Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures
Cross wedge rolling (CWR) is a forming technique wherein the processed material microstructure is controlled by the processing temperature. The initial results on CWR-processed T91 steels at different austenitizing temperatures are discussed with the microstructure analysis by various characterizati...
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| Cite this: | Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures / T. He, L. Min, H.J. Liu // Проблемы прочности. — 2017. — № 1. — С. 72-78. — Бібліогр.: 14 назв. — англ. |
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| citation_txt | Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures / T. He, L. Min, H.J. Liu // Проблемы прочности. — 2017. — № 1. — С. 72-78. — Бібліогр.: 14 назв. — англ. |
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| description | Cross wedge rolling (CWR) is a forming technique wherein the processed material microstructure is controlled by the processing temperature. The initial results on CWR-processed T91 steels at different austenitizing temperatures are discussed with the microstructure analysis by various characterization techniques, such as the optical and scanning electron microscopies. The processed T91 specimens were much harder than water-quenched ones, their hardness being independent of the ausforming temperatures despite their microstructural differences.
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UDC 539.4
Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge
Rolling at Different Austenitizing Temperatures
T. H e,1 L. M in , an d H . J . L iu
Department of Mechanical engineering, Shanghai University of Science Technology, Songjiang,
Shanghai, China
1 hetao@sues.edu.cn
Cross wedge rolling (CWR) is a forming technique wherein the processed material microstructure is
controlled by the processing temperature. The initial results on CWR-processed T91 steels at
different austenitizing temperatures are discussed with the microstructure analysis by various
characterization techniques, such as the optical and scanning electron microscopies. The processed
T91 specimens were much harder than water-quenched ones, their hardness being independent o f the
ausforming temperatures despite their microstructural differences.
K eyw ords: cross wedge rolling, ausforming, ferritic/m artensitic T91 steel, deformation.
In tro d u c tio n . Chrom ium bearing ferritic-m artensitic steels w ere originally designed
for conventional fossil pow er plants. In the 1970s, they were used for high-tem perature
structural applications in the core o f faster reactors in the developed countries [1]. T91 steel
has a low production cost and excellent m echanical, physical, and chem ical properties. This
m akes it extrem ely attractive for pressure vessel applications and for the fossil pow er or
petrochem ical industry piping systems [2].
A ccording to Fig. 1, cross wedge rolling (CW R) is considered as a novel plastic
deform ation process. In order to produce parts such as stepped axes and shafts, the action
o f wedge shape dies and m oves tangentially relative to each other [3]. The benefits o f CW R
are significant w hen com pared with other conventional forming processes, such as high
productivity, great m aterial utilization, good m echanical properties, reduced energy
consumption, as w ell as no harm to the environm ent [4, 5].
Fig. 1. Schematic of CWR with two rolls: (1) rolls with wedge, (2) billet, and (7) guide plates.
In recent years, CW R is used for processing o f various types o f materials. Am ong
them, Silva et al. [6] studied the behavior o f the m icroalloyed steel DIN 38MnSiVS5.
Qakircali et al. [7] carried out experiments to examine the deform ation and fracture of
© T. HE, L. MIN, H. J. LIU, 2017
72 ISSN 0756-171X. npo6n.eubi 2017, N2 1
mailto:hetao@sues.edu.cn
Strength Improvement o f Ferritic/Martensitic T9Î Steel
Ti6A14V alloy. To test the m icrostructure evolution o f 40M nV steel, Wang et al. [8]
perform ed the respective experiments. Zhang et al. [9] investigated the effect o f cross
w edge rolling on the m icrostructure o f GH4169 alloy, w hile He et al. [10] investigated the
deform ation o f Inconel 718 alloy. Due to the advantages that resulted from the study on
T91 steel by CW R, the application prospects are significant. Because tem perature is the
influencing factor for the CW R deform ation and m icrostructure evaluation, the rolling
experim ents o f T91 at different tem peratures were conducted. Subsequently, the m icro
structure evaluation o f T91 is discussed, and the m echanical properties at different
tem peratures are also assessed.
1. E xperim en t. Table 1 listes the chem ical com position o f the as-received (AR) T91
alloy in wt.%. Initially, the as-received T91 was hot-forged and then heat-treated by the
standard norm alization and tem pering procedures. Then, the CW R w as carried out on
CW R m ill H500. The m ain properties o f rolling process are as follows: form ing angle of
a = 35°, stretching angle o f 3 = 5.5°, area reduction o f AA = 66%, and rotating speed o f
n = 10 rpm. Since tem perature is the crotical factor controlling the m icrostructure and
m echanical properties o f T91 alloys, four different rolling tem peratures o f 900, 1040, 1100,
and 1200°C were selected. Billets w ere w ater-quenched prior to processing at elevated
temperatures.
