Papers by Keyword: Quenching

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Authors: Thomas Rieger, Klaus Herrmann, Dagmar Carmele, Stephan Meyer, Thomas Lippmann, Andreas Stark, Wolfgang Bleck, Uwe Klemradt
Abstract: The ‘Quenching and Partitioning’ (Q&P) concept aims to increase the strength level of conventional TRIP-assisted advanced high strength steel (AHSS) by replacing ferritic constituents by tempered martensite. The Q&P heat treatment process involves austenitization and interrupted quenching followed by carbon partitioning from martensite to austenite at elevated temperatures. The final microstructure is traditionally investigated at room temperature after metallographic preparation by microscopy and x-ray analysis with laboratory tubes. Besides other disadvantages the established characterization methods are not adequate to observe the development of the microstructure during Q&P treatment. In the present work the microstructural evolution during Q&P processing was monitored by in-situ diffraction experiments using very hard (100 keV) synchrotron x-ray radiation. Debye-Scherrer rings were recorded as a function of time and temperature during the heat treatment in a state-of-the-art dilatometer (type Bähr DIL805AD) at the Engineering Materials Science beamline HARWI-II (HZG outstation at Deutsches Elektronensynchrotron (DESY), Hamburg). The diffraction patterns contain quantitative information on the phases present in the sample (for more details cf. Abstract Carmele et al, this conference). The evolution of the austenite phase fraction during the partitioning treatment at the quench temperature (1-step Q&P) is discussed exemplarily for a Si-based TRIP steel with additions of Ni.
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Authors: Lydia Giersberg, Benjamin Milkereit, Christoph Schick, Olaf Kessler
Abstract: Isothermal time-temperature-precipitation (TTP) diagrams deliver important material data like temperature and time ranges critical for precipitation. During the last years an in-situ calorimetric method to record continuous cooling precipitation diagrams has been developed to application level by our group. However, isothermal TTP-diagrams were still determined by ex-situ analyses only. In this work in-situ measurements of precipitation reactions were carried out during isothermal soaking. Therefore the whole heat treatment cycle was performed in a differential scanning calorimeter (DSC). Al-Mg-Si-alloys 6063 and 6005A were analysed. Solution annealing and overcritical quenching to several temperatures between 450 °C and 250 °C was followed by isothermal soaking. Based on the heat flow curves during isothermal soaking TTP-diagrams were determined. Further microstructure investigations by scanning electron microscopy and hardness tests after artificial ageing were performed. Both alloys show similar results. In the TTP-diagramms three so-called ”C-curves” could be observed. Every C-curve is expected to represent precipitation of a different phase. Hardness and microstructure investigations correspond with the data of the TTP-diagramms.
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Authors: Margarita D. Bambach, Andreas Stieben, Wolfgang Bleck
Abstract: High performance components such as gear wheels shall be resistant to rolling-contact fatigue. This type of failure is usually caused by effects occurring on a microscopic scale, such as crack initiation at non-metallic inclusions. Much effort has been invested so far in improving the steel cleanliness. However, these high performance components often do not reach the desired service life. Preliminary failure within the guarantee terms still occurs which leads to high warranty costs. Alternative to improving steel cleanliness, the damage tolerance of high performance components could be increased by inducing the TRIP-effect around the crack tip. Due to high local strain hardening, martensite transformation occurs. The high compressive stresses related to it could delay or stop crack propagation by reducing stress concentrations via plastic deformation. In part II of this study, the microstructures and mechanical properties of the steels modified via Al-alloying and heat treated in process routes according to part I are compared to conventional 18CrNiMo7-6. Special interest is paid to the stability of the residual austenite as well as to the change in strain hardening rate under tension.
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Authors: Margarita D. Bambach, Andreas Stieben, Wolfgang Bleck
Abstract: High performance components such as gear wheels shall be resistant to rolling-contactfatigue. This type of failure is usually caused by effects occurring on a microscopic scale, such ascrack initiation at non-metallic inclusions. Much effort has been invested so far in improving thesteel cleanliness. However, these high performance components often do not reach the desiredservice life. Preliminary failure within the guarantee terms still occurs which leads to high warrantycosts. Alternative to improving steel cleanliness, the damage tolerance of high performancecomponents could be increased by inducing the TRIP-effect around the crack tip. Due to high localstrain hardening, martensite transformation occurs. The high compressive stresses related to it coulddelay or stop crack propagation by reducing stress concentrations via plastic deformation. As aresult, rolling-contact fatigue resistance of carburized steels may be increased and preliminaryfailure may be avoided. Part I of this study focuses on modifying the chemical composition ofconventional 18CrNiMo7-6 steel with Al to develop a high-strength, yet ductile matrix with a highwork hardening potential. Dilatometric tests on laboratory melts analyze the possibility of adjustinga microstructure able to produce a TRIP-effect. Both isothermal annealing and Quenching andPartitioning (Q&P) are used to stabilize residual austenite and optimum process routes areidentified.
