Papers by Keyword: Dilatometry

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Authors: Frank Nießen, Matteo Villa, Daniel Apel, Olaf Keßler, Michael Reich, John Hald, Marcel A.J. Somers
Abstract: The austenitization and inter-critical annealing of X4CrNiMo16-5-1 (1.4418) supermartensitic stainless steel were investigated in-situ with synchrotron X-ray diffraction (XRD), dilatometry and differential scanning calorimetry (DSC) under isochronal heating conditions. Austenitization occurred in two stages: the austenitization started at approx. 600 °C, decelerated at approx. 700 °C at 60 to 75 v.% of transformed austenite, and first resumed after heating for approx. 100 °C. This plateau in the transformation curve was more dominant for faster heating rates. Inter-critical annealing at 675 and 700 °C revealed, that austenite can to a certain extent be stabilized to room-temperature. There was good agreement for the transformation curves yielded by dilatometry and XRD. Some deviation occurred due to the different applied heating principles, different temperature monitoring and the impact of surface martensite formation on the XRD measurement. The applicable temperature range for DSC as well as the close proximity of the Ac1- and the Curie-temperature limited the usage of the technique in the present case.
Authors: Yasir Nawab, Nicolas Boyard, Vincent Sobotka, Pascal Casari, Frédéric Jacquemin
Abstract: Residual stresses development during manufacturing of composites depends mostly on the shrinkage behaviour of the polymer matrix from the point where stresses cannot be relaxed anymore. The matrix shrinkage may have a thermal and/or chemical origin and can leads to dimensional instability, ply cracking, delamination and fibre buckling. The approaches for measuring cure shrinkage can be classified as volume and non-volume dilatometry. Each technique has corresponding advantages and drawbacks but volume dilatometry is the one that is mostly used. In the present article, we report a home-built apparatus, named PVT-a mould, on which temperature, volume change and reaction conversion degree are measured simultaneously for an applied pressure. It can also be used to study the composite during curing and for the bulk samples having several millimetre thicknesses. The instrument is preferred over other techniques as it works in conditions close to the industrial ones. This device was used to measure cure shrinkage of resin and thermoset composite material with different fibre fractions as a function of temperature and reaction conversion degree. The heat of cure of the resin measured by PVT-a mould was compared to the results obtained by DSC.
Authors: Abdelali Hayoune
Abstract: In contrast to isothermal aging, few reports document the non-isothermal aging of deformed Al–Mg–Si alloys. The knowledge of non-isothermal aging of pre-deformed Al–Mg–Si alloys is of primary importance to understand the thermal stability as well as to control the microstructure of the final product during industrial processing. Therefore, the present work has been focused to understand the microstructure evolution during the continuous heating of a cold rolled Al–Mg–Si alloy. This has been followed using dilatometry, Differential Scanning Calorimetry, X-Ray Diffraction and microhardness measurement. Based on the results obtained, it is shown that dilatometry is a powerful tool to study phase transformations in deformed Al-Mg-Si alloys, moreover, the microstructural evolution, of the cold rolled sample, can be described as follows: at the earlier stages of the non-isothermal aging, formation and then the reversion of fully coherent GP zones take place. This is followed by the simultaneous occurrence of β” and β’ precipitation and recovery reaction. By continuing aging, the next reactions which will take place are β” and β’ dissolution and recrystallization. Finally, one can observe the formation and then the dissolution of the equilibrium phase β.
Authors: Frans Leysen, Jan Penning, Yvan Houbaert
Abstract: As already intensive studies related to the processing of hot rolled dual phase steels have been reported in the past, the aim of this particular paper is to present some details within a processing strategy, that can be considered as useful for the processing of other special steel types. It will be shown that based on fundamental dilatometric measurements performed in the laboratory, a narrow window of processing parameters can be focused at. Moreover, practical dilatometric curves are shown, taking into account the transformation heat release in the arrested cooling zone (dry section), as to be considered regarding the industrial practice. Furthermore, by introducing a slab insert technique within the development schedule, not only time consuming research can be limited, especially main objectives can be achieved. Some of these objectives are: a) a simultaneous study of the influences of the chemical composition of the steels, b) a close control of the thermomechanical parameters encountered in the industrial environment, such as rolling reductions, strain rate and inter pass time conditions, c) a check of the homogeneity of mechanical properties versus the coil length.