T a b l e 1
Chemical Composition (wt.%) of the As-Received T91 Alloy
Cr Mo V Mn C Si Cu Ni Al Nb N P S
В.ЗЗ 0.92З 0.21 0.44 0.09З 0.4З 0.06 0.З2 0.00B 0.079 0.042 0.01З 0.00З
After rolling, small circular specimens w ith 0 7X 5 m m were cut for optical observation,
scanning electron microscopy, and hardness tests. The specim ens were m echanically
polished conform ing to the standard procedure and etched prior to the optical observation.
By using an LM 300AT m icrohardness tester, the hardness for the therm al stability study
w as m easured based on a 2.9 N (300 g) loading tim e force o f 13 s using a pyram idal shape
diam ond indenter. the scanning electron m icroscopy (SEM ) was perform ed on an FEI
Q uanta 600 m icroscope operating at acceleration voltage o f 20 kV and w orking distance of
10 mm. A t acceleration voltage o f 20 kV and w orking distance o f 10 mm, an FEI Quanta
600 m icroscope w as used to perform SEM.
2. R esu lts an d D iscussion.
2.1. M icrostructure o f A R T91. Figure 2 shows the m icrostructure o f A R T91. The
initial m icrostructure o f the m aterial is a typical tem pered m artensitic lath structure w ith
carbides at the prior austenite grain boundaries (PAGB) and lath boundaries. As reported by
Song et al. [11], sim ilar m icrostructure has been frequently observed in different T01 alloy
batches. In the optical m icroscopic image, the w hite block w as observed as sporadic of
ferritic phase. These phases contribute to a total volum e fraction o f less than 5%. The
ferrite phase is typically form ed at a very slow cooling rate. The prior austenite grain size is
about 20 fxm according to Fig. 2b. The bundles o f tem pered m artenstic laths are the dark
features in the SEM image, w hich are form ed during the tem pering process through
m erging the fine m artensites w ith a sim ilar habit plane (also called packet o f martensite).
2.2. M icrostructure E valuation o f T91 F orm ed by C W R a t D iffe ren t Temperature.
Figure 3 presents the optical m icrographs o f the T91 steel deform ed at 900 and 1040°C,
w ith a fine austenite grain structure, while those deform ed at 1100 and 1200°C have a
coarse structure, w hich appears at the tem peratures above 1100°C. The grain structure was
elongated along the longitudinal direction. A ccording to Fig. 4a and b SEM images, the
deform ed PAGBs are frequently observed, confirm ing the previous observation that the
ISSN Ü556-Î7ÎX. Проблемыг прочности, 2ÜÎ7, N° Î 73
T. He, L. Min, and H. J. Liu
Fig. 2. Tempered martensitic structure of the AR T91 steel: (a) optical microscopy of a typical
tempered martensitic lath structure; (b) SEM images of the as received T91 steel observed.
Fig. 3. Deformed microstructure at different austenitizing temperatures (OP), T91 deformed at 900
(a) and 1040oC (b) show a fine structure and coarsen structure was revealed after deformed at 1100
(c) and 12000C (d). The water-quenched materials (e) reveal large grain size of prior austenite grain
boundaries and the presence of d-ferrite at the PAGB.
74 ISSN 0556-171X. npoôxeMbi nponnocmu, 2017, № 1
Strength Improvement o f Ferritic/Martensitic T91 Steel
Fig. 4. SEM images of the deformed structure of T91 steel in the longitudinal plane. Deformed
PAGBs are observed in the 900 and 1040°C materials while no significant PAGBs are observed in
1100 and 1200°C due to the large grain size.
initial austenite grain boundaries elongated along the longitudinal direction. In contrast, due
to the large size o f the initial austenite grain, no PAGBS were found in Fig. 4c and d, and
no elongated structure was observed in the W Q T91 steel. Instead, (5-ferrite w as observed at
the PAGBs as the white block, w hich can potentially reduce the creep strength o f T91 steel
described by K obayashi et al. [12]. However, after 30 m in o f norm alization at a temperature
above 1100°C, this reduction can be eliminated.
D iscontinues PAGBs were observed in the transverse plane as shown in Fig. 5,
indicating that the PAGBs were partially decom posed during the high-tem perature
deform ation process. Additionally, according to Song et al. [11], sim ilar results have also
been observed in an equal channel angular extrusion (ECA E) processed T91 steels. They
observed that the PAGBS decom pose after up to three passes o f high-tem perature ECAE.
The grain size o f the initial austenite observed in the transverse plane is sm aller than that
observed in the longitudinal plane, indicating that during the ausform ing process, a
pronounced texture can be formed.
2.3. M echan ica l Properties o f T91 F orm ed by CW R. Figure 6 shows the m echanical
properties o f T91 form ed by CWR. Based on Fig. 6a, the average value o f hardness o f T91
at different tem peratures is as follows: 215 HV for the A R material, 419 HV for the
non-rolled parts, and 473, 478, 479, and 482 HV for each o f the rolled parts, respectively.
