Fundamentals of Deformation and Annealing

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Authors: H. Landheer, S. Eric Offerman, Roumen H. Petrov, Leo Kestens
Abstract: The relationship between the misorientation of the austenite crystallites and the favoured sites for ferrite nucleation has been investigated. Ex-situ EBSD measurements were performed on an especially developed high purity ternary iron alloy with 20 wt.% Cr and 12 wt.% Ni with both austenite and ferrite present at room temperature to measure the misorientation between the austenite crystallites. The experimental results are compared to the nucleation models of Clemm and Fisher and Aaronson and co-workers.
435
Authors: Haruo Nakamichi, John F. Humphreys, Pete S. Bate, Ian Brough
Abstract: Recrystallization phenomena in an interstitial free (IF) steel have been investigated by in-situ annealing in the SEM, combined with Electron Back Scattered Diffraction (EBSD) mapping. Sequential recrystallization phenomena, such as initiation and growth of new grains, are clearly distinguished by EBSD mapping at temperatures of up to 1070K. More than 70% of the recrystallized grains are of {111}<121>, {111}<123> and {111}<110> orientation. It is found that many recrystallized grains are formed from {111}<123> deformed grains at the beginning of recrystallization. It is observed that some of α-fibre (RD//<110>) orientations have difficulty in recrystallization compared to γ–fibre deformed grains. In particular, many grains of {001}<110> orientation remain un-recrystallized even after holding for 65 minutes at 1050K.
441
Authors: Mosbah Zidani, Zakaria Boumerzoug, Denis Solas, Thierry Baudin
Abstract: In this work, the effect of the deformation, caused by cold wire drawing, on the microstructure and the texture of low carbon steel wire (0.06 wt % C) is examined. The combined influence of the deformation level and the recrystallization temperature on the development of new grains is studied for all wires. Isothermal tests of annealing allow the determination of the critical temperature of recrystallization estimated above 450°C. The temperature effect is studied below the eutectoid level, at 500°C, 600°C and 680°C. The appearance of a homogeneous recrystallization is noted over the section of the wire. The recrystallized grains keep the same orientation as the deformed grains. The expansion of time of annealing lead to recrystallization in the ferritic grains accompanied by a spheroidization of the lamellar pearlite. The kinetics of recrystallization and spheroidization are accelerated by increasing of annealing temperature and the deformation level. The experimental techniques used in this study are: the Scanning Electron Microscope (SEM), the Electron Back Scattered Diffraction (EBSD), the X-ray diffraction and Vickers microhardness.
447
Authors: Polina Volovitch, Thierry Baudin, Richard Penelle, F. Caleyo, Laurent Barrallier
Abstract: A simple model including the recovery and nucleation kinetics is proposed to simulate recrystallization using a Monte Carlo technique. Nucleation is simulated on the basis of equations describing stored energy evolution and subgrain growth kinetics. The parameters describing the stored energy evolution during recovery are shown to influence not only the relative number, orientation and local distribution of nuclei, but also the recrystallization kinetics and the final texture. The estimated kinetics of nucleation, the mean stored energy evolution as well as the preferential texture of first nuclei are in agreement with experimental observations for annealing 40% cold-rolled IF-Ti steel and cold drawn copper wires.
453
Authors: Francois Gerspach, Nathalie Bozzolo, Francis Wagner
Abstract: Zirconium alloys are widely used for different applications in nuclear industry. Precise knowledge of their texture is of great relevance since this hcp metal exhibits a strong crystal anisotropy. Despite that, the mechanisms of texture change during its deformation and subsequent annealing are still not precisely known. Thus, there is a need for a better understanding of the fundamental mechanisms of recrystallisation. Earlier works on Zr702 [1-3] suggested that the kinetics and local mechanisms of recrystallisation after cold-rolling was controlled by the heterogeneity of the deformed microstructure and that, at the end of recrystallisation (corresponding to the disappearance of the deformed matrix), the position of the major texture components remained almost unaffected. The aim of the present work is to confirm whether these statements can be generalized for various deformation conditions or not.
