- Email: [email protected]
Simulation study on heat-affected zone of high-strain X80 pipeline steel
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) ９６６－９７２
S imu l a t i ons t udyonhe a t Ｇ a f f e c t edz oneo fh i Ｇ s t r a i nX８０p i l i nes t e e l gh pe Yi ngC i１ ∗ , Zhan Ｇ zhanZhang２ ,
１
２
Co l l egeo fI n f o rma t i onSc i enc eandEng i ne e r i ng, No r t he a s t e r nUn i ve r s i t i aon i ng, Ch i na y, Shenyang１１０００４, L Schoo lo fPhy s i c a lSc i enc eandEng i ne e r i ng, Zheng zhouUn i ve r s i t zhou４５００５２, Henan, Ch i na y, Zheng ARTICLEINFO
ABSTRACT
Keywo rds: Hi Ｇ s t r a i nX８０p i l i ne gh pe s t e e l We l d i nghe a ti npu t Pe akt empe r a t ur e Impa c tt oughne s s Mi c r o s t r uc t ur e
Themi c r o s t r uc t ur eevo l u t i onandimpa c t Ｇ t oughne s sva r i a t i ono fhe a t Ｇ a f f e c t edz one ( HAZ) i n X８０h i Ｇ gh s t r a i np i l i nes t e e lwe r ei nve s t i t edv i aawe l d i ngt he rma l Ｇ s imu l a t i ont e chn i r c tt e s t s, pe ga que, Cha pyimpa ands c ann i nge l e c t r onmi c r o s c opyobs e r va t i onsunde rd i f f e r en twe l d i nghe a ti npu t sandpe akt empe r a t ur e s． Ther e su l t si nd i c a t et ha twhenhe a ti npu twa sbe twe en１７and２５kJcm－１, t hec oa r s e Ｇ r a i nedhe a t Ｇ a f Ｇ g f e c t edz oneshowedimp r ovedimpa c tt oughne s s．Whent hehe a ti npu twa si nc r e a s edf ur t he r, t hema r t ens Ｇ i t e Ｇ aus t en i t e ( MＧA)i s l andst r ans f o rmedf r omf i nel a t hi n t oama s s i veb l o ck．The r e f o r e,impa c tt oughne s s wa ssubs t an t i a l l educ ed．Whent hehe a ti npu twa s２０kJcm－１ andt hepe akt empe r a t ur eo ft hef i r s t yr t he rma lc l ewa sbe twe en９００and１３００° C, ah i rimpa c tt oughne s swa sob t a i ned．Whenhe a ti npu t yc ghe wa s２０kJcm－１andt hepe akt empe r a t ur eo ft hef i r s tt he rma lc l ewa s１３００° C, t heimpa c tt oughne s s yc va l uea tt hes e c ondpe akt empe r a t ur eo f９００° Cwa sh i e rt h a nt h a ta tt h es e c ondp e akt emp e r a t u r eo f８００° C gh be c aus eo fg r a i nr e f i n i ngandun i f o rml i spe r s ed MＧAc ons t i t uen t si nt hema t r i xo fba i n i t e． yd
１ I n t r odu c t i on I nr e c en tye a r s, owi ngt ot heex t ens i ver e s e a r ch ont h e rmome c h a n i c a l l on t r o l l e dp r o c e s s e d (TCMP) yc i l i nes t e e l,i t ss t r eng t h, l owＧ t empe r a t u r et oughＧ p pe ne s s, and h i Ｇ s t r a i n de f o rma t i on r e s i s t anc e have gh s i i f i c an t l oved; c ons equen t l t may me e t gn yimpr y, i [ ] t hecons t ruc t i ondemandsi nd i f f e r en ta r e a s１ ．HowＧ eve r, d i f f e r en tme t hods, wi r e s, andf l uxe shaveva Ｇ r i ouse f f e c t sont heme chan i c a lp r ope r t i e so fwe l d i ng o i n t sdu r i ngwe l d i ng． I npa r t i cu l a r, unde rt hewe l d Ｇ j , i ngt he rma lc l e t he mi c r o s t ruc t u r eo ft heba s e yc me t a lbe c ome snon Ｇ un i f o rmandt hepe r f o rmanc eo f [ , ] t hewe l d i ngj o i n ti sde t e r i o r a t ed２ ３ ． The mi c r o s t ruc t u r eo fh i Ｇ s t r a i n X８０ p i l i ne gh pe s t e e li sc ompo s edo ff e r r i t eba i n i t e, wh i chshowsex Ｇ c e l l en ts t r eng t h, t oughne s s, andde f o rma t i onab i l i Ｇ t Ｇ s t r a i nX８０p i l i nes t e e li ssu i t ab l ef o rus e y．Hi gh pe i ns eve r egeo l og i c a lenv i r onmen t ssucha sf r o z enso i l andi na r e a s pr one t o ha z a r dous even t s such a s e a r t hquake s． Be c aus eo ft hee f f e c to ft hewe l d i nghe a tc l eon yc t hema t r i xo fh i Ｇ s t r a i np i l i nes t e e l, f e r r i t eand gh pe ba i n i t eunde r c r o s t ruc t u r eevo l u t i on． S imu l t a Ｇ goami neous l ot heex i s t enc eo fma r t ens i t e Ｇ aus t en Ｇ y, duet i t e ( MＧA) i s l ands, t heimpa c tt oughne s so fwe l ded , Ph． ∗ Co r r e spond i ngau t ho r．As s o c．Pr o f． D． EＧma i laddr e s s:c i i ngneu＠１６３c ． om (Y ． Ci) ． y
o i n t si sr educ ed．Somei nve s t i t i onshaveshown j ga t ha tt hevo l umef r a c t i on, s i z e, andd i s t r i bu t i ono f MＧAi s l andsc ana f f e c tt hel owＧ t empe r a t ur et oughＧ ne s so f we l d i ngj o i n t s made o fp i l i ne s t e e l．A pe h i r vo l umef r a c t i on, l a r rs i z e, and sma l l e r ghe ge spa c i ng be twe en MＧA i s l ands d i s t r i bu t ed on t he r a i nbounda r educ et hel owＧ t empe r a t ur et oughＧ g yr [ , ] ne s so ft hewe l dedj o i n t s４ ５ ．Thes t ud i e sf r om L ie t [ ] [ ] [ ] a l ６ , ZuoandZhou７ , and Wange ta l ８ r eve a l ed t ha th i Ｇ s t r a i np i l i ne s t e e lexh i b i t ed exc e l l en t gh pe me chan i c a lp r ope r t i e sandco r r os i onr e s i s t anc e．I n t hep r oc e s so fp i l d i ng, t hehe a t Ｇ a f f e c t edz one pewe (HAZ) i son l l i t l f t enedandexh i b i t sexc e l Ｇ ys gh yso l en tl owＧ t empe r a t ur et oughne s s．Howeve r, t hel i t Ｇ e r a t ur e scon t a i nf ew r epo r t sont he mi c r os t ruc t ur e evo l u t i ono ff e r r i t eandba i n i t eunde rt hee f f e c t so f t hewe l d i ngt he rma lc l e．The r e f o r e, r e s e a r chon yc t hei n f l uenc eo fwe l d i ngpa r ame t e r sont hepe r f o rmＧ anc eo f we l d i ngj o i n t so fh i Ｇ s t r a i n X８０ p i l i ne gh pe s t e e li sne eded． I nt h i spape r, t hee f f e c t so fwe l d i ng Ｇhe a ti npu t, akt empe r a t ur e, andt hes e conda r he rma lc l e pe yt yc ont heimpa c tt oughne s sandha rdne s so fh i Ｇ s t r a i n gh X８０ p i l i nes t e e l we r ei nve s t i t edt op r ov i de a pe ga t heo r e t i c a lba s i sf o rde t e rmi n i ngt heop t imum we l d Ｇ i ngpa r ame t e r s．
Re c e i ved１５Sep t embe r２０１６; Re c e i vedi nr ev i s edf o rm７J anua r c ep t ed１０J anua r y２０１７; Ac y２０１７ Ava i l ab l eon l i ne１５Sep t embe r２０１７ 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
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
２．Exp e r imen t a lMe t hod s Thechemi c a lc ompo s i t i ono f TMCP h i Ｇ s t r a i n gh i l i nes t e e lX８０i sshowni nTab l e１． p pe Samp l e so f７６ mm×１１ mm×１１ mm havebe en t akenf r om p l a t e s．The HAZ wa ss imu l a t ed wi t ha s i ng l e Ｇ s st he rma lc l eonaGl e eb l e Ｇ ３８００t e s tma Ｇ pa yc ch i ne, andt he pa r ame t e r sa r eshowni n Tab l e s２ and３．Thet e s tp l anf o rt hes e c onda r he rma lc Ｇ yt yc / l i ngp r o c e s s e si sshowni nTab l e４． Pa r ame t e rt８ ５i n Tab l e２r epr e s en t st het imer equ i r edf o ras i ng l e Ｇ s st he rma lc c l et e s to fas amp l ef r om８００t o５００° C． pa y Tab l e１ Chemi c a lc ompo s i t i ono fX８０s t e e l(wt． ％) C
０ ０４７
Mn
１ ７６
P
０ ０１３
S
０ ００１２
S i
Ni＋Cr＋Mo＋Cu
０ ２５
０ ６６
Tab l e２ Va r i a t i ono ft he rma ls imu l a t i onpa r ame t e r swi t hwe l d i ng he a ti npu t We l d i ng he a ti npu t/ (kJcm－１) １７
He a t i ng Pe ak r a t e/ t empe r a t ur e/ (° ° C Cs－１)
２０
２５ ３５ ４５ ５０
１３０
１３００
１３０
１３００
１３０
Re s i denc et ime t８/５/ a th i gh s / t empe r a t ur es
１３００
１３０
１
１１ ８３
１
１３００
１３０
５ ４７
１
１３００
１３０
１
１
１３００
１
Hi rwe l d i nghe a ti npu t sr e su l ti ns l owe rcoo l i ng ghe , ag r a t e s (i e． r e a t e rt８/５ va l ue) ．Thet he rma ls imu Ｇ l a t edspe c imenswe r ema ch i nedi n t oVＧ t t ched ypeno Cha r a c ts e c ime n swi t hd ime n s i on so f５５mm× pyimp p １０ mm×１０ mm．Cha r c tt e s t swe r ec a r r i ed pyimpa ou tonanRKP４５０t e s tma ch i nea tat e s tt empe r a Ｇ t ur eo f －２０° C．Ha r dn e s st e s t swe r ep e r f o rme dus i ng an HVS Ｇ ５０Vi cke r sha rdne s s (HV１０) t e s t e rf o rt he soak i ng z oneo ft het he rma ls imu l a t edspe c imens． Ea chspe c imenwa sme a sur eda tf i vepo i n t s, andt he ave r agev a l u ewa sc a l c u l a t e d． Themi c r o s t r u c t u r ean a l Ｇ y s i so ft hehe a t i ngz oneo ft hespe c imenswa sc a r r i ed
Nb
０ ０５４
３５/２０ ３５/２０
He a t i ngr a t e/ (° Cs－１) １３０ １３０
V
０ ００３
Ti
０ ０１０
Ceq
０ ４２
Pcm
０ １７
Tab l e３ Va r i a t i ono ft he rma ls imu l a t i onpa r ame t e r swi t hd i f f e r en t akt empe r a t u r e s pe
７ ５７
２３ １８ ３８ ３１ ４７ ３０
We l d i nghe a t i npu t/ (kJcm－１)
He a t i ng r a t e/ (° Cs－１)
Pe ak t empe r a t ur e/ ° C
Re s i denc et ime a th i gh t empe r a t ur e/s
３５/２０
１３０
１２００
１
３５/２０
１３０
３５/２０
１３０
３５/２０
１３０
３５/２０
Tab l e４ Va r i a t i ono ft he rma ls imu l a t i onpa r ame t e r swi t hs e c onda r he rma lcy c l e yt We l d i nghe a t i npu t/ (kJcm－１)
９６７
１３０
１３００ １１００
１ １
１０００
１
９００
１
Re s i denc et ime a th i gh t empe r a t ur e/s
Pe akt empe r a t ur e o fp r ima r he rma l yt c l e/° C yc
F i n i sh i ngc oo l i ng t empe r a t ur eo fp r ima r y t he rma lc l e/° C yc
Pe akt empe r a t ur eo f s e c onda r he rma l yt c l e/° C yc
１
１３００
２００
９００
１
１３００
２００
８００
Imp a c tt oughn e s s(－２０° C) andha r dn e s sva r i a t i ono f s i ng l e Ｇ s st he rma lc l e HAZs amp l e swi t hd i f f e r Ｇ pa yc ３．Re s u l t sandDi s c u s s i on en the a ti npu t sa r eshowni nF i １．Whent hehe a t g i npu twa sbe twe en１７and２５kJcm－１ , goodt oughＧ ３ １．Me chan i ca lpr ope r t i e sana l i s ys ne s swa sa ch i evedi nt hewe l d i ngcoa r s e Ｇ r a i nz oneo f g I nt he we l d i ngp r o c e s s, t he HAZc anbed i v i ded t heHAZ．Whent hehe a ti npu twa s２０k Jcm－１ , t he i n t od i f f e r en tz one sont heba s i so ft hee f f e c to ft he Cha r c tene r t －２０° Capp r oa ched３２５J pyimpa gya we l d i ngt he rma lc l e．Ap e a kt emp e r a t u r eo f１１００－ (F yc i １(a)) ．Whent hehe a ti npu twa s３５kJcm－１ , g １３００° Cc o r r e spondst ot hec oa r s e Ｇ r a i nz oneo ft he t g heimpa c tene r a ra r e awe r er e du c e dd r a s t i Ｇ gyandshe HAZ．Thef i ne Ｇ r a i nz oneo ft he HAZc o r r e sponds c g a l l t hi n c r e a s i nghe a ti npu t,t oughn e s sd e t e r i o r a t e d y．Wi t ot empe r a t u r ef r om Ac３t o１１００° C, andt het empe r Ｇ g r adua l l t ht hel owe rhe a ti npu t (１７－２５kJ y．Wi a t ur ef r om Ac１t oAc３ c o r r e spondst ot hei nc omp l e t e cm－１), t heha rdne s so ft hes amp l e wa ss imi l a rt o r e c r t a l l i z a t i onr eg i on o ft he HAZ．The d i f f e r en t t ys ha to ft he ba s e ma t e r i a l; t he ha rdne s s de c r e a s ed he a ti npu t sc ana f f e c tt hec oo l i ngr a t eo ft hewe l ded g r adua l l t hi nc r e a s i ng he a ti npu t．Thus, when y wi o i n t, r e su l t i ngi n mi c r o s t ruc t u r eevo l u t i on, wh i ch t j hehe a ti npu twa sbe twe en１７and２５kJcm－１ ,t he i nt urni n f l uenc e st hepe r f o rmanc eo ft hes t e e l． coa r s e Ｇ r a i nz oneo ft heHAZexh i b i t edgoodt ough Ｇ g ou tonaJSMＧ ６７００Fs c ann i nge l e c t r on mi c r o s c opy．
９６８
Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２ Y ．
F i １． Ef f e c t so fhe a ti npu tonimpa c tt oughne s s (a) and g ha r dne s so fc oa r s e Ｇ r a i nedhe a t Ｇ a f f e c t edz one (b) ． g
ne s sandha rdne s s． Thei n f l uenc eo fd i f f e r en tpe akt empe r a t ur e son t heimpa c tt oughn e s sandha r dn e s si ss howni nF i ２． g Whent hehe a ti npu t wa s３５ kJcm－１ , t he pe ak t empe r a t ur ewa sbe twe en９００and１１００° Candh i gh Cha r c tene r sa ch i eved．Wi t hi nc r e a s i ng pyimpa gy wa , e a kt e m e r a t u r e t h e i m a c te n e r d e c r e a s e dr a Ｇ p p p gy p －１ , i d l ． W h e n t h eh e a t i n u tw a s ２ ０k J c m t h em a x i Ｇ y p mumva l ueo fimpa c tene r w a sr e a c h e da ta e a k gy p t empe r a t ur eo f１１００° C, andt heimp a c tt oughn e s swa s h i rov e rt he who l et emp e r a t u r er ang e (F i ２(a))． ghe g Wi t haf ur t he rde c r e a s eo ft hepe akt empe r a t ur e,t he ; duc t i l i t ft heshe a rz onewa sr educ ed t heshe a ra r Ｇ yo e awa sa l soobv i ous l c r e a s edwhent hehe a ti npu t yde wa s３５kJcm－１ ．TheCha r c tene r e f l e c t s pyimpa gyr t heene r rbeddur i ngf r a c t ur eunde rt heimＧ gyabso edimpa c tl oad, andt hes he a rz on es howst heab i l i t pos y t or e s i s tf u r t he rp r op a a t i ono ft hec r a c k．Thet oughn e s s g wa sde t e rmi nedont heba s i so ft hec r a ckp r opaga t i on [９] ene r hes ameimpa c tene r l ue s, al a r Ｇ gy ．Att gyva rshe a ra r e ar e su l t edi nt heg r e a t e rab i l i t or e s i s t ge yt t hec r a ckg r owt h, t he r ebydemons t r a t i ngt hebe t t e r
F i ２． Ef f e c t so fpe akt empe r a t u r eonimpa c tt oughne s s (a), she a ra r e a (b), andha r dne s so fHAZ (c) ． g
t oughne s s．Comb i ned wi t ht he s etwoi ndexe s, t he impa c tt oughne s sde t e r i o r a t ed wi t hi nc r e a s i ngpe ak t empe r a t u r ewhent hehe a ti npu twa s３５kJcm－１ ． Whent hehe a ti npu twa s２０kJcm－１ , t het oughＧ ne s s wa s no tobv i ous l d e t e r i o r a t e d ．U n d e rt he s e y twohe a t Ｇ i npu tc ond i t i ons, t heha r dne s so ft hes amＧ l eexh i b i t edi t sh i s tva l ue whent hepe akt emＧ p ghe r a t u r ewa s１３００° C．Whent hepe akt empe r a t ur e pe wa sde c r e a s ed, t heha r dne s sde c r e a s ed, a sshowni n F i ２(c) ．Theha r dne s sva l ueunde rahe a ti npu to f g ２０kJcm－１ wa ss l i t l a r rt hant ha tunde ra gh yl ge he a ti npu to f３５kJcm－１ ．Ther e su l t so fCha r py impa c tt e s t sandha r dne s st e s t sshowedt ha t, when t hehe a ti npu twa s２０kJcm－１ , nope r f o rmanc ede Ｇ t e r i o r a t i ono c cu r r edi nt heHAZ． The rma lc l eexpe r imen t swe r ec a r r i edi ndup l i Ｇ yc c a t ef o rt heba s eme t a l; t hehe a ti npu t swe r e３５and ２０kJcm－１ ．Thef i r s t Ｇ he a t Ｇ c l epe akt empe r a t ur e yc (FPT) wa s１３００° C, andt hes e c ond Ｇ he a t Ｇ c l epe ak yc t empe r a t u r e s (SPT) we r e８００and９００° Cr e spe c t i ve Ｇ l e su l t so ft he s etwot he rma lc l e sont he y．Ther yc
Cha r c tt e s tandha rdne s st e s ta r eshowni n pyimpa F i ３．Whe nt hehe a ti npu twa s３５k Jcm－１ andt he g s e conda r he rma lc l ehadbe enexpe r i enc ed, t he yt yc t oughne s swa simp r oveda tt heSPTo f８００° C．HowＧ eve r, whent heSPTwa s９００° C,t het oughne s sde t e Ｇ , r i o r a t ed．Af t e rtwot he rma lc c l e s t h eh a r d n e s so f y t hes t e e lde c r e a s ed．Whe nt hehe a ti npu twa s２０k J cm－１ andt hes e conda r he rma lc l e wa sexpe r i Ｇ yt yc enc ed, t het oughne s sand ha rdne s sa l so de c r e a s ed bu tno tt ot hes ameex t en tobs e r vedi nt hec a s eo f t hehe a ti npu to f３５kJcm－１a tt heSPTo f９００° C, a sshowni nF i ３． g
３ ２．Mi c r o s t ruc t ur eana l i s ys
Themi c r os t ruc t ur ei nt hec en t e ro ft heX８０l a r Ｇ ge s t r a i np i l i nes t e e lp l a t e wa scompos edo fbanded pe ba i n i t eandf e r r i t eandi sshowni nF i ４(a) ．The g we l d i ng t he rma lc l ep r oc e s sc l e a r l t r ong l f Ｇ yc ys ya f e c t edt he mi c r os t ruc t ur e．The mi c r os t ruc t ur e si n t hecoa r s e Ｇ r a i nz oneunde rd i f f e r en the a ti npu t sa r e g showni nF i ４(b－g) ．Theg r a i ns i z ewa sc l e a r l o Ｇ g yc
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
９６９
(a) Ef f e c to fhe a ti npu tonimpa c tt oughne s sf o rd i f f e r en the a t Ｇ c l epe akt empe r a t ur e s; (b) Ef f e c to fhe a t Ｇ c l epe akt empe r a t ur e son yc yc impa c tt oughne s sf o rd i f f e r en the a ti npu t s; (c) Ef f e c to fhe a t Ｇ c l epe akt empe r a t ur e sonha r dne s sf o rd i f f e r en the a ti npu t s． yc
F i ３． Compa r i s ono fimpa c tt oughne s sandha r dne s so fhe a t Ｇ a f f e c t edz one． g
(a) Mi c r o s t r uc t ur eo fma t r i x; (b) CGHAZ mi c r o s t r uc t ur ewi t hahe a ti npu to f１７kJcm－１; (c) CGHAZ mi c r o s t r uc t ur ewi t ha he a ti npu to f２０kJcm－１; (d) CGHAZ mi c r o s t r uc t ur ewi t hahe a ti npu to f２５kJcm－１; (e) CGHAZ mi c r o s t r uc t ur ewi t ha he a ti npu to f３５kJcm－１; (f) CGHAZ mi c r o s t r uc t ur ewi t hahe a ti npu to f４５kJcm－１; (g) CGHAZ mi c r o s t r uc t ur ewi t ha －１ he a ti npu to f５０kJ cm ．
