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Evolution of the residual stress state in a duplex stainless steel during loading
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
Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
1999 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 47, no 9, p. 2669-2684Article in journal (Refereed) Published
Abstract [en]

The evolution of micro- and macrostresses in a duplex stainless steel during loading has been investigated in situ by X-ray diffraction. A 1.5 mm cold-rolled sheet of alloy SAF 2304 solution treated at 1050°C was studied. Owing to differences in the coefficient of thermal expansion between the two phases, compressive residual microstresses were found in the ferritic phase and balancing tensile microstresses in the austenitic phase. The initial microstresses were almost two times higher in the transverse direction compared to the rolling direction. During loading the microstresses increase in the macroscopic elastic regime but start to decrease slightly with increasing load in the macroscopic plastic regime. For instance, the microstresses along the rolling direction in the austenite increase from 60 MPa, at zero applied load, to 110 MPa, at an applied load of 530 MPa. At the applied load of 620 MPa a decrease of the microstress to 90 MPa was observed. During unloading from the plastic regime the microstresses increase by approximately 35 MPa in the direction of applied load but remain constant in the other directions. The initial stress state influences the stress evolution and even after 2.5% plastic strain the main contribution to the microstresses originates from the initial thermal stresses. Finite element simulations show stress variations within one phase and a strong influence of both the elastic and plastic anisotropy of the individual phases on the simulated stress state.

Place, publisher, year, edition, pages
Elsevier , 1999. Vol. 47, no 9, p. 2669-2684
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-30076DOI: 10.1016/S1359-6454(99)00149-4Local ID: 15539OAI: oai:DiVA.org:liu-30076DiVA, id: diva2:250897
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
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. p. 52
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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Johansson (Moverare), JohanOdén, Magnus

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