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Role of interface in nucleation of dynamic recrystallization of austenite
Scripta METALLURGICA et MATERIALIA
Vol. 28, pp. 725-728, 1993 Printed in the U.S.A.
Pergamon Press Ltd. All rights reserved
1K)LE OF INTgR~ACE IN NUCLEATION OF DYNAMIC RI~RYSTALLIZATIONOF AUSTENITE R.Z.Wan8 and T.C.Lei Depsrtmmt of Metab and Tw_hno~oSy, Harbin ln~dtute of Techsmlo~, Harbin 1/I0006, P.R.China (Received November i0, 1992) (Revised January 7, 1993) lutmducti~m
lti.~m~Ithat (DltX)dmhqlk~ffi~ak,
Sralnboundaryp]a~ a n l m p o r t a n t r o k i n the dynamic mcr~aUi~tion and the bulsi~ of orisinal grain boundari~ is the m~t ~ nuclm~
m ~ a n k m o f DRX fl-S). But in two-phsm anoys, inch u ~ - ~ etalnlau jtml, ~ - B b r a i a n d lowcarbon stmls in tlm aun(maito-fe~rl~ (F÷A) temperature range, where the ~ lxxmdszim of mm ~ are parti=ny fully occupied IV another phase, the nudmtion n~¢~.-i.~ of DRX is st/ll unknown QAg).
In this Imps, 8LnSk-phsm au,tmite and different ~ I o s i m obtaind in low carbm steels for the ~ ~,~.~ of ~ ~ aumtmita
of i n v , ~ i p t l ~
of (F÷A) two-phue structuree were the role of interface in tim nucleation
81mcimsm 12 mm in height and 8 mm in ~ , , , e t ~ of ss-,,-mmled ~ 1015 (with 0.17 C. 0.34 Si. 0.46 Mn. 0 . ~ 8, 0.Q~ P in wt.-%) and steel 1~0 (with 0.32 C, 0.24 8/, 0.64 Mn, 0.0~8 S, 0.0~ P, in wt.-%) w ~ Isot]mmmlly ~ at 800 "C cm a Olmble-1600 ~ Mechanical S/mulat~ at a strain rote of 0.002 s-x. ToobWln d i f f ~ n t i n t m f a c e s t a t ~ , t w o t y l ~ o f i n ~ a ~ a t m e n t e w e z ~ u l l b e f o z ~ c o m l n ~ d o n , ~ q ~ o f si~c/ms~ was lmat~i di~ctly to 800 "C, and the other Stoup was first a u s t ~ i=ed at 930 "C f ~ 20 ~ ~ ~ c o o k d a t a m t e o f l ' c / s toS00"C. A l z ~ i i ~ tin~ of 20 min at 800 "C w s s u ~ l i n a l l c u ~ . S l ~ c i n m ~ w ~ wat~ q u m c h ~ ~ t e l y after ddormation. Picric acid was used to etch the ori~'~,] grain boundari~ of austmite. Rmults and ~ 8nslye~ show that steel 1{}30 la fully a ~ before deformation at 800 "C, and steel 1016 c~vskts of a t m ~ t e and ferrite ~ at S00 "C. When ~tml ~0~ is heated directly from ~ o ~ t~lmmture to tim deformat4~ tsmlmratum, austenite gr.~n#_ form in lmarlite smine and at fet~ite grain ~ , and oft~ ~ each oth~, Le., atm(mdte grain boundaries (A/A) ~v~] austmdte/fm~ite (A/F) phase boundaries coulstatthisstat~. Whenstull016is ~oooled from full austsait~ to 800"C, ferrit~form8 a t t h e s r a i n Imumisrlm of austenite u networks. In this cue, almost all A/A grain ~ are replaced by F/A idmse bounda~_m: ~ ~ o f sinsle austenite phsm (steel ~0~0) after c~mpremion atS00 "C is shown in FiS.~ The ssrratsd 8mln bmmdarlm and the m ~ l fine and coarse grain, show that dym,mlc recrystalli=ation of amtmite hss tsken place ~ the bulsins of the original grain boundariee, whichisthe m~t oo~mon mechanim
of ~ . I c
m ~ d U = a t i o n O-e).
