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Creep testing of thick-wall copper electron beam and friction stir welds
KTH, Superseded Departments, Materials Science and Engineering.ORCID iD: 0000-0002-8494-3983
2004 (English)In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, Vol. 824, 51-56 p.Article in journal (Refereed) Published
Abstract [en]

Thick section copper canisters are planned to be used as a corrosion protection of nuclear waste disposal containers for long term underground deposal in Sweden. The copper canisters will have the top and possibly the bottom lid welded to the canister walls using electron beam or friction stir welding. Due to the high external hydrostatic pressure and the relatively high temperature of the waste during the first one hundred years the copper will creep. The creep process will close the manufacturing gap between the cast iron container and the copper canister. The creep ductility must be sufficient to avoid cracking of the weld. Specimens cut from the friction stir welds and the electron beam welds have been creep tested at temperatures ranging from 75 to 175 degreesC. Cross-weld specimens were used for both friction stir and electron beam welds. Weld metal, heat affected zone and base metal were also studied for friction stir welds. The results for the electron beam welds show that the main creep deformation is concentrated to the weld metal where the failure takes place. Weld metal and most cross-weld tests of friction stir weld material show similar creep lives and ductility as base metal tests. Ductility at rupture was found to exceed 30% for friction stir weld specimens, and the Norton power law exponent was determined to be between 30 and 50.

Place, publisher, year, edition, pages
2004. Vol. 824, 51-56 p.
Keyword [en]
Materials Science
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-12073ISI: 000224543500008ISBN: 1-55899-774-1OAI: diva2:300979
QC20100719Available from: 2010-03-02 Created: 2010-03-02 Last updated: 2010-07-20Bibliographically approved
In thesis
1. Mechanical Properties of Welds at Creep Activation Temperatures
Open this publication in new window or tab >>Mechanical Properties of Welds at Creep Activation Temperatures
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Welds in materials intended for service at temperatures above the creep activation temperature often develop damage before the base metal. The weld is a discontinuity in the material and stresses and strains often accumulate in the weld. Knowledge of the properties of the weld is essential to the safe operation of the component containing the weld. The work in this thesis has been aimed at the study of welds in service at high temperatures: The work is divided into two main chapters. The first chapter deals with welds in stainlesssteels and dissimilar metal welds and includes three papers, and the second chapter dealswith welds in copper intended for nuclear waste disposal, also including three papers. Common to both parts is that the temperature is high enough for most of the damage in the welds to result from creep.

In the first part the role of the weld microstructure on the creep crack propagation properties has been studied. Experiments using compact tension specimens have been performed on service exposed, low alloyed heat resistant steels. The results show good correlation with the crack tip parameter, C*, during steady state creep crack growth. The test methodology has also been reviewed and sensitive test parameters have been identified. The results from the creep crack propagation tests on service exposed material has been modeled using uniaxial creep data on both new and ex-service material. The development of the weld microstructure in a dissimilar metal weld between two heat resistant steels has also been investigated. A weld was made between one ferritic and one martensitic steel and the development of the microstructure during welding and post-weldheat treatments has been studied. The results show that the carbon depleted zone that develops near the weld metal in the lower alloyed steel depends on the formation and dissolution of the M23C6-carbide. Variations of the weld parameters and the post-weld heat treatment affect the size and shape of this zone. The process has been successfully modeled by computer simulation.

The second part focuses on oxygen free copper intended for nuclear waste disposal containers. The containers are made with an inner core of cast nodular iron and an outer core of copper for corrosion protection. The copper shell has to be welded and two weld methods has been tested, electron beam welding and friction stir welding. Creep specimens taken from both weld types have been tested as have base metal specimens. The technical specifications of the waste canisters demand that the creep ductility of both the copper shell and the welds has to be as high as possible. The creep test results show that base material doped with at least 30 ppm phosphorus has high creep ductility, and friction stir welds made from this material has almost as high creep strength and creep ductility. Copper without phosphorus does not exhibit the same ductility. The creep properties evaluated from testing has been modeled and extrapolated for the intended purpose

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 69 p.
creep, creep crack propagation, OFHC copper, welds, nuclear waste disposal, creep modeling
National Category
Materials Engineering
urn:nbn:se:kth:diva-12077 (URN)978-91-7415-567-9 (ISBN)
Public defence
2010-03-05, Sal E3, Lindstedtsvägen 3, KTH, Stockholm, 10:00 (English)
QC20100719Available from: 2010-03-02 Created: 2010-03-02 Last updated: 2010-07-19Bibliographically approved

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Andersson, Henrik C. M.Sandstrom, Rolf
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