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      Early Stages of Precipitate Formation in a Dual Hardening Steel∗ Translated title: Frühe Stadien der Ausscheidungsbildung eines dualhärtenden Stahls

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          Abstract

          For plastic mold steels, secondary hardening as well as hardenable, corrosion-resistant steels are used. Secondary hardening can be achieved through alloying with Ni, Ti, Al and Cu. The precipitation sequence of combined Cu and intermetallic NiAl particles depends on the precise ratio of the alloying contents. In this study, a dual hardening iron-based alloy with a high ratio of Ni/Cu and Al/Cu and low Carbon content is investigated. These dual hardening steels represent alloys that utilize both carbidic and intermetallic secondary hardening precipitates to achieve secondary hardening. The investigations focus on the initial precipitation of intermetallic particles in order to analyze the sequence of precipitate formation for a specific ratio of alloying elements. DSC measurements were used to identify characteristic precipitation temperatures between 360 °C and 600 °C and the corresponding heat treatment conditions were reproduced using a quenching dilatometer. The initial stages of precipitate formation were examined using high-resolution atom probe tomography. C-enrichments in the form of retained austenite films were evident in the examined material. Heterogeneous nucleation of Cu-NiAl precipitates on these retained austenite films was attributed to exothermal reactions at 460 °C.

          Kurzfassung

          Für Kunststoffformenstähle werden neben härtbaren, korrosionsbeständigen auch ausscheidungshärtbare Stähle eingesetzt. Zur Ausscheidungshärtung werden unter anderem Legierungselemente wie Ni, Ti, Al und Cu eingesetzt. In Kombination hängt die Ausscheidungssequenz von Cu-Partikeln und intermetallischen NiAl-Teilchen von deren genauem Legierungsverhältnis ab. In dieser Arbeit wurde eine dualhärtende Eisenbasislegierung mit einem hohen Verhältnis von Ni/Cu und Al/Cu und geringen Legierungsgehalten an Kohlenstoff untersucht. Bei diesen dualhärtenden Stählen handelt es sich um Legierungen, die karbidische und intermetallische Sekundärhärteausscheidungen zur Festigkeitssteigerung nutzen. Der Fokus der Untersuchungen wurde dabei auf die zuerst ausgeschiedenen intermetallischen Teilchen gelegt, um bei gegebenem Verhältnis der Legierungselemente die Sequenz der Ausscheidungsbildung zu analysieren. Die charakteristischen Ausscheidungstemperaturen wurden mithilfe von DSC-Messungen zwischen 360 °C und 600 °C identifiziert und die jeweiligen Wärmebehandlungszustände in einem Abschreckdilatometer reproduziert. Anschließend wurden die ersten Stadien der Ausscheidungsbildung mit hochauflösender Atomsondentomographie untersucht. In dem untersuchten Material konnten C-Anreicherungen in Form von Restaustenitfilmen nachgewiesen werden. Eine exotherme Reaktion bei 460 °C konnte der heterogenen Keimbildung von Cu-NiAl-Ausscheidungen an diesen Restaustenitfilmen zugeordnet werden.

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          Most cited references 26

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          Atomic weights of the elements. Review 2000 (IUPAC Technical Report)

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            Quantitative binomial distribution analyses of nanoscale like-solute atom clustering and segregation in atom probe tomography data.

            The applicability of the binomial frequency distribution is outlined for the analysis of the evolution nanoscale atomic clustering of dilute solute in an alloy subject to thermal ageing in 3D atom probe data. The conventional chi(2) statistics and significance testing are demonstrated to be inappropriate for comparison of quantity of solute segregation present in two or more different sized system. Pearson coefficient, mu, is shown to normalize chi(2) with respect to sample size over an order of magnitude. A simple computer simulation is implemented to investigate the binomial analysis and infer meaning in the measured value of mu over a series of systems at different solute concentrations and degree of clustering. The simulations replicate the form of experimental data and demonstrate the effect of detector efficiency to significantly underestimate the measured segregation. The binomial analysis is applied to experimental atom probe data sets and complementary simulations are used to interpret the results.
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              Interfacial segregation at Cu-rich precipitates in a high-strength low-carbon steel studied on a sub-nanometer scale

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                Author and article information

                Journal
                htme
                HTM Journal of Heat Treatment and Materials
                Carl Hanser Verlag
                1867-2493
                2194-1831
                10 October 2019
                : 74
                : 5
                : 293-301
                Affiliations
                1 Department Werkstoffwissenschaft, Montanuniversität Leoben, Franz-Josef-Straße 18, 8700 Leoben, Austria
                2 voestalpine Böhler Edelstahl GmbH & Co KG, Kapfenberg, Austria
                Author notes
                3 matthias.hofinger@ 123456unileoben.ac.at (Corresponding author/Kontakt)
                [∗]

                Lecture presented at the ASMET Werkstofftechnik- und Härtereitagung 2019, March 28–29, 2019, Vienna, Austria

                Article
                HT110390
                10.3139/105.110390
                © 2019, Carl Hanser Verlag, München
                Page count
                References: 30, Pages: 9
                Product
                Self URI (journal page): http://www.hanser-elibrary.com/loi/htme
                Categories
                Scientific Contributions/Fachbeiträge

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