The rolled m aterial hardness is higher by about 15% than that o f the the unrolled one,
especially in the A R material, w hich is more than twice higher. The A R m aterial is typically
a tem pered m artensite structure, w hich is com m only softer than the non-rolled part. The
non-rolled part is a martensite structure quenched at the initial elevated temperature. The
solid solution o f carbon atoms in m artensite can cause asym m etrical distortion o f the crystal
structure, thus, impeding the mobile dislocation and significantly strengthening the materials
ISSN Ü556-171X. Проблемыг прочности, 2Ü17, № І 75
T. He, L. Min, and H. J. Liu
Fig. 5. SEM images of deformed structure of T91 steel observed in the transversal plane. The grain
size of the initial austenite grain is smaller. Discontinuous PAGBs are observed, which may indicate
the decomposition of PAGBs.
Fig. 6. (a) Hardness evolution of ausformed T91 steel at different temperatures; (b) position
depending on as-processed rod radius.
[13]. Both the packet size and block w idth o f m artensites decrease during the ausform ing
process [14]. As com pared to the size effect o f the long and thick m artensite, the thinner
and shorter m artensite can be highly strengthened.
Figure 6b exhibits that at 900°C, the average value o f hardness o f T91 decreased from
the edge to center location, the m axim um value being 486 HV, and the m inim um one being
426 HV. This is m ainly due to the decrease in deform ation from the edge to the center,
76 ISSN 0556-171X. Проблемы прочности, 2017, № 1
Strength Improvement o f Ferritic/Martensitic T9Î Steel
leading to the edge grain size being sm aller than the centers. D ifferent ausform ing results
obtained are due to the shear stress differences from the surface to the center. A smaller
packet size o f m artensite is attributed to a higher shear strength during ausforming, thus,
leading to a higher hardness. It is also observed that, in com parison to the non-rolled part,
the central part has a low er hardness and exhibits zero shear stresses.
C o n c l u s i o n s
1. The m echanical properties o f ausform ed T91 by CW R are apparently higher than
hose o f w ater-quenched T91, especially the A R one. The novel deform ation technology has
the ability to enhance the m aterial strength.
2. The T91 steel specim ens deform ed at 900 and 1040oC have a fine structure, while
those deform ed at 1100 and 1200°C have a coarse structure. The grain structure is
elongated along the longitudinal direction.
3. W ith a tem perature increase from 900 to 1200°C, the m echanical properties
deteriorate from the edge position to the center one, while the center hardness is alm ost
equal to that o f w ater-quenched T91.
A cknow ledgm ents. This study has been perfom ed w ithin fram ework o f the project
ZKL-PR-200305 entitled “T91 Shaft Formed by Cross Wedge Rolling,” E3-0507-16-0201-
16XKCZ01 entitled “Discipline Construction o f M echanical Engineering” and 16030501200
entitled “Research on Key Technologies o f U nderw ater Vehicles for D eep-sea O il and Gas
Fields.” We w ish to thank X. H. Zhang, M. Song, and L. B. Hang for discussions and
advice, w hich resulted in significant improvements. The provision o f m icroscopes at the
M icroscopy and Im aging Center at Texas A& M U niversity is also gratefully acknowledged.
1. R. W. Swindeman, M. L. Santella, P. J. M aziasz, et al., “Issues in replacing C r-M o
steels and stainless steels w ith 9 C r-1M o-V steel,” Int. J. Pres. Ves. Pip., 81, No. 6,
507-512 (2004).
2. M. J. Cohn, J. F. Henry, and D. Nass, “Fabrication, construction, and operation
problem s for grade 91 fossil pow er com ponents,” J. Press. Vess. - T. ASM E , 127,
No. 2, 197-203 (2005).
3. Z. H. Hu, X. H. Xu, and D. Y. Sha, The Principles, Process and M achines o f Helical
Rolling, and Cross Wedge R olling [in Chinese], M etallurgical Industry Press, Beijing
(1985).
4. X. P. Fu and T. A. Dean, “Past developments, current applications and trends in the
cross wedge rolling process,” Int. J. M ach. Tool. M anu., 33, No. 3, 367-400 (1993).
5. Z. Pater, “Theoretical m ethod for estim ation o f m ean pressure on contact area
betw een rolling tools and workpiece in cross wedge rolling processes,” Int. J. Mech.
Sci., 39, No. 2, 233-243 (1997).
6. M. L. N. Silva, G. H. Pires, and S. T. Button, “Damage evolution during cross wedge
rolling o f steel DIN 38M nSiVS5,” Proc. Eng., 10, 752-757 (2011).
