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Strain-induced coarsening of ferrite lamella in cold drawn pearlitic steel wire
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Short communication
Strain-induced coarsening of ferrite lamella in cold drawn pearlitic steel wire Lichu Zhou a, Feng Fang a, *, Jian Zhou b, **, Zonghan Xie c, Jianqing Jiang a, d a
Jiangsu Key Laboratory of Advanced Metallic Materials, Southeast University, Nanjing, 211189, China School of Iron and Steel, Soochow University, Suzhou, 215137, China c School of Mechanical Engineering, University of Adelaide, SA, 5005, Australia d Nanjing Forestry University, Nanjing, 210037, China b
A R T I C L E I N F O
A B S T R A C T
Keywords: Pearlitic steel wire Cold drawing Ferrite lamellae coarsening Drawing strengthening Molecular dynamics
Strain-induced coarsening of ferrite lamellae in pearlitic steel wires during cold drawing was investigated. Experimental results demonstrated that the coarsening of ferrite lamellae was caused by strain-induced grain boundary migration. Drawing strengthening of pearlitic wire was greatly affected by the coarsening process. It is also confirmed by molecular dynamics simulations.
1. Introduction Metals can be strengthened by grain refinement under the so-called Hall-Petch effect [1,2]. Severe plastic deformation is an effective approach for obtaining fine grains [3–6]. However, the deformation-driven grain refinement is commonly limited by dynamic grain coarsening to several hundred nanometers [7]. The grain coars ening has been widely reported in equiaxed nanocrystalline metals comprising equiaxed grains [3,8–10] and been ascribed to grain rotation and coalescence [8–11]. Grain rotation is made possible via grain boundary sliding and causes grains to coalesce when their crystal ori entations become similar. As a result, the original grain boundaries disappear, leaving some defects stored in the grains. This mechanism has also been validated by molecular dynamics (MD) simulations [12–15]. Introducing nano-laminated microstructure into metals is viewed as a solution to further refine grains (in the sense of layer-shaped grains with their thickness much smaller than several hundred nanometers) [4, 16–18]. For example, such lamellar structure with an inter-lamellar spacing <80 nm can form through the pearlite phase transformation in high carbon steels [19,20]. The spacing can be further reduced via heavily deformation, i.e. cold drawing and cold rolling [19,21,22]. Atom probe tomography (APT) and transmission electron microscope (TEM) results reveal that the microstructural integrity of alternating lamellae of ferrite and cementite is essential for pearlite to maintain
nano-lamellar structure in heavily drawn pearlitic steel wires [22–25]. As the cementite plates start to decompose at large drawing strain, lamella thickness of ferrite tends to cease decreasing [4,20]. This sug gests that the coarsening of ferrite nano-lamellae might occur in the absence of cementite barriers. It is noticeable that, owing to structural constraints [4], it is difficult for ferrite lamellae to rotate and coalesce, i. e. the coarsening mechanism in terms of equiaxed nanocrystalline ma terials can hardly apply to the nano-lamellae case. Now, the problems are here: 1st. How strain-induced coarsening of nano-lamellae occur. 2nd. How the coarsening affects the drawing strengthening behavior of the high carbon steel wire. In order to elucidate the deformation-driven coarsening of ferrite nano-lamellae upon drawing, and its effect on the drawing strength ening of the high carbon steel wire. Designed annealing treatment and post-annealing cold drawing were carried out on pearlitic steel wire. Supported by mechanical properties test, high-resolution TEM obser vations and MD simulations, a deep understanding was gained in terms of the strain-induced coarsening behavior of the ferrite nano-lamellae and its effect on the drawing strengthening performance. 2. Experimental method Starting material used in this study are cold drawn pearlitic steel wires in diameter of ~5.25 mm. The pearlitic steel wires were drawn
* Corresponding author. School of materials science and engineering, Southeast University, Nanjing, 211189, China. ** Corresponding author. School of Iron and Steel, Soochow University, Suzhou, 215137, China. E-mail addresses: [email protected] (F. Fang), [email protected] (J. Zhou). https://doi.org/10.1016/j.msea.2019.138602 Received 15 July 2019; Received in revised form 24 October 2019; Accepted 26 October 2019 Available online 30 October 2019 0921-5093/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Lichu Zhou, Materials Science & Engineering A, https://doi.org/10.1016/j.msea.2019.138602
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from high carbon steel rods (Fe-0.84C-0.25Mn-0.40Si-0.01S þ P in wt. %) in a diameter of 13.5 mm, yielding an equivalent strain ε ¼ 1.88. The wires were next annealed at 723 K for 1.2 ks, called annealed wire. Then the annealed wire was cold drawn to 2.34 mm (corresponding to an accumulative strain of ε ¼ 3.49) by multiple drawing. In order to prevent thermally activated recovery or grain boundary migration occurring, the temperature during all the cold drawing processes in this study was controlled and kept under 373 K by water cooling. The drawing speed and compression angle of the drawing die of all the passes was set to be 0.1 m/s and about 8 � , respectively. The strain rate was computed and found to be a max of 11.5 s-1. Tensile tests were performed at room temperature using CMT5105 universal materials tester machine, oper ating at a speed of 4 mm/min. Three identical samples were tested under each condition. TEM samples were prepared by GATAN 691 Precision Ion Polishing System after the samples were mechanically thinned to be less than 40 μm. The microstructure of the wires was examined by FEI T20-G2 and JEOL 2100F TEM at an accelerating voltage of 200 kV.