459
Authors: A.N. Aleshin, Alex M. Arsenkin, Sergey V. Dobatkin
Abstract: The paper is devoted to the problem of thermal stability of ultra-fine grained (submicrocrystalline) materials prepared by severe plastic deformation. A basis of the paper lies in a fact that there is practically no grain growth in submicrocrystalline materials when annealing temperature is less than 0.35Tm. Reasons of high thermal stability of submicrocrystalline materials at low temperatures are widely discussed in literature. One of them is the affect of triple junction drag on grain boundaries motion. During annealing at a low temperature triple junction drag controls microstructure evolution in submicrocrystalline materials, and this phenomenon can be used to improve their thermal stability at high temperatures. The aim of this paper is to investigate grain growth kinetics in a two-step regime, low temperature and high temperature annealing. The experiments on grain growth were performed in submicrocrystalline Armco-iron fabricated by high pressure torsion. It is established that long-time low temperature pre-annealing reduces the grain growth rate in following high temperature annealing by a factor greater than two.
465
Authors: G. Azevedo, Ronaldo Barbosa, Elena V. Pereloma, Dagoberto Brandão Santos
Abstract: Several studies concerning ferrite grain refinement have been developed in recent the last years due to the recognised influence of such microstructures on steels properties. This work was focused on the evaluation of the microstructure and mechanical properties of an ultrafine grained CMn steel obtained by hot torsion deformation and intercritical annealing. After 5 min soaking at 900 and 1200°C, the samples of low carbon steel were quenched and then reheated. Hot torsion deformation was conducted at temperatures of 700 or 740°C. The torsion schedule consisted of 7 isothermal passes leading to a total true strain of ≈1 and generating an ultrafine and inhomogeneous microstructure with grain sizes of the order of 1-m, formed by strain-induced dynamic transformation (SIDT). The samples were heated up to 800oC and held for 1, 2 and 3 h. A more homogeneous microstructure and ferrite grain size were obtained after annealing The microhardness tests showed the reduction in hardness with the increase in annealing time. They also highlighted the effects of the ferrite grain size and the volume fractions of the microstructure constituents.
471
Authors: Jae Hyung Cho, Donald E. Boyce, Paul R. Dawson
Abstract: Texture evolution during friction stir welding of stainless steel was investigated using both predictions by crystal plasticity and EBSD measurements. Two- and three-dimensional Eulerian formulations are used to model friction stir welding. Plane strain deformation is assumed in a two-dimensional model, and an initial uniform texture changes into a torsion texture with monoclinic sample symmetry after deformation. Around the tool pin, the texture strengthens, weakens and restrengthens repeatedly. It is found from a simple circular streamline model that the relative magnitudes of the deformation rate and spin along the streamlines decide textural stability. In order to consider more complicated material behaviors, such as movement along the thickness direction due to a threaded tool pin and a tool shoulder, a three-dimensional Eulerian formulation is also implemented. Materials starting under the tool shoulder travel down to the bottom, producing the longest material streamlines. Those material points are predicted to have stronger texture components than others. EBSD results are compared with the predictions.
479
Authors: Dorothée Dorner, Yoshitaka Adachi, Kaneaki Tsuzaki, Stefan Zaefferer
Abstract: A Goss-oriented single crystal was cold rolled up to 89 % thickness reduction, and subsequently annealed at 550°C or 850°C. During deformation most of the initially Goss-oriented material rotated into the two symmetrical {111}<112> orientations. In addition, Goss regions were observed related to microbands or microshear bands. Goss regions in microshear bands formed during straining, whereas Goss regions between microbands were retained from the initial Goss orientation. The recrystallisation texture for annealing temperatures of both 550°C and 850°C is characterised by a Goss texture. However, the origin of the Goss recrystallisation nuclei appeared to be different for the different annealing conditions. In the material annealed at 550°C, the Goss texture originated from the Goss regions in the microshear bands. In contrast, for an annealing temperature of 850°C, the Goss grains between the microbands are likely to form recrystallisation nuclei.
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Authors: Kim Verbeken, Leo Kestens
Abstract: The scope of this work was to study the physical metallurgical behaviour of the microstructure and the texture of ultra low carbon (ULC) steel during cold rolling and subsequent thermally activated phenomena. It was the intention to contribute to the scientific search for the answer to many open questions raised in recent literature. The powerful tool of quantitative texture analysis, together with modern measurement equipment was used for this purpose. At first, a ULC steel was cold rolled to two different rolling reductions and the local strain heterogeneities after the cold rolling were studied. Secondly, crystallographic orientation selection during primary recrystallization was considered both for cold rolled ULC steel and for a Fe-2.8%Si single crystal. The latter was a re-evaluation of the historic growth selection experiment by Ibe and Lücke. Finally, secondary recrystallization in ULC steels was evaluated in terms of oriented nucleation and selective growth.
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