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Deformation structures in a duplex stainless steel
Dalarna University, School of Technology and Business Studies, Materials Technology. KTH, Materialvetenskap.ORCID iD: 0000-0002-4359-4967
Dalarna University, School of Technology and Business Studies, Materials Technology.
2018 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, p. 176-181Article in journal (Refereed) Published
Abstract [en]

The evolution of the deformation structure with strain has been studied using electron backscatter diffraction (EBSD). Samples from interrupted uniaxial tensile tests and from a cyclic tension/compression test were investigated. The evolution of low angle boundaries (LABs) was studied using boundary maps and by measuring the LAB density. From calculations of local misorientations, smaller orientation changes in the substructure can be illustrated. The different orientations developed with strain within a grain, due to operation of different slip systems in different parts of the grain, were studied using a misorientation profile showing substantial orientation changes after a true strain of 0.24. The texture evolution with increasing strain was followed by using inverse pole figures (IPFs). The observed substructure development in the ferritic and austenitic phases could be successfully correlated with the stress-strain curve from a tensile test. LABs were first observed in the different phases when the strain hardening rate changed in appearance indicating that cross slip started to operate as a significant dislocation recovery mechanism. The evolution of the deformation structure is concluded to occur in a similar manner in the austenitic and ferritic phases but with different texture evolution for the two phases.

Place, publisher, year, edition, pages
2018. Vol. 941, p. 176-181
Keywords [en]
Duplex stainless steel, Electron backscatter diffraction (EBSD), Structure-property relationship, Tensile test
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
URN: urn:nbn:se:du-28343DOI: 10.4028/www.scientific.net/MSF.941.176ISI: 000468152500030Scopus ID: 2-s2.0-85064068590OAI: oai:DiVA.org:du-28343DiVA, id: diva2:1239600
Conference
THERMEC 2018
Available from: 2018-05-09 Created: 2018-08-17 Last updated: 2019-06-10Bibliographically approved
In thesis
1. Experimental Studies of Deformation Structures in Stainless Steels using EBSD
Open this publication in new window or tab >>Experimental Studies of Deformation Structures in Stainless Steels using EBSD
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the focus has been the study of deformation structures in stainless steels by using electron backscatter diffraction (EBSD). Via increased knowledge of the evolution of the substructure during deformation, the design and control of the manufacturing process can be improved.

A relation was found between the active deformation mechanisms, the evolution of low angle boundaries (LABs) and the strain hardening rate. When deformation twinning was an active deformation mechanism in an austenitic stainless steel with lower stacking fault energy (SFE), the strain hardening rate was maintained up to large strains due to formation of LABs. The deformation twin boundaries acted as new obstacles for dislocation slip which in turn increased the formation of LABs even further. During deformation by slip in an austenitic stainless steel with a higher SFE, the strain hardening rate instead decreased when LABs were formed. A high value of SFE promotes dislocation cross slip which in turn increases annihilation of dislocations leading to a minor increase in LAB formation.

Deformation structures formed in surface grains during in situ tensile tests were found to develop at lower strains than in bulk grains obtained from interrupted conventional tensile tests. This behavior is consistent with the fact that dislocations sources and deformation twinning operate at approximately half the stress on a free surface as compared to the bulk.

The deformation structures were quantified by measuring size distributions for entities bounded by LABs and high angle boundaries (HABs). The size distributions were found to be well described by bimodal lognormal distribution functions. The average size for the distribution of small grains and subgrains correlated well with the mean free distance of dislocation slip and to the strain hardening.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 63
Keywords
EBSD, Austenitic stainless steels, Duplex stainless steel, In situ tensile test, Grain boundaries, Grain rotation, Grain size distribution, Texture, Strain hardening, Structure-property relationship, High strain rate, Wire rod rolling, Roll forming
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-28340 (URN)978-91-7729-772-7 (ISBN)
Public defence
2018-06-05, B2, Brinellvägen 23, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2018-08-17 Created: 2018-08-17 Last updated: 2018-08-17Bibliographically approved

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Yvell, KarinEngberg, Göran

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