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Influence of Ti on Weld Microstructure and Mechanical Properties in Large Heat Input Welding of High Strength Low Alloy Steels
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ５,２ ２( ５):４ ３ １ Ｇ ４ ３ ７
I n f l u enc eo fT ion We l d Mi c r o s t r u c t u r eand Me chan i c a lPr ope r t i e si n La r eHe a tI npu tWe l d i ngo fHi t r e ng t hLowAl l o t e e l s g ghS yS AＧ r ong, L i nZHAO, ChuanPAN, Zh i Ｇ l i ngTIAN
( Ch i naI r onandS t e e lRe s e a r chI ns t i t u t eGr oup,Be i i ng１０００８１,Ch i na) j Ab s t r a c t:Thei n f l uenc eo fTionwe l d mi c r o s t r uc t u r eand me chan i c a lp r ope r t i e si nl a r a ti npu twe l d i ngo fh i gehe gh s t r eng t hl owa l l oys t e e l si si nve s t i t ed．Ther e su l t si nd i c a t et ha tamode r a t eamoun to fTii ss t i l le f f e c t i vef o rg r a i n ga r e f i nemen te venunde rl a r rhe a ti npu tandal a r to fa c i cu l a rf e r r i t e( AF)i sf o rmedi nt hewe l dme t a lwhen ge geamoun Tic on t en ti swi t h i n０ ０２８％－０ ０３８％．Wi t hi nc r e a s i ngTic on t en t,p r oeu t e c t o i df e r r i t ei nt hewe l dme t a lde c r e a s e s, whe r e a sba i n i t eand MＧAc ons t i t uen ti nc r e a s e．Thet fi nc l us i oni nt hewe l dsva r i e sf r om Mn ＧS i ＧAl ＧOt oTi ＧMn Ｇ ypeo Al ＧOandf i na l l oTi ＧAl ＧOa sTic on t en ti nc r e a s e sf r om０upt o０ ０６４％．Asf o radd i ng０ ０２８％－０ ０３８％ Ti,h i yt gh we l dt oughne s sc ou l dbea t t a i neds i nc emo s ti nc l us i onsl e s st han２μm wh i chc on t a i nTi r ov i det hee f f e c t i venu Ｇ ２O３ p c l e if o ra c i cu l a rf e r r i t ef o rma t i on．Howe v e r,t h et oughn e s so ft h ewe l dme t a l ss e v e r e l e du c e swh e nT ic on t e n ti so v e rt he yr op t imumr angeo f０ ０２８％－０ ０３８％． Ke r d s:l a r a ti npu twe l d i ng;Ti;mi c r o s t r uc t u r e;a c i cu l a rf e r r i t e;i nc l us i on;h i t r eng t hl owa l l oys t e e l gehe ghs ywo
The me chan i c a lpr ope r t i e so ft he we l d ma i n l y dependon mi c r o s t ruc t u r e,we l d i nghe a ti npu t,and chemi c a lcompo s i t i ono ft hewe l ds．The mi c r o s t ruc Ｇ ( t u r eo fconven t i ona lh i t r eng t hl ow a l l oy HS Ｇ ghs LA)s t e e lwe l dsma i n l ons i s t so ff e r r i t e,ba i n i t e, yc ma r t ens i t eando t he rmi c r o Ｇ s e s．Al a r t pha geamoun ( ) o fa c i cu l a rf e r r i t e AF i se s s en t i a lf o rob t a i n i nga c omb i na t i ono fexc e l l en t we l dt oughne s sand me Ｇ [ ] chan i c a ls t r eng t ha tt hes amet ime１Ｇ４ ．I ti s we l l knownt ha t AF nuc l e a t e sa ts omef i nei nc l us i ons wi t hac e r t a i n mi c r o Ｇ chemi s t r i cha r ei de a lnu Ｇ y,wh c l e a t i on s i t e s f o ri n t r ag r anu l a r a c i cu l a r f e r r i t e [ ] ( IAF)５Ｇ８ ．Tii soneo ft hemo s timpo r t an tmi c r o Ｇ a l Ｇ l oy i nge l emen t s． I ti sr epo r t edt ha twi t hah i l t Ｇ ghme i ngpo i n t,Ti２O３ e f f e c t i ve l r omo t e sf i neIAF be Ｇ yp , c aus eTi２O３i ss t ab l ei nt hewe l d i ngt he rma lc c l e s y andc ou l dke epi t sp i nn i nge f f e c t sa th i rt empe r a Ｇ ghe t u r e．Mo r eove r,t he r ea r eal a r ro fc a t i on genumbe va c anc i e si ns i deTi２O３ ,and Mn３＋ e a s i l i f f us e si n Ｇ yd , t ot heox i de st hr ought he s eva c anc i e s andhenc et he chemi c a ld r i v i ng f o r c ef o rmed by t he dep l e t i on z one s．Tha ti s why AF nuc l e a t e s mo r ee a s i l y on [ ９ Ｇ １１] Ti２O３t hanaus t en i t eg r a i nbounda r i e s ． Ticon t en ti nt hewe l dme t a l sa f f e c t si nc l us i ons．
The r ea r esomer e s e a r che sdonef o ri t se f f e c t son r a i nr e f i nemen ti nl owe r we l d i ng he a ti npu t．At g ve r owl eve l so fTi, l a r i z edmangane s e Ｇ s i l i c a t e s yl ges , , a r ef avo r ed wh i ch a r ei ne f f e c t i ve f o r AF and b l ockyf e r r i t ei sp r edomi nan t l o rmeda sar e su l t． I n yf con t r a s t,a th i rl eve l so fTi,no ton l i n i t eand ghe yba somebr i t t l emi c r o Ｇ s e sa r ef avo r ed,bu tha rdena Ｇ pha b i l i t ft he we l dsi s obv i ous l nc r e a s ed．Me an Ｇ yo yi [ ] wh i l e,we l dab i l i t sa l sode t e r i o r a t ed１２Ｇ１７ ．Soi ti s yi impo r t an tt or e s t r i c tt i t an i uml eve lt oanapp r op r i a t e r angef o rob t a i n i ng mo r eAFandbe t t e rwe l dab i l i t y． I nadd i t i on,t heequ i l i br i umbe twe end i s so l u t i onand r e c i i t a t i oni nt hei nc l us i onschange swi t hi nc r e a s Ｇ p p , i ngt hehe a ti npu t so mi c r os t ruc t ur echange sa c Ｇ co rd i ng l c aus eo ft heva r i a t i on o ft hei nc l us i on y be t i z eandd i s t r i bu t i on． ype,s , I nt h i ss t udy e l e c t r oga sa r c we l d i ng ( EGW ) /cmi wi t hahe a ti npu to f８５kJ sc a r r i edou t．Mi c r o Ｇ s t ruc t ur eandme chan i c a lp r ope r t i e so ft hewe l dme t Ｇ a l swi t hd i f f e r en tt i t an i uml eve l sa r ei nve s t i t edt o ga e l uc i da t et hee f f e c t so ft i t an i umi nh i a ti npu t ghhe we l d i ng．Theop t imum r angeo fTicon t en t si sa l so d i s cus s ed,wh i chwou l dbehe l f u lf o rf ur t he rr e l a t Ｇ p edr e s e a r ch．
Founda t i onI t em: I t em Spons o r edbyNa t i ona lHi chno l ogyRe s e a r chandDeve l opmen tPr o e c to fCh i na ( ２００９AA０３Z５３０) ghTe j B i o r aphy: AＧ r ong,Do c t o rCand i ad t e; E Ｇma i l: a r ong_a tm＠１２６ c om; Re c e i v e dDa t e:De c embe r２３,２０１３ g
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 ２２
４３２
１ Exp e r imen t a l TheABSEH３６s t e e lp l a t ewi t hd imens i onso f ８００mm×２００mm×２０mmi sus eda st heba s eme t a l andt hes i ng l e Ｇ a s sE GW w e l d sa r ed e o s i t e d i nv e r Ｇ p p t i c a l Ｇ uppos i t i onus i ngf l uxc o r edwi r e so f１ ６mmi n d i ame t e rwi t hd i f f e r e n tT ic on t e n t s( c l a s s i f i c a t i onAWS