comprises alternating ferrite nano-lamellae and isolated cementite nanoparticles. Moreover, these cementite nanoparticles locate at boundaries between ferrite lamellae, and the boundaries are quite straight (Insert in Fig. 1b). In this study, the 723 K-annealing was designed to cause the cementite spheroidization; meanwhile, not cause the coarsening of ferrite nano-lamellae. As presented in Fig. 1c, the distribution of ferrite lamellae thicknesses of the cold drawn wire and annealed wire are quite similar. It indicates that the ferrite nanolamellae did not undergo thermal-activated coarsening during the annealing. Representative tensile stress-strain curves of the two wires are shown in Fig. 1d. The tensile strength of the cold drawn wire is near 1900 MPa, and the ductility of the wire was relatively low, about 2.5% at maximum tensile stress. After the 723K-annealing, the tensile strength of the wire decreases slightly to 1820 MPa and ductility increases to about 7 % at maximum tensile stress. The annealing softening in heavily drawn pearlitic steel wire is generally considered to be attributed to dislocation recovery, cementite spheroidization [26] and redistribution of residual stress [27,28]. During cold drawing deformation, the ferrite lamellae in pearlitic steel wire, which is equivalent to grain size, would refine linearly as the reduction in the wire’s diameter, thus the strength of the wire increases quickly [20,22,24,29]. For instance, as presented in Fig. 2a, the tensile strength of the cold drawn pearlitic wire increases from 1880 MPa at ε ¼ 1.88 to about 3100 MPa at ε ¼ 3.49, which exhibits an average work hardening rate of 757 MPa during the cold drawing. However, the
3. Result and discussion Fig. 1 presents the microstructure and mechanical properties of the starting materials used in this study. The cold drawn wire corresponding to ε ¼ 1.88 exhibits a typical pearlite lamellar microstructure, consisting of wider ferrite nano-lamellae and thinner cementite plates (Fig. 1a). The microstructure of the annealed wire is presented in Fig. 1b. It
Fig. 1. Microstructures and tensile performances of different pearlitic steel wires. (a) The cold drawn wire strained to ε ¼ 1.88. (b) The cold drawn wire strained to ε ¼ 1.88 and then subjected to annealing at 723 K for 20 min, called annealed wire. (c) Distribution of ferrite lamellae thickness in the two wires. (d) Representative engineering tensile stress-strain curve for the two wires. 2
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annealed wire exhibits quite weak drawing strengthening performance the average tensile increases from 1820 MPa at ε ¼ 1.88 to about 2100 MPa at ε ¼ 3.49. The average work hardening rate of the annealed wire is about 177MPa, which is a quarter of that of the cold drawn one. Fig. 2 c-e present microstructure of the annealed wires drawn to ε ¼ 2.20, 2.63 and 3.49, respectively. The ferrite lamellae with uniform thickness in the annealed wire weren’t refined after the post-annealing drawing deformation. On the contrary, the lamellae have transformed into some distorted lamellae with nonuniform thickness, which dis tributes a wide range from about 30 nm to 150 nm. The average thick ness of ferrite lamellae in annealed wires drawn to different ε is measured and plotted in Fig. 2f. Unusually, the average thickness of ferrite lamellae in the annealed wire increased from slightly less than
50 nm (ε ¼ 1.88) to near 80 nm (ε ¼ 2.20). The increase in average thickness indicates that many ferrite nano-lamellae have coarsened after the cold drawing deformation, namely strain-induced coarsening of nano-lamellae occurred. Notably, from ε ¼ 2.4 to ε ¼ 3.5, the average thickness of ferrite lamellae remains around 70 nm. It indicated that a dynamic balance between grain coarsening and grain refinement had been achieved during the cold drawing process. Since there is no grain refinement of the annealed wire after cold drawing, the drawing strengthening can be considered to be mainly caused by dislocation density increase [30]. Moreover, the dislocation density increase also leads to a significant decrease in ductility of the wires. The ductility of the annealed wire greatly decreases after cold drawing. The annealed wires corresponding to ε ¼ 2.20, 2.63 and 3.49 possess similar ductility,
Fig. 2. (a) Tensile strength evolution of the annealed wire, (b) Representative engineering tensile stress-strain curves for annealed wires corresponding to different strains, Microstructures of annealed pearlitic steel wires cold drawn to different drawing strains: (c) ε ¼ 2.20, (d) ε ¼ 2.63, (e) ε ¼ 3.49. (f) Average lamella thickness of ferrite in pearlitic wires versus drawing strains. 3
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no higher than 3% at maximum tensile stress (Fig. 2b). It indicates that the ductility of the heavily drawn high-carbon steel wire is more determined by the dislocation density than the cementite geometry [26, 31–33]. Typical coarsening ferrite lamellae in annealed wire subject postannealing drawing is presented as TEM micrographs in Fig. 3. The bright-field and dark-field TEM micrographs were obtained from annealed wire drawn to ε ¼ 2.63 and taken at the same location. It can be observed that part ferrite lamellae have transformed into irregular shapes with large boundary spacing. The distribution of ferrite lamellae thickness in Fig. 3c indicates that many ferrite nano-lamellae have coarsened after the post-annealing cold drawing. The ferrite lamellae thickness of the annealed wire changes from 30 to 70 nm (ε ¼ 1.88 & after annealing) to 30–140 nm (drawn to ε ¼ 2.63). Locations of cementite particles are marked with arrows in Fig. 3b. The cementite particles, which was supposed to be located on the boundary between ferrite nano-lamellae, have been wrapped inside the ferrite. Whereas cementite particles were not considered to be the carrier for plastic deformation, the boundaries between ferrite nano-lamellae were sup posed to migrate during the cold drawing deformation. Thus, the lamellae coarsening should be attributed to the strain-induced boundary migration. It is well-known that grain boundary (GB) migration is able to be driven by shear stress/strain at room temperature for nanocrystalline materials when contribution of dislocation activities to overall plasticity
becomes less important than the case in coarse-grained materials [34]. Owing to lamellar geometries [4], coarsening mechanism of the ferrite nano-lamellae is expected to be irrelevant to grain rotation. Our TEM results, combined with the statistical result of ferrite lamellae thickness, suggested that coarsening of ferrite nano-lamellae found in this study is caused by strain-induced grain boundary migration [8,34,35]. MD simulations with regard to fcc metals [12,15,35] indicated that the GB migration along a GB normal is coupled to grain translation along a direction parallel to the GB, i.e. the coupling phenomenon. The extent of coupling has been well predicted via a geometric model [35]. To understand the behavior of the boundary between ferrite nanolamellae during the plastic deformation, molecular dynamics simula tions whose geometry is based on our HRTEM results were carried out. Fig. 4a presents a TEM micrograph obtained from the annealed wire strained to 2.37. A bowed boundary between two ferrite nano-lamellae, which was about to migrate, is marked in figure. A high-resolution TEM micrograph of the bowed boundary is presented in Fig. 4b. Both the two ferrite nano-lamellae are observed along a [001]ferrite zone axis. <110>ferrite crystal orientations are marked on the micrograph. The boundary between the two lamellae in Fig. 4b has a misorientation about 5� , which means it is a typical low-angle boundary in nanolamellar structure [29,36]. As displayed in Fig. 4e, the sample contains two equally sized bcc Fe grains of a total size of 13.9 � 37.2 � 14.3 nm3. A flat GB is located in the middle of the y scale and it is a 4.98� Σ265 [100] symmetric tilt GB. To
Fig. 3. TEM characterization of annealed wires cold drawn to ε ¼ 2.63. (a) Bright-field TEM micrograph, (b) Bright-field TEM micrograph, (c) Distribution of ferrite lamellae thickness in the annealed wires strained to different ε showing part ferrite lamellae was coarsened by drawing process. 4
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Fig. 4. TEM micrographs and MD simulation basing on the micrograph. (a) TEM micrographs showing a bowed boundary between ferrite lamellae in the annealed wire at ε ¼ 2.37, (b) HRTEM micrographs of the boundary region in (a), (c) Fast Fourier transform image of the upper lamellae in (b), (d) Fast Fourier transform image of the lower lamellae in (b). MD simulation results showing configurations, (e) after relaxation and (f) sheared at 1.2 ns for a 4.98� Σ265 [100] tilt GB. The direction of the simple shear and the GB position are indicated. (g) GB position as a function of shearing time. In (e) and (f), the atoms are colored based on their local environments: blue and grey for bcc and disorder respectively (see online article for color version of this figure). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
minimize system energy and obtain an equilibrium configuration, the sample underwent static relaxation and 50 ps relaxation at 300 K. After that, the sample was sheared at 300 K along the x direction via setting a slab at uppermost y to be 1 m/s and a slab at lowermost y to be 0 m/s (for more details of the sample building as well as shearing, one can refer to Refs. [35,37]). According to Fig. 4e and f, it is clearly seen that the GB maintains a dislocation structure (clusters of disorder atoms correspond to disloca tion core regions) throughout the simulation. This structure is typical for low angle GBs. During the shearing, the GB migrates downwards, and the upper grain grows at the expense of the lower one. The GB position is plotted as a function of time in Fig. 4g. Initial motionless positions are attributed to elastic response of the sample to the shearing. From 0.6 to 1.0 ns, the GB starts to move rapidly, leaving behind some defects (e.g. vacancies) in the growing grain. After that, steady state migration without generating defects occurs until 1.6 ns at which moment the GB approaches the lower slab of fixed atoms. The velocity of the GB migration at the steady stage is measured to be 11.0�1.4 m/s, yielding a coupling factor (defined as the velocity of grain translation divided by the one of GB migration) equal to 0.092�0.012, which is in good agreement the theoretical value of 0.087 predicted by the geometric model [35]. Thus, our simulation results demonstrate that ferrite nano-lamellae of low-angle misorientation can grow thick via the shear-induced GB migration. It is noted that the simple shear used in the MD simulations differs from the drawing deformation in the practical case, which is too complicated to be realized in MD. The MD results, therefore, can only partly explain the ferrite lamellae coarsening.
