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Delaminations by Cleavage Cracking in Duplex Stainless Steels at Sub-zero Temperatures
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.ORCID iD: 0000-0002-8494-3983
2014 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 45A, no 3, 1327-1337 p.Article in journal (Refereed) Published
Abstract [en]

Impact toughness testing was conducted on 10 and 30 mm plates of 2205 together with a 30 mm plate of LDX 2101(A (R)) duplex stainless steel (DSS). The testing temperatures were between 153 K (-120 A degrees C) and room temperature. Interrupted fracture toughness tests of the 10 mm plate and a 50 mm plate of 2205 were also performed. The conclusion from the fractographic investigation was that the delaminations that occur in hot-rolled DSSs were cleavage fractures. The toughness anisotropy can be explained by the cleavage fracture and the appearance of the microstructure. The result from the interrupted fracture toughness test revealed that the delaminations initiated prior to the maximum force plateau and propagated ahead of the stable crack growth during testing. Estimated upper limit for the fracture delamination initiation toughness at sub-zero temperatures for the 2205 base metal according to the crack-tip opening displacement method was 28 to 61 mu m for the 10 mm plate, 70 to 106 mu m for the 30 mm plate and below 100 mu m for the 50 mm plate.

Place, publisher, year, edition, pages
2014. Vol. 45A, no 3, 1327-1337 p.
Keyword [en]
Duplex stainless steel, Cleavage fracture, Impact toughness, Fracture toughness, Delamination, Splits
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-133673DOI: 10.1007/s11661-013-2055-6ISI: 000331094900025Scopus ID: 2-s2.0-84896761832OAI: oai:DiVA.org:kth-133673DiVA: diva2:662710
Note

QC 20140321

Available from: 2013-11-08 Created: 2013-11-08 Last updated: 2017-12-06Bibliographically approved
In thesis
1. The fracture mechanisms in duplex stainless steels at sub-zero temperatures
Open this publication in new window or tab >>The fracture mechanisms in duplex stainless steels at sub-zero temperatures
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of the thesis was to study the susceptibility for brittle failures and the fracture process of duplex stainless steels at sub-zero temperatures (°C). In the first part of the thesis plates of hot-rolled duplex stainless steel with various thicknesses were used to study the influence of delamination (also known as splits) on the fracture toughness. The methods used were impact and fracture toughness testing. Light optical microscopy and scanning electron microscopy were used to investigate the microstructure and fracture surfaces. It was concluded that the delaminations caused a loss of constraint along the crack front which resulted in a stable fracture process despite the presence of cleavage cracks. These delaminations occurred when cleavage cracks are constrained by the elongated austenite lamellae. The pop-in phenomenon which is frequently observed in duplex stainless steels during fracture toughness testing was shown to occur due to these delaminations. The susceptibility for pop-in behaviour during testing increased with decreasing plate thickness. The toughness anisotropy was also explained by the delamination phenomenon.In the second part of the thesis duplex stainless steel weld metals from lean duplex and super duplex were investigated. For the lean duplex weldments with different nickel contents, tensile, impact and fracture toughness testing were conducted from room temperature to sub-zero temperatures. The result showed that increased nickel content decreased the susceptibility for critical cleavage initiation at sub-zero temperatures. The super duplex stainless steel weldment was post weld heat treated. The fracture sequence at low temperature was critical cleavage fracture initiation after minor crack-tip blunting and ductile fracture. Energy-dispersive X-ray spectroscopy investigation of the weld metals showed that substitutional element partitioning is small in the weld metal. However, for the post weld heat treated weldments element partitioning occurred which resulted in decreased nickel content in the ferrite.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. vii, 58 p.
Keyword
Duplex stainless steel, Weldments, Delamination, Fracture toughness, Impact toughness, Cleavage fracture, Nickel
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-133677 (URN)978-91-7501-931-4 (ISBN)
Public defence
2013-11-29, B3, Brinellvägen 23, KTH, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note

QC 20131108

Available from: 2013-11-08 Created: 2013-11-08 Last updated: 2013-11-08Bibliographically approved

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Sandström, Rolf

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