du.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Engberg, Göran
Publications (10 of 12) Show all publications
Molnar, D., Sun, X., Lu, S., Li, W., Engberg, G. & Vitos, L. (2019). Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel. Materials Science & Engineering: A, 759, 490-497
Open this publication in new window or tab >>Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel
Show others...
2019 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, p. 490-497Article in journal (Refereed) Published
Abstract [en]

The stacking fault energy (SFE) is often used as a key parameter to predict and describe the mechanical behaviour of face centered cubic material. The SFE determines the width of the partial dislocation ribbon, and shows strong correlation with the leading plastic deformation modes. Based on the SFE, one can estimate the critical twinning stress of the system as well. The SFE mainly depends on the composition of the system, but temperature can also play an important role. In this work, using first principles calculations, electron backscatter diffraction and tensile tests, we show a correlation between the temperature dependent critical twinning stress and the developing microstructure in a typical austenitic stainless steel (316L) during plastic deformation. We also show that the deformation twins contribute to the strain hardening rate and gradually disappear with increasing temperature. We conclude that, for a given grain size there is a critical temperature above which the critical twinning stress cannot be reached by normal tensile deformation, and the disappearance of the deformation twinning leads to lower strain hardening rate and decreased ductility.

Keywords
Deformation twinning, microstructure, first principles, stacking fault energy, stainless steel
National Category
Metallurgy and Metallic Materials
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-30092 (URN)10.1016/j.msea.2019.05.079 (DOI)000472813900052 ()2-s2.0-85066090205 (Scopus ID)
Funder
Vinnova, 2014-03374
Available from: 2019-05-23 Created: 2019-05-23 Last updated: 2019-12-05Bibliographically approved
Molnar, D., Engberg, G., Li, W., Lu, S., Hedström, P., Kwon, S. K. & Vitos, L. (2019). Experimental study of the gamma-surface of austenitic stainless steels. Acta Materialia, 173, 34-43
Open this publication in new window or tab >>Experimental study of the gamma-surface of austenitic stainless steels
Show others...
2019 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 173, p. 34-43Article in journal (Refereed) Published
Abstract [en]

We introduce a theory-guided experimental approach to study the γ-surface of austenitic stainless steels. The γ-surface includes a series of intrinsic energy barriers (IEBs), which are connected to the unstable stacking fault (USF), the intrinsic stacking fault (ISF), the unstable twinning fault (UTF) and the extrinsic stacking fault (ESF) energies. The approach uses the relationship between the Schmid factors and the effective energy barriers for twinning and slip. The deformation modes are identified as a function of grain orientation using in situ electron backscatter diffraction measurements. The observed critical grain orientation separating the twinning and slip regimes yields the USF energy, which combined with the universal scaling law provides access to all IEBs. The measured IEBs and the critical twinning stress are verified by direct first-principles calculations. The present advance opens new opportunities for modelling the plastic deformation mechanisms in multi-component alloys.

Keywords
stacking fault energy, twinning, electron backscatter diffraction, plasticity, first-principles
National Category
Metallurgy and Metallic Materials
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-29982 (URN)10.1016/j.actamat.2019.04.057 (DOI)000472812300005 ()2-s2.0-85065259834 (Scopus ID)
Available from: 2019-05-07 Created: 2019-05-07 Last updated: 2019-12-05Bibliographically approved
Safara Nosar, N., Engberg, G. & Ågren, J. (2019). Modeling microstructure evolution in a martensitic stainless steel subjected to hot working using a physically based model. Metallurgical and Materials Transactions. A, 50(3), 1480-1488
Open this publication in new window or tab >>Modeling microstructure evolution in a martensitic stainless steel subjected to hot working using a physically based model
2019 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50, no 3, p. 1480-1488Article in journal (Refereed) Published
Abstract [en]