F i ４． SEM mi c r og r aphsshowi ngba s eme t a landc oa r s e Ｇ r a i nedhe a t Ｇ a f f e c t edz onea td i f f e r en the a ti npu t s． g g
a r s ea tape akt empe r a t u r eo f１３００° Cbu twa ss t i l l sma l l e rt han８０ μm．Be c aus e Tiand Nbc a rbon i Ｇ t r i de swe r eno td i s s o l vedc omp l e t e l t１３００° C, t he ya i nn i nge f f e c twa ssubs t an t i a l． I nadd i t i on, t hed r ag p e f f e c to ft hes o l i d Ｇ s o l u t i on Nbs o l u t ec ana l s op r e Ｇ [ ] ven taus t en i t eg r a i ng r owt h１０ ．Whent hehe a ti npu t wa sl owe r(１７k Jcm－１ ,t８/５＝５ ４７s) a ndt h ec oo l i ng r a t ewa sf a s t e r,t h emi x t u r eo fl a t hba i n i t eands l i t l gh y mo r eg r anu l a rba i n i t ewe r eobs e r vedi nt he ma t r i x． Di s con t i nuousf i nel a t hg r ew pa r a l l e lf r omt heaus Ｇ t en i t eg r a i nbounda r ot hei n t e r i o r．MＧAc ons t i t u Ｇ yt en td i s t r i bu t edbe twe ent hef e r r i t el a t hs．Whent he he a ti npu t swe r e２５kJcm－１(t８/５ ＝１１ ８３s) and３５ －１ ( ) kJ cm t８/５ ＝２３ １８s r e spe c t i ve l he mi c r o Ｇ y, t s t ruc t u r ei nt heHAZwa sma i n l ompo s edo fg r an Ｇ yc u l a rba i n i t eandt hel a t hba i n i t e．Thel ame l l a rspa c Ｇ i ngi nc r e a s ed, ands ome qua s i Ｇmu l t i l a t e r a lf e r r i t e s we r eobs e r ved． I ns i det heo r i i na laus t en i t eg r a i ns, g t heba i n i t ehadal a r rdens i t fh i Ｇ ang l eg r a i n ge yo gh bounda r i e sandt hee f f e c t i veg r a i ns i z ewa ssma l l e r, wh i ch wa sbene f i c i a lf o rimp r ov i ngt het oughne s s． Thegoodd i s t r i bu t i ono fl a r r d MＧAi s l andso f ge, ha
r anu l a rba i n i t ei nt hef e r r i t e ma t r i xa l sol e adt o g s t r e s sconc en t r a t i onandr e su l t edi nt hegene r a t i ono f t hemi c r oc r a cks． Be c aus eo ft heeme r eo fal a r genc ge numbe ro fg r anu l a rba i n i t e, t heimpa c tt oughne s s wa sr educ edsubs t an t i a l l y． Whent hewe l d i nghe a ti npu twa si nc r e a s edt o４５ kJcm－１ (t８/５ ＝３８ ３１s) andt hecoo l i ngr a t e wa s de c r e a s edf ur t he r, t he mi c r os t ruc t ur ei nt he HAZ wa s ma i n l edo fg r anu l a rba i n i t ei n wh i ch ycompos t he MＧAb l ockwa ss l i h t l l a r e ． A t t h e s a m e t i m e, g y g somemo r equa s i Ｇmu l t i l a t e r a lf e r r i t e sf o rmed．When t hehe a ti npu twa s５０kJcm－１ , t heg r anu l a rba i n Ｇ i t eand po l li n t r ag r anu l a rf e r r i t ei nt he HAZ ygona mi c r os t ruc t ur echangedex t ens i ve l r, be Ｇ y．Howeve c aus eo ft hef o rma t i on o fg r a i n Ｇbounda r l l o t r i o Ｇ ya mo r i cf e r r i t e, t heo r i i na laus t en i t eg r a i nbounda Ｇ ph g r snol onge robs e r ved． Suchh i a ti npu t sr e Ｇ y wa ghhe su l t edi ng r e a tr e s i denc et imeabovet hepha s e Ｇ t r ans Ｇ f o rma t i ont empe r a t ur e, wh i ch t hen p r omo t ed t he f o rma t i ono fg r a i n Ｇbounda r l l o t r i omo r i cf e r r i t e ya ph andi n t r ag r anu l a rf e r r i t ewi t hav e r l owc oo l i ngr a t e． ys I ncompa r i sont ot hehe a ti npu ta t４５kJcm－１ , t he
９７０
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
eme r eo fg r a i n Ｇ bounda r l l o t r i omo r i cf e r r i t e genc ya ph andi n t r ag r anu l a rf e r r i t ea l l owedt heha r dne s st obe l owe r edwi t hou tac on t i nua lde c l i nei nt het oughne s s a the a ti npu t so f５０ kJcm－１ ．Henc e, t hes i z e, shape, andd i s t r i bu t i ono f MＧAi s l ands wou l da l so s t r ong l n f l uenc et he t oughne s so ft he c oa r s e Ｇ yi r a i n e dz o n e ． A ni n c r e a s ei nt h eh e a ti n u t w o u l d g p l e adt oani nc r e a s ei nt hevo l umef r a c t i ono ff e r r i t e andi nt heha r dne s so ft he MＧA i s l ands．Fu r t he r Ｇ , mo r et he MＧAi s l andswou l dbet r ans f o rmedf r om f i nel a t ht oama s s i veb i l o ck． I nadd i t i on, be c aus e gb mo r es t r e s swa sc onc en t r a t eda tt hei n t e r f a c eo ft he r i i d MＧAi s l andsandt he ma t r i x, c r a ck i ng wou l d g , e a s i l c cu ri nt hec oa r s eg r a i ns r e su l t i ngi nade Ｇ yo [ ] c r e a s ei nimpa c tt oughne s s１１ ． Themi c r o s t ruc t u r e so ft heHAZa td i f f e r en tpe ak t empe r a t u r e swi t hahe a ti npu to f２０o r３５kJcm－１ a r eshowni nF i ５．Fr om F i ４(c,e) t oF i ５, i t g g g
c anbeobs e r vedt ha tt hemi c r os t ruc t ur ei nt heHAZ wa scompos edo fl a t hand g r anu l a rba i n i t ea tpe ak t empe r a t ur e so f１２００and１３００° C．Thet oughne s s andt hei nc r e a s ei nt heha rdne s sde c r e a s edbe c aus eo f t hecoa r s eg r a i n．Wi t ht hed e c r e a s eo ft hep e akt emp e r Ｇ a t u r e, t heg r a i ns i z eb e c amef i n e randasma l lamoun to f f e r r i t eappe a r ed．Thet oughne s si nc r e a s ed, andt he ha rdne s sde c r e a s ed g r adua l l hepe akt emＧ y．Whent , e r a t u r ew a s１ ０ ０ ０ ° C t h em i c r o s t r u c t u r ew a sc o mＧ p , , edo ff e r r i t e g r anu l a rb a i n i t e andasma l lamoun t pos o feven muchf i ne r ma r t ens i t e; a tt ha tpo i n t, t he impa c tt oughne s s wa sf ur t he ri nc r e a s ed．Whent he akt empe r a t ur ewa sa t９００° C, t hemi c r os t ruc t ur e pe wa sf ur t he rr e f i ned．Af t e raus t en i t i z a t i on, f e r r i t e, r anu l a rba i n i t eandasma l lamoun to f ma r t ens i t e g we r ef o rmed dur i ng t he coo l i ng p r oc e s s and t he t oughne s sr e a chedi t smax imumva l ue． Acompa r i sono ft hehe a ti npu to f３５k Jcm－１ wi t h
(a),(b) FPT (f i r s tpe akt empe r a t ur e) o f１２００° C; (c),(d) FPTo f１１００° C; (e),(f) FPTo f１０００° C; (g),(h) FPTo f９００° C．
F i ５． SEM mi c r og r aphsshowi nghe a t Ｇ a f f e c t edz onemi c r o s t r uc t u r ea td i f f e r en tpe akt empe r a t u r e sanda t２０kJcm－１ (a, c, g －１ (b, d, f, h) ． e, g) o r３５kJcm
２０kJcm－１ r eve a l st ha tt hef o rme rhadas l owe r coo l i ng r a t e, wh i ch r e su l t edi nt he c oa r s eg r a i n, ma s s i veMＧAi s l ands, andl owt oughne s s．Whent he he a ti npu t swe r e２０and３５kJcm－１ ,t hepe akt emＧ r a t u r e wa s be twe en ９００ and １１００° C, and t he pe h i rimpa c tt oughne s sc ou l dber e a ched wi t ht he ghe s l i tde c r e a s ei n ha r dne s s．The HAZ mi c r o s t ruc Ｇ gh t ur e swe r e ma i n l ompo s edo ft hea f o r emen t i oned yc
mi c r os t ruc t ur e si nt hep i l i nes t e e l．Al t hought he pe he a ti npu to f３５kJcm－１ r e su l t edi nah i rpe ak ghe t empe r a t ur eo ft he ne a r Ｇ f us i on Ｇ l i ne a r e a, coa r s e r r a i n, andl owe rt oughne s s, t hel owe rpe akt empe r Ｇ g a t ur er eg i onwa sad a c en tt ot heg r e a t e rt oughne s s, j wh i cht huscou l de f f e c t i ve l r even tc r a ck expan Ｇ yp s i on．The r e f o r e, t he we l d i ngp r oc e s si nvo l v i ngt he he a ti npu to f３５kJcm－１ cou l ds t i l lmo r es t r ong l y
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
i n f l uenc et oughne s si nt he HAZ and enhanc et he [１２] we l d i nge f f i c i enc y ． The mi c r o s t ruc t u r eo ft heba s e me t a la f t e rs e c Ｇ onda r he rma lc l i ngi sshowni nF i ６．Whent he yt yc g he a ti npu twa s３５kJcm－１ andt hepe akt empe r a Ｇ t ur eo ft hef i r s tt he rma lc l ewa s１３００° C, t hemi Ｇ yc c r os t ruc t u r e si nt hema t r i xwe r ema i n l c o m o s e do f y p l a t hba i n i t e, g r anu l a rba i n i t e, and qua s i Ｇ o l o n a p yg l f e r r i t e, wh i ch had subs t an t i a l l l o w e r t oughne s s y t hant heo r i i na lp l a t e s．Thes e c onda r he rma lc Ｇ g yt yc l i ng wa st henc a r r i edou ta tt hepe akt empe r a t u r eo f ８００° C, wh i chi sbe twe ent hetwo Ｇ s et empe r a Ｇ pha t ur e, andt her e s i denc et ime wa ss osho r tt ha tt he