EG７０T ＧG)．Thewe l d i ngi sp e r f o rme dwi t havo l t a eo f g ３４V,acur r en to f３４０A,aspe edo f７ ８cm/mi n, i n /cm．The wh i cht hewe l d i nghe a ti npu ti sabou t８５kJ sh i e l d i ngga si s１００％ CO２ ．Af t e rwe l d i ng,chemi c a l compos i t i onso f we l d me t a l s wi t h va r i ous Ticon Ｇ t en t sa r eana l z edandl i s t edi nTab l e１． y Theimpa c tt e s t sa r ec a r r i edou ta t－２０ ℃ and
Tab l e１ Ch emi c a lc ompo s i t i ono fwe l dme t a landba s eme t a l ma s s％
Compo s i t i on
C
Mn
S i
Ni
Mo
Ti
０ ２７ ０ ３０
Ba s eme t a l
０ １６０
１ ３９
０ ３２
０ ０２
０ ０２
We l dNo ２
０ ０６３
１ １９
０ ４０
０ ５０
０ ３６
We l dNo １ We l dNo ３ We l dNo ４
０ ０５６ ０ ０５９ ０ ０６３
１ １３ １ １５ １ ２０
０ ４２ ０ ４３ ０ ５３
０ ４２ ０ ４２ ０ ４８
０ ３６
－４０ ℃ ,r e spe c t i ve l cke r sha r dne s st e s tandt en Ｇ y．Vi s i l et e s t sa r epe r f o rmeda tr oom t empe r a t u r e．The spe c imensf o r mi c r o s t ruc t u r e obs e r va t i on a r e me Ｇ chan i c a l l l i shedande t ched wi t h３％ n i t a ls o l u Ｇ ypo t i on,and add i t i ona l l he s amp l e sa r ee t ched by yt Lepr ar e agen tf o rd i s t i ngu i sh i ng MＧA c ons t i t uen t s． Tr ansmi s s i one l e c t r on mi c r o s c opy ( TEM )obs e r va Ｇ t i oni sc a r r i edou tunde ranHＧ ８００t r ansmi s s i one l e c Ｇ t r onmi c r os c ope． Toquan t i t a t i ve l l z et hes i z eandnumbe ro f yana y , i nc l us i onsand MＧA c ons t i t uen t s no tl e s st han２０
B
Mg
Al
０ ００１
０ ００２５
０ ００１５
０ ０１３０
０ ００３８
０ ０４８
０ ０３８
０ ００４５
０ ００１１
０ ０１１０
０ ００４２
０ ０３８
－
０ ０２８ ０ ０６４
－
０ ００５２ ０ ００４６
－
０ ００１６ ０ ００１６
－
０ ００７５ ０ ００６０
N
－
０ ００３３ ０ ００３２
O
－
０ ０３５ ０ ０３３
op t i c a lmi c r os copy ( OM)mi c r og r aphsa r er andoml y chos enf o re a chwe l d,andt heda t aa r eme a sur edby so f twa r e．
２ Re s u l t sandDi s c u s s i on
２ １ Ef f e c to fT ionmi c r o s t r u c t u r e F i １ showst he mi c r os t ruc t ur eo ft he we l d g , me t a l s．Wi t hou tTiadd i t i on t hewe l dme t a lcons i s t s ma i n l fp r oeu t e c t o i df e r r i t e,AF and ba i n i t e,a s yo showni nF i １( a)．Wi t hi nc r e a s i ngTicon t en to ft he g , we l dme t a l AFi sobv i ous l a vo r e dwh i l et heb l o c ky yf
( a)We l dNo １ ( ０％ Ti)wi t h５５％－６５％ AF; ( b)We l dNo ２ ( ０ ０２８％ Ti)wi t h８０％－９０％ AF; ( c)We l dNo ３ ( ０ ０３８％ Ti)wi t h８０％－９０％ AF; ( d)We l dNo ４ ( ０ ０６４％ Ti)wi t habou t５％ AF．
F i １ SEM mi c r o r aph so fwe l dme t a l swi t hd i f f e r en tT ic on t en t s g g
I s sue５ I n f l uenc eo fTion We l d Mi c r o s t r uc t u r eand Me chan i c a lPr ope r t i e si nLa r a tI npu tWe l d i ngo fS t e e l s geHe
r oeu t e c t o i df e r r i t ede c r e a s e s,a sshowni nF i １ p gs ( b)and１( c)．Wi t hi nc r e a s i ngTiupt o０ ０６４％ ,t he we l dmi c ros t ruc t ur ei sobs e rvedcont a i n i ngal a rge amoun to fba i n i t ea sshowni nF i １( d)． g F i ２s howst h ewe l d mi c r o s t r u c t u r eob s e r v e dby g TEM． I n c l u s i on si nt h ewe l dme t a lma i v i dedi n t o ybed twot s,name l hee f f e c t i vei nc l us i onsandt he ype y,t i ne f f e c t i vei nc l us i ons．Mo s tAFi sob s e r v e dt ob enu Ｇ ( c l e a t e dont hee f f e c t i v ei n c l u s i on sa ss howni nF i ２ a) g wh i l et hei ne f f e c t i veone sc ou l dno tbet henuc l e io f , ( ) , AF a sshowni nF i ２ b ．Fu r t he rmo r et he r ea r e g noi nc l us i onsa r ound p r oeu t e c t o i df e r r i t eandba i n Ｇ i t e,a sshowni nF i ２( c)and２( d)． gs MＧA cons t i t uen ti sa l s oobs e r vedi nt he we l d
４３３
me t a l s．F i ３s howst hef i n epha s es t r u c t u r e so fMＧA g cons t i t uen t s,wh i cha r ecompos edo fma r t ens i t eand r e t a i nedaus t en i t e．Mo r l ogyo fMＧAcons t i t uen t s pho [ , ] a f f e c t s me chan i c a lp r ope r t i e so ft he we l ds１８ １９ ． Thus,a l ls amp l e sa r ee t chedbyLep r ar e agen tt or e Ｇ , , ve a lMＧAcons t i t uen t s wh i chi swh i t e whe r e a sf e r Ｇ r i t ei sg r ay andc emen t i t eo rc a rb i dei sb l a ck,a s showni nF i ４．Ast ot heshape,MＧA cons t i t uen t g , , cou l dbed i v i dedi n t otwot s name l t r i ngand ype y s b l ock．Thea r e af r a c t i ono f MＧA cons t i t uen ti nt he we l di si nc r e a s edf r om２ ６％ t o３ ０％－３ ９％ a sTi con t en ti sf r om０t ot her angeo f０ ０２８％－０ ０３８％ , andr e a che s５ ３％ wi t h０ ０６４％ Ti,andt heg r os so f , MＧAc on s t i t u e n ti si n c r e a s e dwi t hT ia dd i t i on a st her e Ｇ
( a)AFande f f e c t i vei nc l us i on ( ０ ０２８％ Ti); ( b)I ne f f e c t i vei nc l us i ons ( ０％ Ti); ( c)Pr oeu t e c t o i df e r r i t e( ０％ Ti); ( d)Ba i n i t e( ０ ０６４％ Ti)．
F i ２ Mi c r o s t r u c t u r ei nwe l dme t a l sob s e r v e dbyTEM g
( a)MＧAc ons t i t uen t; ( b)Re t a i nedaus t en i t ei n MＧA ( da rkf i e l d); ( c)El e c t r ond i f f r a c t i onpa t t e r no fMＧAc ons t i t uen t．
F i ３ F i n epha s es t r u c t u r eo fMＧAc on s t i t u en t( ０ ０２８％ T i) g
４３４
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 ２２
( a)We l dNo １ ( ０％ Ti); ( b)We l dNo ２ ( ０ ０２８％ Ti); ( c)We l dNo ３ ( ０ ０３８％ Ti); ( d)We l dNo ４ ( ０ ０６４％ Ti)．
F i ４ Mo rpho l o fMＧAc on s t i t u en tc ompo s e do fs t r i ngs hap e( A)andb l o cks hap e( B) g g yo
