a l l ur i c a lI ndus t r e s s, Be i i ng, ２０００． g yPr j [１３] MC．Zhao, K．Yang, F R．Xi ao, YY．Shan, Ma t e r．Sc i． Eng．A３５５ (２００３) １２６ Ｇ １３６． [１４] K．He, D V．Edmonds, Ma t e r． Sc i．Te chno l． １８ (２００２) ２８９ Ｇ ２９６． [１５] WJ．Hu i, S L．Chen, YJ．Zhang, C W．Shao, H．Dong, Ma t e r．De s． ６６ (２０１５) ２２７ Ｇ ２３４． [１６] WJ．Hu i, YJ． Zhang, C W． Shao, S L．Chen, X L． Zhao, H．Dong, J．Ma t e r． Sc i．Te chno l． ３２ (２０１６) ５４５ Ｇ ５５１． [１７] M．Gome z, L．Ranc e l, E．Es cude r o, S F．Med i na, J．Ma t e r． Sc i．Te chno l． ３０ (２０１４) ５１１ Ｇ ５１６． [１８] R． Pe t r o v, L．Ke s t e n s, Y．Houb a e r t, Ma t e r．Ch a r a c t． ５３ (２００４) ５１ Ｇ ６１． [１９] G．Mi t o, R．Ho r i, B．Poo r i, T．Fur uha r a, I S I JI n t． yamo gan j ５１ (２０１１) １７３３ Ｇ １７３９． [２０] X Z． Zhang, QZ． Ca i, GF． Zhou, QF． Chen, YZ．Xi ong, J．Ma t e r． Sc i． ４６ (２０１１) １７８９ Ｇ １７９５． [２１] WJ．Hu i, S L． Chen, C W． Shao, YJ． Zhang, H．Dong, J． I r onS t e e lRe s． I n t． ２２ (２０１５) ６１５ Ｇ ６２１． [２２] R．Lagnebo S iwe ck i, S． Za a c, B．Hu t ch i ns on, Sc an． J． r j g, T． Me t a l l． ２８ (１９９９) １８６ Ｇ ２４２． [２３] T N．Bake r, Ma t e r． Sc i．Te chno l． ２５ (２００９) １０８３ Ｇ １１０７． [２４] F． I sh i kawa, T．Takaha sh i, I S I JI n t． ３５ (１９９５) １１２８ Ｇ １１３３．