When A/A grain boundazlm and A/F phsam boundaries coexist before deformation (steel 101~ heated from r ~ m temlmratu~ to 800 "C), the m i ~ after defc~ation are givem in l~g.lb, c and ld. At the ~nof0.~ tTtg.~b),~pla~ of the ~ ] au~nite grain~~ teglntobuke, u ~ n b y armwn, indicating that the dynamic recrystallisati~n of austenit@ in thk auatenito-fm~.ite two phs~ gtructtms begins to nucleate by the mine bulging mechmnism as in the case of single-phase austenite. Fig.lc and ld show the development of DP,X in austenite upon further deformation; the a ~ t e keeps eq,,ia~ed 725 0956-716X/93 $6.00 + .00 Copyright (c) 1993 Pergamon Press Ltd.
726
DYNAMIC
RECRYSTALLIZATION
Vol.
28, No. 6
through DRX although the original austenite 8zatn~ are elongated after deformation (Fis.ld). When steel 1016 was __~_!edfrom a fully amtenite state to deformation temperature and the A/A v a i n lxnmdaries are almost completely occupied by AfF phase boundari~ prior to compression, the formation m~hJ,;-m of DRX nuclei changes absolutely. In this cue, the onset of DP,X in austenite was greatly delayed, and at a strain as high as 0.46, the nuclei of DRX in austenite prefmlmtially form at A/F nh~m boundaries, as shuw~ by an arrow in Fis.2a. Fi~.2b iA the m i ~ of the u m e area ~w.hed with nital. Fig. 3a siv~ another example of DRX nuclei at A/F phme boundary; the further development of such nuclei are given in Fig.3b. In some cases, DRX nuclei of austenite appear wjtht, the austenite Sty;n-; as show~ by an arrow in Fig.3c. After ~ Btralns, the elong&ted ~ &tl~ca~DJte gralna Wn] be divided into mm~ll~r grminm throt~h DRX W~.ad). It can be seen from the above results that the nucleation of DRX in austenite depends on the interface state; ammmite dynamically recrystallizes through the ~ of A/A grain boundaries am long as A/A grain ixmndariw exist before defm~mation whether the aumenite is in the single phase state or in the (A÷F) two phase state. In the aimnse of A/A boundaries, the austenite cRnnot recrystR11;~ by the bulging ~ ; tlm DRX of austenite can only take place through the formation and submqu~t movement of new A/A boundarie~ In most casm the nuclei form at A/F phue boundari~, as shown in Fig.2 and Fig.3. Th/scan be ez~laiued by two factors: Firstly, the deforms~on_ of austenite is more severe and hence more deformation energy stored near AfF boundaries, i.e., the moving force for r e c r ~ t i o ~ is bigger in areas near AfF boundaries than within the grains. Secondly, when the DRX nuclei form on the base of A/F boundaries, it will reduce the area o£ A/A interface needed to form a u n i t volumeof DRX nucleus and will lower the resistance of dynamic t~ysta]lisation. Within the austenite grains, those places of concentrated strain such as deformation bands can also become the nucleation sites of DRX. Th/s is the case shown in Fig.3c. Compared with the dynamic r~ystsllisation of aumt~ite through the bulslnS m ~ ¢ ~ , , , I , the DRX in the latter case takm place with more difficulty because of the necessity to f ~ new A/A boundarim. So the DRX in the latt~ case begins to nucleate at a ndatively l a r p r strain (me Fig.2 and Fig.8).
Summ~ The type of interface plays an important role in the nucleation of dyr~__micr e c r ~ t i o n of amdmnite. DRX of austenite takes place through the bulging of the original A/A grain boundaries as long as A/A grain boundaries exist ~ to deforma~on whether the austenite is in the Idn~le phase ~;ate o~r in the austen/teferrite two phsss sta~. In the almm~ of A/A boundaries, the DRX of austenite proceeds through the formation and su_t~_~mmt m o ~ m t of new A/A Stain boundarim at A/F phs~ boundadm. Oompared with the enmmon bulging meehan;,~, the latter nucleation m~_l~,;~m of DRX takw place with more difficulty because ot the n ~ m i t y of formtnS new A/A grain botmdarl~ Refm~mcm 1. H. J. McQu~m and J. J. JonM, in R. J. ~ u l t (ed.), Plastic Defo~mation of Materials, ~SmatiN cm Matsdals Science and T w J ~ b ~ y , VoL 6, P. 398, Academic Pros f197D. 2. 8. 8akai, T. Sakai and K. Tak~,~,, ~ m s . ISIJ, 17, 718 flgT/). 8. S. ~ , l~crystail~t~n in Metals and Alloys, P. 2O9, MIR Publislm~ ~ ~l~l). 4. H. J. M~lu~n and J. J. Jons~ J. Applied M ~ 1 ~ k i n s , 3. 2 ~ C~9~). ~. T. &tka/, J. J. J ~ Acta M~alL 82, 189 (~S~). e.I. ~ u r ~ Tran~ ISIJ, ~ , 7 ~ 0SS~). ?. H. J. McQu~m, K ~ and M. K w , , , , ~ , Z. M ~ l k d e . e~, aae C~gm). 8. B. Derby andM. F. Ashby, 8cri~ta M~all. m, 879 flgST). 9. T. C'~-dra, D. Bsmleich and D. P. Dunne, in I t C. G i f ~ (ed.), Smmsth of Metals and OCSMA e ~ ) , VoL ~, P. era, Persmon, Oxford (lssa).