su l t．The r e f o r e,t heop t imum Tic on t en ti si nt he r angeo f０ ０２８％ －０ ０３８％ ,and AFi se f f e c t i ve l y r omo t eda tt h i sl eve l． p ２ ２ Ef f e c to fT ioni nc l u s i on s F i ５s h o w s t h ed i s t r i b u t i onandmo r l ogyo f g pho t hei nc l us i onsi nd i f f e r en twe l d me t a l s．Wi t hou tTi, asma l lnumbe ro fi nc l us i ons wi t hl a r rs i z e sd i s Ｇ ge t r i bu t ei nt hewe l d．P l en t o f f i n e i n c l u s i o n sa r eo b Ｇ y s e r vedi nt hewe l dme t a l sa sTii swi t h i nt her angeo f ０ ０２８％－０ ０３８％．Wi t hf u r t he radd i t i ono fT iupt o ０ ０６４％ ,t hei n c l u s i on sa r eobv i ou s l o a r s e n e dandt he yc numbe rde c r e a s e s．Tab l e２showst hes t a t i s t i c a lr e Ｇ su l t so ft hei nc l us i on．Thenumbe rdens i t r ama t i c Ｇ yd a l l nc r e a s e sf r om４ ６×１０３ mm－２t o９×１０３ mm－２ yi wi t hi nc r e a s i ng Tiadd i t i onf r om ０t ot her angeo f ３ －２ , ０ ０２８％ －０ ０３８％ andr educ e st o３×１０ mm wi t h０ ０６４％ Ti．Asar e su l t,t hea r e af r a c t i ono f t hei nc l us i onswi t hanop t imumr angeo fTii sh i r ghe t hant heo t he r s．Mo r eove r,Tic on t en tha sas i i f i Ｇ gn c an te f f e c tont hei nc l us i ons i z ea s we l l．I ti s we l l knownt ha ti nc l us i onsl e s st han２ μm a r ee f f e c t i ve
f o rAFf o rma t i on．Thepe r c en t ageo fi nc l us i onsl e s s t han２ μmi sove r８５％ i nt her angeo f０ ０２８％ － ０ ０３８％Ti,andd r opst oabou t５０％ whent hecon Ｇ , t en t sa r e０ and０ ０６４％ r e spe c t i ve l r e f o r e, y．The t hee f f e c to fTioni nc l us i ons i z ei sno ts imp l i ne a r, yl
bu tpa r abo l i c．I nc l us i ons i z ede c r e a s e sa tf i r s tand t heni n c r e a s e swi t hi n c r e a s i ngT ia ss howni nT ab l e２． F i ６showsTicon t en ti ni nc l us i onsme a sur ed g ( ) byene r i spe r s i vespe c t r os copy EDS ．Ticon t en t gyd i nt hei nc l us i onsi nc r e a s e s wi t h Tiadd i t i oni nt he we l d me t a l．EDSr e su l t si nd i c a t et ha t wi t hou tT i, , , t hei n c l u s i on s ma i n l on t a i ns i l i c on mang an e s e a l u Ｇ yc
mi numandoxygen．Wi t h０ ０２８％ －０ ０３８％ Tii n t hewe l d me t a l,Tiand Alcon t en t si nc r e a s e,wh i l e , , S i MnandOl eve l sde c r e a s e．Al t houghTi Aland O con t en t si nt hei nc l us i onsr e a ch t he max imum wi t ht he max imum Ticon t en to f０ ０６４％ i nt he we l dme t a l,MnandS il eve l sd r opt ot hemi n imum． Add i t i ona l l t en t si nt hei nc l us i ons y,Mnand Scon , ke epa tl owe rl eve l s andchanges l i t l na l lwe l d gh yi me t a l s,Asde s c r i bedabove,t het fi nc l us i on ypeo va r i e sf r om Mn ＧS i ＧAl ＧOwi t h０T it oT i ＧMn ＧAl ＧOwi t h
I s sue５ I n f l uenc eo fTion We l d Mi c r o s t r uc t u r eand Me chan i c a lPr ope r t i e si nLa r a tI npu tWe l d i ngo fS t e e l s geHe
４３５
( a)We l dNo １ ( ０％ Ti); ( b)We l dNo ２ ( ０ ０２８％ Ti); ( c)We l dNo ３ ( ０ ０３８％ Ti); ( d)We l dNo ４ ( ０ ０６４％ Ti)．
F i ５ I nc l u s i on si nwe l dme t a l sc on t a i n i ngv a r i ou sT ic on t en t s g Tab l e２ S t a t i s t i c a lr e s u l t so fi nc l u s i onana l s i s y
We l d numbe r
I nc l us i onnumbe rdens i t y/ ( Namm－２)
Ar e af r a c t i ono f /％ i nc l us i ons
We l dNo ２
１００３４
０ ４２
We l dNo ４
３７４５
We l dNo １ We l dNo ３
４６６７ ９０５０
０ １８ ０ ４５ ０ ２７
F i ６ L i n e a rr e l a t i onb e twe enT ic on t en t si n g bo t hwe l dme t a l sandi nc l u s i on s
t her angeo f０ ０２８％－０ ０３８％ Tiandt hent oTi ＧAl Ｇ O wi t h０ ０６４％ Ti． Thechemi c a lc ompo s i t i onsi nd i f f e r en tpa r t so f
S i z ed i s t r i bu t i on/％
０－１μm
１－２μm
２－３μm
＞３μm
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t hei nc l us i onsa r eana l z edby EDSt oc l a r i f he i r y yt componen t sa s we l l．F i ７showst heevo l u t i on o f g d i f f e r en tox i de si nt he we l d me t a l sandt hei nc l u Ｇ s i ons．Wi t hou tTiadd i t i on,MnO andS iO２ ma i n l y oc curi nt hec en t e ro fi nc l us i ons,wh i l eAl２O３ ,MnS and MgOs eg r ega t ea tt heedge．Wi t hi nc r e a s i ng Ti con t en t,Tix Oy i sg r adua l l o rmedi nt heco r eand yf MgOandAl２O３ movei n t ot hec en t r a la r e af r omt he edge,wh i l eMnOandS iO２ a r eexpe l l edt ot heedge． Wi t h０ ０３８％ Ti,Tix Oy ,MnOand MgO ga t he ri n t hec e n t e rand Al f ft hec e n t e r．On l e Ｇ y Tix Oy r ２O３ o ma i nsi nt hei nc l us i onco r e,andt heo t he rox i de s sucha s MgO,S iO２ and Al２O３ ga t he ri nt heedge whenTicon t en ti s０ ０６４％． Ast empe r a t ur ede c r e a s e sdur i ngso l i d i f i c a t i on, so l ub i l i t fSandOa l sode c r e a s e sandox i de swi t h yo h i l t i ngpo i n t sa r ef i r s t l o rmed．I tha sbe en gh me yf a s sumedt ha tSexs i s t sa sasu l i decoa t i ngo rshe l l ph
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J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
F i ７ Ev o l u t i ono fi nc l u s i on swi t hT iadd i t i oni nwe l dme t a l s g
a r oundanox i deo rs i l i c a t et o r ea tl owe rt emＧ ypec [ ] r a t ur e１５ ．Wi t hou tTi,domi nan tox i de si nt hei n Ｇ pe c l us i onsa r eMnO,S iO２ ,Al２O３ and MgO．Wi t h Ti r ang i ngi n０ ０２８％－０ ０３８％ ,Ti２O３i ss i i f i c an t l gn y i nc r e a s ed,andt hef o rma t i ono fAFi sp r omo t edbe Ｇ c aus eo fi t se f f e c t i vene s sf o rIAFnuc l e a t i on．Mo r eo Ｇ , , ve r MnO and S iO２ a r e pa r t i a l l i d i z ed de Ｇ y deox c r e a s edandexpe l l edt ot heedge sa l ong wi t hs ome Al２O３ and MgO wi t hi nc r e a s i ng Ti．Wi t h０ ０６４％ , a s i l omb i ne swi t h MnOand Ti exc e s s i veTix Oy e yc a sar e su l t,pa r t so fTi２O３a r er ep l a c edbys omei ne f Ｇ f e c t i ve mangane s et i t ana t e s,sucha s Mn２TiO４ and [] MnTi２O４ １ ． ２ ３ Ef f e c to fT ionme chan i c a lpr ope r t i e s Ha rdne s so fe a ch we l di s me a su r ed．Theha r d Ｇ ne s si nc r e a s e sf r om ２０９t o２４６ HV wi t hi nc r e a s i ng Tif r om０t o０ ０６４％ ,c l o s e l r oa ch i ngt ot hea c Ｇ yapp c ep t anc ec r i t e r i ono f２４８ HVf o rs ou rs e r v i c ei na c Ｇ [ ] c o r danc ewi t h NACE MR０１７５２０ ．Th i s me anst ha t Tiadd i t i oni nc r e a s e st hesus c ep t i v i t fhyd r ogeni n Ｇ yo duc ed c r a ck i ng．On t he o t he r hand,t he t ens i l e s t r eng t ho ft hewe l dsi nc r e a s e sby２８％ f r om５８５t o ７５０ MPaandt hey i e l ds t r eng t hi nc r e a s e sby ２６％ f r om４６０t o５８０ MPawi t hi nc r e a s i ngTit o０ ０６４％ , whe r e a st hee l onga t i onde c r e a s e sby２０％ f r om２５％ t o２０％． F i ８showst heimpa c tabs o rbedene r fe a ch g gyo