９７１
f e r r i t eandaus t en i t ed i dno tr e a chequ i l i br i umi nt h i s two Ｇ s er eg i on．The r e f o r e, t he o r i i na l ba i n i t e pha g f e a t ur e swe r er e t a i neddur i ngcoo l i ng．Al so, t hef i Ｇ na lmi c r os t ruc t ur e s we r e ma i n l edo fl a t h y compos ba i n i t e, g r anu l a rba i n i t e, qua s i Ｇ l lf e r r i t eand po ygona asma l lamoun to fpo l lf e r r i t e．Be c aus eo ft he ygona , eme r e n c eo fas m a l la m o u n to f o l o n a lf e r r i t e g p yg t het oughne s swa simp r oved, whe r e a st heha rdne s s wa sr educ ed．Whent hes e cond pe akt empe r a t ur e s , wa s９００° C t he mi c r os t ruc t ur e so ft he HAZ we r e ma i n l ed o fg r anu l a rba i n i t e, f e r r i t e, and ycompos MＧAi s l andd i s t r i bu t edon g r a i nbounda r i e s, wh i ch wa sex t r eme l rmf u lt ot hes t e e lt oughne s s． yha
(a) ２０kJcm－１andSPT (s e c ondpe akt empe r a t ur e) o f８００° C; (b) ３５kJcm－１andSPTo f８００° C; (c) ２０kJcm－１andSPTo f９００° C; (d) ３５kJcm－１andSPTo f９００° C．
F i ６． SEM mi c r og r aphsshowi ngba s eme t a lmo r l ogya f t e rs e c ondt he rma lcy c l e． pho g
Compa r ed wi t ht het oughne s sa t８００° C, t ha ta t ９００° C wa sl owe r．Comp l e t eaus t en i t i z a t i ono c cur r ed a t９００° C, wh i ch wa sj us tt heno rma l i z i ngp r o c e s s． Be c aus eo ft hehe a ti npu to f３５k Jcm－１a ndt h es l ow coo l i ng r a t e, pha s et r ans f o rma t i on wou l d oc cur t hr oughatwo Ｇ s er eg i on．Thus, t heamoun t so f pha f e r r i t eandma r t ens i t ewe r ei nc r e a s ed．Whent hehe a t i npu twa s３５kJcm－１ andt hes e c onda r he rma l yt c l et empe r a t u r ewa s８００° C, t heo r i i na laus t en i t e yc g r a i n bounda r sc l e a r l e r ved．MＧA i s l ands g y wa y obs we r esma l landwe l ld i s t r i bu t edi ns i det heg r a i n．At ９００° C, t he MＧAi s l ands we r el a r rand ma s s i ve, ge t heg r a i nbounda r sno tobv i ous, andt heimpa c t ywa
t oughne s swa sl ow． Whent hehe a ti npu t wa s２０ kJcm－１ andt he , s e conda r t h e r m a l c c l et e m e r a t u r ew a sa t８ ０ ０ ° C y y p aus t en i t i z a t i onoc cur r edpa r t i a l l tt hec r i t i c a lt emＧ ya r a t ur e．Howeve r, aus t en i t enuc l e a t i oncou l de a s i l pe y oc cura tt heg r a i nbounda r i e sbe c aus eo ft hesho r t d i s t anc ef o rt hed i f f us i ono fc a rbonanda l l oy i nge l e Ｇ men t sont heg r a i nbounda r i e s, wh i cht r an s f o rme dt o [ , ] MＧAi s l and sdu r i ngt her a i dc oo l i ngp r o c e s s１３ １４ ．The p MＧAcons t i t uen td i s t r i bu t edont heg r a i nbounda r i e s andwi t har e l a t i ve l i a rboncon t en tcou l dno t yh ghc bef u l l i ned wi t ht he ma t r i x．Af t e rt hes t e e l ycomb wa ssub e c t edt oex t e rna lf o r c eo ri n t e rna ls t r e s s, j
９７２
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
c r a ck i ngo c cu r r edandt het oughne s so ft hes t e e lwa s [ ] r educ ed１５Ｇ１７ ．Be c aus eo fc r a ck p r opaga t i on a l ong r a i nbounda r i e s, impa c tt oughne s s wa sde c r e a s ed． g Mo r eove r, t hef i neba i n i t es t ruc t u r eandt hed i s t r i Ｇ bu t i on o f MＧA c ons t i t uen t ss t r ong l n f l uenc et he yi [ ] me chan i c a lp r ope r t i e so fs t e e l１８Ｇ２０ ．Whent hehe a t －１ i npu twa s２０kJcm andt hes e c onda r t h e r m a l y ( ) , c c l et e m e r a t u r e h i h e rt h a n w a s９ ０ ０° C A y p g c ３ r a i nr e f i n e m e n ta n du n i f o r m d i s t r i b u t i o no f t h e M Ｇ g Acons t i t uen twe r er e a l i z ed, wh i chc ou l de f f e c t i ve l y even tc r a ckexpans i on andsubs t an t i a l l nc r e a s e pr yi t oughne s s．Whent hehe a ti npu twa s３５kJcm－１ andt hes e c onda r he rma lc l et empe r a t u r e wa s yt yc ８００o r９００° C,t heva l ueo ft heimpa c tt oughne s swa s r e l a t i ve l ow． yl
４．Conc l u s i on s
(１) Wh e nt h ewe l d i ngh e a ti npu tf o rt h eh i Ｇ s t r a i n gh X８０p i l i nes t e e lwa s１７－２５kJcm－１ , be t t e rimＧ pe c tt oughne s swa sa ch i evedi nt hec oa r s e Ｇ r a i na r e a pa g o ft he HAZ．Ast he we l d i ng he a ti npu t wa si n Ｇ c r e a s ed f u r t he r, t he impa c tt oughne s s de c r e a s ed r e a t l heha r dne s sde c r e a s eds l i t l t hi n Ｇ g yandt gh y．Wi c r e a s i nghe a ti npu t,t hevo l umef r a c t i ono ff e r r i t ea l Ｇ soi nc r e a s ed, andt hef i nel a t h MＧA i s l ands we r e t r ans f o rmedi n t o a ma s s i ve b l o ck, wh i ch f u r t he r c aus edt heha r dne s st obei nc r e a s ed．Be c aus eo ft he l a r t r e s sc onc en t r a t i onbe twe ent her i i d MＧAi s Ｇ ges g l andandt hema t r i x, c r a ckswou l df o rme a s i l t h Ｇ ywi i nt hec oa r s e Ｇ r a i nz one． g (２) Whent hehe a ti npu twa s３５kJcm－１ and t hepe akt empe r a t u r ewa sbe twe en９００and１１００° C, h i rimp a c tt oughn e s swa sa c h i e v e d．Wh e nt h ep e ak ghe t empe r a t u r ewa s１２００－１３００° C, t h emi c r o s t r u c t u r ei n t hema t r i xwa sma i n l ompo s edo fg r anu l a rba i n i t e． yc Theg r a i nwa sc oa r s eandt heMＧAi s l andswe r ema s Ｇ s i ve, wh i chr e su l t edi nal owimpa c tt oughne s sanda h i a r dn e s s．Wh e nt h eh e a ti npu twa s２０k Jcm－１ ghh andt h ep e a kt empe r a t u r ewa s９００－１３００° C, g r e a t e r
impa c tt oughne s swa sa ch i eved． (３) Whent hehe a ti npu twa s３５kJcm－１ and t hef i r s tpe akt empe r a t ur ewa s１３００° C, l owimpa c t t oughne s swa sa ch i eveda f t e rs e conda r he rma lc Ｇ yt y c l ebe twe en８００and９００° C．Whent hehe a ti npu twa s ２０kJcm－１ , t heimpa c tt oughne s sa f t e rt hes e c Ｇ onda r t h e r m a l c c l ea t９ ０ ０ ° C w a sh i h e rt h a nt h a t y y g a t８００° C．
Re f e r enc e s
[１] M． So l iman, H．Pa l kowsk i, Ma t e r．De s． ８８ (２０１５) ７５９ Ｇ ７７３． [２] YH．Yang, L．Sh i, Z．Xu, HS．Lu, X．Chen, X．Wang, Eng．Fr a c t．Me ch． １４８ (２０１５) ３３７ Ｇ ３４９． [３] YH．Chen, Y．Wang, B．Han, Tr ans a c t i onso fMa t e r i a l sand He a tTr e a tmen t２８ (２００７) No １, ７９ Ｇ ８２ (i nCh i ne s e) ． [４] L Y．Lan, C L．Qi u, D W． Zhao, X H．Gao, L X．Du, Ma Ｇ t e r． Sc i．Eng．A５２９ (２０１１) １９２ Ｇ ２００． [５] B C．Kim, S． Le e, N J．Kim, D Y． Le e, Me t a l l．Ma t e r．T r a n s．A ２２ (１９９１) １３９ Ｇ １４９． [６] R T． L i, X R． Zuo, YY．Hu, Z W．Wang, D X．Hu, Ma t e r． Cha r a c t． ６２ (２０１１) ８０１ Ｇ ８０６． [７] X R． Zuo, Z Y． Zhou, Ma t e r．Re s． １８ (２０１５) ３６ Ｇ ４１． [８] YP．Wang, X R．Zuo, J L．L i, S t e e l．Re s． I n t．８６ (２０１５) １２６０ Ｇ １２７０． [９] HH． Sayyed, I n t． J．Pr e s．Ve s．P i ８５ (２００８) ８７９ Ｇ ８８４． p． [１０] Y．Gu, P．Ti an, X．Wang, X L．Han, B．L i ao, F R．Xi ao, Ma t e r．De s． ８９ (２０１５) ５８９ Ｇ ５９６． [１１] WW．Xu, QF．Wang, T．Pan, H．Su, C F．Yang, J． I r on S t e e lRe s． I n t． １４ (２００７) No ５, ２３４ Ｇ ２３９． [１２] M． Zr i l i c, V．Gr abu l ov, Z． Bur z i c, M．Ar s i c, S． Sedmak, I n t． J．Pr e s．Ve s．P i ８４ (２００７) １３９ Ｇ １５０． p． [１３] S．Moe i n i f a r, AH．Kokab i, HR．Mada ah Ho s s e i n i, Ma t． De s． ３１ (２０１０) ２９４８ Ｇ ２９５５． [１４] X X．Chen, Z K．Xue, Ac t a J．Di, L．Ca i, X X．Xi ng, C ) ２８ (２０１５) ８８３ Me t a l l． S i n．(Eng l．Le t t． Ｇ ８９１． [１５] S J． Sun, M．Pugh, Ma t． Sc i．Eng．A３３５ (２００２) ２９８ Ｇ ３０８． [１６] C t a l l．Ma t e r．Tr ans．A２５ (１９９４) L．Dav i s, J E．Ki ng, Me ５６３ Ｇ ５７３． [１７] P．Mohs r l s en, OM．Aks e l s en, E． en i, J K．So l be r g, M．Ka t a l l．Ma t e r．Tr ans．A４５ (２０１４) ３８４ Ｇ ３９４． Øs t by, Me [１８] C L．He, HB．Wu, W．Yang, X M．Wang, S J． Shang, X Ac t a Me t a l l． S i n． ３９ (２００３) No １０, １０１９ Ｇ １０２４ (i nCh i ne s e) ． [１９] Y．Zhong, F R．Xi ao, J W．Zhang, YY．Shan, W．Wang, t a Ma t e r． ５４ (２００６) No ２, ４３５ Ｇ ４４３． K．Yang, Ac [２０] C H． Ch e n, J．Ma t e r． S c i． ４６ (２０１１) ６４２４ Ｇ W．L i, Y．Wa ng, Y ６４３１．