Remarkably, a large quantity of dislocations is also observed inside the ferrite lamellae as presented in Fig. 3a. It indicates that the dislocation activities still predominated while the boundary migration occurred. The grain boundary can play a role as a source for dislocation emission. On the other hand, ferrite in pearlitic steel wire possesses a high density of dislocation, even subjected to post-drawing annealing [25,27]. Accumulation of dislocation slipping at the boundary may also increase or decrease the misorientation between neighbor ferrite nano-lamellae. The role of dislocation activities played during the boundary migration deserves further attention. The most severe consequence caused by strain-induced coarsening is the decrease in the work hardening rate, which extends and disturbs the process for preparing high-strength metal materials by plastic defor mation [5]. Li etc. have reported that the drawing strengthening rate of pearlitic steel wire decreased near to 50% from the highest value when drawing strain ε > 4.5 [20,38]. The decrease was presumed to be related to cementite dissolution [24,39,40]. Strain-induced cementite decom position occurred and the part of cementite, which acts as a continuous barrier to boundary migration before, disappeared. Thus, the drawing strengthening rate decreased obviously as a result of strain-induced coarsening. Tomota and Tashiro have also reported that the drawing strengthening of a low-carbon steel wire [41]. The low-carbon steel wire exhibited a relatively small and stable drawing strengthening rate. The wire could be strengthened to about 3GPa with special and skillful method when drawing strain ε is almost up to 11 and equivalent to an area reduction of 99.998%. The strain-induced coarsening also means the nano-lamellar 5
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structure, which could be obtained by specific plastic deformation [17, 18], tend to exhibit structural instability when subjected general plastic strain. Taking additional account of stress and strain state of the nano-lamellar structure or enhancing the lamellar boundaries before service is necessary. Decorating boundary by heterogeneous element or introducing a hetero-phase into the boundary, which is called boundary complexion have been proposed to inhibit grain boundary migration [42,43]. Specific boundary complexion is also beneficial to both strength and toughness of nanocrystalline [44]. Enhancing the bound aries prevent deterioration in performance and low strain hardening response during service.
[11] M. Jin, A.M. Minor, E.A. Stach, J.W.M. Jr, Direct observation of deformationinduced grain growth during the nanoindentation of ultrafine-grained Al at room temperature, Acta Mater. 52 (18) (2004) 5381–5387. [12] A.J. Haslam, D. Moldovan, V. Yamakov, D. Wolf, S.R. Phillpot, H. Gleiter, Stressenhanced grain growth in a nanocrystalline material by molecular-dynamics simulation, Acta Mater. 51 (7) (2003) 2097–2112. [13] J. Monk, D. Farkas, Strain-induced grain growth and rotation in nickel nanowires, Phys. Rev. B Condens. Matter 75 (4) (2007). [14] J. Schiøtz, Strain-induced coarsening in nanocrystalline metals under cyclic deformation, Mater. Sci. Eng. 375-377 (1) (2004) 975–979. [15] F. Sansoz, V. Dupont, Grain growth behavior at absolute zero during nanocrystalline metal indentation, Appl. Phys. Lett. 89 (11) (2006), 561-Z06. [16] X.C. Liu, H.W. Zhang, K. Lu, Strain-induced ultrahard and ultrastable nanolaminated structure in nickel, Science 342 (6156) (2013) 337–340. [17] X. Liu, H. Zhang, K. Lu, Formation of nano-laminated structure in nickel by means of surface mechanical grinding treatment, Acta Mater. 96 (2015) 24–36. [18] X.C. Liu, H.W. Zhang, K. Lu, Formation of nanolaminated structure in an interstitial-free steel, Scr. Mater. 95 (1) (2015) 54–57. [19] J. Embury, R. Fisher, The structure and properties of drawn pearlite, Acta Metall. 14 (2) (1966) 147–159. [20] Y. Li, D. Raabe, M. Herbig, P.-P. Choi, S. Goto, A. Kostka, H. Yarita, C. Borchers, R. Kirchheim, Segregation stabilizes nanocrystalline bulk steel with near theoretical strength, Phys. Rev. Lett. 113 (10) (2014) 106104. [21] G. Langford, Deformation of pearlite, Metall. Mater. Trans. A 8 (6) (1977) 861–875. [22] X. Zhang, A. Godfrey, X. Huang, N. Hansen, Q. Liu, Microstructure and strengthening mechanisms in cold-drawn pearlitic steel wire, Acta Mater. 59 (9) (2011) 3422–3430. [23] Y. Ivanisenko, W. Lojkowski, R. Valiev, H.-J. Fecht, The mechanism of formation of nanostructure and dissolution of cementite in a pearlitic steel during high pressure torsion, Acta Mater. 51 (18) (2003) 5555–5570. [24] Y. Li, P. Choi, C. Borchers, S. Westerkamp, S. Goto, D. Raabe, R. Kirchheim, Atomic-scale mechanisms of deformation-induced cementite decomposition in pearlite, Acta Mater. 59 (10) (2011) 3965–3977. [25] X. Zhang, N. Hansen, A. Godfrey, X. Huang, Dislocation-based plasticity and strengthening mechanisms in sub-20 nm lamellar structures in pearlitic steel wire, Acta Mater. 114 (2016) 176–183. [26] L. Xiang, L. Liang, Y. Wang, Y. Chen, H. Wang, L. Dai, One-step annealing optimizes strength-ductility tradeoff in pearlitic steel wires, Mater. Sci. Eng. 757 (2019) 1–13. [27] Y. Chen, G. Csisz� ar, J. Cizek, X. Shi, C. Borchers, Y. Li, F. Liu, R. Kirchheim, Defect recovery in severely deformed ferrite lamellae during annealing and its impact on the softening of cold-drawn pearlitic steel wires, Metall. Mater. Trans. A 47 (2) (2016) 726–738. [28] M. Elices, Influence of residual stresses in the performance of cold-drawn pearlitic wires, J. Mater. Sci. 39 (12) (2004) 3889–3899. [29] X. Zhang, A. Godfrey, N. Hansen, X. Huang, Hierarchical structures in cold-drawn pearlitic steel wire, Acta Mater. 