we l da t －２０and －４０ ℃．AsTicon t en ti nc r e a s e s f r om ０t o０ ０２８％ ,t heimpa c tabso rbedene r n Ｇ gyi c r e a s e sf r om８５t o１５６Ja t －２０ ℃ andf r om ６９t o , １４６Ja t －４０ ℃ r e spe c t i ve l t hi nc r e a s i ng Ti y．Wi add i t i ont o０ ０３８％ ,t heimpa c tabso rbed ene r gy s l i t l c r e a s e s．Howeve r,t heva l ued r ama t i c a l l gh yde y de c r e a s e st o１７Ja t－２０ ℃ and１６Ja t－４０ ℃ wi t h i nc r e a s i ng Tit o０ ０６４％．F i ９showst hef r a c t ur e g sur f a c eo ft he we l da f t e rl ow t empe r a t ur eimpa c t , t e s t s．Wi t hi nc r e a s i ngTicon t en tt hef r a c t ur emode change sf r om qua s i Ｇ c l e avaget oduc t i l ef r a c t ur eand f i na l l t oc l e a v a e ． I t i s t h e r e f o r e s h o w n t h a tm ode r Ｇ y g a t eTip r omo t e sAFf o rma t i onbe c aus eo ft hee f f e c Ｇ t i vene s so fi nc l us i onssma l l e rt han２μmanda c co rd Ｇ i ng l hewe l dt oughne s si ss i i f i c an t l r oved． y,t gn yimp Wi t h Ticon t en ti nt her ange o f０ ０２８％ － ０ ０３８％ ,t he we l d me t a lp r e s en t sexc e l l en tt oughＧ , ne s sduet ol a r e a m o u n t s o fA F a l t h o u h t h e r os s g g g o fMＧAcons t i t uen ti sh i rt hant he s ewi t hou tTi． ghe Ac co rd i ngt op r ev i ousr e s e a r che s,AFi so fsoc a l l ed [ １２] “ ” ba ske t Ｇwe ave s t ruc t ur eandi n t e r l ock i ngna t ur e ． So c r a ck p r opaga t i ng d i r e c t i ons a r e cons t an t l y changedbyt he i rchao t i ca r r angemen tandh i l e ghang , , r a i nbounda r i e s anda sar e su l ti tcou l dp r ov i de g t hewe l dwi t hbe t t e rl owt empe r a t ur et oughne s sand [, ] h i rr e s i s t anc et oc r a cksdur i ngde f o rma t i on４ １２ ． ghe The r e f o r e,t hemo r eAFob t a i nsi nt hewe l dme t a l s, t heh i rt hel owt empe r a t ur et oughne s sa ch i eve s, ghe event hought heamoun to fMＧAcons t i t uen ti nc r e a Ｇ s e swi t hTiadd i t i on． I ti sobv i oust ha tt hede l e t e r i Ｇ ouse f f e c to f MＧA cons t i t uen ti s we akened wh i l ea l a r to fAFa r ef o rmedi nt hewe l d．Howev Ｇ geamoun , e rt het oughne s so fwe l d me t a li ss eve r e l t e r i o Ｇ yde r a t edbyexc e s s i veadd i t i ono fTiowi ngt ot hei n Ｇ c r e a s eo fMＧAcons t i t uen tandba i n i t e．
３ Conc l u s i on s
F i ８ Impa c tab s o r b e den e r fwe l d s g g yo
E f f e c t so fT ii nt hel a r ehe a ti npu twe l d sa r ed i s Ｇ g cus s edandt her e su l t sshowt ha tamode r a t eamoun t o fTii ss t i l le f f e c t i vef o r mi c r os t ruc t ur a limp r ove Ｇ men tandi nc l us i onr e f i nemen tb e c au s eo ft hee f f e c t i v e
I s sue５ I n f l uenc eo fTion We l d Mi c r o s t r uc t u r eand Me chan i c a lPr ope r t i e si nLa r a tI npu tWe l d i ngo fS t e e l s geHe
４３７
( a)We l dNo １ ( ０％ Ti); ( b)We l dNo ２ ( ０ ０２８％ Ti); ( c)We l dNo ３ ( ０ ０３８％ Ti); ( d)We l dNo ４ ( ０ ０６４％ Ti)．
F i ９ Fr a c t u r es u r f a c eo fwe l dme t a l sa f t e rimpa c tt e s ta t－２０ ℃ g
c omp l exi nc l us i ons． ( ) １ I nl a r eh e a ti npu twe l d i ngo fh i t r e ng t h g ghs l owa l l o t e e l s,t he we l d me t a lc ons i s t s ma i n l f ys yo , , r o e u t e c t o i df e r r i t e A F b a i n i t ea n d M Ｇ Ac o n s t i t u Ｇ p en t．Al a r to fAFi sf o rmedwhenTic on Ｇ geamoun t en ti swi t h i n０ ０２８％－０ ０３８％． ( ２)I n c l u s i on si nt h ewe l d me t a lma ed i v i d e d yb i n t otwog r oup s,e f f e c t i vei nc l us i onsandi ne f f e c t i ve i nc l us i ons．Mo s to ft hee f f e c t i vei nc l us i onsa r el e s s t han２μmi ns i z eandc on t a i nTi２O３ ．Wi t hi nc r e a s i ng Tic on t en t,t het ft hei nc l us i on va r i e sf r om ypeo Mn ＧS i ＧAl ＧOt oTi ＧMn ＧAl ＧOandf i na l l oTi ＧAl ＧO． yt ( ３)T ia dd i t i oni se f f e c t i v ef o ri n c r e a s i ngt h ewe l d s t r e ng t h．Exc e l l en tt oughne s sc ou l d be ob t a i ned whenT ic on t e n ti sw i t h i n０ ０２８％－０ ０３８％ ,ow i ngt o al a r to fAF,whe r e a st het oughne s sd r a Ｇ geamoun ma t i c a l l d e c r e a s e sw i t he x c e s s i v eT i ． y Re f e r enc e s:
[ １] J S．Byun,J H． Sh im,YW． Cho,D N． Le e,Ac t aMa t e r． ５１ ( ２００３)No ６,１５９３ Ｇ １６０６．
[ ２] WW．Bo s e f i l ho,AL M．Ca r va l ho,M．S t r angwood,Ma t e r． Cha r a c t． ５８ ( ２００７)２９ Ｇ ３９．
[ ３] AM． Pan i agua ＧMe r c ado,VM．Lop r z ＧHi r a t a,HJ．Do r an t e s Ｇ , , , Ro s a l e s P．Es t r adaDi a z E．Di a zVa l de z Ma t e r．Cha r a c t． ６０ ( ２００９)３６ Ｇ ３９．
[ ４] T．Weg r z Sz opa,M．Mi r o s,We l d i ngI n t． ２３ ( ２００９)５４ Ｇ yn,P． ５９． [ M．Xue,J． I r onS t e e lRe s． I n t． ５] F．Cha i,H． Su,C F．Yang,D ２１ ( ２０１４)３６９ Ｇ ３７４． [ ６] AG．Fox,D G．Br o t he r s,Sc r i t a Me t a l l．Ma t e r． ３２ ( １９９５) p No ７,１０６１ Ｇ １０６６． [ H．L i u,J． I r onS t e e lRe s． X．Xi a,Z G．Yang,Z ７] C． Zhang,Z I n t． １７ ( ２０１０)No ６,３６ Ｇ ４２． [ ８] F．Cha i,C F．Yang,H． Su,YQ． Zhang,Z．Xu,J． I r onS t e e l Re s． I n t． １６ ( ２００９)No １,６９ Ｇ ７４． [ ９] T．Ryousuke,J．Yang,K．Mamo r u,I S I JI n t． ４７ ( ２００７)１３７９ Ｇ １３８６． [ １０] X L．Wan,R．We i,KM．Wu,Ma t e r．Cha r a c t．６１ ( ２０１０) ７２６ Ｇ ７３１． [ １１] K．Yamamo t o,T．Ha s egawa,J I．Takamur a,I S I JI n t．３６ ( １９９６)８０ Ｇ ８６． [ １２] S S．Babu,Cur r en tOp i n i oni nSo l i dS t a t eand Ma t e r i a l sSc i Ｇ enc e８ ( ２００８)２６７ Ｇ ２７８． [ １３] J L．Le e,Ac t a Me t a l l．Ma t e r． ４２ ( １９９４)３２９１ Ｇ ３２９８． [ １４] YT．Pan,J L．Le e,Ma t e r．De s． １５ ( １９９４)３３１ Ｇ ３３８． [ １５] S A．Cour t,G．Po l l a r d,Me t a l l og r aphy２２ ( １９８９)２１９ Ｇ ２４３． [ １６] S．S t ＧLa u r e n t,G L．Es é r a n c e,Ma t e r．S c i．Eng．A１４９ ( １９９２) p
２０３ Ｇ ２１６． [ １７] B．Be i dokh t i,AH．Koukab i,A．Do l a t i,Ma t e r．Cha r a c t． ６０ ( ２００９)２２５ Ｇ ２３３． [ １８] S．Moe i n i f a r,AH．Kokab i,HR M．Ho s s e i n i,Ma t e r．De s． ３１ ( ２０１０)２９８４ Ｇ ２９５５． [ １９] Y W．Sh i,Z X．Ha n,J．Ma t e r．Pr o c e s s．T e c hno l．２０７ ( ２００８) ３０ Ｇ ３９． [ ２０] B．Be i dokh t i,AH．Koukab i,A．Do l a t i,J．Ma t e r．Pr o c e s s． Te chno l． ２０９ ( ２００９)４０２７ Ｇ ４０３５．
