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Microstructure development in a high-nickel austenitic stainless steel using EBSD during in situ tensile deformation
Materials Science, Dalarna University, Falun, Sweden.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0003-1102-4342
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-7656-9733
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2018 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 135, p. 228-237Article in journal (Refereed) Published
Abstract [en]

Plastic deformation of surface grains has been observed by electron backscatter diffraction technique during in situ tensile testing of a high-nickel austenitic stainless steel. The evolution of low- and high-angle boundaries as well as the orientation changes within individual grains has been studied. The number of low-angle boundaries and their respective misorientation increases with increasing strain and some of them also evolve into high-angle boundaries leading to grain fragmentation. The annealing twin boundaries successively lose their integrity with increasing strain. The changes in individual grains are characterized by an increasing spread of orientations and by grains moving towards more stable orientations with < 111 > or < 001 > parallel to the tensile direction. No deformation twins were observed and deformation was assumed to be caused by dislocation slip only.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 135, p. 228-237
Keywords [en]
Austenitic stainless steels, Electron backscatter diffraction (EBSD), In situ tension test, Grain boundaries, grain rotation
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-222442DOI: 10.1016/j.matchar.2017.11.046ISI: 000423248200027Scopus ID: 2-s2.0-85035068432OAI: oai:DiVA.org:kth-222442DiVA, id: diva2:1183831
Note

QC 20180219

Available from: 2018-02-19 Created: 2018-02-19 Last updated: 2018-05-14Bibliographically 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
Series
TRITA-ITM-AVL ; 2018:24
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
Identifiers
urn:nbn:se:kth:diva-227663 (URN)978-91-7729-772-7 (ISBN)
Public defence
2018-06-05, B2, Brinellvägen 23, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note

QC 20180514

Available from: 2018-05-14 Created: 2018-05-09 Last updated: 2018-05-14Bibliographically approved

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Hedström, PeterBorgenstam, Annika

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