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Lembke M.I.,Steeltec AG | Olschewski G.,Steeltec AG | Roelofs H.,Swiss Steel AG | Klumper-Westkamp H.,IWT - Foundation Institute of Materials Engineering
HTM - Journal of Heat Treatment and Materials

Modern bainitic long products with ultimate tensile strength values in the range 800-1400 MPa provide new property profiles and permit the manufacturing of complex components without subsequent quench and temper (Q&T) treatment. Abrasion resistance and fatigue limit can be enhanced by surface hardening or coating. The IWT in Bremen systematically evaluated the behaviour of bainitic steel grades 7MnB8 and 18MnCrSiMoS641 in nitriding and nitrocarburizing processes in comparison to conventional (ferritic-pearlitic) steels 44SMn282 and 16MnCrS5Pb+HH3. The results were analyzed based on metallographic analysis, hardness measurement and element concentration profiles. Regular and compact layers of approx. 8 μm in thickness were obtained after nitriding at rN = 2 bar-1/2 and a temperature of 520 °C during 10 h with the selected steel grades. The resulting surface hardness was in the range obtained for quenched and tempered steels. © Carl Hanser Verlag GmbH & Co. KG. Source

Morales-Rivas L.,CSIC - National Center for Metallurgical Research | Yardley V.A.,Ruhr University Bochum | Capdevila C.,CSIC - National Center for Metallurgical Research | Garcia-Mateo C.,CSIC - National Center for Metallurgical Research | And 2 more authors.
Journal of Materials Science

An alternative procedure for indirect and automatic measurement of the prior austenite grain size (PAGS) in bainite/martensite is proposed in this work. It consists in the determination of an effective grain size by means of statistical post-processing of electron backscatter diffraction (EBSD) data. The algorithm developed for that purpose, which is available on-line, has been applied to simulated EBSD maps as well as to both nanocrystalline bainitic steel and commercial hot-rolled air-cooled steel with a granular bainitic microstructure. The new proposed method has been proven to be robust, and results are in good agreement with conventional PAGS measurements. The added value of the procedure comes from its simplicity, as no parent reconstruction is involved during the process, and its suitability for low-magnification EBSD maps, thus allowing a large step size and coverage of a substantially broader area of the sample than the previous methods reported. © Springer Science+Business Media New York 2014. Source

In order to achieve the goals for a sustainable development, concrete with recycled aggregates (concrete and mixtures from concrete and masonry, e.g. clay bricks and calcium silicate blocks etc.) is going to be used more and more in the future. Due to its thermal insulating properties, the demand for concrete with light-weight aggregates (e.g. foam glass) will also increase. As an essential element of this development, an increasing amount of cements with a reduced clinker factor as well as of mineral additions such as fly ash and ground granulated blast furnace slag is used for concrete production. Therefore, as a general tendency, the carbonation resistance of concrete mixes decreases while the risk of corrosion damages increases. The goal of the investigations described in this paper was to evaluate and to assess the corrosion resistance of a stainless rebar (Top12, composition corresponds approx. to steel grade 1.4003) in various carbonated concrete mixes and to compare the results with common rebars. The results lead to the conclusion that, in contrast to common rebars, Top12 is durable in all investigated concrete mixes, including strongly carbonated recycling concretes. Copyright © 2010 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Source

Smolenicki D.,ETH Zurich | Boos J.,ETH Zurich | Kuster F.,ETH Zurich | Roelofs H.,Swiss Steel AG | Wyen C.F.,Rieter Machine Works Ltd.
CIRP Annals - Manufacturing Technology

In order to represent actual cutting process conditions, an in-process tribometer is examined to measure friction during orthogonal turning process at cutting speeds up to 300 m/min. The tribometer consists of a spring preloaded tungsten carbide pin with spherical tip mounted behind the cutting edge and rubbing on the freshly generated workpiece surface. The pin preload is set according to feed force. A 3D-force measuring device in the fixation of the pin allows evaluating friction coefficient from tangential and normal forces. Experiments show strongly different results when contacting fresh and oxidized surfaces and decreasing friction coefficient with increasing cutting speed. © 2014 CIRP. Source

Morales-Rivas L.,CSIC - National Center for Metallurgical Research | Roelofs H.,Swiss Steel AG | Hasler S.,Swiss Steel AG | Garcia-Mateo C.,CSIC - National Center for Metallurgical Research | Caballero F.G.,CSIC - National Center for Metallurgical Research
Advanced Materials Research

Chemical segregation of alloying elements during solidification of steel grades leads to development of a banded microstructure, causing a degree of anisotropy that can be detrimental to the mechanical behavior under service conditions. It is well-known that the presence of strongly orientated martensite bands in carbide-free bainitic microstructures, associated to inhomogeneous Mn redistribution during solidification, leads to a remarkable deterioration in toughness in advanced high strength bainitic steels. In this study, while bands were clearly visible on light optical micrographs of continuously cooled carbide-free bainitic steels, scanning electron microscopy examination revealed only a gradual transition between matrix and bands, both with a granular bainitic structure. Electron backscatter diffraction was used to quantify the bainitic packet size and volume fraction of martensite/austenite constituent between and within the bands, after a process of optimization of the analysis settings in order to minimize the inherent difficulties linked to submicrometric and minority phase indexation. The quantitative microstructural results showed negligible morphological differences between bainitic structure bands and matrix, only solute segregation of Cr and Mo was detected by energy-dispersive X-ray spectroscopy within bands, which must be responsible for a stronger resistance against metallographic etching in those regions. © (2014) Trans Tech Publications, Switzerland. Source

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