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ５,２ ２( ５):４ ３ １ Ｇ ４ ３ ７
I n f l u enc eo fT ion We l d Mi c r o s t r u c t u r eand Me chan i c a lPr ope r t i e si n La r eHe a tI npu tWe l d i ngo fHi t r e ng t hLowAl l o t e e l s g ghS yS AＧ r ong, L i nZHAO, ChuanPAN, Zh i Ｇ l i ngTIAN
( Ch i naI r onandS t e e lRe s e a r chI ns t i t u t eGr oup,Be i i ng１０００８１,Ch i na) j Ab s t r a c t:Thei n f l uenc eo fTionwe l d mi c r o s t r uc t u r eand me chan i c a lp r ope r t i e si nl a r a ti npu twe l d i ngo fh i gehe gh s t r eng t hl owa l l oys t e e l si si nve s t i t ed．Ther e su l t si nd i c a t et ha tamode r a t eamoun to fTii ss t i l le f f e c t i vef o rg r a i n ga r e f i nemen te venunde rl a r rhe a ti npu tandal a r to fa c i cu l a rf e r r i t e( AF)i sf o rmedi nt hewe l dme t a lwhen ge geamoun Tic on t en ti swi t h i n０ ０２８％－０ ０３８％．Wi t hi nc r e a s i ngTic on t en t,p r oeu t e c t o i df e r r i t ei nt hewe l dme t a lde c r e a s e s, whe r e a sba i n i t eand MＧAc ons t i t uen ti nc r e a s e．Thet fi nc l us i oni nt hewe l dsva r i e sf r om Mn ＧS i ＧAl ＧOt oTi ＧMn Ｇ ypeo Al ＧOandf i na l l oTi ＧAl ＧOa sTic on t en ti nc r e a s e sf r om０upt o０ ０６４％．Asf o radd i ng０ ０２８％－０ ０３８％ Ti,h i yt gh we l dt oughne s sc ou l dbea t t a i neds i nc emo s ti nc l us i onsl e s st han２μm wh i chc on t a i nTi r ov i det hee f f e c t i venu Ｇ ２O３ p c l e if o ra c i cu l a rf e r r i t ef o rma t i on．Howe v e r,t h et oughn e s so ft h ewe l dme t a l ss e v e r e l e du c e swh e nT ic on t e n ti so v e rt he yr op t imumr angeo f０ ０２８％－０ ０３８％． Ke r d s:l a r a ti npu twe l d i ng;Ti;mi c r o s t r uc t u r e;a c i cu l a rf e r r i t e;i nc l us i on;h i t r eng t hl owa l l oys t e e l gehe ghs ywo
The me chan i c a lpr ope r t i e so ft he we l d ma i n l y dependon mi c r o s t ruc t u r e,we l d i nghe a ti npu t,and chemi c a lcompo s i t i ono ft hewe l ds．The mi c r o s t ruc Ｇ ( t u r eo fconven t i ona lh i t r eng t hl ow a l l oy HS Ｇ ghs LA)s t e e lwe l dsma i n l ons i s t so ff e r r i t e,ba i n i t e, yc ma r t ens i t eando t he rmi c r o Ｇ s e s．Al a r t pha geamoun ( ) o fa c i cu l a rf e r r i t e AF i se s s en t i a lf o rob t a i n i nga c omb i na t i ono fexc e l l en t we l dt oughne s sand me Ｇ [ ] chan i c a ls t r eng t ha tt hes amet ime１Ｇ４ ．I ti s we l l knownt ha t AF nuc l e a t e sa ts omef i nei nc l us i ons wi t hac e r t a i n mi c r o Ｇ chemi s t r i cha r ei de a lnu Ｇ y,wh c l e a t i on s i t e s f o ri n t r ag r anu l a r a c i cu l a r f e r r i t e [ ] ( IAF)５Ｇ８ ．Tii soneo ft hemo s timpo r t an tmi c r o Ｇ a l Ｇ l oy i nge l emen t s． I ti sr epo r t edt ha twi t hah i l t Ｇ ghme i ngpo i n t,Ti２O３ e f f e c t i ve l r omo t e sf i neIAF be Ｇ yp , c aus eTi２O３i ss t ab l ei nt hewe l d i ngt he rma lc c l e s y andc ou l dke epi t sp i nn i nge f f e c t sa th i rt empe r a Ｇ ghe t u r e．Mo r eove r,t he r ea r eal a r ro fc a t i on genumbe va c anc i e si ns i deTi２O３ ,and Mn３＋ e a s i l i f f us e si n Ｇ yd , t ot heox i de st hr ought he s eva c anc i e s andhenc et he chemi c a ld r i v i ng f o r c ef o rmed by t he dep l e t i on z one s．Tha ti s why AF nuc l e a t e s mo r ee a s i l y on [ ９ Ｇ １１] Ti２O３t hanaus t en i t eg r a i nbounda r i e s ． Ticon t en ti nt hewe l dme t a l sa f f e c t si nc l us i ons．
The r ea r esomer e s e a r che sdonef o ri t se f f e c t son r a i nr e f i nemen ti nl owe r we l d i ng he a ti npu t．At g ve r owl eve l so fTi, l a r i z edmangane s e Ｇ s i l i c a t e s yl ges , , a r ef avo r ed wh i ch a r ei ne f f e c t i ve f o r AF and b l ockyf e r r i t ei sp r edomi nan t l o rmeda sar e su l t． I n yf con t r a s t,a th i rl eve l so fTi,no ton l i n i t eand ghe yba somebr i t t l emi c r o Ｇ s e sa r ef avo r ed,bu tha rdena Ｇ pha b i l i t ft he we l dsi s obv i ous l nc r e a s ed．Me an Ｇ yo yi [ ] wh i l e,we l dab i l i t sa l sode t e r i o r a t ed１２Ｇ１７ ．Soi ti s yi impo r t an tt or e s t r i c tt i t an i uml eve lt oanapp r op r i a t e r angef o rob t a i n i ng mo r eAFandbe t t e rwe l dab i l i t y． I nadd i t i on,t heequ i l i br i umbe twe end i s so l u t i onand r e c i i t a t i oni nt hei nc l us i onschange swi t hi nc r e a s Ｇ p p , i ngt hehe a ti npu t so mi c r os t ruc t ur echange sa c Ｇ co rd i ng l c aus eo ft heva r i a t i on o ft hei nc l us i on y be t i z eandd i s t r i bu t i on． ype,s , I nt h i ss t udy e l e c t r oga sa r c we l d i ng ( EGW ) /cmi wi t hahe a ti npu to f８５kJ sc a r r i edou t．Mi c r o Ｇ s t ruc t ur eandme chan i c a lp r ope r t i e so ft hewe l dme t Ｇ a l swi t hd i f f e r en tt i t an i uml eve l sa r ei nve s t i t edt o ga e l uc i da t et hee f f e c t so ft i t an i umi nh i a ti npu t ghhe we l d i ng．Theop t imum r angeo fTicon t en t si sa l so d i s cus s ed,wh i chwou l dbehe l f u lf o rf ur t he rr e l a t Ｇ p edr e s e a r ch．
Founda t i onI t em: I t em Spons o r edbyNa t i ona lHi chno l ogyRe s e a r chandDeve l opmen tPr o e c to fCh i na ( ２００９AA０３Z５３０) ghTe j B i o r aphy: AＧ r ong,Do c t o rCand i ad t e; E Ｇma i l: a r ong_a tm＠１２６ c om; Re c e i v e dDa t e:De c embe r２３,２０１３ g
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 ２２
４３２
１ Exp e r imen t a l TheABSEH３６s t e e lp l a t ewi t hd imens i onso f ８００mm×２００mm×２０mmi sus eda st heba s eme t a l andt hes i ng l e Ｇ a s sE GW w e l d sa r ed e o s i t e d i nv e r Ｇ p p t i c a l Ｇ uppos i t i onus i ngf l uxc o r edwi r e so f１ ６mmi n d i ame t e rwi t hd i f f e r e n tT ic on t e n t s( c l a s s i f i c a t i onAWS