Vol.
28, No. 6
DYNAMIC
RECRYSTALLIZATION
Ris.I ~ s h o w i n t t l h m D R X o f a u s t m m i t i ( A ) . to 800 "C, the strain rats is 0.0M f ~ a: steel I0~0, e -0.8, b: steel 101~ E -0.1, c: ~
727
B~pecimsmmwambsated directly 101B, ~ -0.4~, d: stmel 1016, e -0.8
Fig.2 ~ s b o w i n s t h e D R X n u c l e a / ~ u ~ n o f a u s t e n i t m a t A / F p l ~ u m b o u n d m . y . was l~mmstsnissd befm~ brans d d o r m ~ at 800 "C, strain rate is 0.00~ r ~. g -0.46. a: picric ac/d stch, b: tlm mine area I a, nital etch
Specimen
728
DYNAMIC RECRYSTALLIZATION
Vol. 28, No. 6
I~Is.$ Mic:ustrueuu~ s h e n d ~ n u e l ~ t i o n and duvulopms~ a t I ~ , Z d austmitu (A). Saml~S were l ~ a U S t s n i s ~ betca~ ~ d d c r m , d at 800 "C, strain rats is 0 . 0 ~ f ~ a: £ -0.46, b: £ -0.6, c: £ -(L46, d: z -0.8, pierle acid ulr.h
Vol. 28, pp. 725-728, 1993 Printed in the U.S.A.
Pergamon Press Ltd. All rights reserved
1K)LE OF INTgR~ACE IN NUCLEATION OF DYNAMIC RI~RYSTALLIZATIONOF AUSTENITE R.Z.Wan8 and T.C.Lei Depsrtmmt of Metab and Tw_hno~oSy, Harbin ln~dtute of Techsmlo~, Harbin 1/I0006, P.R.China (Received November i0, 1992) (Revised January 7, 1993) lutmducti~m
lti.~m~Ithat (DltX)dmhqlk~ffi~ak,
Sralnboundaryp]a~ a n l m p o r t a n t r o k i n the dynamic mcr~aUi~tion and the bulsi~ of orisinal grain boundari~ is the m~t ~ nuclm~
m ~ a n k m o f DRX fl-S). But in two-phsm anoys, inch u ~ - ~ etalnlau jtml, ~ - B b r a i a n d lowcarbon stmls in tlm aun(maito-fe~rl~ (F÷A) temperature range, where the ~ lxxmdszim of mm ~ are parti=ny fully occupied IV another phase, the nudmtion n~¢~.-i.~ of DRX is st/ll unknown QAg).