S imu l a t i ons t udyonhe a t Ｇ a f f e c t edz oneo fh i Ｇ s t r a i nX８０p i l i nes t e e l gh pe Yi ngC i１ ∗ , Zhan Ｇ zhanZhang２ ,
１
２
Co l l egeo fI n f o rma t i onSc i enc eandEng i ne e r i ng, No r t he a s t e r nUn i ve r s i t i aon i ng, Ch i na y, Shenyang１１０００４, L Schoo lo fPhy s i c a lSc i enc eandEng i ne e r i ng, Zheng zhouUn i ve r s i t zhou４５００５２, Henan, Ch i na y, Zheng ARTICLEINFO
ABSTRACT
Keywo rds: Hi Ｇ s t r a i nX８０p i l i ne gh pe s t e e l We l d i nghe a ti npu t Pe akt empe r a t ur e Impa c tt oughne s s Mi c r o s t r uc t ur e
Themi c r o s t r uc t ur eevo l u t i onandimpa c t Ｇ t oughne s sva r i a t i ono fhe a t Ｇ a f f e c t edz one ( HAZ) i n X８０h i Ｇ gh s t r a i np i l i nes t e e lwe r ei nve s t i t edv i aawe l d i ngt he rma l Ｇ s imu l a t i ont e chn i r c tt e s t s, pe ga que, Cha pyimpa ands c ann i nge l e c t r onmi c r o s c opyobs e r va t i onsunde rd i f f e r en twe l d i nghe a ti npu t sandpe akt empe r a t ur e s． Ther e su l t si nd i c a t et ha twhenhe a ti npu twa sbe twe en１７and２５kJcm－１, t hec oa r s e Ｇ r a i nedhe a t Ｇ a f Ｇ g f e c t edz oneshowedimp r ovedimpa c tt oughne s s．Whent hehe a ti npu twa si nc r e a s edf ur t he r, t hema r t ens Ｇ i t e Ｇ aus t en i t e ( MＧA)i s l andst r ans f o rmedf r omf i nel a t hi n t oama s s i veb l o ck．The r e f o r e,impa c tt oughne s s wa ssubs t an t i a l l educ ed．Whent hehe a ti npu twa s２０kJcm－１ andt hepe akt empe r a t ur eo ft hef i r s t yr t he rma lc l ewa sbe twe en９００and１３００° C, ah i rimpa c tt oughne s swa sob t a i ned．Whenhe a ti npu t yc ghe wa s２０kJcm－１andt hepe akt empe r a t ur eo ft hef i r s tt he rma lc l ewa s１３００° C, t heimpa c tt oughne s s yc va l uea tt hes e c ondpe akt empe r a t ur eo f９００° Cwa sh i e rt h a nt h a ta tt h es e c ondp e akt emp e r a t u r eo f８００° C gh be c aus eo fg r a i nr e f i n i ngandun i f o rml i spe r s ed MＧAc ons t i t uen t si nt hema t r i xo fba i n i t e． yd
１ I n t r odu c t i on I nr e c en tye a r s, owi ngt ot heex t ens i ver e s e a r ch ont h e rmome c h a n i c a l l on t r o l l e dp r o c e s s e d (TCMP) yc i l i nes t e e l,i t ss t r eng t h, l owＧ t empe r a t u r et oughＧ p pe ne s s, and h i Ｇ s t r a i n de f o rma t i on r e s i s t anc e have gh s i i f i c an t l oved; c ons equen t l t may me e t gn yimpr y, i [ ] t hecons t ruc t i ondemandsi nd i f f e r en ta r e a s１ ．HowＧ eve r, d i f f e r en tme t hods, wi r e s, andf l uxe shaveva Ｇ r i ouse f f e c t sont heme chan i c a lp r ope r t i e so fwe l d i ng o i n t sdu r i ngwe l d i ng． I npa r t i cu l a r, unde rt hewe l d Ｇ j , i ngt he rma lc l e t he mi c r o s t ruc t u r eo ft heba s e yc me t a lbe c ome snon Ｇ un i f o rmandt hepe r f o rmanc eo f [ , ] t hewe l d i ngj o i n ti sde t e r i o r a t ed２ ３ ． The mi c r o s t ruc t u r eo fh i Ｇ s t r a i n X８０ p i l i ne gh pe s t e e li sc ompo s edo ff e r r i t eba i n i t e, wh i chshowsex Ｇ c e l l en ts t r eng t h, t oughne s s, andde f o rma t i onab i l i Ｇ t Ｇ s t r a i nX８０p i l i nes t e e li ssu i t ab l ef o rus e y．Hi gh pe i ns eve r egeo l og i c a lenv i r onmen t ssucha sf r o z enso i l andi na r e a s pr one t o ha z a r dous even t s such a s e a r t hquake s． Be c aus eo ft hee f f e c to ft hewe l d i nghe a tc l eon yc t hema t r i xo fh i Ｇ s t r a i np i l i nes t e e l, f e r r i t eand gh pe ba i n i t eunde r c r o s t ruc t u r eevo l u t i on． S imu l t a Ｇ goami neous l ot heex i s t enc eo fma r t ens i t e Ｇ aus t en Ｇ y, duet i t e ( MＧA) i s l ands, t heimpa c tt oughne s so fwe l ded , Ph． ∗ Co r r e spond i ngau t ho r．As s o c．Pr o f． D． EＧma i laddr e s s:c i i ngneu＠１６３c ． om (Y ． Ci) ． y
o i n t si sr educ ed．Somei nve s t i t i onshaveshown j ga t ha tt hevo l umef r a c t i on, s i z e, andd i s t r i bu t i ono f MＧAi s l andsc ana f f e c tt hel owＧ t empe r a t ur et oughＧ ne s so f we l d i ngj o i n t s made o fp i l i ne s t e e l．A pe h i r vo l umef r a c t i on, l a r rs i z e, and sma l l e r ghe ge spa c i ng be twe en MＧA i s l ands d i s t r i bu t ed on t he r a i nbounda r educ et hel owＧ t empe r a t ur et oughＧ g yr [ , ] ne s so ft hewe l dedj o i n t s４ ５ ．Thes t ud i e sf r om L ie t [ ] [ ] [ ] a l ６ , ZuoandZhou７ , and Wange ta l ８ r eve a l ed t ha th i Ｇ s t r a i np i l i ne s t e e lexh i b i t ed exc e l l en t gh pe me chan i c a lp r ope r t i e sandco r r os i onr e s i s t anc e．I n t hep r oc e s so fp i l d i ng, t hehe a t Ｇ a f f e c t edz one pewe (HAZ) i son l l i t l f t enedandexh i b i t sexc e l Ｇ ys gh yso l en tl owＧ t empe r a t ur et oughne s s．Howeve r, t hel i t Ｇ e r a t ur e scon t a i nf ew r epo r t sont he mi c r os t ruc t ur e evo l u t i ono ff e r r i t eandba i n i t eunde rt hee f f e c t so f t hewe l d i ngt he rma lc l e．The r e f o r e, r e s e a r chon yc t hei n f l uenc eo fwe l d i ngpa r ame t e r sont hepe r f o rmＧ anc eo f we l d i ngj o i n t so fh i Ｇ s t r a i n X８０ p i l i ne gh pe s t e e li sne eded． I nt h i spape r, t hee f f e c t so fwe l d i ng Ｇhe a ti npu t, akt empe r a t ur e, andt hes e conda r he rma lc l e pe yt yc ont heimpa c tt oughne s sandha rdne s so fh i Ｇ s t r a i n gh X８０ p i l i nes t e e l we r ei nve s t i t edt op r ov i de a pe ga t heo r e t i c a lba s i sf o rde t e rmi n i ngt heop t imum we l d Ｇ i ngpa r ame t e r s．
Re c e i ved１５Sep t embe r２０１６; Re c e i vedi nr ev i s edf o rm７J anua r c ep t ed１０J anua r y２０１７; Ac y２０１７ Ava i l ab l eon l i ne１５Sep t embe r２０１７ 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
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
２．Exp e r imen t a lMe t hod s Thechemi c a lc ompo s i t i ono f TMCP h i Ｇ s t r a i n gh i l i nes t e e lX８０i sshowni nTab l e１． p pe Samp l e so f７６ mm×１１ mm×１１ mm havebe en t akenf r om p l a t e s．The HAZ wa ss imu l a t ed wi t ha s i ng l e Ｇ s st he rma lc l eonaGl e eb l e Ｇ ３８００t e s tma Ｇ pa yc ch i ne, andt he pa r ame t e r sa r eshowni n Tab l e s２ and３．Thet e s tp l anf o rt hes e c onda r he rma lc Ｇ yt yc / l i ngp r o c e s s e si sshowni nTab l e４． Pa r ame t e rt８ ５i n Tab l e２r epr e s en t st het imer equ i r edf o ras i ng l e Ｇ s st he rma lc c l et e s to fas amp l ef r om８００t o５００° C． pa y Tab l e１ Chemi c a lc ompo s i t i ono fX８０s t e e l(wt． ％) C
０ ０４７
Mn
１ ７６
P
０ ０１３
S
０ ００１２
S i
Ni＋Cr＋Mo＋Cu
０ ２５
０ ６６
Tab l e２ Va r i a t i ono ft he rma ls imu l a t i onpa r ame t e r swi t hwe l d i ng he a ti npu t We l d i ng he a ti npu t/ (kJcm－１) １７
He a t i ng Pe ak r a t e/ t empe r a t ur e/ (° ° C Cs－１)
２０
２５ ３５ ４５ ５０
１３０
１３００
１３０
１３００
１３０
Re s i denc et ime t８/５/ a th i gh s / t empe r a t ur es
１３００
１３０
１
１１ ８３
１
１３００
１３０
５ ４７
１
１３００
１３０
１
１
１３００
１
Hi rwe l d i nghe a ti npu t sr e su l ti ns l owe rcoo l i ng ghe , ag r a t e s (i e． r e a t e rt８/５ va l ue) ．Thet he rma ls imu Ｇ l a t edspe c imenswe r ema ch i nedi n t oVＧ t t ched ypeno Cha r a c ts e c ime n swi t hd ime n s i on so f５５mm× pyimp p １０ mm×１０ mm．Cha r c tt e s t swe r ec a r r i ed pyimpa ou tonanRKP４５０t e s tma ch i nea tat e s tt empe r a Ｇ t ur eo f －２０° C．Ha r dn e s st e s t swe r ep e r f o rme dus i ng an HVS Ｇ ５０Vi cke r sha rdne s s (HV１０) t e s t e rf o rt he soak i ng z oneo ft het he rma ls imu l a t edspe c imens． Ea chspe c imenwa sme a sur eda tf i vepo i n t s, andt he ave r agev a l u ewa sc a l c u l a t e d． Themi c r o s t r u c t u r ean a l Ｇ y s i so ft hehe a t i ngz oneo ft hespe c imenswa sc a r r i ed
Nb
０ ０５４
３５/２０ ３５/２０
He a t i ngr a t e/ (° Cs－１) １３０ １３０
V
０ ００３
Ti
０ ０１０