EG７０T ＧG)．Thewe l d i ngi sp e r f o rme dwi t havo l t a eo f g ３４V,acur r en to f３４０A,aspe edo f７ ８cm/mi n, i n /cm．The wh i cht hewe l d i nghe a ti npu ti sabou t８５kJ sh i e l d i ngga si s１００％ CO２ ．Af t e rwe l d i ng,chemi c a l compos i t i onso f we l d me t a l s wi t h va r i ous Ticon Ｇ t en t sa r eana l z edandl i s t edi nTab l e１． y Theimpa c tt e s t sa r ec a r r i edou ta t－２０ ℃ and
Tab l e１ Ch emi c a lc ompo s i t i ono fwe l dme t a landba s eme t a l ma s s％
Compo s i t i on
C
Mn
S i
Ni
Mo
Ti
０ ２７ ０ ３０
Ba s eme t a l
０ １６０
１ ３９
０ ３２
０ ０２
０ ０２
We l dNo ２
０ ０６３
１ １９
０ ４０
０ ５０
０ ３６
We l dNo １ We l dNo ３ We l dNo ４
０ ０５６ ０ ０５９ ０ ０６３
１ １３ １ １５ １ ２０
０ ４２ ０ ４３ ０ ５３
０ ４２ ０ ４２ ０ ４８
０ ３６
－４０ ℃ ,r e spe c t i ve l cke r sha r dne s st e s tandt en Ｇ y．Vi s i l et e s t sa r epe r f o rmeda tr oom t empe r a t u r e．The spe c imensf o r mi c r o s t ruc t u r e obs e r va t i on a r e me Ｇ chan i c a l l l i shedande t ched wi t h３％ n i t a ls o l u Ｇ ypo t i on,and add i t i ona l l he s amp l e sa r ee t ched by yt Lepr ar e agen tf o rd i s t i ngu i sh i ng MＧA c ons t i t uen t s． Tr ansmi s s i one l e c t r on mi c r o s c opy ( TEM )obs e r va Ｇ t i oni sc a r r i edou tunde ranHＧ ８００t r ansmi s s i one l e c Ｇ t r onmi c r os c ope． Toquan t i t a t i ve l l z et hes i z eandnumbe ro f yana y , i nc l us i onsand MＧA c ons t i t uen t s no tl e s st han２０
B
Mg
Al
０ ００１
０ ００２５
０ ００１５
０ ０１３０
０ ００３８
０ ０４８
０ ０３８
０ ００４５
０ ００１１
０ ０１１０
０ ００４２
０ ０３８
－
０ ０２８ ０ ０６４
－
０ ００５２ ０ ００４６
－
０ ００１６ ０ ００１６
－
０ ００７５ ０ ００６０
N
－
０ ００３３ ０ ００３２
O
－
０ ０３５ ０ ０３３
op t i c a lmi c r os copy ( OM)mi c r og r aphsa r er andoml y chos enf o re a chwe l d,andt heda t aa r eme a sur edby so f twa r e．
２ Re s u l t sandDi s c u s s i on
２ １ Ef f e c to fT ionmi c r o s t r u c t u r e F i １ showst he mi c r os t ruc t ur eo ft he we l d g , me t a l s．Wi t hou tTiadd i t i on t hewe l dme t a lcons i s t s ma i n l fp r oeu t e c t o i df e r r i t e,AF and ba i n i t e,a s yo showni nF i １( a)．Wi t hi nc r e a s i ngTicon t en to ft he g , we l dme t a l AFi sobv i ous l a vo r e dwh i l et heb l o c ky yf
( a)We l dNo １ ( ０％ Ti)wi t h５５％－６５％ AF; ( b)We l dNo ２ ( ０ ０２８％ Ti)wi t h８０％－９０％ AF; ( c)We l dNo ３ ( ０ ０３８％ Ti)wi t h８０％－９０％ AF; ( d)We l dNo ４ ( ０ ０６４％ Ti)wi t habou t５％ AF．
F i １ SEM mi c r o r aph so fwe l dme t a l swi t hd i f f e r en tT ic on t en t s g g
I s sue５ I n f l uenc eo fTion We l d Mi c r o s t r uc t u r eand Me chan i c a lPr ope r t i e si nLa r a tI npu tWe l d i ngo fS t e e l s geHe
r oeu t e c t o i df e r r i t ede c r e a s e s,a sshowni nF i １ p gs ( b)and１( c)．Wi t hi nc r e a s i ngTiupt o０ ０６４％ ,t he we l dmi c ros t ruc t ur ei sobs e rvedcont a i n i ngal a rge amoun to fba i n i t ea sshowni nF i １( d)． g F i ２s howst h ewe l d mi c r o s t r u c t u r eob s e r v e dby g TEM． I n c l u s i on si nt h ewe l dme t a lma i v i dedi n t o ybed twot s,name l hee f f e c t i vei nc l us i onsandt he ype y,t i ne f f e c t i vei nc l us i ons．Mo s tAFi sob s e r v e dt ob enu Ｇ ( c l e a t e dont hee f f e c t i v ei n c l u s i on sa ss howni nF i ２ a) g wh i l et hei ne f f e c t i veone sc ou l dno tbet henuc l e io f , ( ) , AF a sshowni nF i ２ b ．Fu r t he rmo r et he r ea r e g noi nc l us i onsa r ound p r oeu t e c t o i df e r r i t eandba i n Ｇ i t e,a sshowni nF i ２( c)and２( d)． gs MＧA cons t i t uen ti sa l s oobs e r vedi nt he we l d
４３３
me t a l s．F i ３s howst hef i n epha s es t r u c t u r e so fMＧA g cons t i t uen t s,wh i cha r ecompos edo fma r t ens i t eand r e t a i nedaus t en i t e．Mo r l ogyo fMＧAcons t i t uen t s pho [ , ] a f f e c t s me chan i c a lp r ope r t i e so ft he we l ds１８ １９ ． Thus,a l ls amp l e sa r ee t chedbyLep r ar e agen tt or e Ｇ , , ve a lMＧAcons t i t uen t s wh i chi swh i t e whe r e a sf e r Ｇ r i t ei sg r ay andc emen t i t eo rc a rb i dei sb l a ck,a s showni nF i ４．Ast ot heshape,MＧA cons t i t uen t g , , cou l dbed i v i dedi n t otwot s name l t r i ngand ype y s b l ock．Thea r e af r a c t i ono f MＧA cons t i t uen ti nt he we l di si nc r e a s edf r om２ ６％ t o３ ０％－３ ９％ a sTi con t en ti sf r om０t ot her angeo f０ ０２８％－０ ０３８％ , andr e a che s５ ３％ wi t h０ ０６４％ Ti,andt heg r os so f , MＧAc on s t i t u e n ti si n c r e a s e dwi t hT ia dd i t i on a st her e Ｇ
( a)AFande f f e c t i vei nc l us i on ( ０ ０２８％ Ti); ( b)I ne f f e c t i vei nc l us i ons ( ０％ Ti); ( c)Pr oeu t e c t o i df e r r i t e( ０％ Ti); ( d)Ba i n i t e( ０ ０６４％ Ti)．
F i ２ Mi c r o s t r u c t u r ei nwe l dme t a l sob s e r v e dbyTEM g
( a)MＧAc ons t i t uen t; ( b)Re t a i nedaus t en i t ei n MＧA ( da rkf i e l d); ( c)El e c t r ond i f f r a c t i onpa t t e r no fMＧAc ons t i t uen t．
F i ３ F i n epha s es t r u c t u r eo fMＧAc on s t i t u en t( ０ ０２８％ T i) g
４３４
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 ２２
( a)We l dNo １ ( ０％ Ti); ( b)We l dNo ２ ( ０ ０２８％ Ti); ( c)We l dNo ３ ( ０ ０３８％ Ti); ( d)We l dNo ４ ( ０ ０６４％ Ti)．
F i ４ Mo rpho l o fMＧAc on s t i t u en tc ompo s e do fs t r i ngs hap e( A)andb l o cks hap e( B) g g yo
su l t．The r e f o r e,t heop t imum Tic on t en ti si nt he r angeo f０ ０２８％ －０ ０３８％ ,and AFi se f f e c t i ve l y r omo t eda tt h i sl eve l． p ２ ２ Ef f e c to fT ioni nc l u s i on s F i ５s h o w s t h ed i s t r i b u t i onandmo r l ogyo f g pho t hei nc l us i onsi nd i f f e r en twe l d me t a l s．Wi t hou tTi, asma l lnumbe ro fi nc l us i ons wi t hl a r rs i z e sd i s Ｇ ge t r i bu t ei nt hewe l d．P l en t o f f i n e i n c l u s i o n sa r eo b Ｇ y s e r vedi nt hewe l dme t a l sa sTii swi t h i nt her angeo f ０ ０２８％－０ ０３８％．Wi t hf u r t he radd i t i ono fT iupt o ０ ０６４％ ,t hei n c l u s i on sa r eobv i ou s l o a r s e n e dandt he yc numbe rde c r e a s e s．Tab l e２showst hes t a t i s t i c a lr e Ｇ su l t so ft hei nc l us i on．Thenumbe rdens i t r ama t i c Ｇ yd a l l nc r e a s e sf r om４ ６×１０３ mm－２t o９×１０３ mm－２ yi wi t hi nc r e a s i ng Tiadd i t i onf r om ０t ot her angeo f ３ －２ , ０ ０２８％ －０ ０３８％ andr educ e st o３×１０ mm wi t h０ ０６４％ Ti．Asar e su l t,t hea r e af r a c t i ono f t hei nc l us i onswi t hanop t imumr angeo fTii sh i r ghe t hant heo t he r s．Mo r eove r,Tic on t en tha sas i i f i Ｇ gn c an te f f e c tont hei nc l us i ons i z ea s we l l．I ti s we l l knownt ha ti nc l us i onsl e s st han２ μm a r ee f f e c t i ve