61 (13) (2013) 4898–4909. [30] X. Zhang, N. Hansen, A. Godfrey, X. Huang, Dislocation-based plasticity and strengthening mechanisms in sub-20nm lamellar structures in pearlitic steel wire, Acta Mater. 114 (2016) 176–183. [31] L. Zhou, L. Wang, H. Chen, Z. Xie, F. Fang, Effects of chromium additions upon microstructure and mechanical properties of cold drawn pearlitic steel wires, J. Mater. Eng. Perform. 27 (2) (2018) 1–10. [32] Y. Tu, X. Wang, H. Huang, X. Zhou, J. Jiang, Effect of Si on the aging behavior of cold-drawn pearlitic steel wires, Metall. Mater. Trans. A 48 (2) (2017) 659–665. [33] J. Languillaume, G. Kapelski, B. Baudelet, Evolution of the tensile strength in heavily cold drawn and annealed pearlitic steel wires, Mater. Lett. 33 (3) (1997) 241–245. [34] S. Zhiwei, E.A. Stach, J.M.K. Wiezorek, J.A. Knapp, D.M. Follstaedt, S.X. Mao, Grain boundary-mediated plasticity in nanocrystalline nickel, Science 305 (5684) (2004) 654–657. [35] J.W. Cahn, Y. Mishin, A. Suzuki, Coupling grain boundary motion to shear deformation, Acta Mater. 54 (19) (2006) 4953–4975. [36] T. Furuhara, T. Mizoguchi, T. Maki, Ultra-fine (αþ θ) duplex structure formed by cold rolling and annealing of pearlite, ISIJ Int. 45 (3) (2005) 392–398. [37] A. Suzuki, Y.M. Mishin, Atomic mechanisms of grain boundary motion, Mater. Sci. Forum 502 (2005) 157–162. [38] C. Borchers, R. Kirchheim, Cold-drawn pearlitic steel wires, Prog. Mater. Sci. 82 (2016) 405–444. [39] Y. Li, P. Choi, S. Goto, C. Borchers, D. Raabe, R. Kirchheim, Evolution of strength and microstructure during annealing of heavily cold-drawn 6.3 GPa hypereutectoid pearlitic steel wire, Acta Mater. 60 (9) (2012) 4005–4016. [40] J. Languillaume, G. Kapelski, B. Baudelet, Cementite dissolution in heavily cold drawn pearlitic steel wires, Acta Mater. 45 (3) (1997) 1201–1212. [41] Y. Tomota, T. Suzuki, A. Kanie, Y. Shiota, M. Uno, A. Moriai, N. Minakawa, Y. Morii, In situ neutron diffraction of heavily drawn steel wires with ultra-high strength under tensile loading, Acta Mater. 53 (2) (2005) 463–467.
4. Conclusion Nano-lamellae ferrite without continuous cementite segregation would coarse when subjected to cold drawing deformation. The ferrite nano-lamellae with an average thickness of 50 nm would coarse to an average thickness of 70 nm. TEM analyses and MD simulation reveal ferrite lamellae can grow thick via the shear-induced GB migration. As a result of strain-induced coarsening, the drawing strengthening perfor mance of the high carbon steel wire decrease to the quarter of typical pearlitic steel wire. Data availability statement All data included in this study are available upon request by contact with the corresponding authors. Declaration of competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was supported by the Natural Science Foundation of China (51874204), Science and Technology Advancement Program of Jiangsu Province, China (BA2017112) and the 333 projects of Jiangsu Province, China (BRA2018045). The study was also partly supported by IndustryUniversity Research Cooperation Project of Jiangsu Province, China (BY2018194). Z Xie acknowledges the support of the Australian Research Council Discovery Projects. References [1] E. Hall, The deformation and ageing of mild steel: III discussion of results, Proc. Phys. Soc. Sect. B 64 (9) (1951) 747. [2] N. Petch, The cleavage strengh of polycrystals, J. of the Iron and Steel Inst. 174 (1953) 25–28. [3] R. Pippan, F. Wetscher, M. Hafok, A. Vorhauer, I. Sabirov, The limits of refinement by severe plastic deformation, Adv. Eng. Mater. 8 (11) (2010) 1046–1056. [4] D. Raabe, P.-P. Choi, Y. Li, A. Kostka, X. Sauvage, F. Lecouturier, K. Hono, R. Kirchheim, R. Pippan, D. Embury, Metallic composites processed via extreme deformation: toward the limits of strength in bulk materials, MRS Bull. 35 (12) (2010) 982–991. [5] R.Z. Valiev, R.K. Islamgaliev, I.V. Alexandrov, Bulk nanostructured materials from severe plastic deformation, Prog. Mater. Sci. 45 (2) (2000) 103–189. [6] Y. Estrina, Extreme grain refinement by severe plastic deformation: a wealth of challenging science, Acta Mater. 61 (3) (2013) 782–817. [7] R. Pippan, S. Scheriau, A. Taylor, M. Hafok, A. Hohenwarter, A. Bachmaier, Saturation of fragmentation during severe plastic deformation, Annu. Rev. Mater. Res. 40 (1) (2010) 319–343. [8] T.J. Rupert, D.S. Gianola, Y. Gan, K.J. Hemker, Experimental observations of stressdriven grain boundary migration, Science 326 (5960) (2009) 1686–1690. [9] Y.B. Wang, J.C. Ho, X.Z. Liao, H.Q. Li, S.P. Ringer, Y.T. Zhu, Mechanism of grain growth during severe plastic deformation of a nanocrystalline Ni–Fe alloy, Appl. Phys. Lett. 94 (1) (2009) 103. [10] Y.B. Wang, B.Q. Li, M.L. Sui, S.X. Mao, Deformation-induced grain rotation and growth in nanocrystalline Ni, Appl. Phys. Lett. 92 (1) (2008) 66.
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L. Zhou et al.
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[42] N. Zhou, T. Hu, J. Luo, Grain boundary complexions in multicomponent alloys: challenges and opportunities, Curr. Opin. Solid State Mater. Sci. 20 (5) (2016) 268–277. [43] J. Hu, Y. Shi, X. Sauvage, G. Sha, K. Lu, Grain boundary stability governs hardening and softening in extremely fine nanograined metals, Science 355 (6331) (2017) 1292–1296.
[44] A. Khalajhedayati, Z. Pan, T.J. Rupert, Manipulating the interfacial structure of nanomaterials to achieve a unique combination of strength and ductility, Nat. Commun. 7 (2016).