The microstructure evolution of a martensitic Stainless steel subjected to hot compression is simulated with a physically based model. The model is based on coupled sets of evolution equations for dislocations, vacancies, recrystallization and grain growth. The advantage of this model is that with only a few experiments, the material dependent parameters of the model can be calibrated and used for a new alloy in any deformation condition. The experimental data of this work is obtained from a series of hot compression, and subsequent stress relaxation tests performed in a Gleeble thermo-mechanical simulator. These tests are carried out at various temperatures ranging from 900 to 1200⁰C, strains up to 0.7 and strain rates of 0.01, 1 and 10 s-1. The grain growth, flow stress, and stress relaxations are simulated by finding reasonable values for model parameters. The flow stress data obtained at the strain rate of 10 s-1 were used to calibrate the model parameters and the predictions of the model for the lower strain rates were quite satisfactory. An assumption in the model is that the structure of second phase particles does not change during the short time of deformation. The results show a satisfactory agreement between the experimental data and simulated flow stress, as well as less than 5% difference for grain growth simulations and predicting the dominant softening mechanisms during stress relaxation according to the strain rates and temperatures under deformation.

Keywords
Modeling, Dislocation density, Flow Stress, Grain Growth, Recrystallization, Hot Compression, Martensitic Stainless Steel
National Category
Metallurgy and Metallic Materials Manufacturing, Surface and Joining Technology
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-29041 (URN)10.1007/s11661-018-5073-6 (DOI)000457551800036 ()2-s2.0-85058849719 (Scopus ID)
Available from: 2018-12-10 Created: 2018-12-10 Last updated: 2019-03-05Bibliographically approved
Safara Nosar, N., Golpayegani, A., Engberg, G. & Ågren, J. (2019). Study of the mean size and fraction of the second-phase particles in a 13% chromium steel at high temperature. Philosophical Magazine, 1-17
Open this publication in new window or tab >>Study of the mean size and fraction of the second-phase particles in a 13% chromium steel at high temperature
2019 (English)In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, p. 1-17Article in journal (Refereed) Published
Abstract [en]

The mean size and fraction of the second-phase particles in a 13% chromium steel are investigated, while no plastic deformation was applied. The results of the measurement are compared with the modelling results from a physicallybased model. The heating sequence is performed on samples using a Gleeble thermo-mechanical simulator over the temperature range of 850?1200°C. Using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), the size distribution and composition of the carbides were evaluated, respectively. For obtaining particle size distribution (PSD), an image-processing software was employed to analyse the SEM images. Additionally, the relation between the 2D shape factor and size of the particles is also studied at different temperatures and most of the particles turned out to have a shape factor close to two. In order to measure the carbide weight fraction, electrochemical phase isolation was employed. The Ms and fraction of the martensite phase after quenching of samples are calculated and the results were comparable with the measured hardness values at corresponding temperatures. The measured hardness of the samples is found to comply very well with the measured mean size of the precipitates. The calculated mean size of the particles from the model shows very good agreement with both hardness value and experimentally measured mean size, while the calculated volume fraction from simulation follows a slightly different trend.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
National Category
Metallurgy and Metallic Materials
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-31030 (URN)10.1080/14786435.2019.1674455 (DOI)2-s2.0-85074354022 (Scopus ID)
Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-11-21Bibliographically approved
Engberg, G., Grehk, M. & Yvell, K. (2018). Analysis of the plastic deformation behavior for two austenitic NiCr-steels with different stacking fault energies. Paper presented at International Conference on Computational Materials Science and Thermodynamic Systems. International Journal of Computational Physics Series, 1(1), 137-141
Open this publication in new window or tab >>Analysis of the plastic deformation behavior for two austenitic NiCr-steels with different stacking fault energies
2018 (English)In: International Journal of Computational Physics Series, ISSN 2631-8350, Vol. 1, no 1, p. 137-141Article in journal (Refereed) Published
Abstract [en]