f o rAFf o rma t i on．Thepe r c en t ageo fi nc l us i onsl e s s t han２ μmi sove r８５％ i nt her angeo f０ ０２８％ － ０ ０３８％Ti,andd r opst oabou t５０％ whent hecon Ｇ , t en t sa r e０ and０ ０６４％ r e spe c t i ve l r e f o r e, y．The t hee f f e c to fTioni nc l us i ons i z ei sno ts imp l i ne a r, yl
bu tpa r abo l i c．I nc l us i ons i z ede c r e a s e sa tf i r s tand t heni n c r e a s e swi t hi n c r e a s i ngT ia ss howni nT ab l e２． F i ６showsTicon t en ti ni nc l us i onsme a sur ed g ( ) byene r i spe r s i vespe c t r os copy EDS ．Ticon t en t gyd i nt hei nc l us i onsi nc r e a s e s wi t h Tiadd i t i oni nt he we l d me t a l．EDSr e su l t si nd i c a t et ha t wi t hou tT i, , , t hei n c l u s i on s ma i n l on t a i ns i l i c on mang an e s e a l u Ｇ yc
mi numandoxygen．Wi t h０ ０２８％ －０ ０３８％ Tii n t hewe l d me t a l,Tiand Alcon t en t si nc r e a s e,wh i l e , , S i MnandOl eve l sde c r e a s e．Al t houghTi Aland O con t en t si nt hei nc l us i onsr e a ch t he max imum wi t ht he max imum Ticon t en to f０ ０６４％ i nt he we l dme t a l,MnandS il eve l sd r opt ot hemi n imum． Add i t i ona l l t en t si nt hei nc l us i ons y,Mnand Scon , ke epa tl owe rl eve l s andchanges l i t l na l lwe l d gh yi me t a l s,Asde s c r i bedabove,t het fi nc l us i on ypeo va r i e sf r om Mn ＧS i ＧAl ＧOwi t h０T it oT i ＧMn ＧAl ＧOwi t h
I s sue５ I n f l uenc eo fTion We l d Mi c r o s t r uc t u r eand Me chan i c a lPr ope r t i e si nLa r a tI npu tWe l d i ngo fS t e e l s geHe
４３５
( a)We l dNo １ ( ０％ Ti); ( b)We l dNo ２ ( ０ ０２８％ Ti); ( c)We l dNo ３ ( ０ ０３８％ Ti); ( d)We l dNo ４ ( ０ ０６４％ Ti)．
F i ５ I nc l u s i on si nwe l dme t a l sc on t a i n i ngv a r i ou sT ic on t en t s g Tab l e２ S t a t i s t i c a lr e s u l t so fi nc l u s i onana l s i s y
We l d numbe r
I nc l us i onnumbe rdens i t y/ ( Namm－２)
Ar e af r a c t i ono f /％ i nc l us i ons
We l dNo ２
１００３４
０ ４２
We l dNo ４
３７４５
We l dNo １ We l dNo ３
４６６７ ９０５０
０ １８ ０ ４５ ０ ２７
F i ６ L i n e a rr e l a t i onb e twe enT ic on t en t si n g bo t hwe l dme t a l sandi nc l u s i on s
t her angeo f０ ０２８％－０ ０３８％ Tiandt hent oTi ＧAl Ｇ O wi t h０ ０６４％ Ti． Thechemi c a lc ompo s i t i onsi nd i f f e r en tpa r t so f
S i z ed i s t r i bu t i on/％
０－１μm
１－２μm
２－３μm
＞３μm
５５
３０
１５
－
１０ ５０ １０
４５ ４０ ３５
３０ １０ ３５
１５ －
２０
t hei nc l us i onsa r eana l z edby EDSt oc l a r i f he i r y yt componen t sa s we l l．F i ７showst heevo l u t i on o f g d i f f e r en tox i de si nt he we l d me t a l sandt hei nc l u Ｇ s i ons．Wi t hou tTiadd i t i on,MnO andS iO２ ma i n l y oc curi nt hec en t e ro fi nc l us i ons,wh i l eAl２O３ ,MnS and MgOs eg r ega t ea tt heedge．Wi t hi nc r e a s i ng Ti con t en t,Tix Oy i sg r adua l l o rmedi nt heco r eand yf MgOandAl２O３ movei n t ot hec en t r a la r e af r omt he edge,wh i l eMnOandS iO２ a r eexpe l l edt ot heedge． Wi t h０ ０３８％ Ti,Tix Oy ,MnOand MgO ga t he ri n t hec e n t e rand Al f ft hec e n t e r．On l e Ｇ y Tix Oy r ２O３ o ma i nsi nt hei nc l us i onco r e,andt heo t he rox i de s sucha s MgO,S iO２ and Al２O３ ga t he ri nt heedge whenTicon t en ti s０ ０６４％． Ast empe r a t ur ede c r e a s e sdur i ngso l i d i f i c a t i on, so l ub i l i t fSandOa l sode c r e a s e sandox i de swi t h yo h i l t i ngpo i n t sa r ef i r s t l o rmed．I tha sbe en gh me yf a s sumedt ha tSexs i s t sa sasu l i decoa t i ngo rshe l l ph
４３６
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 ２２
F i ７ Ev o l u t i ono fi nc l u s i on swi t hT iadd i t i oni nwe l dme t a l s g
a r oundanox i deo rs i l i c a t et o r ea tl owe rt emＧ ypec [ ] r a t ur e１５ ．Wi t hou tTi,domi nan tox i de si nt hei n Ｇ pe c l us i onsa r eMnO,S iO２ ,Al２O３ and MgO．Wi t h Ti r ang i ngi n０ ０２８％－０ ０３８％ ,Ti２O３i ss i i f i c an t l gn y i nc r e a s ed,andt hef o rma t i ono fAFi sp r omo t edbe Ｇ c aus eo fi t se f f e c t i vene s sf o rIAFnuc l e a t i on．Mo r eo Ｇ , , ve r MnO and S iO２ a r e pa r t i a l l i d i z ed de Ｇ y deox c r e a s edandexpe l l edt ot heedge sa l ong wi t hs ome Al２O３ and MgO wi t hi nc r e a s i ng Ti．Wi t h０ ０６４％ , a s i l omb i ne swi t h MnOand Ti exc e s s i veTix Oy e yc a sar e su l t,pa r t so fTi２O３a r er ep l a c edbys omei ne f Ｇ f e c t i ve mangane s et i t ana t e s,sucha s Mn２TiO４ and [] MnTi２O４ １ ． ２ ３ Ef f e c to fT ionme chan i c a lpr ope r t i e s Ha rdne s so fe a ch we l di s me a su r ed．Theha r d Ｇ ne s si nc r e a s e sf r om ２０９t o２４６ HV wi t hi nc r e a s i ng Tif r om０t o０ ０６４％ ,c l o s e l r oa ch i ngt ot hea c Ｇ yapp c ep t anc ec r i t e r i ono f２４８ HVf o rs ou rs e r v i c ei na c Ｇ [ ] c o r danc ewi t h NACE MR０１７５２０ ．Th i s me anst ha t Tiadd i t i oni nc r e a s e st hesus c ep t i v i t fhyd r ogeni n Ｇ yo duc ed c r a ck i ng．On t he o t he r hand,t he t ens i l e s t r eng t ho ft hewe l dsi nc r e a s e sby２８％ f r om５８５t o ７５０ MPaandt hey i e l ds t r eng t hi nc r e a s e sby ２６％ f r om４６０t o５８０ MPawi t hi nc r e a s i ngTit o０ ０６４％ , whe r e a st hee l onga t i onde c r e a s e sby２０％ f r om２５％ t o２０％． F i ８showst heimpa c tabs o rbedene r fe a ch g gyo