633
Authors: D. Ruvalcaba, Dmitry G. Eskin, Laurens Katgerman
Abstract: In the present research the possibility of studying the solidification of aluminum alloys by using the quenching technique is analyzed. Since the quenching technique does not provide reliable information (i.e. due to an overestimation of solid fraction) when measuring the solid fraction over 2D images from samples quenched at high temperature, the overestimation problem is investigated by analyzing 3D reconstructed microstructures from quenched samples. The 3D reconstructed microstructure may provide better understanding about the cause of overestimation of solid fraction when quenching at high temperatures. Consequently, the reconstruction of the microstructure that has existed before quenching may be possible after identifying and removing the solid phase that develops during quenching. In the present research, binary aluminum alloys are solidified and quenched at different temperatures, and then 3D reconstructed images are analyzed. The possibility of reconstructing the microstructure that develops during solidification before quenching is discussed.
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Authors: Michael P. Howson, Bradley P. Wynne, Peter S. Davies, Sinan S. Al-Bermani, Jesus Talamantes-Silva
Abstract: The present work explores the importance of model parameters and input variables when simulating the quenching of thick sectioned nuclear forgings. The modelling approach adopted uses values of specific heat capacity, containing latent heat release, to simulate cooling curves; rather than calculating transformation kinetics based upon a mathematical model. Termed the effective specific heat (Cpeff), two different methods were used to establish values: differential scanning calorimetry (DSC) and thermos dynamic predictive software. Values were then included in finite element (FE) models to simulate the characteristic cooling at the mid-wall position in a thick section forging and were validated against production thermocouple data. The investigation found that the formation of ferrite, bainite and martensite or lower bainite were all represented by the data established using DSC and critical formation temperatures were comparable with others in the literature. Conversely, values calculated using the thermodynamic software failed to represent ferrite formation and predicted different critical transformation temperatures for bainite. The simulated cooling curve that used the software predicted Cpeff data was comparable to the thermocouple data either side of the bainite transformation, however during the transformation the effects of latent heat on cooling rate were over predicting leading to disparities. The equivalent DSC cooling curves produced a near exact match.
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Authors: M. Borrell, R.I. Grynszpan, N. Ji
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Authors: Dong Ying Ju, Ryuji Mukai, Nobuaki Minakawa, Yukio Morii, Atsushi Moriai
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Authors: Pei Xing Liu, Xiang Yun Yu, Kai Wang, Bin Zhu, Li Jian, Yi Sheng Zhang
Abstract: A new hot stamping process with quenching and partitioning treatment is proposed in the paper. Compared to direct hot stamping process, the microstructures with some retained austenite not only including martensite are formed according to the constrained carbon equilibrium (CCE) model. During the new hot stamping process, tools with high temperature are used to control the quenching temperature (QT) between Ms and Mf, and the partitioning treatment of the part is also implemented in the tools by prolonging holding times. In this paper, different holding times (partitioning times) controlled by servo press, are used to research the influence of partitioning time on mechanical properties.
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Authors: Zhi Qiang Jiang, Xi Lan Feng, Xian Zhang Feng
Abstract: The microstructures of B-bearing cast steel containing 0.8-1.2 wt.%B, 0.8-1.2 wt.%Cr, 1.0-1.5 wt.%Mn, 0.6-1.0 wt.%Si and 0.10-0.25 wt.%C have been characterized by means of optical OM, SEM, EPMA and XRD. The solidification structure of B-steel consists of pearlite, ferrite, martensite and boride (Fe2B), while the hardness is 1430-1480 HV. Borides distribute along the grain boundary in the form of eutectic. Fine lath martensite and eutectic Fe2B can be obtained by water quenching at 1223 K-1273 K. The hardness and impact toughness of the B-steel exceed 55 HRC and 150 kJ/m2, respectively. The abrasion resistance determined using a pin abrasion tester is obviously higher than that of the martensitic cast steel and nears to the high chromium white cast iron.
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