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Short communication
Strain-induced coarsening of ferrite lamella in cold drawn pearlitic steel wire Lichu Zhou a, Feng Fang a, *, Jian Zhou b, **, Zonghan Xie c, Jianqing Jiang a, d a
Jiangsu Key Laboratory of Advanced Metallic Materials, Southeast University, Nanjing, 211189, China School of Iron and Steel, Soochow University, Suzhou, 215137, China c School of Mechanical Engineering, University of Adelaide, SA, 5005, Australia d Nanjing Forestry University, Nanjing, 210037, China b
A R T I C L E I N F O
A B S T R A C T
Keywords: Pearlitic steel wire Cold drawing Ferrite lamellae coarsening Drawing strengthening Molecular dynamics
Strain-induced coarsening of ferrite lamellae in pearlitic steel wires during cold drawing was investigated. Experimental results demonstrated that the coarsening of ferrite lamellae was caused by strain-induced grain boundary migration. Drawing strengthening of pearlitic wire was greatly affected by the coarsening process. It is also confirmed by molecular dynamics simulations.
1. Introduction Metals can be strengthened by grain refinement under the so-called Hall-Petch effect [1,2]. Severe plastic deformation is an effective approach for obtaining fine grains [3–6]. However, the deformation-driven grain refinement is commonly limited by dynamic grain coarsening to several hundred nanometers [7]. The grain coars ening has been widely reported in equiaxed nanocrystalline metals comprising equiaxed grains [3,8–10] and been ascribed to grain rotation and coalescence [8–11]. Grain rotation is made possible via grain boundary sliding and causes grains to coalesce when their crystal ori entations become similar. As a result, the original grain boundaries disappear, leaving some defects stored in the grains. This mechanism has also been validated by molecular dynamics (MD) simulations [12–15]. Introducing nano-laminated microstructure into metals is viewed as a solution to further refine grains (in the sense of layer-shaped grains with their thickness much smaller than several hundred nanometers) [4, 16–18]. For example, such lamellar structure with an inter-lamellar spacing <80 nm can form through the pearlite phase transformation in high carbon steels [19,20]. The spacing can be further reduced via heavily deformation, i.e. cold drawing and cold rolling [19,21,22]. Atom probe tomography (APT) and transmission electron microscope (TEM) results reveal that the microstructural integrity of alternating lamellae of ferrite and cementite is essential for pearlite to maintain
nano-lamellar structure in heavily drawn pearlitic steel wires [22–25]. As the cementite plates start to decompose at large drawing strain, lamella thickness of ferrite tends to cease decreasing [4,20]. This sug gests that the coarsening of ferrite nano-lamellae might occur in the absence of cementite barriers. It is noticeable that, owing to structural constraints [4], it is difficult for ferrite lamellae to rotate and coalesce, i. e. the coarsening mechanism in terms of equiaxed nanocrystalline ma terials can hardly apply to the nano-lamellae case. Now, the problems are here: 1st. How strain-induced coarsening of nano-lamellae occur. 2nd. How the coarsening affects the drawing strengthening behavior of the high carbon steel wire. In order to elucidate the deformation-driven coarsening of ferrite nano-lamellae upon drawing, and its effect on the drawing strength ening of the high carbon steel wire. Designed annealing treatment and post-annealing cold drawing were carried out on pearlitic steel wire. Supported by mechanical properties test, high-resolution TEM obser vations and MD simulations, a deep understanding was gained in terms of the strain-induced coarsening behavior of the ferrite nano-lamellae and its effect on the drawing strengthening performance. 2. Experimental method Starting material used in this study are cold drawn pearlitic steel wires in diameter of ~5.25 mm. The pearlitic steel wires were drawn
* Corresponding author. School of materials science and engineering, Southeast University, Nanjing, 211189, China. ** Corresponding author. School of Iron and Steel, Soochow University, Suzhou, 215137, China. E-mail addresses: [email protected] (F. Fang), [email protected] (J. Zhou). https://doi.org/10.1016/j.msea.2019.138602 Received 15 July 2019; Received in revised form 24 October 2019; Accepted 26 October 2019 Available online 30 October 2019 0921-5093/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Lichu Zhou, Materials Science & Engineering A, https://doi.org/10.1016/j.msea.2019.138602
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from high carbon steel rods (Fe-0.84C-0.25Mn-0.40Si-0.01S þ P in wt. %) in a diameter of 13.5 mm, yielding an equivalent strain ε ¼ 1.88. The wires were next annealed at 723 K for 1.2 ks, called annealed wire. Then the annealed wire was cold drawn to 2.34 mm (corresponding to an accumulative strain of ε ¼ 3.49) by multiple drawing. In order to prevent thermally activated recovery or grain boundary migration occurring, the temperature during all the cold drawing processes in this study was controlled and kept under 373 K by water cooling. The drawing speed and compression angle of the drawing die of all the passes was set to be 0.1 m/s and about 8 � , respectively. The strain rate was computed and found to be a max of 11.5 s-1. Tensile tests were performed at room temperature using CMT5105 universal materials tester machine, oper ating at a speed of 4 mm/min. Three identical samples were tested under each condition. TEM samples were prepared by GATAN 691 Precision Ion Polishing System after the samples were mechanically thinned to be less than 40 μm. The microstructure of the wires was examined by FEI T20-G2 and JEOL 2100F TEM at an accelerating voltage of 200 kV.