we l da t －２０and －４０ ℃．AsTicon t en ti nc r e a s e s f r om ０t o０ ０２８％ ,t heimpa c tabso rbedene r n Ｇ gyi c r e a s e sf r om８５t o１５６Ja t －２０ ℃ andf r om ６９t o , １４６Ja t －４０ ℃ r e spe c t i ve l t hi nc r e a s i ng Ti y．Wi add i t i ont o０ ０３８％ ,t heimpa c tabso rbed ene r gy s l i t l c r e a s e s．Howeve r,t heva l ued r ama t i c a l l gh yde y de c r e a s e st o１７Ja t－２０ ℃ and１６Ja t－４０ ℃ wi t h i nc r e a s i ng Tit o０ ０６４％．F i ９showst hef r a c t ur e g sur f a c eo ft he we l da f t e rl ow t empe r a t ur eimpa c t , t e s t s．Wi t hi nc r e a s i ngTicon t en tt hef r a c t ur emode change sf r om qua s i Ｇ c l e avaget oduc t i l ef r a c t ur eand f i na l l t oc l e a v a e ． I t i s t h e r e f o r e s h o w n t h a tm ode r Ｇ y g a t eTip r omo t e sAFf o rma t i onbe c aus eo ft hee f f e c Ｇ t i vene s so fi nc l us i onssma l l e rt han２μmanda c co rd Ｇ i ng l hewe l dt oughne s si ss i i f i c an t l r oved． y,t gn yimp Wi t h Ticon t en ti nt her ange o f０ ０２８％ － ０ ０３８％ ,t he we l d me t a lp r e s en t sexc e l l en tt oughＧ , ne s sduet ol a r e a m o u n t s o fA F a l t h o u h t h e r os s g g g o fMＧAcons t i t uen ti sh i rt hant he s ewi t hou tTi． ghe Ac co rd i ngt op r ev i ousr e s e a r che s,AFi so fsoc a l l ed [ １２] “ ” ba ske t Ｇwe ave s t ruc t ur eandi n t e r l ock i ngna t ur e ． So c r a ck p r opaga t i ng d i r e c t i ons a r e cons t an t l y changedbyt he i rchao t i ca r r angemen tandh i l e ghang , , r a i nbounda r i e s anda sar e su l ti tcou l dp r ov i de g t hewe l dwi t hbe t t e rl owt empe r a t ur et oughne s sand [, ] h i rr e s i s t anc et oc r a cksdur i ngde f o rma t i on４ １２ ． ghe The r e f o r e,t hemo r eAFob t a i nsi nt hewe l dme t a l s, t heh i rt hel owt empe r a t ur et oughne s sa ch i eve s, ghe event hought heamoun to fMＧAcons t i t uen ti nc r e a Ｇ s e swi t hTiadd i t i on． I ti sobv i oust ha tt hede l e t e r i Ｇ ouse f f e c to f MＧA cons t i t uen ti s we akened wh i l ea l a r to fAFa r ef o rmedi nt hewe l d．Howev Ｇ geamoun , e rt het oughne s so fwe l d me t a li ss eve r e l t e r i o Ｇ yde r a t edbyexc e s s i veadd i t i ono fTiowi ngt ot hei n Ｇ c r e a s eo fMＧAcons t i t uen tandba i n i t e．
３ Conc l u s i on s
F i ８ Impa c tab s o r b e den e r fwe l d s g g yo
E f f e c t so fT ii nt hel a r ehe a ti npu twe l d sa r ed i s Ｇ g cus s edandt her e su l t sshowt ha tamode r a t eamoun t o fTii ss t i l le f f e c t i vef o r mi c r os t ruc t ur a limp r ove Ｇ men tandi nc l us i onr e f i nemen tb e c au s eo ft hee f f e c t i v e
I s sue５ I n f l uenc eo fTion We l d Mi c r o s t r uc t u r eand Me chan i c a lPr ope r t i e si nLa r a tI npu tWe l d i ngo fS t e e l s geHe
４３７
( a)We l dNo １ ( ０％ Ti); ( b)We l dNo ２ ( ０ ０２８％ Ti); ( c)We l dNo ３ ( ０ ０３８％ Ti); ( d)We l dNo ４ ( ０ ０６４％ Ti)．
F i ９ Fr a c t u r es u r f a c eo fwe l dme t a l sa f t e rimpa c tt e s ta t－２０ ℃ g
c omp l exi nc l us i ons． ( ) １ I nl a r eh e a ti npu twe l d i ngo fh i t r e ng t h g ghs l owa l l o t e e l s,t he we l d me t a lc ons i s t s ma i n l f ys yo , , r o e u t e c t o i df e r r i t e A F b a i n i t ea n d M Ｇ Ac o n s t i t u Ｇ p en t．Al a r to fAFi sf o rmedwhenTic on Ｇ geamoun t en ti swi t h i n０ ０２８％－０ ０３８％． ( ２)I n c l u s i on si nt h ewe l d me t a lma ed i v i d e d yb i n t otwog r oup s,e f f e c t i vei nc l us i onsandi ne f f e c t i ve i nc l us i ons．Mo s to ft hee f f e c t i vei nc l us i onsa r el e s s t han２μmi ns i z eandc on t a i nTi２O３ ．Wi t hi nc r e a s i ng Tic on t en t,t het ft hei nc l us i on va r i e sf r om ypeo Mn ＧS i ＧAl ＧOt oTi ＧMn ＧAl ＧOandf i na l l oTi ＧAl ＧO． yt ( ３)T ia dd i t i oni se f f e c t i v ef o ri n c r e a s i ngt h ewe l d s t r e ng t h．Exc e l l en tt oughne s sc ou l d be ob t a i ned whenT ic on t e n ti sw i t h i n０ ０２８％－０ ０３８％ ,ow i ngt o al a r to fAF,whe r e a st het oughne s sd r a Ｇ geamoun ma t i c a l l d e c r e a s e sw i t he x c e s s i v eT i ． y Re f e r enc e s:
[ １] J S．Byun,J H． Sh im,YW． Cho,D N． Le e,Ac t aMa t e r． ５１ ( ２００３)No ６,１５９３ Ｇ １６０６．
[ ２] WW．Bo s e f i l ho,AL M．Ca r va l ho,M．S t r angwood,Ma t e r． Cha r a c t． ５８ ( ２００７)２９ Ｇ ３９．
[ ３] AM． Pan i agua ＧMe r c ado,VM．Lop r z ＧHi r a t a,HJ．Do r an t e s Ｇ , , , Ro s a l e s P．Es t r adaDi a z E．Di a zVa l de z Ma t e r．Cha r a c t． ６０ ( ２００９)３６ Ｇ ３９．
[ ４] T．Weg r z Sz opa,M．Mi r o s,We l d i ngI n t． ２３ ( ２００９)５４ Ｇ yn,P． ５９． [ M．Xue,J． I r onS t e e lRe s． I n t． ５] F．Cha i,H． Su,C F．Yang,D ２１ ( ２０１４)３６９ Ｇ ３７４． [ ６] AG．Fox,D G．Br o t he r s,Sc r i t a Me t a l l．Ma t e r． ３２ ( １９９５) p No ７,１０６１ Ｇ １０６６． [ H．L i u,J． I r onS t e e lRe s． X．Xi a,Z G．Yang,Z ７] C． Zhang,Z I n t． １７ ( ２０１０)No ６,３６ Ｇ ４２． [ ８] F．Cha i,C F．Yang,H． Su,YQ． Zhang,Z．Xu,J． I r onS t e e l Re s． I n t． １６ ( ２００９)No １,６９ Ｇ ７４． [ ９] T．Ryousuke,J．Yang,K．Mamo r u,I S I JI n t． ４７ ( ２００７)１３７９ Ｇ １３８６． [ １０] X L．Wan,R．We i,KM．Wu,Ma t e r．Cha r a c t．６１ ( ２０１０) ７２６ Ｇ ７３１． [ １１] K．Yamamo t o,T．Ha s egawa,J I．Takamur a,I S I JI n t．３６ ( １９９６)８０ Ｇ ８６． [ １２] S S．Babu,Cur r en tOp i n i oni nSo l i dS t a t eand Ma t e r i a l sSc i Ｇ enc e８ ( ２００８)２６７ Ｇ ２７８． [ １３] J L．Le e,Ac t a Me t a l l．Ma t e r． ４２ ( １９９４)３２９１ Ｇ ３２９８． [ １４] YT．Pan,J L．Le e,Ma t e r．De s． １５ ( １９９４)３３１ Ｇ ３３８． [ １５] S A．Cour t,G．Po l l a r d,Me t a l l og r aphy２２ ( １９８９)２１９ Ｇ ２４３． [ １６] S．S t ＧLa u r e n t,G L．Es é r a n c e,Ma t e r．S c i．Eng．A１４９ ( １９９２) p
２０３ Ｇ ２１６． [ １７] B．Be i dokh t i,AH．Koukab i,A．Do l a t i,Ma t e r．Cha r a c t． ６０ ( ２００９)２２５ Ｇ ２３３． [ １８] S．Moe i n i f a r,AH．Kokab i,HR M．Ho s s e i n i,Ma t e r．De s． ３１ ( ２０１０)２９８４ Ｇ ２９５５． [ １９] Y W．Sh i,Z X．Ha n,J．Ma t e r．Pr o c e s s．T e c hno l．２０７ ( ２００８) ３０ Ｇ ３９． [ ２０] B．Be i dokh t i,AH．Koukab i,A．Do l a t i,J．Ma t e r．Pr o c e s s． Te chno l． ２０９ ( ２００９)４０２７ Ｇ ４０３５．