Deformation textures in wire drawn perlitic steel

Transcription

1 Int J Mater Form (2010) 3:7 11 DOI /s ORIGINAL RESEARCH Deformation textures in wire drawn perlitic steel M. Zidani & S. Messaoudi & T. Baudin & D. Solas & M. H. Mathon Received: 29 April 2009 /Accepted: 15 June 2009 /Published online: 3 July 2009 # Springer/ESAFORM 2009 Abstract In this study, we followed the deformation microstructure and texture evolution during the cold wire drawing of a perlitic steel wire intended for civil engineering applications. The deformation level effect on the microstructure evolution and on the texture evolution is characterized. Wire drawing induces the lengthening of the perlitic grains along the drawing axis and leads to a strong hardness increase. X-ray texture measurements were performed. The reference state (initial wire) revealed an isotropic texture. The quantitative analysis show the development of the α fibre (<110>//ND (ND // wire) with the deformation. Moreover, the {001}<110>orientation (rotated Cube) is also present. The experimental techniques used in this study are the: Optical Microscopy (OM), the Electron Back Scattered Diffraction (EBSD), the X-ray diffraction, the Neutron diffraction and the Vickers microhardness. M. Zidani (*) : S. Messaoudi Department of Metallurgy, University of Biskra, B.P: 145, Biskra 07000, Algeria zidani.sabih@gmail.com S. Messaoudi msalim45@hotmail.com T. Baudin : D. Solas CNRS, UMR8182, ICMMO, Orsay 91405, France T. Baudin thierry.baudin@lpces.u-psud.fr D. Solas denis.solas@lpces.u-psud.fr M. H. Mathon Laboratoire Léon Brillouin, CEA(DSM-DRECAM)-CNRS, CEA Saclay, Gif sur Yvette, France Keywords Deformation by wire drawing. Texture. Pearlite. Neutron diffraction Introduction Wiredrawing is one of the most frequently applied techniques in the wire manufacturing industry. This process is one of the oldest metal forming processes. The wiredrawing provokes a hardening of the structure by increasing density dislocations. The structure of drawn-wire after a series of section reduction is characterized by a regular orientation of the grains «texture». Numerous studies [1 3] show two kinds of texture in the wire : the first one called standard, the other one called cylindrical fiber texture. These two kinds of texture are observed in FCC or BCC materials as copper, aluminium or steel, whatever the diameter (10 mm to 0.1 mm). However, the state of harddrawn metals is unstable from a thermo-dynamic point of view. Heating of this type of material brings about a process of regeneration and recrystallization that restores all the properties featured by the metal before deformation. In this paper, the deformation microstructure and texture evolution are studied during the cold wire drawing of a pearlitic steel wire intended for civil engineering applications. This work improves previous studies of a low carbon steel [4, 5]. Material The material used in this study is a commercial steel wire containing approximately 0.83 wt. % of carbon (initial section S o =12.00 mm); it has been provided by the Tréfissoud firm (Algeria). The composition is given in Table 1. Different techniques have been used: Optical

2 8 Int J Mater Form (2010) 3:7 11 Table 1 Chemical composition (%wt) of the used steel Elements C Si Mn P S Cr Ni MO Cu Result (% Max) 0,85 0,015 0,73 0, ,072 0,028 Néant 0,027 microscopy (OM) observations of the wire were made along a longitudinal plane after etching with Nital. In order to evaluate the wire mechanical properties microhardness Vickers measurements (Load 500 g) were performed. On the other hand, specimens were prepared for Electron Back Scattered Diffraction (EBSD) analysis in the standard manner. A Zeiss 940 SEM with a tungsten filament was used. The SEM device is coupled with the OIM (Orientation Imaging Microscopy) software. X-ray diffraction was characterizing the texture evolution during drawing. The deformation level of wire drawing is: " ¼ S i S f 100 ð1þ S i S i and S f designate respectively the initial and the final sections of the wire. For this work, a large number of drawn wires specimens were chosen (from 10 to % of section reduction, but results of only 3 reduction amounts are presented, i.e %, 52,81 % and %) Results and discussion The initial microstructure of as-received steel wire After hot rolling, the initial wire has a pearlitic structure (Fig. 1a). The pearlite has a lamellar structure (Fig. 1b). The microstructure and texture characterization of the reference state (initial wire) revealed relatively heterogeneous microstructure in the section of the wire. We impute these grain size inhomogeneities to the speed variation of cooling during the wire drawing between the core zone and the periphery (Fig. 1a, b)[2]. A later study by microhardness (Variation of the microhardness measured on the wire section) shows well the difference of measurements these zones of initial wire and of drawn wire (Fig. 5). The texture corresponds to an isotropic state (without texture) (Fig. 2) Microstructures and textures of drawn-wires Figure 3 shows different (OM) micrographs of the as deformed microstructure on longitudinal section of the wire. The drawing process leads obviously to the alignment of lamella of pearlite along the wire axis. This phenomenon is more visible when the level of wire drawing increases (Fig. 3 b,b). The cold wire drawing effect on the hardness is presented in (Fig. 4). One notes a light rise of the hardness value with the deformation level increase which becomes important starting from the reduction level (53 %). This hardening is interpreted by the mechanism of deformation, inducing a very strong density of dislocations, and to the reduction of the inter lamellate pearlite spacing [6, 7]. It is generally accepted that the cementite interfaces act as barriers to slip propagation in the ferrite [8]. Boumerzoug et al. [9] noticed the same phenomenon for low carbon steel wire (ferrito-pearlitic) deformed by cold wire drawing, but in their study the evolution of hardness is very remarkable after the first deformation level (27 %). Then, the hardening is dependent on the one hand, with the reduction in the ferritic grain size and the reduction in the interlamellar length between cementite plates and on the other hand, with the interaction of dislocations with the microstructure. Measurements of the microhardness on the section of wire between the centre and the periphery presented on Fig. 5 shows an increase with the deformation level. Moreover, the microhardness increases from the centre to the periphery of all the wires. The Fig. 6 presents the {110} pole figures obtained by X-ray diffraction. For drawn wire, one observed a reinforcement of the texture intensity with the increase of the deformation level (Fig. 6 a c). The Fig. 7 shows the ϕ 2 =45 plot section of the Orientation Distribution Function (ODF) of the drawn wire. The quantitative analysis show the development of the α fibre (<110>//ND (ND // wire drawing axis) with the deformation. Moreover, the {001}<110> orientation (rotated cube) is also present. This texture has been observed, by Kanetsuki et al. [10] in pearlitic steels deformed by wire drawing, by Montesin et al. [11] in pearlitic steels intended to the manufacture of pneumatic wires and by Zidani [12] in low carbon steel (0,06% C) after cold wire drawing. In our case, the <110>//ND fibre is majority on the whole section of the wire for the different level of deformation. a: Core b: Periphery Fig. 1 (OM) Microstructures of as-received pearlitic steel. a Core, b Periphery