comprises alternating ferrite nano-lamellae and isolated cementite nanoparticles. Moreover, these cementite nanoparticles locate at boundaries between ferrite lamellae, and the boundaries are quite straight (Insert in Fig. 1b). In this study, the 723 K-annealing was designed to cause the cementite spheroidization; meanwhile, not cause the coarsening of ferrite nano-lamellae. As presented in Fig. 1c, the distribution of ferrite lamellae thicknesses of the cold drawn wire and annealed wire are quite similar. It indicates that the ferrite nanolamellae did not undergo thermal-activated coarsening during the annealing. Representative tensile stress-strain curves of the two wires are shown in Fig. 1d. The tensile strength of the cold drawn wire is near 1900 MPa, and the ductility of the wire was relatively low, about 2.5% at maximum tensile stress. After the 723K-annealing, the tensile strength of the wire decreases slightly to 1820 MPa and ductility increases to about 7 % at maximum tensile stress. The annealing softening in heavily drawn pearlitic steel wire is generally considered to be attributed to dislocation recovery, cementite spheroidization [26] and redistribution of residual stress [27,28]. During cold drawing deformation, the ferrite lamellae in pearlitic steel wire, which is equivalent to grain size, would refine linearly as the reduction in the wire’s diameter, thus the strength of the wire increases quickly [20,22,24,29]. For instance, as presented in Fig. 2a, the tensile strength of the cold drawn pearlitic wire increases from 1880 MPa at ε ¼ 1.88 to about 3100 MPa at ε ¼ 3.49, which exhibits an average work hardening rate of 757 MPa during the cold drawing. However, the
3. Result and discussion Fig. 1 presents the microstructure and mechanical properties of the starting materials used in this study. The cold drawn wire corresponding to ε ¼ 1.88 exhibits a typical pearlite lamellar microstructure, consisting of wider ferrite nano-lamellae and thinner cementite plates (Fig. 1a). The microstructure of the annealed wire is presented in Fig. 1b. It
Fig. 1. Microstructures and tensile performances of different pearlitic steel wires. (a) The cold drawn wire strained to ε ¼ 1.88. (b) The cold drawn wire strained to ε ¼ 1.88 and then subjected to annealing at 723 K for 20 min, called annealed wire. (c) Distribution of ferrite lamellae thickness in the two wires. (d) Representative engineering tensile stress-strain curve for the two wires. 2
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annealed wire exhibits quite weak drawing strengthening performance the average tensile increases from 1820 MPa at ε ¼ 1.88 to about 2100 MPa at ε ¼ 3.49. The average work hardening rate of the annealed wire is about 177MPa, which is a quarter of that of the cold drawn one. Fig. 2 c-e present microstructure of the annealed wires drawn to ε ¼ 2.20, 2.63 and 3.49, respectively. The ferrite lamellae with uniform thickness in the annealed wire weren’t refined after the post-annealing drawing deformation. On the contrary, the lamellae have transformed into some distorted lamellae with nonuniform thickness, which dis tributes a wide range from about 30 nm to 150 nm. The average thick ness of ferrite lamellae in annealed wires drawn to different ε is measured and plotted in Fig. 2f. Unusually, the average thickness of ferrite lamellae in the annealed wire increased from slightly less than
50 nm (ε ¼ 1.88) to near 80 nm (ε ¼ 2.20). The increase in average thickness indicates that many ferrite nano-lamellae have coarsened after the cold drawing deformation, namely strain-induced coarsening of nano-lamellae occurred. Notably, from ε ¼ 2.4 to ε ¼ 3.5, the average thickness of ferrite lamellae remains around 70 nm. It indicated that a dynamic balance between grain coarsening and grain refinement had been achieved during the cold drawing process. Since there is no grain refinement of the annealed wire after cold drawing, the drawing strengthening can be considered to be mainly caused by dislocation density increase [30]. Moreover, the dislocation density increase also leads to a significant decrease in ductility of the wires. The ductility of the annealed wire greatly decreases after cold drawing. The annealed wires corresponding to ε ¼ 2.20, 2.63 and 3.49 possess similar ductility,
Fig. 2. (a) Tensile strength evolution of the annealed wire, (b) Representative engineering tensile stress-strain curves for annealed wires corresponding to different strains, Microstructures of annealed pearlitic steel wires cold drawn to different drawing strains: (c) ε ¼ 2.20, (d) ε ¼ 2.63, (e) ε ¼ 3.49. (f) Average lamella thickness of ferrite in pearlitic wires versus drawing strains. 3
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no higher than 3% at maximum tensile stress (Fig. 2b). It indicates that the ductility of the heavily drawn high-carbon steel wire is more determined by the dislocation density than the cementite geometry [26, 31–33]. Typical coarsening ferrite lamellae in annealed wire subject postannealing drawing is presented as TEM micrographs in Fig. 3. The bright-field and dark-field TEM micrographs were obtained from annealed wire drawn to ε ¼ 2.63 and taken at the same location. It can be observed that part ferrite lamellae have transformed into irregular shapes with large boundary spacing. The distribution of ferrite lamellae thickness in Fig. 3c indicates that many ferrite nano-lamellae have coarsened after the post-annealing cold drawing. The ferrite lamellae thickness of the annealed wire changes from 30 to 70 nm (ε ¼ 1.88 & after annealing) to 30–140 nm (drawn to ε ¼ 2.63). Locations of cementite particles are marked with arrows in Fig. 3b. The cementite particles, which was supposed to be located on the boundary between ferrite nano-lamellae, have been wrapped inside the ferrite. Whereas cementite particles were not considered to be the carrier for plastic deformation, the boundaries between ferrite nano-lamellae were sup posed to migrate during the cold drawing deformation. Thus, the lamellae coarsening should be attributed to the strain-induced boundary migration. It is well-known that grain boundary (GB) migration is able to be driven by shear stress/strain at room temperature for nanocrystalline materials when contribution of dislocation activities to overall plasticity
becomes less important than the case in coarse-grained materials [34]. Owing to lamellar geometries [4], coarsening mechanism of the ferrite nano-lamellae is expected to be irrelevant to grain rotation. Our TEM results, combined with the statistical result of ferrite lamellae thickness, suggested that coarsening of ferrite nano-lamellae found in this study is caused by strain-induced grain boundary migration [8,34,35]. MD simulations with regard to fcc metals [12,15,35] indicated that the GB migration along a GB normal is coupled to grain translation along a direction parallel to the GB, i.e. the coupling phenomenon. The extent of coupling has been well predicted via a geometric model [35]. To understand the behavior of the boundary between ferrite nanolamellae during the plastic deformation, molecular dynamics simula tions whose geometry is based on our HRTEM results were carried out. Fig. 4a presents a TEM micrograph obtained from the annealed wire strained to 2.37. A bowed boundary between two ferrite nano-lamellae, which was about to migrate, is marked in figure. A high-resolution TEM micrograph of the bowed boundary is presented in Fig. 4b. Both the two ferrite nano-lamellae are observed along a [001]ferrite zone axis. <110>ferrite crystal orientations are marked on the micrograph. The boundary between the two lamellae in Fig. 4b has a misorientation about 5� , which means it is a typical low-angle boundary in nanolamellar structure [29,36]. As displayed in Fig. 4e, the sample contains two equally sized bcc Fe grains of a total size of 13.9 � 37.2 � 14.3 nm3. A flat GB is located in the middle of the y scale and it is a 4.98� Σ265 [100] symmetric tilt GB. To
Fig. 3. TEM characterization of annealed wires cold drawn to ε ¼ 2.63. (a) Bright-field TEM micrograph, (b) Bright-field TEM micrograph, (c) Distribution of ferrite lamellae thickness in the annealed wires strained to different ε showing part ferrite lamellae was coarsened by drawing process. 4
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Fig. 4. TEM micrographs and MD simulation basing on the micrograph. (a) TEM micrographs showing a bowed boundary between ferrite lamellae in the annealed wire at ε ¼ 2.37, (b) HRTEM micrographs of the boundary region in (a), (c) Fast Fourier transform image of the upper lamellae in (b), (d) Fast Fourier transform image of the lower lamellae in (b). MD simulation results showing configurations, (e) after relaxation and (f) sheared at 1.2 ns for a 4.98� Σ265 [100] tilt GB. The direction of the simple shear and the GB position are indicated. (g) GB position as a function of shearing time. In (e) and (f), the atoms are colored based on their local environments: blue and grey for bcc and disorder respectively (see online article for color version of this figure). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
minimize system energy and obtain an equilibrium configuration, the sample underwent static relaxation and 50 ps relaxation at 300 K. After that, the sample was sheared at 300 K along the x direction via setting a slab at uppermost y to be 1 m/s and a slab at lowermost y to be 0 m/s (for more details of the sample building as well as shearing, one can refer to Refs. [35,37]). According to Fig. 4e and f, it is clearly seen that the GB maintains a dislocation structure (clusters of disorder atoms correspond to disloca tion core regions) throughout the simulation. This structure is typical for low angle GBs. During the shearing, the GB migrates downwards, and the upper grain grows at the expense of the lower one. The GB position is plotted as a function of time in Fig. 4g. Initial motionless positions are attributed to elastic response of the sample to the shearing. From 0.6 to 1.0 ns, the GB starts to move rapidly, leaving behind some defects (e.g. vacancies) in the growing grain. After that, steady state migration without generating defects occurs until 1.6 ns at which moment the GB approaches the lower slab of fixed atoms. The velocity of the GB migration at the steady stage is measured to be 11.0�1.4 m/s, yielding a coupling factor (defined as the velocity of grain translation divided by the one of GB migration) equal to 0.092�0.012, which is in good agreement the theoretical value of 0.087 predicted by the geometric model [35]. Thus, our simulation results demonstrate that ferrite nano-lamellae of low-angle misorientation can grow thick via the shear-induced GB migration. It is noted that the simple shear used in the MD simulations differs from the drawing deformation in the practical case, which is too complicated to be realized in MD. The MD results, therefore, can only partly explain the ferrite lamellae coarsening.