Authors: Ch. Cunat, France-Anne Kuhnast, A. Aharoune, M. Fiorani, Z. Ayadi
Authors: M.M. Cisneros-Guerrero, R.E. Campos-Cambranis, M. Castro-Román, M.J. Pérez-López
Authors: E. Paravicini Bagliani, E. Anelli, Marco Boniardi
Abstract: Innovative treatments like quenching and partitioning (Q&P) have been recently proposed to improve the combination of strength and ductility of high strength steels by stabilization of significant fractions of retained austenite in a microstructure of tempered martensite. The decomposition of austenite into bainite and carbides precipitation are the two main competitive processes that reduce the content of retained austenite achievable at room temperature. A medium carbon low-silicon steel (0.46% C and 0.25% Si) has been studied to identify in which limits the austenite can be enriched in C and stabilized by Q&P, although a silicon content well below 1.5%, commonly used to retard cementite precipitation, is adopted; indeed, high Si contents are detrimental to the surface quality of the product due to the formation of adherent scale in high temperature manufacturing cycles. The heat treatments have been carried out with a quenching dilatometer, investigating the carbon partitioning process mainly below Ms, where cementite precipitation is not activated. The dilatometric curves show the progressive enrichment of carbon in the untransformed austenite and the occurrence of austenite phase transformation during the isothermal holding below Ms. A range of temperatures and times has been found where a content of about 10% of retained austenite can be stabilized at room temperature, a percentage much lower than the theoretical maximum achievable with the carbon content of this steel.
Authors: Philipp Nusskern, Jürgen Hoffmeister, Volker Schulze
Abstract: A new approach for case hardening of powder metallurgical steels is surface densification prior to heat treatment, hence avoiding hardening to the core caused by open porosity. With regard to this process chain a porosity and carbon dependent model of the transformation kinetics is essential. In powder metallurgical materials the transformation behavior is mainly influenced by the chemical composition, homogeneity and porosity. Using a prealloyed powder, e.g. Astaloy 85 Mo, a homogeneous distribution of alloying elements after sintering can be assumed and the transformation behaviour is mainly determined by pores and the carbon profile caused by case hardening. The effect of carbon is widely known but up to now, only a few details about the effect of porosity on the transformation can be found in literature. It is reported that a decreasing relative density causes a reduction of incubation and overall isothermal transformation time. In the present study, the transformation kinetics of a powder metallurgical steel based on Astaloy 85 Mo were investigated for the carbon levels 0.5 and 0.8 wt% as well as the relative densities 6.8, 7.2 and 7.8 g/cm³. The investigations were carried out using a high-speed quenching dilatometer. The isothermal time temperature transformation diagrams for this powder-metallurgical alloy are presented and Avrami-type equations are fitted to the measured data. A good correlation can be found for the transformation model and the experimental results verifying the used modeling approach showing the potential to be applied within case hardening simulations.
Authors: Se Jong Kim, Yi Gil Cho, Dong Woo Suh, Sung Joon Kim, Gyo Sung Kim, Heung Nam Han
Abstract: In general, plastic strain occurs over a certain stress, called yield stress. However, it has been reported that the permanent strain could happen during boundary migrating even under the extremely slight externally applied stress. In this study, we performed dilatometry experiments under the various compressive stresses and measured the amount of recrystallization and growth induced permanent strain. A new empirical constitutive equation was suggested to describe the recrystallization and growth induced plasticity. This equation was verified by comparing the calculated values with dilatometric experimental data under the various compressive stresses.
Authors: N. Antón, L.E.G. Cambronero, J.M. Ruiz Prieto, Francisco Velasco, José M. Torralba
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