Ceq
０ ４２
Pcm
０ １７
Tab l e３ Va r i a t i ono ft he rma ls imu l a t i onpa r ame t e r swi t hd i f f e r en t akt empe r a t u r e s pe
７ ５７
２３ １８ ３８ ３１ ４７ ３０
We l d i nghe a t i npu t/ (kJcm－１)
He a t i ng r a t e/ (° Cs－１)
Pe ak t empe r a t ur e/ ° C
Re s i denc et ime a th i gh t empe r a t ur e/s
３５/２０
１３０
１２００
１
３５/２０
１３０
３５/２０
１３０
３５/２０
１３０
３５/２０
Tab l e４ Va r i a t i ono ft he rma ls imu l a t i onpa r ame t e r swi t hs e c onda r he rma lcy c l e yt We l d i nghe a t i npu t/ (kJcm－１)
９６７
１３０
１３００ １１００
１ １
１０００
１
９００
１
Re s i denc et ime a th i gh t empe r a t ur e/s
Pe akt empe r a t ur e o fp r ima r he rma l yt c l e/° C yc
F i n i sh i ngc oo l i ng t empe r a t ur eo fp r ima r y t he rma lc l e/° C yc
Pe akt empe r a t ur eo f s e c onda r he rma l yt c l e/° C yc
１
１３００
２００
９００
１
１３００
２００
８００
Imp a c tt oughn e s s(－２０° C) andha r dn e s sva r i a t i ono f s i ng l e Ｇ s st he rma lc l e HAZs amp l e swi t hd i f f e r Ｇ pa yc ３．Re s u l t sandDi s c u s s i on en the a ti npu t sa r eshowni nF i １．Whent hehe a t g i npu twa sbe twe en１７and２５kJcm－１ , goodt oughＧ ３ １．Me chan i ca lpr ope r t i e sana l i s ys ne s swa sa ch i evedi nt hewe l d i ngcoa r s e Ｇ r a i nz oneo f g I nt he we l d i ngp r o c e s s, t he HAZc anbed i v i ded t heHAZ．Whent hehe a ti npu twa s２０k Jcm－１ , t he i n t od i f f e r en tz one sont heba s i so ft hee f f e c to ft he Cha r c tene r t －２０° Capp r oa ched３２５J pyimpa gya we l d i ngt he rma lc l e．Ap e a kt emp e r a t u r eo f１１００－ (F yc i １(a)) ．Whent hehe a ti npu twa s３５kJcm－１ , g １３００° Cc o r r e spondst ot hec oa r s e Ｇ r a i nz oneo ft he t g heimpa c tene r a ra r e awe r er e du c e dd r a s t i Ｇ gyandshe HAZ．Thef i ne Ｇ r a i nz oneo ft he HAZc o r r e sponds c g a l l t hi n c r e a s i nghe a ti npu t,t oughn e s sd e t e r i o r a t e d y．Wi t ot empe r a t u r ef r om Ac３t o１１００° C, andt het empe r Ｇ g r adua l l t ht hel owe rhe a ti npu t (１７－２５kJ y．Wi a t ur ef r om Ac１t oAc３ c o r r e spondst ot hei nc omp l e t e cm－１), t heha rdne s so ft hes amp l e wa ss imi l a rt o r e c r t a l l i z a t i onr eg i on o ft he HAZ．The d i f f e r en t t ys ha to ft he ba s e ma t e r i a l; t he ha rdne s s de c r e a s ed he a ti npu t sc ana f f e c tt hec oo l i ngr a t eo ft hewe l ded g r adua l l t hi nc r e a s i ng he a ti npu t．Thus, when y wi o i n t, r e su l t i ngi n mi c r o s t ruc t u r eevo l u t i on, wh i ch t j hehe a ti npu twa sbe twe en１７and２５kJcm－１ ,t he i nt urni n f l uenc e st hepe r f o rmanc eo ft hes t e e l． coa r s e Ｇ r a i nz oneo ft heHAZexh i b i t edgoodt ough Ｇ g ou tonaJSMＧ ６７００Fs c ann i nge l e c t r on mi c r o s c opy．
９６８
Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２ Y ．
F i １． Ef f e c t so fhe a ti npu tonimpa c tt oughne s s (a) and g ha r dne s so fc oa r s e Ｇ r a i nedhe a t Ｇ a f f e c t edz one (b) ． g
ne s sandha rdne s s． Thei n f l uenc eo fd i f f e r en tpe akt empe r a t ur e son t heimpa c tt oughn e s sandha r dn e s si ss howni nF i ２． g Whent hehe a ti npu t wa s３５ kJcm－１ , t he pe ak t empe r a t ur ewa sbe twe en９００and１１００° Candh i gh Cha r c tene r sa ch i eved．Wi t hi nc r e a s i ng pyimpa gy wa , e a kt e m e r a t u r e t h e i m a c te n e r d e c r e a s e dr a Ｇ p p p gy p －１ , i d l ． W h e n t h eh e a t i n u tw a s ２ ０k J c m t h em a x i Ｇ y p mumva l ueo fimpa c tene r w a sr e a c h e da ta e a k gy p t empe r a t ur eo f１１００° C, andt heimp a c tt oughn e s swa s h i rov e rt he who l et emp e r a t u r er ang e (F i ２(a))． ghe g Wi t haf ur t he rde c r e a s eo ft hepe akt empe r a t ur e,t he ; duc t i l i t ft heshe a rz onewa sr educ ed t heshe a ra r Ｇ yo e awa sa l soobv i ous l c r e a s edwhent hehe a ti npu t yde wa s３５kJcm－１ ．TheCha r c tene r e f l e c t s pyimpa gyr t heene r rbeddur i ngf r a c t ur eunde rt heimＧ gyabso edimpa c tl oad, andt hes he a rz on es howst heab i l i t pos y t or e s i s tf u r t he rp r op a a t i ono ft hec r a c k．Thet oughn e s s g wa sde t e rmi nedont heba s i so ft hec r a ckp r opaga t i on [９] ene r hes ameimpa c tene r l ue s, al a r Ｇ gy ．Att gyva rshe a ra r e ar e su l t edi nt heg r e a t e rab i l i t or e s i s t ge yt t hec r a ckg r owt h, t he r ebydemons t r a t i ngt hebe t t e r
F i ２． Ef f e c t so fpe akt empe r a t u r eonimpa c tt oughne s s (a), she a ra r e a (b), andha r dne s so fHAZ (c) ． g
t oughne s s．Comb i ned wi t ht he s etwoi ndexe s, t he impa c tt oughne s sde t e r i o r a t ed wi t hi nc r e a s i ngpe ak t empe r a t u r ewhent hehe a ti npu twa s３５kJcm－１ ． Whent hehe a ti npu twa s２０kJcm－１ , t het oughＧ ne s s wa s no tobv i ous l d e t e r i o r a t e d ．U n d e rt he s e y twohe a t Ｇ i npu tc ond i t i ons, t heha r dne s so ft hes amＧ l eexh i b i t edi t sh i s tva l ue whent hepe akt emＧ p ghe r a t u r ewa s１３００° C．Whent hepe akt empe r a t ur e pe wa sde c r e a s ed, t heha r dne s sde c r e a s ed, a sshowni n F i ２(c) ．Theha r dne s sva l ueunde rahe a ti npu to f g ２０kJcm－１ wa ss l i t l a r rt hant ha tunde ra gh yl ge he a ti npu to f３５kJcm－１ ．Ther e su l t so fCha r py impa c tt e s t sandha r dne s st e s t sshowedt ha t, when t hehe a ti npu twa s２０kJcm－１ , nope r f o rmanc ede Ｇ t e r i o r a t i ono c cu r r edi nt heHAZ． The rma lc l eexpe r imen t swe r ec a r r i edi ndup l i Ｇ yc c a t ef o rt heba s eme t a l; t hehe a ti npu t swe r e３５and ２０kJcm－１ ．Thef i r s t Ｇ he a t Ｇ c l epe akt empe r a t ur e yc (FPT) wa s１３００° C, andt hes e c ond Ｇ he a t Ｇ c l epe ak yc t empe r a t u r e s (SPT) we r e８００and９００° Cr e spe c t i ve Ｇ l e su l t so ft he s etwot he rma lc l e sont he y．Ther yc
Cha r c tt e s tandha rdne s st e s ta r eshowni n pyimpa F i ３．Whe nt hehe a ti npu twa s３５k Jcm－１ andt he g s e conda r he rma lc l ehadbe enexpe r i enc ed, t he yt yc t oughne s swa simp r oveda tt heSPTo f８００° C．HowＧ eve r, whent heSPTwa s９００° C,t het oughne s sde t e Ｇ , r i o r a t ed．Af t e rtwot he rma lc c l e s t h eh a r d n e s so f y t hes t e e lde c r e a s ed．Whe nt hehe a ti npu twa s２０k J cm－１ andt hes e conda r he rma lc l e wa sexpe r i Ｇ yt yc enc ed, t het oughne s sand ha rdne s sa l so de c r e a s ed bu tno tt ot hes ameex t en tobs e r vedi nt hec a s eo f t hehe a ti npu to f３５kJcm－１a tt heSPTo f９００° C, a sshowni nF i ３． g
３ ２．Mi c r o s t ruc t ur eana l i s ys
Themi c r os t ruc t ur ei nt hec en t e ro ft heX８０l a r Ｇ ge s t r a i np i l i nes t e e lp l a t e wa scompos edo fbanded pe ba i n i t eandf e r r i t eandi sshowni nF i ４(a) ．The g we l d i ng t he rma lc l ep r oc e s sc l e a r l t r ong l f Ｇ yc ys ya f e c t edt he mi c r os t ruc t ur e．The mi c r os t ruc t ur e si n t hecoa r s e Ｇ r a i nz oneunde rd i f f e r en the a ti npu t sa r e g showni nF i ４(b－g) ．Theg r a i ns i z ewa sc l e a r l o Ｇ g yc
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
９６９
(a) Ef f e c to fhe a ti npu tonimpa c tt oughne s sf o rd i f f e r en the a t Ｇ c l epe akt empe r a t ur e s; (b) Ef f e c to fhe a t Ｇ c l epe akt empe r a t ur e son yc yc impa c tt oughne s sf o rd i f f e r en the a ti npu t s; (c) Ef f e c to fhe a t Ｇ c l epe akt empe r a t ur e sonha r dne s sf o rd i f f e r en the a ti npu t s． yc
F i ３． Compa r i s ono fimpa c tt oughne s sandha r dne s so fhe a t Ｇ a f f e c t edz one． g
(a) Mi c r o s t r uc t ur eo fma t r i x; (b) CGHAZ mi c r o s t r uc t ur ewi t hahe a ti npu to f１７kJcm－１; (c) CGHAZ mi c r o s t r uc t ur ewi t ha he a ti npu to f２０kJcm－１; (d) CGHAZ mi c r o s t r uc t ur ewi t hahe a ti npu to f２５kJcm－１; (e) CGHAZ mi c r o s t r uc t ur ewi t ha he a ti npu to f３５kJcm－１; (f) CGHAZ mi c r o s t r uc t ur ewi t hahe a ti npu to f４５kJcm－１; (g) CGHAZ mi c r o s t r uc t ur ewi t ha －１ he a ti npu to f５０kJ cm ．