Remarkably, a large quantity of dislocations is also observed inside the ferrite lamellae as presented in Fig. 3a. It indicates that the dislocation activities still predominated while the boundary migration occurred. The grain boundary can play a role as a source for dislocation emission. On the other hand, ferrite in pearlitic steel wire possesses a high density of dislocation, even subjected to post-drawing annealing [25,27]. Accumulation of dislocation slipping at the boundary may also increase or decrease the misorientation between neighbor ferrite nano-lamellae. The role of dislocation activities played during the boundary migration deserves further attention. The most severe consequence caused by strain-induced coarsening is the decrease in the work hardening rate, which extends and disturbs the process for preparing high-strength metal materials by plastic defor mation [5]. Li etc. have reported that the drawing strengthening rate of pearlitic steel wire decreased near to 50% from the highest value when drawing strain ε > 4.5 [20,38]. The decrease was presumed to be related to cementite dissolution [24,39,40]. Strain-induced cementite decom position occurred and the part of cementite, which acts as a continuous barrier to boundary migration before, disappeared. Thus, the drawing strengthening rate decreased obviously as a result of strain-induced coarsening. Tomota and Tashiro have also reported that the drawing strengthening of a low-carbon steel wire [41]. The low-carbon steel wire exhibited a relatively small and stable drawing strengthening rate. The wire could be strengthened to about 3GPa with special and skillful method when drawing strain ε is almost up to 11 and equivalent to an area reduction of 99.998%. The strain-induced coarsening also means the nano-lamellar 5
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structure, which could be obtained by specific plastic deformation [17, 18], tend to exhibit structural instability when subjected general plastic strain. Taking additional account of stress and strain state of the nano-lamellar structure or enhancing the lamellar boundaries before service is necessary. Decorating boundary by heterogeneous element or introducing a hetero-phase into the boundary, which is called boundary complexion have been proposed to inhibit grain boundary migration [42,43]. Specific boundary complexion is also beneficial to both strength and toughness of nanocrystalline [44]. Enhancing the bound aries prevent deterioration in performance and low strain hardening response during service.
[11] M. Jin, A.M. Minor, E.A. Stach, J.W.M. Jr, Direct observation of deformationinduced grain growth during the nanoindentation of ultrafine-grained Al at room temperature, Acta Mater. 52 (18) (2004) 5381–5387. [12] A.J. Haslam, D. Moldovan, V. Yamakov, D. Wolf, S.R. Phillpot, H. Gleiter, Stressenhanced grain growth in a nanocrystalline material by molecular-dynamics simulation, Acta Mater. 51 (7) (2003) 2097–2112. [13] J. Monk, D. Farkas, Strain-induced grain growth and rotation in nickel nanowires, Phys. Rev. B Condens. Matter 75 (4) (2007). [14] J. Schiøtz, Strain-induced coarsening in nanocrystalline metals under cyclic deformation, Mater. Sci. Eng. 375-377 (1) (2004) 975–979. [15] F. Sansoz, V. Dupont, Grain growth behavior at absolute zero during nanocrystalline metal indentation, Appl. Phys. Lett. 89 (11) (2006), 561-Z06. [16] X.C. Liu, H.W. Zhang, K. Lu, Strain-induced ultrahard and ultrastable nanolaminated structure in nickel, Science 342 (6156) (2013) 337–340. [17] X. Liu, H. Zhang, K. Lu, Formation of nano-laminated structure in nickel by means of surface mechanical grinding treatment, Acta Mater. 96 (2015) 24–36. [18] X.C. Liu, H.W. Zhang, K. Lu, Formation of nanolaminated structure in an interstitial-free steel, Scr. Mater. 95 (1) (2015) 54–57. [19] J. Embury, R. Fisher, The structure and properties of drawn pearlite, Acta Metall. 14 (2) (1966) 147–159. [20] Y. Li, D. Raabe, M. Herbig, P.-P. Choi, S. Goto, A. Kostka, H. Yarita, C. Borchers, R. Kirchheim, Segregation stabilizes nanocrystalline bulk steel with near theoretical strength, Phys. Rev. Lett. 113 (10) (2014) 106104. [21] G. Langford, Deformation of pearlite, Metall. Mater. Trans. A 8 (6) (1977) 861–875. [22] X. Zhang, A. Godfrey, X. Huang, N. Hansen, Q. Liu, Microstructure and strengthening mechanisms in cold-drawn pearlitic steel wire, Acta Mater. 59 (9) (2011) 3422–3430. [23] Y. Ivanisenko, W. Lojkowski, R. Valiev, H.-J. Fecht, The mechanism of formation of nanostructure and dissolution of cementite in a pearlitic steel during high pressure torsion, Acta Mater. 51 (18) (2003) 5555–5570. [24] Y. Li, P. Choi, C. Borchers, S. Westerkamp, S. Goto, D. Raabe, R. Kirchheim, Atomic-scale mechanisms of deformation-induced cementite decomposition in pearlite, Acta Mater. 59 (10) (2011) 3965–3977. [25] X. Zhang, N. Hansen, A. Godfrey, X. Huang, Dislocation-based plasticity and strengthening mechanisms in sub-20 nm lamellar structures in pearlitic steel wire, Acta Mater. 114 (2016) 176–183. [26] L. Xiang, L. Liang, Y. Wang, Y. Chen, H. Wang, L. Dai, One-step annealing optimizes strength-ductility tradeoff in pearlitic steel wires, Mater. Sci. Eng. 757 (2019) 1–13. [27] Y. Chen, G. Csisz� ar, J. Cizek, X. Shi, C. Borchers, Y. Li, F. Liu, R. Kirchheim, Defect recovery in severely deformed ferrite lamellae during annealing and its impact on the softening of cold-drawn pearlitic steel wires, Metall. Mater. Trans. A 47 (2) (2016) 726–738. [28] M. Elices, Influence of residual stresses in the performance of cold-drawn pearlitic wires, J. Mater. Sci. 39 (12) (2004) 3889–3899. [29] X. Zhang, A. Godfrey, N. Hansen, X. Huang, Hierarchical structures in cold-drawn pearlitic steel wire, Acta Mater. 