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Microstructure characterization of 316L deformed at high strain rates using EBSD
Material Science, Dalarna University, Falun, Sweden.
2016 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 122, p. 14-21Article in journal (Refereed) Published
Abstract [en]

Specimens from split Hopkinson pressure bar experiments, at strain rates between ~ 1000–9000 s− 1 at room temperature and 500 �C, have been studied using electron backscatter diffraction. No significant differences in the microstructures were observed at different strain rates, but were observed for different strains and temperatures. Size distribution for subgrains with boundary misorientations > 2� can be described as a bimodal lognormal area distribution. The distributions were found to change due to deformation. Part of the distribution describing the large subgrains decreased while the distribution for the small subgrains increased. This is in accordance with deformation being heterogeneous and successively spreading into the undeformed part of individual grains. The variation of the average size for the small subgrain distribution varies with strain but not with strain rate in the tested interval. The mean free distance for dislocation slip, interpreted here as the average size of the distribution of small subgrains, displays a variation with plastic strain which is in accordance with the different stages in the stress-strain curves. The rate of deformation hardening in the linear hardening range is accurately calculated using the variation of the small subgrain size with strain.

Place, publisher, year, edition, pages
2016. Vol. 122, p. 14-21
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-227660DOI: 10.1016/j.matchar.2016.10.017ISI: 000390728300003Scopus ID: 2-s2.0-84994056236OAI: oai:DiVA.org:kth-227660DiVA, id: diva2:1205023
Note

QC 20180514

Available from: 2018-05-09 Created: 2018-05-09 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
Keyword
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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