3 Int J Mater Form (2010) 3: Fig. 2 a {110} Pole figure and b ϕ 2 =45 plot section of the ODF (X-Ray diffraction): of as received pearlitic steel Fig. 3 (OM) Microstructures of pearlitic steel wire after cold wiredrawing: (a, A) ε 1 =31.6%, and (b, B) ε 3 =74.44% a A b B Drawing Axis Fig. 4 Vickers micro-hardness curve of pearlitic steel wire after cold wire drawing Fig. 5 Microhardness evolution on the section of wire after cold wire drawing

4 10 Int J Mater Form (2010) 3:7 11 Fig. 6 {110} Pole figures (X-Ray diffraction) of pearlitic steel wire after reduction (a) ε 1 = 31.6%, (b) ε 2 =52.81% and (c) ε 3 =74.44% Max=6.0 a b Fibre α (majority) <110> (111) [1-11] (111) [0-11] (001) [110] Fig. 7 a ϕ 2 =45 Plot section of the ODF (Levels: 1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0) of pearlitic steel wire after reduction (ε 2 =52.81 %) and b position of ideal orientations The addition of the analysis by Neutrons diffraction is dictated by the precision this one by X-ray diffraction contribution. This analysis confirms the existence of majority fibres in the deformation structure whose acuity increases with the deformation level (Fig. 8). This tendency is very strong for α majority fibre Conclusion Fig. 8 {110} pole figures (Neutron diffraction) after reduction by wire drawing (ε=75%) The study of wire of steel drawn, enabled us to deduce the following conclusions: The characterization of the microstructure and texture of the reference state (initial wire) revealed relatively heterogeneous microstructure in the section of the wire. Moreover, the texture corresponds to an isotropic state (without texture).

5 Int J Mater Form (2010) 3: Wire drawing causes a reinforcement of the components of the <110>//DN fibre texture, typically Observed in BCC materials. The texture acuity increases with the deformation level and leads to a strong hardness increase. References 1. He S, Van Bael A, Li SY, Van Houtte P, Mei F, Sarban A (2003) Mater Sci and Engineering A 346: Jakani S (2005) Effet des Impuretés sur les Mécanismes de Recristallisation du cuivre Tréfilé, Thesis. Université Paris-Sud, Orsay 3. Humphreys FJ, Hatherly M (1996) Recovery after deformation, Ch.5 in recrystallization andrelated annealing phenomena. Pergamon Press, 127, Oxford 4. Zidani M, Boumerzoug Z, Baudin T, Penelle R (2006) Mater Sci Forum : Zidani M, Boumerzoug Z, Baudin T, Solas D (2007) Mater Sci Forum 550: Sevillano JG (1991) J Phys III 1: Languillame J (1995) Thesis, Institut National Polytechnique de Grenoble 8. Watte P, Van Houtte P, Aernouldt E, Gil Sevillano J, Van Raemdonck W, Lefer I (1994) Mater Sci Forum 1689: Boumerzoug Z, Lahraki N, Zidani M (2004) Recrystalization and Grain Growth, Annecy, France,September 10. Kanetsuki Y, Ogawa R (1981) ICOTOM Montesin T, Heizmann JJ (1990) Revue de Métallurgie, p Zidani M ( 2006) Texture et recristallisation lors de recuits du fil d acier doux (0,06%) tréfilé à froid Thesis, Université de Biskra