F i ４． SEM mi c r og r aphsshowi ngba s eme t a landc oa r s e Ｇ r a i nedhe a t Ｇ a f f e c t edz onea td i f f e r en the a ti npu t s． g g
a r s ea tape akt empe r a t u r eo f１３００° Cbu twa ss t i l l sma l l e rt han８０ μm．Be c aus e Tiand Nbc a rbon i Ｇ t r i de swe r eno td i s s o l vedc omp l e t e l t１３００° C, t he ya i nn i nge f f e c twa ssubs t an t i a l． I nadd i t i on, t hed r ag p e f f e c to ft hes o l i d Ｇ s o l u t i on Nbs o l u t ec ana l s op r e Ｇ [ ] ven taus t en i t eg r a i ng r owt h１０ ．Whent hehe a ti npu t wa sl owe r(１７k Jcm－１ ,t８/５＝５ ４７s) a ndt h ec oo l i ng r a t ewa sf a s t e r,t h emi x t u r eo fl a t hba i n i t eands l i t l gh y mo r eg r anu l a rba i n i t ewe r eobs e r vedi nt he ma t r i x． Di s con t i nuousf i nel a t hg r ew pa r a l l e lf r omt heaus Ｇ t en i t eg r a i nbounda r ot hei n t e r i o r．MＧAc ons t i t u Ｇ yt en td i s t r i bu t edbe twe ent hef e r r i t el a t hs．Whent he he a ti npu t swe r e２５kJcm－１(t８/５ ＝１１ ８３s) and３５ －１ ( ) kJ cm t８/５ ＝２３ １８s r e spe c t i ve l he mi c r o Ｇ y, t s t ruc t u r ei nt heHAZwa sma i n l ompo s edo fg r an Ｇ yc u l a rba i n i t eandt hel a t hba i n i t e．Thel ame l l a rspa c Ｇ i ngi nc r e a s ed, ands ome qua s i Ｇmu l t i l a t e r a lf e r r i t e s we r eobs e r ved． I ns i det heo r i i na laus t en i t eg r a i ns, g t heba i n i t ehadal a r rdens i t fh i Ｇ ang l eg r a i n ge yo gh bounda r i e sandt hee f f e c t i veg r a i ns i z ewa ssma l l e r, wh i ch wa sbene f i c i a lf o rimp r ov i ngt het oughne s s． Thegoodd i s t r i bu t i ono fl a r r d MＧAi s l andso f ge, ha
r anu l a rba i n i t ei nt hef e r r i t e ma t r i xa l sol e adt o g s t r e s sconc en t r a t i onandr e su l t edi nt hegene r a t i ono f t hemi c r oc r a cks． Be c aus eo ft heeme r eo fal a r genc ge numbe ro fg r anu l a rba i n i t e, t heimpa c tt oughne s s wa sr educ edsubs t an t i a l l y． Whent hewe l d i nghe a ti npu twa si nc r e a s edt o４５ kJcm－１ (t８/５ ＝３８ ３１s) andt hecoo l i ngr a t e wa s de c r e a s edf ur t he r, t he mi c r os t ruc t ur ei nt he HAZ wa s ma i n l edo fg r anu l a rba i n i t ei n wh i ch ycompos t he MＧAb l ockwa ss l i h t l l a r e ． A t t h e s a m e t i m e, g y g somemo r equa s i Ｇmu l t i l a t e r a lf e r r i t e sf o rmed．When t hehe a ti npu twa s５０kJcm－１ , t heg r anu l a rba i n Ｇ i t eand po l li n t r ag r anu l a rf e r r i t ei nt he HAZ ygona mi c r os t ruc t ur echangedex t ens i ve l r, be Ｇ y．Howeve c aus eo ft hef o rma t i on o fg r a i n Ｇbounda r l l o t r i o Ｇ ya mo r i cf e r r i t e, t heo r i i na laus t en i t eg r a i nbounda Ｇ ph g r snol onge robs e r ved． Suchh i a ti npu t sr e Ｇ y wa ghhe su l t edi ng r e a tr e s i denc et imeabovet hepha s e Ｇ t r ans Ｇ f o rma t i ont empe r a t ur e, wh i ch t hen p r omo t ed t he f o rma t i ono fg r a i n Ｇbounda r l l o t r i omo r i cf e r r i t e ya ph andi n t r ag r anu l a rf e r r i t ewi t hav e r l owc oo l i ngr a t e． ys I ncompa r i sont ot hehe a ti npu ta t４５kJcm－１ , t he
９７０
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
eme r eo fg r a i n Ｇ bounda r l l o t r i omo r i cf e r r i t e genc ya ph andi n t r ag r anu l a rf e r r i t ea l l owedt heha r dne s st obe l owe r edwi t hou tac on t i nua lde c l i nei nt het oughne s s a the a ti npu t so f５０ kJcm－１ ．Henc e, t hes i z e, shape, andd i s t r i bu t i ono f MＧAi s l ands wou l da l so s t r ong l n f l uenc et he t oughne s so ft he c oa r s e Ｇ yi r a i n e dz o n e ． A ni n c r e a s ei nt h eh e a ti n u t w o u l d g p l e adt oani nc r e a s ei nt hevo l umef r a c t i ono ff e r r i t e andi nt heha r dne s so ft he MＧA i s l ands．Fu r t he r Ｇ , mo r et he MＧAi s l andswou l dbet r ans f o rmedf r om f i nel a t ht oama s s i veb i l o ck． I nadd i t i on, be c aus e gb mo r es t r e s swa sc onc en t r a t eda tt hei n t e r f a c eo ft he r i i d MＧAi s l andsandt he ma t r i x, c r a ck i ng wou l d g , e a s i l c cu ri nt hec oa r s eg r a i ns r e su l t i ngi nade Ｇ yo [ ] c r e a s ei nimpa c tt oughne s s１１ ． Themi c r o s t ruc t u r e so ft heHAZa td i f f e r en tpe ak t empe r a t u r e swi t hahe a ti npu to f２０o r３５kJcm－１ a r eshowni nF i ５．Fr om F i ４(c,e) t oF i ５, i t g g g
c anbeobs e r vedt ha tt hemi c r os t ruc t ur ei nt heHAZ wa scompos edo fl a t hand g r anu l a rba i n i t ea tpe ak t empe r a t ur e so f１２００and１３００° C．Thet oughne s s andt hei nc r e a s ei nt heha rdne s sde c r e a s edbe c aus eo f t hecoa r s eg r a i n．Wi t ht hed e c r e a s eo ft hep e akt emp e r Ｇ a t u r e, t heg r a i ns i z eb e c amef i n e randasma l lamoun to f f e r r i t eappe a r ed．Thet oughne s si nc r e a s ed, andt he ha rdne s sde c r e a s ed g r adua l l hepe akt emＧ y．Whent , e r a t u r ew a s１ ０ ０ ０ ° C t h em i c r o s t r u c t u r ew a sc o mＧ p , , edo ff e r r i t e g r anu l a rb a i n i t e andasma l lamoun t pos o feven muchf i ne r ma r t ens i t e; a tt ha tpo i n t, t he impa c tt oughne s s wa sf ur t he ri nc r e a s ed．Whent he akt empe r a t ur ewa sa t９００° C, t hemi c r os t ruc t ur e pe wa sf ur t he rr e f i ned．Af t e raus t en i t i z a t i on, f e r r i t e, r anu l a rba i n i t eandasma l lamoun to f ma r t ens i t e g we r ef o rmed dur i ng t he coo l i ng p r oc e s s and t he t oughne s sr e a chedi t smax imumva l ue． Acompa r i sono ft hehe a ti npu to f３５k Jcm－１ wi t h
(a),(b) FPT (f i r s tpe akt empe r a t ur e) o f１２００° C; (c),(d) FPTo f１１００° C; (e),(f) FPTo f１０００° C; (g),(h) FPTo f９００° C．
F i ５． SEM mi c r og r aphsshowi nghe a t Ｇ a f f e c t edz onemi c r o s t r uc t u r ea td i f f e r en tpe akt empe r a t u r e sanda t２０kJcm－１ (a, c, g －１ (b, d, f, h) ． e, g) o r３５kJcm
２０kJcm－１ r eve a l st ha tt hef o rme rhadas l owe r coo l i ng r a t e, wh i ch r e su l t edi nt he c oa r s eg r a i n, ma s s i veMＧAi s l ands, andl owt oughne s s．Whent he he a ti npu t swe r e２０and３５kJcm－１ ,t hepe akt emＧ r a t u r e wa s be twe en ９００ and １１００° C, and t he pe h i rimpa c tt oughne s sc ou l dber e a ched wi t ht he ghe s l i tde c r e a s ei n ha r dne s s．The HAZ mi c r o s t ruc Ｇ gh t ur e swe r e ma i n l ompo s edo ft hea f o r emen t i oned yc
mi c r os t ruc t ur e si nt hep i l i nes t e e l．Al t hought he pe he a ti npu to f３５kJcm－１ r e su l t edi nah i rpe ak ghe t empe r a t ur eo ft he ne a r Ｇ f us i on Ｇ l i ne a r e a, coa r s e r r a i n, andl owe rt oughne s s, t hel owe rpe akt empe r Ｇ g a t ur er eg i onwa sad a c en tt ot heg r e a t e rt oughne s s, j wh i cht huscou l de f f e c t i ve l r even tc r a ck expan Ｇ yp s i on．The r e f o r e, t he we l d i ngp r oc e s si nvo l v i ngt he he a ti npu to f３５kJcm－１ cou l ds t i l lmo r es t r ong l y
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
i n f l uenc et oughne s si nt he HAZ and enhanc et he [１２] we l d i nge f f i c i enc y ． The mi c r o s t ruc t u r eo ft heba s e me t a la f t e rs e c Ｇ onda r he rma lc l i ngi sshowni nF i ６．Whent he yt yc g he a ti npu twa s３５kJcm－１ andt hepe akt empe r a Ｇ t ur eo ft hef i r s tt he rma lc l ewa s１３００° C, t hemi Ｇ yc c r os t ruc t u r e si nt hema t r i xwe r ema i n l c o m o s e do f y p l a t hba i n i t e, g r anu l a rba i n i t e, and qua s i Ｇ o l o n a p yg l f e r r i t e, wh i ch had subs t an t i a l l l o w e r t oughne s s y t hant heo r i i na lp l a t e s．Thes e c onda r he rma lc Ｇ g yt yc l i ng wa st henc a r r i edou ta tt hepe akt empe r a t u r eo f ８００° C, wh i chi sbe twe ent hetwo Ｇ s et empe r a Ｇ pha t ur e, andt her e s i denc et ime wa ss osho r tt ha tt he
