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Annealing oxides on duplex stainless steels
2010 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

In this report, the relation between the oxide formation and the pickling behaviour of duplex stainless steels is investigated. A duplex stainless steel 2205 (EN 1.4462), and two single phases, ferritic and austenitic stainless steels with the same composition as the phases inside the 2205, have been annealed. The surface and composition of the oxide have been analyzed using scanning electron microscopy (SEM), energy dispersive X-ray (EDS), focused ion beam (FIB) and glow discharge optical emission spectroscopy (GDOES). The thickness of the oxide scales increased when the annealing time and temperature were increased. The ferritic stainless steel has the thickest oxide, whereas the austenitic has the thinnest one. Nodules in the middle of the grains and thick oxides on the grain boundaries are observed on the austenitic stainless steel but also in a lower content on the austenitic phase of duplex stainless steel. The oxide scale on the 2205 is not homogenous, showing different types of oxide depending on the phase. The pickling behaviour of the same samples is also reviewed: oxide surface study and relative weight loss is discussed. The austenitic stainless steel has the highest pickling rate, followed by the 2205 and the ferritic stainless steel respectively. The oxide on the austenitic stainless steel is spalled from the surface mostly on the zones where nodules are placed, whereas the oxide on the ferritic stainless steel is dissolved during the process. The 2205 exhibit a mixture of both pickling behaviours: some grains are pickled fast, whereas in others the oxide still remains on the surface. The existence of thicker oxide on the top of grain boundaries, iron-enriched nodules with a porous structure, thick chromium depleted region and non protective silicon oxide could be attributed to the faster pickling rate on the austenitic stainless steel and the austenitic phase regions on the 2205.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Stainless steels, Duplex stainless steel, Ferritic stainless, steel, Austenitic stainless steel, Annealing oxides, Pickling, Microstructure, Nodule formation, FIB, Confocal Microscope
Keyword [sv]
URN: urn:nbn:se:ltu:diva-49263ISRN: LTU-EX--10/105--SELocal ID: 6a19ca33-85ac-4716-ac7a-8301709cf534OAI: diva2:1022610
Subject / course
Student thesis, at least 30 credits
Educational program
Materials Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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