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Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals
University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB.,Trollhättan, Trollhättan, Sweden. (PTW)ORCID iD: 0000-0001-6242-3517
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0001-8822-2705
The University of Manchester, School of Materials,Manchester,UK.
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0001-5110-449X
2018 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 3, p. 517-533Article in journal (Refereed) Published
Abstract [en]

Super duplex stainless steel (SDSS) weld metal microstructures, covering the complete temperature range from ambient to liquidus, were produced by arc heat treatment for 1 and 10 min. Temperature modeling and thermodynamic calculations complemented microstructural studies, hardness mapping and sensitization testing. After 1 min, intermetallics such as sigma and chi phase had precipitated, resulting in moderate sensitization at 720–840 °C. After 10 min, larger amounts of intermetallics resulted in hardness up to 400 HV0.5 and more severe sensitization at 580–920 °C. Coarse and fine secondary austenite precipitated at high and low temperatures, respectively: The finer secondary austenite was more detrimental to corrosion resistance due to its lower content of Cr, Mo, and N as predicted by thermodynamic calculations. Increased hardness and etching response suggest that 475 °C embrittlement had occurred after 10 min. Results are summarized as time-temperature-precipitation and property diagrams for hardness and sensitization.

Place, publisher, year, edition, pages
International Institute of Welding , 2018. Vol. 62, no 3, p. 517-533
Keywords [en]
Super duplex stainless steel, Weld metal, Time-temperature-precipitation diagram, Sensitization, Hardness, Sigma phase, Stationary arc, Heat treatment, Secondary austenite
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-12054DOI: 10.1007/s40194-018-0548-zScopus ID: 000441244700007OAI: oai:DiVA.org:hv-12054DiVA, id: diva2:1181066
Note

First Online: 17 January 2018

Available from: 2018-02-07 Created: 2018-02-07 Last updated: 2018-09-14Bibliographically approved
In thesis
1. Super duplex stainless steels: Microstructure and propertiesof physically simulated base and weld metal
Open this publication in new window or tab >>Super duplex stainless steels: Microstructure and propertiesof physically simulated base and weld metal
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High-temperature processing and application of super duplex stainless steel(SDSS) are associated with the risk of changes in the ferrite/austenite balance and precipitation of secondary phases. This study was therefore aimed at improving knowledge about effects of thermal cycles on the microstructure and properties of SDSS base and weld metal. Controlled and repeatable thermal cycles were physically simulated using the innovative multiple TIG reheating/remelting and the arc heat treatment techniques. In the first technique, one to four autogenous TIG-remelting passes were applied. During arc heat treatment, a stationary arc was applied on a disc mounted on a water-cooled chamber thereby subjecting the material to a steady state temperature gradient from 0.5 minute to 600 minutes. Microstructures and properties were assessed and linked to thermal history through thermal cycle analysis, thermodynamic calculations and temperature field modelling, Remelting studies showed that nitrogen loss from the melt pool was a function of arc energy and initial nitrogen content and could cause highly ferritic microstructures. Heat affected zones were sensitized by nitride formation next to the fusion boundary and sigma phase precipitation in regions subjected to peak temperatures of 828-1028°C. Accumulated time in the critical temperature range, peak temperature and the number of thermal cycles are the most relevant criteria when evaluating the risk of sigma phase precipitation. Arc heat treatment produced graded microstructures in SDSS base and weld metal with the formation of a ferritic region at high temperature due to solid-state nitrogen loss, precipitation of sigma, chi, nitrides, and R-phase with different morphologies at 550-1010°C and spinodal decomposition below 500°C. This caused sensitization and/or increased hardness and embrittlement. Results were summarized as time-temperature-precipitation and properties diagrams for base and weld metal together with guidelines for processing and welding of SDSS.

Place, publisher, year, edition, pages
Trollhättan: University West, 2018. p. 102
Series
PhD Thesis: University West ; 24
Keywords
Super duplex stainless steel; weld metal; physical simulation; phase balance; precipitation; secondary phases; corrosion; nitrogen loss; arc heat treatment; production technology
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12850 (URN)978-91-87531-98-9 (ISBN)978-91-87531-97-2 (ISBN)
Public defence
2018-09-28, F127, lhättan, 09:00 (English)
Supervisors
Available from: 2018-09-04 Created: 2018-08-30

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Hosseini, VahidKarlsson, LeifWessman, Sten

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