Two austenitic stainless steels, with low and medium stacking fault energies (SFE), 20 mJ/m2 and 30 mJ/m2 respectively, have been studied by conventional tensile tests and in situ tensile tests in a FEG-SEM equipped for EBSD. High angle boundaries (HAB) and low angle boundaries (LAB) with misorientations >= 10o and >= 2o respectively have been determined, and size distributions for the LABs have been derived by linear intercepts. It was found that the size distributions could be described by bimodal lognormal functions. For the steel with highest SFE plastic deformation took place by dislocation slip only while the steel with low SFE deformed by slip and twinning. Using a model for slip based on the evolution of the dislocation density with the generation of dislocations inversely proportional to the mean free distance of slip and recovery of dislocations proportional to the dislocation density the stress strain-curves were analyzed and the results compared with the measured quantities. The mean free distance of slip as evaluated from the stress-strain curve for the steel with the highest SFE correlates very well with the mean size of the LABs intercept. The rate of recovery also gave an expected stress dependence. The stress needed to start deformation twinning was based on the assumption that Shockley partials become completely separated in the slip plane. The thus calculated values for the twinning stress showed an excellent agreement with the observed start of twinning as given by EBSD evaluation of twin boundaries (TB). For the alloy with low SFE both surface grains (in situ test) and bulk grains (from interrupted conventional tests) were studied. The stress needed for slip and twinning of surface grains was, as expected, in the order of 0.5-0.6 times the applied stress.

Place, publisher, year, edition, pages
NSSEL Publishing, 2018
Keywords
Austenitic stainless steels, Electron backscatter diffraction (EBSD), In situ tension test, Grain boundaries, Flow stress model
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-30084 (URN)10.29167/A1I1P137-141 (DOI)
Conference
International Conference on Computational Materials Science and Thermodynamic Systems
Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-05-22Bibliographically approved
Safara Nosar, N., Sandberg, F. & Engberg, G. (2018). Characterization of hot deformation behavior in a 13% chromium steel. Paper presented at Thermec 2018. Materials Science Forum, 941, 458-467
Open this publication in new window or tab >>Characterization of hot deformation behavior in a 13% chromium steel
2018 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, p. 458-467Article in journal (Refereed) Published
Abstract [en]

The behavior of a 13% chromium steel subjected to hot deformation has been studied by performing hot compression tests in the temperature range of 850 to 1200 ⁰C and strain rates from 0.01 to 10 s-1. The uniaxial isothermal compression tests were performed on a Gleeble thermo-mechanical simulator. The best function that fits the peak stress for the material and its relation to the Zener-Hollomon parameter (Z) is illustrated. The average activation energy of this alloy for the entire test domain was reviled to be about 557 [kJ mol-1] from the calculations and the dynamic recrystallization (DRX) kinetic were studied to find the fraction DRX in the course of deformation.

Keywords
13% chromium steel, hot deformation, Zener-Hollomon parameter, Dynamic recrystallization Kinetic
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-29043 (URN)10.4028/www.scientific.net/MSF.941.458 (DOI)000468152500075 ()2-s2.0-85064075652 (Scopus ID)
Conference
Thermec 2018
Available from: 2018-12-10 Created: 2018-12-10 Last updated: 2019-06-10Bibliographically approved
Molnar, D., Engberg, G., Li, W. & Vitos, L. (2018). Deformation properties of austenitic stainless steels with different stacking fault energies. Paper presented at THERMEC 2018. Materials Science Forum, 941, 190-197
Open this publication in new window or tab >>Deformation properties of austenitic stainless steels with different stacking fault energies
2018 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, p. 190-197Article in journal (Refereed) Published
Abstract [en]

In FCC metals a single parameter – stacking fault energy (SFE) – can help to predict the expectable way of deformation such as martensitic deformation, deformation twinning or pure dislocation glide. At low SFE one can expect the perfect dislocations to dissociate into partial dislocations, but at high SFE this separation is more restricted. The role of the magnitude of the stacking fault energy on the deformation microstructures and tensile behaviour of different austenitic steels have been investigated using uniaxial tensile testing and electron backscatter diffraction (EBSD). The SFE was determined by using quantum mechanical first-principles approach. By using plasticity models we make an attempt to explain and interpret the different strain hardening behaviour of stainless steels with different stacking fault energies.

