Comparison of the rolling texture of particular phases of dual-phase steel with single-phase steels
J. Čapek, K. Trojan, N. Ganev
Department of Solid State Engineering, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague
jiri.capek@fjfi.cvut.cz
Duplex steels are dual-phase steels with 50/50 proportion of ferrite (α-Fe) and austenite (γ-Fe) phases. Because of the combination of properties of both the phases in dual-phase microstructure, duplex steels are distinguished by good properties in many environments, where the standard austenitic and ferritic steels are usually used [1]. Due to very often presence of preferred orientation (texture) in these materials, analysis and consequent interpretation of the texture is crucial, especially in material engineering. The importance of study the texture resides in the anisotropy of most material properties induced by its presence. Because of different mechanical properties of ferrite and austenite phases, their behaviour during deformation, generally spoken, is different in dual-phase steel in comparison with single-phase steels [2].
The plate shape samples of size 19×120 mm2 and different thicknesses were made of AISI 420 (ferritic), AISI 304 (austenitic) and AISI 318LN (duplex) type of stainless steels. The samples were cold-rolled with 0, 10, 20, 30, 40, and 50% reduction of thickness, so the final thickness of all samples was 1.5 mm. Samples made of ferritic, austenitic and duplex steel were marked as F0–F50, A0–A50 and D0–D50, respectively.
The X'Pert PRO MPD diffractometer with cobalt radiation was used to the RD-TD plane samples analyses by X-ray diffraction, where rolling (RD), transversal (TD) and normal (ND) directions create a coordination system of the sample. Texture analysis was performed based on orientation distribution function (ODF) calculated from experimental pole figures obtained by analysis of three diffraction lines {110}/{220}, {200}, {211} of ferrite phase and {111}/{311}, {200}, {220} of austenite phases.
The rolling texture of ferrite may be described by several texture fibres [3], for example, the limited α1, ε, and γ, see Fig. 1. Ferritic steel exhibits the typical texture components: {001}<110>, {112}<110>, and {111}<110>. For austenitic steel, the rolling texture is usually composed of α, τ, and η texture fibres. The typical texture components of these materials are Brass, Goss, and Copper [3]. Nevertheless, it is necessary to expect that dual-phase steel should have different behaviour of the constituent phases in comparison with single-phase steel. It has been found that ODFs of ferrite phase of the duplex steel do not consist of texture fibres, but only of the particular texture components. For austenite phase of the duplex steel, fewer texture components and fibres are generated compared to the austenitic steel.
The presence of two phases results in a decrease of strain hardening speed. The reason for that behaviour is the partition of plastic deformation occurring within both the phases, during cold rolling. The strain hardening of austenite is very high at low deformations, but at about 15% thickness reduction it gets increasingly concentrated within the ferrite phase, which has a larger number of active slip systems and a considerably higher stacking-fault energy [4]. Therefore, the typical texture fibres of the phases in the dual-phase steel are not generated but only strong separated texture components are presented. However, the typical texture component and fibres are generated in the sample with higher deformation.
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Sample F50 |
Sample D50 – α phase |
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Sample A50 |
Sample D50 – γ phase |
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Figure 1. Selected orientation distribution functions in the φ1=0° (left) and φ2=45° (right) sections for α phases, and φ2=0° (left) and φ2=45° (right) sections for γ phases. |
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1. R. Dakhlaoui, C. Braham, A. Baczmański, Mater. Sci. Eng.: A., 444, (2007), 6-17.
2. J. Ryś, W. Ratuszek, M. Witkowska, Arch. Metall. Mater., 51, (2006), 495-502.
3. H. J. Bunge, Texture Analysis in Materials Science. London: Butterworth. 1982.
4. I. Alvarez-Armas, S. Degallaix-Moreuil, Duplex stainless steels. John Wiley & Sons. 2013.
This work was supported by the Grant Agency of the Czech Technical University in Prague, grant No. SGS19/190/OHK4/3T/14.