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Fracture toughness of a welded super duplex stainless steel
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
Scania CV AB, Södertälje, Sweden.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.ORCID iD: 0000-0002-8494-3983
2014 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 606, 40-45 p.Article in journal (Refereed) Published
Abstract [en]

Fracture toughness testing was conducted on standard single-edge notched bend bar specimens of base and weld metal. The material was the SAF 2906 super duplex stainless steel. The aim was to evaluate the susceptibility for brittle failure at sub-zero temperatures for the base and weld metal. The base metal was tested between -103 and -60. °C and was evaluated according to the crack-tip opening displacement method. The fracture event at and below -80. °C can be described as ductile until critical cleavage initiation occurs, which caused unstable failure of the specimen. The welding method used was submerged arc welding with a 7. wt% nickel filler metal. The welded specimens were post-weld heat treated (PWHT) at 1100. °C for 20. min and then quenched. Energy-dispersive X-ray spectroscopy analysis showed that during PWHT substitutional element partitioning occurred which resulted in decreased nickel content in the ferrite. The PWHT weld metal specimens were tested at -72. °C. The fracture sequence was critical cleavage fracture initiation after minor crack-tip blunting and ductile fracture.

Place, publisher, year, edition, pages
2014. Vol. 606, 40-45 p.
Keyword [en]
Duplex stainless steel, Super duplex, Fracture toughness, Weldments, Cleavage fracture, Post weld heat treatment
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-133676DOI: 10.1016/j.msea.2014.03.049ISI: 000337775800005Scopus ID: 2-s2.0-84897951163OAI: oai:DiVA.org:kth-133676DiVA: diva2:662730
Note

QC 20140519. Updated from submitted to published.

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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