7. M. Qakircali, C. K ilifaslan, M. Guden, et al., “Cross wedge rolling o f a Ti6Al4V
(ELI) alloy: the experim ental studies and the finite elem ent sim ulation o f the
deform ation and failure,” Int. J. Adv. M anuf. Technol., 65, 1273-1287 (2012).
8. M. T. W ang, X. T. Li, M. H. Jiang, and F. S. Du, “N um erical sim ulation and modeling
o f hot deformation microstructure evolution o f a non-quenched and tempered steel in
cross w edge rolling,” Trans. M ater. H eat Treat., 34, 168-172 (2013).
9. N. Zhang, B. Y. W ang, and J. G. Lin, “Effect o f cross wedge rolling on the
m icrostructure o fG H 4169 alloy,” Int. J. Min. Met. M ater., 19, No. 9, 836-842 (2012).
ISSN Ü556-Î7ÎX. Проблемыг прочности, 2ÜÎ7, N2 Î l l
10. T. He, B. Y. W ang, and Z. H. Hu, “Therm al m echanical coupled sim ulation o f Inconel
718 alloy cross wedge rolling,” J. Plast. Eng., 15, 157-159 (2008).
11. M. Song, R. Zhu, D. C. Foley, et al., “Enhancem ent o f strength and ductility in
ultrafine-grained T91 steel through therm om echanical treatm ents,” J. M ater. Sci., 48,
No. 21, 7360-7373 (2013).
12. S. Kobayashi, K. Sawada, T. Hara, et al., “The form ation and dissolution o f residual d
ferrite in A SM E Grade 91 steel plates,” M ater. Sci. Eng. A , 592, 241-248 (2014).
13. H. Bhadeshia and R. Honeycombe, Steels: M icrostructure and Properties, Butterworth
Heinem ann (2011).
14. G. M iyamoto, N. Iwata, N. Takayam a, and T. Furuhara, “M apping the parent
austenite orientation reconstructed from the orientation o f m artensite by EBSD and its
application to ausform ed m artensite,” Acta M ater., 58, No. 19, 6393-6403 (2010).
Received 30. 08. 2016
T. He, L. Min, and H. J. Liu
78 ISSN 0556-171X. Проблемы прочности, 2017, N2 1
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| id | nasplib_isofts_kiev_ua-123456789-173584 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0556-171X |
| language | English |
| last_indexed | 2025-12-07T16:19:22Z |
| publishDate | 2017 |
| publisher | Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| record_format | dspace |
| spelling | He, T. Min, L. Liu, H.J. 2020-12-12T13:58:31Z 2020-12-12T13:58:31Z 2017 Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures / T. He, L. Min, H.J. Liu // Проблемы прочности. — 2017. — № 1. — С. 72-78. — Бібліогр.: 14 назв. — англ. 0556-171X https://nasplib.isofts.kiev.ua/handle/123456789/173584 539.4 Cross wedge rolling (CWR) is a forming technique wherein the processed material microstructure is controlled by the processing temperature. The initial results on CWR-processed T91 steels at different austenitizing temperatures are discussed with the microstructure analysis by various characterization techniques, such as the optical and scanning electron microscopies. The processed T91 specimens were much harder than water-quenched ones, their hardness being independent of the ausforming temperatures despite their microstructural differences. This study has been perfomed within framework of the project ZKL-PR-200305 entitled “T91 Shaft Formed by Cross Wedge Rolling,” E3-0507-16-0201-16XKCZ01 entitled “Discipline Construction of Mechanical Engineering” and 16030501200 entitled “Research on Key Technologies of Underwater Vehicles for Deep-sea Oil and Gas Fields.” We wish to thank X. H. Zhang, M. Song, and L. B. Hang for discussions and advice, which resulted in significant improvements. The provision of microscopes at the Microscopy and Imaging Center at Texas A&M University is also gratefully acknowledged. Remove selected en Інститут проблем міцності ім. Г.С. Писаренко НАН України Проблемы прочности Научно-технический раздел Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures Повышение прочности феррито-мартенситной стали Т91 после прокатки при различных температурах аустенизации Article published earlier |
| spellingShingle | Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures He, T. Min, L. Liu, H.J. Научно-технический раздел |
| title | Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures |
| title_alt | Повышение прочности феррито-мартенситной стали Т91 после прокатки при различных температурах аустенизации |
| title_full | Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures |
| title_fullStr | Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures |
| title_full_unstemmed | Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures |
| title_short | Strength Improvement of Ferritic/Martensitic T91 Steel by Cross Wedge Rolling at Different Austenitizing Temperatures |
| title_sort | strength improvement of ferritic/martensitic t91 steel by cross wedge rolling at different austenitizing temperatures |
| topic | Научно-технический раздел |
| topic_facet | Научно-технический раздел |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/173584 |
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