Elemental partitioning and microstructural development in duplex stainless steel weld metal |
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Affiliation: | 1. Ural Federal University, Department of Mathematical Physics, Ekaterinburg, 620000, Russian Federation;2. Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology (INT), 76344 Eggenstein-Leopoldshafen, Germany;3. Friedrich-Schiller-Universität-Jena, Physikalisch-Astronomische Fakultät, 07743 Jena, Germany;1. National Institute for Plasma, Laser and Radiation Physics (NILPRP), Atomistilor 409, P.O. Box MG 36, R-077125 Magurele, Bucharest, Romania;2. “Politehnica” University of Bucharest, Physics Department, Independentei 313, Bucharest, Romania;3. “Politehnica” University of Bucharest, Faculty of Applied Chemistry and Materials Science, Department of Oxide Materials and Nanomaterials, Gh. Polizu 1-7, Bucharest, Romania;4. “Babes-Boyai” University, Faculty of Chemistry and Chemical Engineering, Arany Janos 11, Cluj-Napoca, Romania;1. National Institutes for Quantum and Radiological Science and Technology (QST), Naka, Ibaraki-ken 311-0193, Japan;2. Association EURATOM, CIEMAT, Avda. Complutense 40, 28040 Madrid, Spain;3. Fusion for Energy, 85748 Garching bei Munchen, Germany;4. Toshiba Corporation, Yokohama, Kanagawa-ken 235-8523, Japan;1. Department of Surgery, Hamad General Hospital, Doha, Qatar;2. Trauma Surgery, Hamad General Hospital, Doha, Qatar;3. Clinical Research, Trauma Surgery, Hamad General Hospital, Doha, Qatar;4. Clinical medicine, Weill Cornell Medical college, Doha, Qatar |
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Abstract: | A thermodynamic analysis which is capable of estimating the austenite/ferrite equilibria in duplex stainless steels has been carried out using the sublattice thermodynamic model. The partitioning of alloying elements between the austenite and ferrite phases has been calculated as a function of temperature. The results showed that chromium partitioning was not influenced significantly by the temperature. The molybdenum, on the other hand, was found to partition preferentially into ferrite phase as the temperature decreases. A strong partitioning of nickel into the austenite was observed to decrease gradually with increasing temperature. Among the alloying elements, average nitrogen concentration was found to have the most profound effect on the phase balance and the partitioning of nitrogen into the austenite. The partitioning coefficient of nitrogen (the ratio of the mole fraction of nitrogen in the austenite to that in the ferrite) was found to be as high as 7.0 around 1300 K. Consequently, the volume fraction of austenite was influenced by relatively small additions of nitrogen. The results are compared with the experimentally observed data in a duplex stainless steel weld metal in conjunction with the solid state δ → δ + γ phase transformation. Particular attention was given to the morphological instability of grain boundary austenite allotriomorphs. A compariso between the experimental results and calculations indicated that the instability associated with irregular austenite perturbations results from the high degree of undercooling. The results suggest that the model can be used successfully to understand the development of the microstructure in duplex stainless steel weld metals. |
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