61 (13) (2013) 4898–4909. [30] X. Zhang, N. Hansen, A. Godfrey, X. Huang, Dislocation-based plasticity and strengthening mechanisms in sub-20nm lamellar structures in pearlitic steel wire, Acta Mater. 114 (2016) 176–183. [31] L. Zhou, L. Wang, H. Chen, Z. Xie, F. Fang, Effects of chromium additions upon microstructure and mechanical properties of cold drawn pearlitic steel wires, J. Mater. Eng. Perform. 27 (2) (2018) 1–10. [32] Y. Tu, X. Wang, H. Huang, X. Zhou, J. Jiang, Effect of Si on the aging behavior of cold-drawn pearlitic steel wires, Metall. Mater. Trans. A 48 (2) (2017) 659–665. [33] J. Languillaume, G. Kapelski, B. Baudelet, Evolution of the tensile strength in heavily cold drawn and annealed pearlitic steel wires, Mater. Lett. 33 (3) (1997) 241–245. [34] S. Zhiwei, E.A. Stach, J.M.K. Wiezorek, J.A. Knapp, D.M. Follstaedt, S.X. Mao, Grain boundary-mediated plasticity in nanocrystalline nickel, Science 305 (5684) (2004) 654–657. [35] J.W. Cahn, Y. Mishin, A. Suzuki, Coupling grain boundary motion to shear deformation, Acta Mater. 54 (19) (2006) 4953–4975. [36] T. Furuhara, T. Mizoguchi, T. Maki, Ultra-fine (αþ θ) duplex structure formed by cold rolling and annealing of pearlite, ISIJ Int. 45 (3) (2005) 392–398. [37] A. Suzuki, Y.M. Mishin, Atomic mechanisms of grain boundary motion, Mater. Sci. Forum 502 (2005) 157–162. [38] C. Borchers, R. Kirchheim, Cold-drawn pearlitic steel wires, Prog. Mater. Sci. 82 (2016) 405–444. [39] Y. Li, P. Choi, S. Goto, C. Borchers, D. Raabe, R. Kirchheim, Evolution of strength and microstructure during annealing of heavily cold-drawn 6.3 GPa hypereutectoid pearlitic steel wire, Acta Mater. 60 (9) (2012) 4005–4016. [40] J. Languillaume, G. Kapelski, B. Baudelet, Cementite dissolution in heavily cold drawn pearlitic steel wires, Acta Mater. 45 (3) (1997) 1201–1212. [41] Y. Tomota, T. Suzuki, A. Kanie, Y. Shiota, M. Uno, A. Moriai, N. Minakawa, Y. Morii, In situ neutron diffraction of heavily drawn steel wires with ultra-high strength under tensile loading, Acta Mater. 53 (2) (2005) 463–467.
4. Conclusion Nano-lamellae ferrite without continuous cementite segregation would coarse when subjected to cold drawing deformation. The ferrite nano-lamellae with an average thickness of 50 nm would coarse to an average thickness of 70 nm. TEM analyses and MD simulation reveal ferrite lamellae can grow thick via the shear-induced GB migration. As a result of strain-induced coarsening, the drawing strengthening perfor mance of the high carbon steel wire decrease to the quarter of typical pearlitic steel wire. Data availability statement All data included in this study are available upon request by contact with the corresponding authors. Declaration of competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was supported by the Natural Science Foundation of China (51874204), Science and Technology Advancement Program of Jiangsu Province, China (BA2017112) and the 333 projects of Jiangsu Province, China (BRA2018045). The study was also partly supported by IndustryUniversity Research Cooperation Project of Jiangsu Province, China (BY2018194). Z Xie acknowledges the support of the Australian Research Council Discovery Projects. References [1] E. Hall, The deformation and ageing of mild steel: III discussion of results, Proc. Phys. Soc. Sect. B 64 (9) (1951) 747. [2] N. Petch, The cleavage strengh of polycrystals, J. of the Iron and Steel Inst. 174 (1953) 25–28. [3] R. Pippan, F. Wetscher, M. Hafok, A. Vorhauer, I. Sabirov, The limits of refinement by severe plastic deformation, Adv. Eng. Mater. 8 (11) (2010) 1046–1056. [4] D. Raabe, P.-P. Choi, Y. Li, A. Kostka, X. Sauvage, F. Lecouturier, K. Hono, R. Kirchheim, R. Pippan, D. Embury, Metallic composites processed via extreme deformation: toward the limits of strength in bulk materials, MRS Bull. 35 (12) (2010) 982–991. [5] R.Z. Valiev, R.K. Islamgaliev, I.V. Alexandrov, Bulk nanostructured materials from severe plastic deformation, Prog. Mater. Sci. 45 (2) (2000) 103–189. [6] Y. Estrina, Extreme grain refinement by severe plastic deformation: a wealth of challenging science, Acta Mater. 61 (3) (2013) 782–817. [7] R. Pippan, S. Scheriau, A. Taylor, M. Hafok, A. Hohenwarter, A. Bachmaier, Saturation of fragmentation during severe plastic deformation, Annu. Rev. Mater. Res. 40 (1) (2010) 319–343. [8] T.J. Rupert, D.S. Gianola, Y. Gan, K.J. Hemker, Experimental observations of stressdriven grain boundary migration, Science 326 (5960) (2009) 1686–1690. [9] Y.B. Wang, J.C. Ho, X.Z. Liao, H.Q. Li, S.P. Ringer, Y.T. Zhu, Mechanism of grain growth during severe plastic deformation of a nanocrystalline Ni–Fe alloy, Appl. Phys. Lett. 94 (1) (2009) 103. [10] Y.B. Wang, B.Q. Li, M.L. Sui, S.X. Mao, Deformation-induced grain rotation and growth in nanocrystalline Ni, Appl. Phys. Lett. 92 (1) (2008) 66.
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L. Zhou et al.
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[42] N. Zhou, T. Hu, J. Luo, Grain boundary complexions in multicomponent alloys: challenges and opportunities, Curr. Opin. Solid State Mater. Sci. 20 (5) (2016) 268–277. [43] J. Hu, Y. Shi, X. Sauvage, G. Sha, K. Lu, Grain boundary stability governs hardening and softening in extremely fine nanograined metals, Science 355 (6331) (2017) 1292–1296.
[44] A. Khalajhedayati, Z. Pan, T.J. Rupert, Manipulating the interfacial structure of nanomaterials to achieve a unique combination of strength and ductility, Nat. Commun. 7 (2016).
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