９７１
f e r r i t eandaus t en i t ed i dno tr e a chequ i l i br i umi nt h i s two Ｇ s er eg i on．The r e f o r e, t he o r i i na l ba i n i t e pha g f e a t ur e swe r er e t a i neddur i ngcoo l i ng．Al so, t hef i Ｇ na lmi c r os t ruc t ur e s we r e ma i n l edo fl a t h y compos ba i n i t e, g r anu l a rba i n i t e, qua s i Ｇ l lf e r r i t eand po ygona asma l lamoun to fpo l lf e r r i t e．Be c aus eo ft he ygona , eme r e n c eo fas m a l la m o u n to f o l o n a lf e r r i t e g p yg t het oughne s swa simp r oved, whe r e a st heha rdne s s wa sr educ ed．Whent hes e cond pe akt empe r a t ur e s , wa s９００° C t he mi c r os t ruc t ur e so ft he HAZ we r e ma i n l ed o fg r anu l a rba i n i t e, f e r r i t e, and ycompos MＧAi s l andd i s t r i bu t edon g r a i nbounda r i e s, wh i ch wa sex t r eme l rmf u lt ot hes t e e lt oughne s s． yha
(a) ２０kJcm－１andSPT (s e c ondpe akt empe r a t ur e) o f８００° C; (b) ３５kJcm－１andSPTo f８００° C; (c) ２０kJcm－１andSPTo f９００° C; (d) ３５kJcm－１andSPTo f９００° C．
F i ６． SEM mi c r og r aphsshowi ngba s eme t a lmo r l ogya f t e rs e c ondt he rma lcy c l e． pho g
Compa r ed wi t ht het oughne s sa t８００° C, t ha ta t ９００° C wa sl owe r．Comp l e t eaus t en i t i z a t i ono c cur r ed a t９００° C, wh i ch wa sj us tt heno rma l i z i ngp r o c e s s． Be c aus eo ft hehe a ti npu to f３５k Jcm－１a ndt h es l ow coo l i ng r a t e, pha s et r ans f o rma t i on wou l d oc cur t hr oughatwo Ｇ s er eg i on．Thus, t heamoun t so f pha f e r r i t eandma r t ens i t ewe r ei nc r e a s ed．Whent hehe a t i npu twa s３５kJcm－１ andt hes e c onda r he rma l yt c l et empe r a t u r ewa s８００° C, t heo r i i na laus t en i t e yc g r a i n bounda r sc l e a r l e r ved．MＧA i s l ands g y wa y obs we r esma l landwe l ld i s t r i bu t edi ns i det heg r a i n．At ９００° C, t he MＧAi s l ands we r el a r rand ma s s i ve, ge t heg r a i nbounda r sno tobv i ous, andt heimpa c t ywa
t oughne s swa sl ow． Whent hehe a ti npu t wa s２０ kJcm－１ andt he , s e conda r t h e r m a l c c l et e m e r a t u r ew a sa t８ ０ ０ ° C y y p aus t en i t i z a t i onoc cur r edpa r t i a l l tt hec r i t i c a lt emＧ ya r a t ur e．Howeve r, aus t en i t enuc l e a t i oncou l de a s i l pe y oc cura tt heg r a i nbounda r i e sbe c aus eo ft hesho r t d i s t anc ef o rt hed i f f us i ono fc a rbonanda l l oy i nge l e Ｇ men t sont heg r a i nbounda r i e s, wh i cht r an s f o rme dt o [ , ] MＧAi s l and sdu r i ngt her a i dc oo l i ngp r o c e s s１３ １４ ．The p MＧAcons t i t uen td i s t r i bu t edont heg r a i nbounda r i e s andwi t har e l a t i ve l i a rboncon t en tcou l dno t yh ghc bef u l l i ned wi t ht he ma t r i x．Af t e rt hes t e e l ycomb wa ssub e c t edt oex t e rna lf o r c eo ri n t e rna ls t r e s s, j
９７２
Y ． Cie ta l．/Journa lofI r onandSt e e lRe s ear ch, In t e rna t i ona l２４ (２０１７) ９６６－９７２
c r a ck i ngo c cu r r edandt het oughne s so ft hes t e e lwa s [ ] r educ ed１５Ｇ１７ ．Be c aus eo fc r a ck p r opaga t i on a l ong r a i nbounda r i e s, impa c tt oughne s s wa sde c r e a s ed． g Mo r eove r, t hef i neba i n i t es t ruc t u r eandt hed i s t r i Ｇ bu t i on o f MＧA c ons t i t uen t ss t r ong l n f l uenc et he yi [ ] me chan i c a lp r ope r t i e so fs t e e l１８Ｇ２０ ．Whent hehe a t －１ i npu twa s２０kJcm andt hes e c onda r t h e r m a l y ( ) , c c l et e m e r a t u r e h i h e rt h a n w a s９ ０ ０° C A y p g c ３ r a i nr e f i n e m e n ta n du n i f o r m d i s t r i b u t i o no f t h e M Ｇ g Acons t i t uen twe r er e a l i z ed, wh i chc ou l de f f e c t i ve l y even tc r a ckexpans i on andsubs t an t i a l l nc r e a s e pr yi t oughne s s．Whent hehe a ti npu twa s３５kJcm－１ andt hes e c onda r he rma lc l et empe r a t u r e wa s yt yc ８００o r９００° C,t heva l ueo ft heimpa c tt oughne s swa s r e l a t i ve l ow． yl
４．Conc l u s i on s
(１) Wh e nt h ewe l d i ngh e a ti npu tf o rt h eh i Ｇ s t r a i n gh X８０p i l i nes t e e lwa s１７－２５kJcm－１ , be t t e rimＧ pe c tt oughne s swa sa ch i evedi nt hec oa r s e Ｇ r a i na r e a pa g o ft he HAZ．Ast he we l d i ng he a ti npu t wa si n Ｇ c r e a s ed f u r t he r, t he impa c tt oughne s s de c r e a s ed r e a t l heha r dne s sde c r e a s eds l i t l t hi n Ｇ g yandt gh y．Wi c r e a s i nghe a ti npu t,t hevo l umef r a c t i ono ff e r r i t ea l Ｇ soi nc r e a s ed, andt hef i nel a t h MＧA i s l ands we r e t r ans f o rmedi n t o a ma s s i ve b l o ck, wh i ch f u r t he r c aus edt heha r dne s st obei nc r e a s ed．Be c aus eo ft he l a r t r e s sc onc en t r a t i onbe twe ent her i i d MＧAi s Ｇ ges g l andandt hema t r i x, c r a ckswou l df o rme a s i l t h Ｇ ywi i nt hec oa r s e Ｇ r a i nz one． g (２) Whent hehe a ti npu twa s３５kJcm－１ and t hepe akt empe r a t u r ewa sbe twe en９００and１１００° C, h i rimp a c tt oughn e s swa sa c h i e v e d．Wh e nt h ep e ak ghe t empe r a t u r ewa s１２００－１３００° C, t h emi c r o s t r u c t u r ei n t hema t r i xwa sma i n l ompo s edo fg r anu l a rba i n i t e． yc Theg r a i nwa sc oa r s eandt heMＧAi s l andswe r ema s Ｇ s i ve, wh i chr e su l t edi nal owimpa c tt oughne s sanda h i a r dn e s s．Wh e nt h eh e a ti npu twa s２０k Jcm－１ ghh andt h ep e a kt empe r a t u r ewa s９００－１３００° C, g r e a t e r
impa c tt oughne s swa sa ch i eved． (３) Whent hehe a ti npu twa s３５kJcm－１ and t hef i r s tpe akt empe r a t ur ewa s１３００° C, l owimpa c t t oughne s swa sa ch i eveda f t e rs e conda r he rma lc Ｇ yt y c l ebe twe en８００and９００° C．Whent hehe a ti npu twa s ２０kJcm－１ , t heimpa c tt oughne s sa f t e rt hes e c Ｇ onda r t h e r m a l c c l ea t９ ０ ０ ° C w a sh i h e rt h a nt h a t y y g a t８００° C．
Re f e r enc e s
[１] M． So l iman, H．Pa l kowsk i, Ma t e r．De s． ８８ (２０１５) ７５９ Ｇ ７７３． [２] YH．Yang, L．Sh i, Z．Xu, HS．Lu, X．Chen, X．Wang, Eng．Fr a c t．Me ch． １４８ (２０１５) ３３７ Ｇ ３４９． [３] YH．Chen, Y．Wang, B．Han, Tr ans a c t i onso fMa t e r i a l sand He a tTr e a tmen t２８ (２００７) No １, ７９ Ｇ ８２ (i nCh i ne s e) ． [４] L Y．Lan, C L．Qi u, D W． Zhao, X H．Gao, L X．Du, Ma Ｇ t e r． Sc i．Eng．A５２９ (２０１１) １９２ Ｇ ２００． [５] B C．Kim, S． Le e, N J．Kim, D Y． Le e, Me t a l l．Ma t e r．T r a n s．A ２２ (１９９１) １３９ Ｇ １４９． [６] R T． L i, X R． Zuo, YY．Hu, Z W．Wang, D X．Hu, Ma t e r． Cha r a c t． ６２ (２０１１) ８０１ Ｇ ８０６． [７] X R． Zuo, Z Y． Zhou, Ma t e r．Re s． １８ (２０１５) ３６ Ｇ ４１． [８] YP．Wang, X R．Zuo, J L．L i, S t e e l．Re s． I n t．８６ (２０１５) １２６０ Ｇ １２７０． [９] HH． Sayyed, I n t． J．Pr e s．Ve s．P i ８５ (２００８) ８７９ Ｇ ８８４． p． [１０] Y．Gu, P．Ti an, X．Wang, X L．Han, B．L i ao, F R．Xi ao, Ma t e r．De s． ８９ (２０１５) ５８９ Ｇ ５９６． [１１] WW．Xu, QF．Wang, T．Pan, H．Su, C F．Yang, J． I r on S t e e lRe s． I n t． １４ (２００７) No ５, ２３４ Ｇ ２３９． [１２] M． Zr i l i c, V．Gr abu l ov, Z． Bur z i c, M．Ar s i c, S． Sedmak, I n t． J．Pr e s．Ve s．P i ８４ (２００７) １３９ Ｇ １５０． p． [１３] S．Moe i n i f a r, AH．Kokab i, HR．Mada ah Ho s s e i n i, Ma t． De s． ３１ (２０１０) ２９４８ Ｇ ２９５５． [１４] X X．Chen, Z K．Xue, Ac t a J．Di, L．Ca i, X X．Xi ng, C ) ２８ (２０１５) ８８３ Me t a l l． S i n．(Eng l．Le t t． Ｇ ８９１． [１５] S J． Sun, M．Pugh, Ma t． Sc i．Eng．A３３５ (２００２) ２９８ Ｇ ３０８． [１６] C t a l l．Ma t e r．Tr ans．A２５ (１９９４) L．Dav i s, J E．Ki ng, Me ５６３ Ｇ ５７３． [１７] P．Mohs r l s en, OM．Aks e l s en, E． en i, J K．So l be r g, M．Ka t a l l．Ma t e r．Tr ans．A４５ (２０１４) ３８４ Ｇ ３９４． Øs t by, Me [１８] C L．He, HB．Wu, W．Yang, X M．Wang, S J． Shang, X Ac t a Me t a l l． S i n． ３９ (２００３) No １０, １０１９ Ｇ １０２４ (i nCh i ne s e) ． [１９] Y．Zhong, F R．Xi ao, J W．Zhang, YY．Shan, W．Wang, t a Ma t e r． ５４ (２００６) No ２, ４３５ Ｇ ４４３． K．Yang, Ac [２０] C H． Ch e n, J．Ma t e r． S c i． ４６ (２０１１) ６４２４ Ｇ W．L i, Y．Wa ng, Y ６４３１．