In this Imps, 8LnSk-phsm au,tmite and different ~ I o s i m obtaind in low carbm steels for the ~ ~,~.~ of ~ ~ aumtmita
of i n v , ~ i p t l ~
of (F÷A) two-phue structuree were the role of interface in tim nucleation
81mcimsm 12 mm in height and 8 mm in ~ , , , e t ~ of ss-,,-mmled ~ 1015 (with 0.17 C. 0.34 Si. 0.46 Mn. 0 . ~ 8, 0.Q~ P in wt.-%) and steel 1~0 (with 0.32 C, 0.24 8/, 0.64 Mn, 0.0~8 S, 0.0~ P, in wt.-%) w ~ Isot]mmmlly ~ at 800 "C cm a Olmble-1600 ~ Mechanical S/mulat~ at a strain rote of 0.002 s-x. ToobWln d i f f ~ n t i n t m f a c e s t a t ~ , t w o t y l ~ o f i n ~ a ~ a t m e n t e w e z ~ u l l b e f o z ~ c o m l n ~ d o n , ~ q ~ o f si~c/ms~ was lmat~i di~ctly to 800 "C, and the other Stoup was first a u s t ~ i=ed at 930 "C f ~ 20 ~ ~ ~ c o o k d a t a m t e o f l ' c / s toS00"C. A l z ~ i i ~ tin~ of 20 min at 800 "C w s s u ~ l i n a l l c u ~ . S l ~ c i n m ~ w ~ wat~ q u m c h ~ ~ t e l y after ddormation. Picric acid was used to etch the ori~'~,] grain boundari~ of austmite. Rmults and ~ 8nslye~ show that steel 1{}30 la fully a ~ before deformation at 800 "C, and steel 1016 c~vskts of a t m ~ t e and ferrite ~ at S00 "C. When ~tml ~0~ is heated directly from ~ o ~ t~lmmture to tim deformat4~ tsmlmratum, austenite gr.~n#_ form in lmarlite smine and at fet~ite grain ~ , and oft~ ~ each oth~, Le., atm(mdte grain boundaries (A/A) ~v~] austmdte/fm~ite (A/F) phase boundaries coulstatthisstat~. Whenstull016is ~oooled from full austsait~ to 800"C, ferrit~form8 a t t h e s r a i n Imumisrlm of austenite u networks. In this cue, almost all A/A grain ~ are replaced by F/A idmse bounda~_m: ~ ~ o f sinsle austenite phsm (steel ~0~0) after c~mpremion atS00 "C is shown in FiS.~ The ssrratsd 8mln bmmdarlm and the m ~ l fine and coarse grain, show that dym,mlc recrystalli=ation of amtmite hss tsken place ~ the bulsins of the original grain boundariee, whichisthe m~t oo~mon mechanim
of ~ . I c
m ~ d U = a t i o n O-e).
When A/A grain boundazlm and A/F phsam boundaries coexist before deformation (steel 101~ heated from r ~ m temlmratu~ to 800 "C), the m i ~ after defc~ation are givem in l~g.lb, c and ld. At the ~nof0.~ tTtg.~b),~pla~ of the ~ ] au~nite grain~~ teglntobuke, u ~ n b y armwn, indicating that the dynamic recrystallisati~n of austenit@ in thk auatenito-fm~.ite two phs~ gtructtms begins to nucleate by the mine bulging mechmnism as in the case of single-phase austenite. Fig.lc and ld show the development of DP,X in austenite upon further deformation; the a ~ t e keeps eq,,ia~ed 725 0956-716X/93 $6.00 + .00 Copyright (c) 1993 Pergamon Press Ltd.
726
DYNAMIC
RECRYSTALLIZATION
Vol.
28, No. 6
through DRX although the original austenite 8zatn~ are elongated after deformation (Fis.ld). When steel 1016 was __~_!edfrom a fully amtenite state to deformation temperature and the A/A v a i n lxnmdaries are almost completely occupied by AfF phase boundari~ prior to compression, the formation m~hJ,;-m of DRX nuclei changes absolutely. In this cue, the onset of DP,X in austenite was greatly delayed, and at a strain as high as 0.46, the nuclei of DRX in austenite prefmlmtially form at A/F nh~m boundaries, as shuw~ by an arrow in Fis.2a. Fi~.2b iA the m i ~ of the u m e area ~w.hed with nital. Fig. 3a siv~ another example of DRX nuclei at A/F phme boundary; the further development of such nuclei are given in Fig.3b. In some cases, DRX nuclei of austenite appear wjtht, the austenite Sty;n-; as show~ by an arrow in Fig.3c. After ~ Btralns, the elong&ted ~ &tl~ca~DJte gralna Wn] be divided into mm~ll~r grminm throt~h DRX W~.ad). It can be seen from the above results that the nucleation of DRX in austenite depends on the interface state; ammmite dynamically recrystallizes through the ~ of A/A grain boundaries am long as A/A grain ixmndariw exist before defm~mation whether the aumenite is in the single phase state or in the (A÷F) two phase state. In the aimnse of A/A boundaries, the austenite cRnnot recrystR11;~ by the bulging ~ ; tlm DRX of austenite can only take place through the formation and submqu~t movement of new A/A boundarie~ In most casm the nuclei form at A/F phue boundari~, as shown in Fig.2 and Fig.3. Th/scan be ez~laiued by two factors: Firstly, the deforms~on_ of austenite is more severe and hence more deformation energy stored near AfF boundaries, i.e., the moving force for r e c r ~ t i o ~ is bigger in areas near AfF boundaries than within the grains. Secondly, when the DRX nuclei form on the base of A/F boundaries, it will reduce the area o£ A/A interface needed to form a u n i t volumeof DRX nucleus and will lower the resistance of dynamic t~ysta]lisation. Within the austenite grains, those places of concentrated strain such as deformation bands can also become the nucleation sites of DRX. Th/s is the case shown in Fig.3c. Compared with the dynamic r~ystsllisation of aumt~ite through the bulslnS m ~ ¢ ~ , , , I , the DRX in the latter case takm place with more difficulty because of the necessity to f ~ new A/A boundarim. So the DRX in the latt~ case begins to nucleate at a ndatively l a r p r strain (me Fig.2 and Fig.8).
