Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Weld oxide formation on lean duplex stainless steel
Outokumpu Stainless, Avesta Research Centre.
Outokumpu Stainless, Avesta Research Centre.
Outokumpu Stainless Research Foundation.
2008 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 50, no 9, 2620-2634 p.Article in journal (Refereed) Published
Abstract [en]

Weld oxides have a strong influence on corrosion resistance, but have hitherto only been studied to a limited extent for duplex stainless steels. X-ray photoelectron spectroscopy (XPS) has here been used to study heat tint formed on gas tungsten arc (GTA) welds on the commercial duplex grades LDX 2101 (EN 1.4162/UNS S32101) and 2304 (EN 1.4362/UNS S32304) welded with and without nitrogen additions to the shielding gas. The process of heat tint formation is discussed in terms of transport phenomena to explain the effect of atmosphere, temperature and composition. The oxides formed were found to be enriched in manganese and corrosion testing shows that nitrogen has a strong influence on the weld oxide. A mechanism is proposed including evaporation from the weld pool and subsequent redeposition.

Place, publisher, year, edition, pages
2008. Vol. 50, no 9, 2620-2634 p.
Keyword [en]
Stainless steel, EPMA, XPS, Oxidation, Pitting corrosion
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-9294DOI: 10.1016/j.corsci.2008.06.024ISI: 000260358900023OAI: oai:DiVA.org:kth-9294DiVA: diva2:54547
Note
QC 20101126 Uppdaterad från submitted till published (20101126).Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Welds in the lean duplex stainless steel LDX 2101: effect of microstructure and weld oxides on corrosion properties
Open this publication in new window or tab >>Welds in the lean duplex stainless steel LDX 2101: effect of microstructure and weld oxides on corrosion properties
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Duplex stainless steels are a very attractive alternative to austenitic grades due to their higher strength and good corrosion performance. The austenitic grades can often be welded autogenously, while the duplex grades normally require addition of filler metal. This is to counteract segregation of important alloying elements and to give sufficient austenite formation to prevent precipitation of chromium nitrides that could have a negative effect on impact toughness and pitting resistance. The corrosion performance of the recently-developed lean duplex stainless steel LDX 2101 is higher than that of 304 and can reach the level of 316. This thesis summarises pitting resistance tests performed on laser and gas tungsten arc (GTA) welded LDX 2101. It is shown here that this material can be autogenously welded, but additions of filler metal, nitrogen in the shielding gas and use of hybrid methods increases the austenite formation and the pitting resistance by further suppressing formation of chromium nitride precipitates in the weld metal. If the weld metal austenite formation is sufficient, the chromium nitride precipitates in the heat-affected zone (HAZ) could cause local pitting, however, this was not seen in this work. Instead, pitting occurred 1–3 mm from the fusion line, in the parent metal rather than in the high temperature HAZ (HTHAZ). This is suggested here to be controlled by the heat tint, and the effect of residual weld oxides on the pitting resistance is studied. The composition and the thickness of weld oxide formed on LDX 2101 and 2304 were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the 300 series. A new approach on heat tint formation is consequently presented. Evaporation of material from the weld metal and subsequent deposition on the weld oxide are suggested to contribute to weld oxide formation. This is supported by element loss in LDX 2101 weld metal, and nitrogen additions to the GTA shielding gas further increase the evaporation.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vi, 37 p.
Keyword
Duplex stainless steel, welding, weld metal, HAZ, nitrogen, manganese, austenite formation, phase balance, precipitates, pitting resistance, heat input, solidification, element loss, evaporation, deposition, weld oxides, discoloration, mechanical properties, thermo-mechanical simulation, Geeble, GTA, laser, LOM, SEM, EDS, TEM, Leco, EPMA, ferroxyl test, XPS, post weld cleaning, pickling
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-9299 (URN)978-91-7415-109-1 (ISBN)
Presentation
2008-10-03, Sal 408, KTH, Brinellvägen 23, Stockholm, 10:00 (English)
Supervisors
Note
QC 20101126Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2010-11-26Bibliographically approved
2. Microstructure and properties of welds in the lean duplex stainless steel LDX 2101
Open this publication in new window or tab >>Microstructure and properties of welds in the lean duplex stainless steel LDX 2101
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Duplex stainless steels can be very attractive alternatives to austenitic grades due to their almost double strength at equal pitting corrosion resistance. When welding, the duplex alloys normally require addition of filler metal, while the commodity austenitic grades can often be welded autogenously. Over-alloyed consumables are used to counteract segregation of important alloying elements and to balance the two phases, ferrite and austenite, in the duplex weld metal. This work focuses on the weldability of the recently-developed lean duplex stainless steel LDX 2101® (EN 1.4162, UNS S32101). The pitting corrosion resistance of this grade is better than that of austenitic AISI 304 (EN 1.4307) and can reach the level of AISI 316L (EN 1.4404). The austenite formation is rapid in LDX 2101 compared to older duplex grades. Pitting resistance tests performed show that 1-2.5 mm thick laser and gas tungsten arc (GTA) welded LDX 2101 can have good corrosion properties even when welding autogenously. Additions of filler metal, nitrogen in the shielding gas, nitrogen-based backing gas and use of laser hybrid welding methods, however, increase the austenite formation. The pitting resistance may also be increased by suppressing formation of chromium nitrides in the weld metal and heat affected zone (HAZ). After thorough post-weld cleaning (pickling), pitting primarily occurred 1-3 mm from the fusion line, in the parent metal rather than in the HAZ. Neither the chromium nitride precipitates found in the HAZ, nor the element depletion along the fusion line that was revealed by electron probe microanalysis (EPMA) were found to locally decrease the pitting resistance. The preferential pitting location is suggested to be controlled by the residual weld oxide composition that varies over the surface. The composition and thickness of weld oxide formed on LDX 2101 and 2304 (EN 1.4362, UNS S32304) were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the AISI 300 series. A new approach to heat tint formation is presented; whereby evaporation of material from the weld metal and subsequent deposition on the already-formed weld oxide are suggested to contribute to weld oxide formation. This is consistent with manganese loss from the weld metal, and nitrogen additions to the GTA shielding gas enhance the evaporation. The segregation of all elements apart from nitrogen is low in autogenously welded LDX 2101. This means that filler wire additions may not be required as for other duplex grades assuming that there is no large nitrogen loss that could cause excessive ferrite contents. As the nitrogen appears to be controlling the austenite formation, it becomes essential to avoid losing nitrogen during welding by choosing nitrogen-containing shielding and backing gas.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. vii, 65 p.
Keyword
Duplex stainless steel, welding, HAZ, nitrogen, manganese, microstructure, austenite formation, phase balance, precipitates, element distribution, segregation, depletion, solidification, pitting corrosion resistance, solidification, element loss, evaporation, deposition, weld oxide, thermo-mechanical simulation, thermodynamic modelling, EPMA, XPS, post-weld cleaning, pickling
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-27387 (URN)978-91-7415-801-4 (ISBN)
Public defence
2010-12-17, Sal Q2, Osquldasväg 10 NB, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101213Available from: 2010-12-13 Created: 2010-12-13 Last updated: 2010-12-13Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Westin, Elin M.
In the same journal
Corrosion Science
Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 211 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf