Papers by Keyword: Hot Deformation

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Authors: Mehran Maalekian, M.L. Lendinez, Ernst Kozeschnik, Hans P. Brantner, Horst Cerjak
Abstract: The welding continuous cooling transformation (WCCT) behavior of eutectoid carbon steel was investigated in different peak temperatures and in the undeformed and deformed conditions. The corresponding WCCT and welding continuous cooling compression transformation (WCCCT) diagrams were constructed by means of dilatometric and metallographic analyses in addition to hardness measurements. It was found that the higher austenitizing temperature slightly accelerates pearlitic transformation, i.e., it shifts the WCCT diagram to shorter times. Furthermore, heavy hot deformation of austenite could strongly promote the formation of pearlite, that is, the WCCCT diagram moved toward the top left corner compared to the WCCT diagram, while martensite start temperature was lowered slightly, which is a characteristic of a displacive transformation mechanism.
Authors: Cheng Liu, L. Zhuang, Menno van der Winden, T.J. Hurd
Authors: Dipti Samantaray, Sumantra Mandal, Shaju K. Albert, A.K. Bhaduri, Tammana Jayakumar
Abstract: In this paper, the deformation behaviour of a high-nitrogen grade 316LN stainless steel (with 0.14%N) has been studied over a wide range of temperatures (1123-1423K) and strain rates (0.001-10 s-1). The key deformation controlling mechanisms have been investigated using thermal activation parameters, such as activation volume and activation enthalpy. The chromium nitride precipitates, dislocation intersections, both conservative and recovery, are found to be the key deformation controlling mechanism at different temperature–strain-rate domain during hot deformation of this material.
Authors: Soon Wuk Cheong, Hasso Weiland
Abstract: The softening process consists of recovery and recrystallization. Despite the significant effect of recovery on the softening, recovery has not enjoyed the attention as much as recrystallizaion has mostly due to difficulties in the microstructural characterization of recovery. The present study introduced GOS qualitatively and quantitatively to gauge the microstructural evolution occurring during annealing. Then the GOS analysis was applied to discern alloying effects on recrystallization in hot deformed Al-Cu-Mg alloys. Recovery seems accountable for the retardation of recrystallization in the Mn containing alloys. By adding Zr to Al-Cu-Mg-Mn, recrystallization could be further inhibited.
Authors: Philippe Bocher, J. Azar, Brent L. Adams, John J. Jonas
Authors: Paulo Roberto Cetlin, John J. Jonas, Steve Yue
Authors: Jian Hui Zhang, Kenong Xia, Erik Strom, Zeng Yong Zhong, Chang Hai Li
Abstract: This paper presents the true stress - strain curves and data analyses of a Ni-containing TiAl and its reference alloy based on the isothermal compression tests at 1000°C and 0.01 - 1.0s-1 strain rates. The results show that the minor Ni addition makes the flow softening coming sooner and therefore significantly lowers the peak stress. Those effects, in addition with a better balance between the work hardening and flow softening during hot deformation, improve the steady state flow behavior of TiAl. The Ni-influence mechanisms are also suggested based on the TEM observation of dislocation configurations and lamellar breakdown during the deformation.
Authors: Henri Järvinen, Sanna Järn, Emmi Lepikko, Martti Järvenpää, Pasi Peura
Abstract: Two types of press hardening experiments were carried out to investigate the behavior of ZnFe coated 22MnB5 steel in direct press hardening process. The coating properties were studied using variable process temperatures and times with a flat-die and a forming tool. Coatings were analyzed with optical and scanning electron microscopes. The results indicated that steels that have low coating weights may be processed successfully with short dwell times. For high coating weights a significantly longer dwell time is needed. The behavior of ZnFe coating in hot press forming experiments was in line with literature and the findings of the flat-die experiments. Thus, the feasibility of the experimental press hardening equipment was confirmed.
Authors: Philippe Bocher, Mohammad Jahazi, Lionel Germain, Priti Wanjara, Nathalie Gey, Michel Humbert
Abstract: The presence of hcp regions with grains having relatively close orientations has been reported in commercial near alpha titanium billets (IMI 834, Ti 6246, etc). The size of these textured regions (called macrozones) is significantly larger than the average grain size of the microstructure observed after thermomechanical processing. The elongated shape of these large hcp regions suggests that they are eventually related to large prior b grains that pancaked during the ingot break down process. In this contribution, Orientation Image Microscopy was used to study the relationship between the hcp local microtexture heterogeneities and the prior b orientations. Specifically, the orientations of the primary (equiaxed) ap grains and the secondary (lamellar) as colonies produced after the transformation of the b phase were discriminated from OIM maps. Furthermore, from the as inherited OIM map, it was possible to reconstruct the corresponding b OIM map over large regions. The analysis showed that the large hcp macrozones observed in the as received material are not related to corresponding bcc macrozones. However, within an hcp macrozone, various clusters of b grains with similar orientations can be found. In such coherent regions, randomly orientated b grains were also observed, which could be related to microstructural changes during deformation (continuous dynamic recrystallization) as suggested by hot deformation results.
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