Papers by Keyword: Heat Treatments

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Authors: B. Barroqueiro, João Dias-de-Oliveira, António Andrade-Campos
Abstract: Multiphase steels offer impressive mechanical properties. However, their characterization still represents a challenge. In a quenching processes, phenomena such as undesirable strains or residual stress are inevitable and can be the cause for non-admissible final parts. Microstructural phase transformations generally magnify the problem. This fact leads to the need of numerical tools capable of quantifying these residual stresses, due to the non-existence of efficient non-destructive experimental procedure capable of measuring them. In this work, a numerical multiscale transient model, that uses the Asymptotic Expansion Homogenisation (AEH) method combined with finite element method (FEM), is proposed. The implementation of the AEH method is carried out using the commercial program Abaqus, considering an uncoupled and quasi-static transient problem with implicit time integration. Within the homogenisation method, the existence of two distinct scales is assumed, defining a micro and a macroscale. Within the smaller scale, the evolution of a steel periodic microstructure is analysed in detail and an equivalent homogeneous material model is established for macroscopic use. However, the microstructural evolution leads to the need of new equivalent homogeneous models in order to predict the macro response. Consequently, several mechanical, thermomechanical and transient thermal homogenization procedures are carried in order to establish different equivalent homogeneous models.
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Authors: Dragoş Cristian Achiţei, Mirabela Georgiana Minciună
Abstract: The paper presents a study on the structure of AISI 420 steel after heat treatments. The experiments start with a spectral analysis for determination of percents for alloying elements. Based on obtained results was establish of heat treatments parameters, which can be applied on AISI 420 steel. By thermal processing can be influenced positive on structural modifications and implied on mechanical properties. Structural modifications were highlight by X-ray diffraction analysis.
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Authors: Spencer Jeffs, Robert Lancaster, Sean Davies
Abstract: Direct Laser Deposition (DLD) is a modern Additive Layer Manufacturing (ALM) technology that offers the possibility of lean manufacture and the ability to produce near-net shape components with complex geometries. Anisotropic microstructures are typically produced due to thermal cycles that occur during the layer by layer process, resulting in epitaxial grains forming along the build direction. Therefore, build direction, whether horizontal (0°) or vertical (90°), may have a pronounced effect upon mechanical properties. While, it is generally accepted that the mechanical properties of cast materials are well understood, the same cannot be said for materials produced using DLD. Although, mechanical testing of materials usually dictates the use of round bar specimens, due to the cost of manufacture and fundamental nature of this study a miniaturised test technique better lends itself to characterise the cast and DLD built alloys’ properties. The Small Punch (SP) creep test is a widely utilised miniaturised test technique for characterising and ranking the creep response of metallic material properties when large quantities may not be readily available. This paper will apply the SP creep test to characterise the properties of DLD variants of the nickel based superalloy C263 in comparison to the traditional cast material. Tests were performed at elevated temperatures akin to those experienced in service. Interpretation of the microstructures and SP creep results has been carried out; relating build direction, microstructures, minimum displacement rate and time to rupture.
128
Authors: Jin Wang, Nobuya Shinozaki, Zhen Su Zeng, Nobuaki Sakoda
Abstract: A study of the effects of heat treatments of plasma sprayed SUS316L stainless steel coatings was performed. The stainless steel coatings were treated at the conditions of 1273 K and 1373 K for 45 minutes in flowing argon. The effectiveness of the heat treatment was determined using an electron probe microanalyzer (EPMA). The results indicated that the heat treatments were able to significantly affect the composition and the microstructure. After the heat treatment, the interconnected micro-pores were found to appear in the large-scale rod-like oxide in the coating and the content of chromium and manganese in the oxides became higher than that in the as-sprayed coating. The heat-treatment became more effective with increasing temperature.
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Authors: A. Al Sumait, C. Delgado, F. Aldhabib, X. Sun, F. Alzubi, K. Tovalin, A. Cheng, R.M. Campo, Y.J. Li, B. Ramsey, L. Zeng, O.S. Es-Said
Abstract: The objective of the study was to optimize the strength and ductility values of the 4330M steel. Optimization was conducted through different types of heat treatments. Tensile testing, hardness testing, optical microscopy, and Scanning Electron Microscopy (SEM) were used to evaluate the mechanical properties and microstructure of the as-received and the heat treated samples. The alloy was provided from two vendors; vendor H and vendor S. Results showed that by increasing the tempering temperatures, strength values decreases, while ductility values remain unchanged. Vendor H samples had higher strength values and much finer grain structure which was revealed only at 5000x magnification.
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Authors: Doru Dumitru Băitanu, Dan Gelu Găluşcă, Dragoş Cristian Achiţei, Mirabela Georgiana Minciună
Abstract: The applications of stainless steels may be meeting in chemical industry, food industry, civil building, but present an increased interest also in machine constructions or household.This paper highlight the structural modifications obtained after temperature variations for AISI 321 stainless steel. The modifications of structure and proprieties can be induced by heat treatments applied to semi-products before or after the obtaining of final parts, but also by heating at regimes which respect the exploitation conditions of part. In the experiments, it is applied quenching to put into solution, with modification of final treatment temperature and maintaining time, aiming the dissolution of complex carbides and in this mode an easy processing. The treatment parameters were chosen, after the determination of alloying elements by AISI 321 samples, by optic spectrometry. The dilatometric analysis aimed to highlight the structural modifications, specific to thermal fatigue phenomenon, due to temperatures variations.
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Authors: T. Shimabukuro, R. Daouk, J. Skupnjak, M. Nordman, M. Burrell, L. Sutanto, A. Abad, Hamid Garmestani, N. Ula, J. Foyos, K. Almahmoud, O. Almahmoud, O.S. Es-Said
Abstract: Three Ti-6Al-4V plate materials produced by powder metallurgy technique, included pre-alloyed hydride-dehydride (HDH) plate rolled to 75% reduction in thickness, and two blended elemental (BE) powder plates rolled to 75% and 87% reduction were evaluated. The objective of this study was to determine differences in microstructure and toughness between the pre-alloyed HDH and BE Ti-6Al-4V materials processed to the same product form. Heat treatments were performed below the beta transus temperature at 982, 871, 760, and 732°C (1800, 1600, 1400, and 1350°F) for 1, 2, and 4 hours in order to determine differences in heat treating response, and above the beta transus at 1076°C (1970°F) to determine the transformation temperature. The samples were evaluated by optical microscopy and scanning electron microscopy. Charpy impact testing was performed in order to determine differences in the energy absorbed during fracture. Pole figures (0002) of selected conditions were also performed in order to determine any differences in texture between the various conditions.
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