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Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. Swerea KIMAB AB.
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2018 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 139, p. 390-400Article in journal (Refereed) Published
Abstract [en]

A novel arc heat treatment technique was applied to design a uniquely graded super duplex stainless steel (SDSS), by subjecting a single sample to a steady state temperature gradient for 10 h. A new experimental approach was used to map precipitation in microstructure, covering aging temperatures of up to 1430 °C. The microstructure was characterized and functionality was evaluated via hardness mapping. Nitrogen depletion adjacent to the fusion boundary depressed the upper temperature limit for austenite formation and influenced the phase balance above 980 °C. Austenite/ferrite boundaries deviating from Kurdjumov–Sachs orientation relationship (OR) were preferred locations for precipitation of σ at 630–1000 °C, χ at 560–1000 °C, Cr2N at 600–900 °C and R between 550 °C and 700 °C. Precipitate morphology changed with decreasing temperature; from blocky to coral-shaped for σ, from discrete blocky to elongated particles for χ, and from polygonal to disc-shaped for R. Thermodynamic calculations of phase equilibria largely agreed with observations above 750 °C when considering nitrogen loss. Formation of intermetallic phases and 475 °C-embrittlement resulted in increased hardness. A schematic diagram, correlating information about phase contents, morphologies and hardness, as a function of exposure temperature, is introduced for evaluation of functionality of microstructures.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 139, p. 390-400
Keywords [en]
475 °C-embrittlement, Chi phase, Functionally graded microstructure, Nitrogen loss, R-phase, Sigma phase
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-227576DOI: 10.1016/j.matchar.2018.03.024ISI: 000431469300042Scopus ID: 2-s2.0-85044113030OAI: oai:DiVA.org:kth-227576DiVA, id: diva2:1208838
Funder
Knowledge FoundationVINNOVA
Note

QC 20180521

Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2018-05-21Bibliographically approved

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Örnek, Cem

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