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Deformation behaviour of a prestrained duplex stainless steel
Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-2286-5588
2002 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, Vol. 337, no 1-2, 25-38 p.Article in journal (Refereed) Published
Abstract [en]

The anisotropic flow behaviour due to a change in strain path during uniaxial deformation of a duplex stainless steel has been investigated. The anisotropic flow behaviour of the as-received material could be predicted from the crystallographic texture. However, it was found that prestraining introduces a transient work hardening behaviour during the second stage deformation, which causes an anisotropic flow behaviour immediately after yielding that cannot be described by the crystallographic texture. Samples subjected to a coaxial second stage deformation show a small increase in flow stress and similar work hardening rate as in the monotonic loading. Samples subjected to noncoaxial second stage deformation show a pronounced transient stage characterised by early yielding and a high work hardening rate in the first part of the transient stage. Beyond the earliest stage of deformation a higher flow stress and a lower work hardening rate compared to monotonic loading is observed for the noncoaxial samples. The transient phenomena are discussed based on the measured internal stresses and the differences in dislocation structures in the two different phases.

Place, publisher, year, edition, pages
2002. Vol. 337, no 1-2, 25-38 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-30008DOI: 10.1016/S0921-5093(02)00022-9Local ID: 15451OAI: oai:DiVA.org:liu-30008DiVA: diva2:250827
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-10-02
In thesis
1. Microstresses and anisotropic mechanical behaviour of duplex stainless steels
Open this publication in new window or tab >>Microstresses and anisotropic mechanical behaviour of duplex stainless steels
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The evolution of deformation during monotonic and cyclic loading of a two-phase material like duplex stainless steel is more complex than in a single-phase material. One reason for this is the microstresses formed due to differences in thermal and mechanical properties between the two phases. Another factor contributing to a complex load partitioning between the two phases is that hot and cold rolled duplex stainless steel exhibits anisotropic material properties. The aim of this thesis has therefore been to investigate the influence of microstresses and an isotropy on the mechanical properties of duplex stainless steels.

The effect of microstresses was clearly revealed when X-ray diffraction was used to study the evolution of microstresses during cyclic loading. Even if the hardness and yield strength were found to be higher in the austenitic phase compared to the ferritic phase more plastic deformation occurs in austenite during cyclic tensile loading. This was also confirmed by transmission electron microscopy investigations of the dislocation structure in both phases. The main reason for the higher degree of plastic deformation in the austenitic phase is that the microstresses are tensile in this phase and compressive in the ferritic phase.

Measurements of the crystallographic texture were used as input to theoretical predictions of both elastic and plastic anisotropy. The predicted anisotropic material properties were then used in finite element simulations to study the flow behavior and the load partitioning between phases during deformation in different loading directions. The experiments and the simulations show that the microstresses and the anisotropy make the load partitioning between the two phases dependent on the loading direction. For loading in the rolling direction, both phases deform plastically to the same degree, while more plastic deformation occurs in the austenitic phase during loading in the transverse direction. For loading in the 45°-direction more plastic deformation occurs in the ferritic phase.

The anisotropic flow behaviour of the as-received material can be predicted from the crystallographic texture. However, it was found that prestraining introduces a transient work hardening behaviour during the second stage deformation, whjch causes an anisotropic flow behaviour immediately after yielding that cannot be described by the crystallographic texture. Instead the an isotropy can be associated with the rearrangement of the dislocation structure that occurs during changes in the loading path. Prestraining also alters the microstresses from being higher in the transverse direction to being higher in the rolling direction. At the same time the fatigue limit is changed from being higher in the rolling direction to being higher in the transverse direction. This study shows that microstresses have a significant influence on fatigue crack initiation and the fatigue limit of duplex stainless steels.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2001. 52 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 699
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-30059 (URN)15519 (Local ID)91-737-3043-2 (ISBN)15519 (Archive number)15519 (OAI)
Public defence
2001-06-11, Sal Schrödinger, Fysikhuset, Linköpings Universitet, Linköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-02-14

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Moverare, JohanOdén, Magnus

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