Summ~ The type of interface plays an important role in the nucleation of dyr~__micr e c r ~ t i o n of amdmnite. DRX of austenite takes place through the bulging of the original A/A grain boundaries as long as A/A grain boundaries exist ~ to deforma~on whether the austenite is in the Idn~le phase ~;ate o~r in the austen/teferrite two phsss sta~. In the almm~ of A/A boundaries, the DRX of austenite proceeds through the formation and su_t~_~mmt m o ~ m t of new A/A Stain boundarim at A/F phs~ boundadm. Oompared with the enmmon bulging meehan;,~, the latter nucleation m~_l~,;~m of DRX takw place with more difficulty because ot the n ~ m i t y of formtnS new A/A grain botmdarl~ Refm~mcm 1. H. J. McQu~m and J. J. JonM, in R. J. ~ u l t (ed.), Plastic Defo~mation of Materials, ~SmatiN cm Matsdals Science and T w J ~ b ~ y , VoL 6, P. 398, Academic Pros f197D. 2. 8. 8akai, T. Sakai and K. Tak~,~,, ~ m s . ISIJ, 17, 718 flgT/). 8. S. ~ , l~crystail~t~n in Metals and Alloys, P. 2O9, MIR Publislm~ ~ ~l~l). 4. H. J. M~lu~n and J. J. Jons~ J. Applied M ~ 1 ~ k i n s , 3. 2 ~ C~9~). ~. T. &tka/, J. J. J ~ Acta M~alL 82, 189 (~S~). e.I. ~ u r ~ Tran~ ISIJ, ~ , 7 ~ 0SS~). ?. H. J. McQu~m, K ~ and M. K w , , , , ~ , Z. M ~ l k d e . e~, aae C~gm). 8. B. Derby andM. F. Ashby, 8cri~ta M~all. m, 879 flgST). 9. T. C'~-dra, D. Bsmleich and D. P. Dunne, in I t C. G i f ~ (ed.), Smmsth of Metals and OCSMA e ~ ) , VoL ~, P. era, Persmon, Oxford (lssa).
Vol.
28, No. 6
DYNAMIC
RECRYSTALLIZATION
Ris.I ~ s h o w i n t t l h m D R X o f a u s t m m i t i ( A ) . to 800 "C, the strain rats is 0.0M f ~ a: steel I0~0, e -0.8, b: steel 101~ E -0.1, c: ~
727
B~pecimsmmwambsated directly 101B, ~ -0.4~, d: stmel 1016, e -0.8
Fig.2 ~ s b o w i n s t h e D R X n u c l e a / ~ u ~ n o f a u s t e n i t m a t A / F p l ~ u m b o u n d m . y . was l~mmstsnissd befm~ brans d d o r m ~ at 800 "C, strain rate is 0.00~ r ~. g -0.46. a: picric ac/d stch, b: tlm mine area I a, nital etch
Specimen
728
DYNAMIC RECRYSTALLIZATION
Vol. 28, No. 6
I~Is.$ Mic:ustrueuu~ s h e n d ~ n u e l ~ t i o n and duvulopms~ a t I ~ , Z d austmitu (A). Saml~S were l ~ a U S t s n i s ~ betca~ ~ d d c r m , d at 800 "C, strain rats is 0 . 0 ~ f ~ a: £ -0.46, b: £ -0.6, c: £ -(L46, d: z -0.8, pierle acid ulr.h