Place, publisher, year, edition, pages
Switzerland: , 2018
Keywords
Ab Initio, Deformation, EBSD, Modelling, SEM, Stainless Steel, Tensile Testing, Thermec’2018
National Category
Metallurgy and Metallic Materials
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-29197 (URN)10.4028/www.scientific.net/MSF.941.190 (DOI)000468152500032 ()2-s2.0-85064085774 (Scopus ID)
Conference
THERMEC 2018
Available from: 2018-12-26 Created: 2018-12-26 Last updated: 2019-12-05Bibliographically approved
Yvell, K. & Engberg, G. (2018). Deformation structures in a duplex stainless steel. Paper presented at THERMEC 2018. Materials Science Forum, 941, 176-181
Open this publication in new window or tab >>Deformation structures in a duplex stainless steel
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.

Keywords
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:nbn:se:du-28343 (URN)10.4028/www.scientific.net/MSF.941.176 (DOI)000468152500030 ()2-s2.0-85064068590 (Scopus ID)
Conference
THERMEC 2018
Available from: 2018-05-09 Created: 2018-08-17 Last updated: 2019-06-10Bibliographically approved
Yvell, K., Grehk, T. M., Hedström, P., Borgenstam, A. & Engberg, G. (2018). EBSD analysis of surface and bulk microstructure evolution during interrupted tensile testing of a Fe-19Cr-12Ni alloy. Materials Characterization, 141, 8-18
Open this publication in new window or tab >>EBSD analysis of surface and bulk microstructure evolution during interrupted tensile testing of a Fe-19Cr-12Ni alloy
Show others...
2018 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 141, p. 8-18Article in journal (Refereed) Published
Abstract [en]

Abstract The microstructure evolution in both surface and bulk grains in a pure Fe-19Cr-12Ni alloy has been analyzed using electron backscatter diffraction after tensile testing interrupted at different strains. Surface grains were studied during in situ tensile testing performed in a scanning electron microscope, whereas bulk grains were studied after conventional tensile testing. The evolution of the deformation structure in surface and bulk grains displays a strong resemblance but the strain needed to obtain a similar deformation structure is lower in the case of surface grains. Both slip and twinning are observed to be important deformation mechanisms, whereas deformation-induced martensite formation is of minor importance. Since the stacking fault energy (SFE) is low, 17mJ/m2, dynamic recovery by cross slip of un-dissociated dislocations is unfavorable. This reduces the annihilation of dislocations which in turn leads to a significant increase of low angle boundaries with increasing strain. The low SFE also favors formation of deformation twins which reduces the slip distance, leading to a hardening similar to the Hall-Petch relation. The combination of a low ability for cross-slip and a reduced slip distance caused by twinning is concluded to be the main reason for maintaining a high strain-hardening rate up to strains close to necking.

Keywords
Austenitic stainless steels, Electron backscatter diffraction (EBSD), In situ tension test, Grain boundaries, Grain rotation
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-27537 (URN)10.1016/j.matchar.2018.04.035 (DOI)000435428100002 ()2-s2.0-85046128454 (Scopus ID)
Note

Open Access APC beslut 12/2018

Available from: 2018-04-27 Created: 2018-04-27 Last updated: 2018-08-17Bibliographically approved
Yvell, K., Grehk, T. M., Hedström, P., Borgenstam, A. & Engberg, G. (2018). Microstructure development in a high-nickel austenitic stainless steel using EBSD during in situ tensile deformation. Materials Characterization, 135(Supplement C), 228-237
Open this publication in new window or tab >>Microstructure development in a high-nickel austenitic stainless steel using EBSD during in situ tensile deformation
Show others...
2018 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 135, no Supplement C, 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.

Keywords
Austenitic stainless steels, Electron backscatter diffraction (EBSD), In situ tension test, Grain boundaries, grain rotation
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
urn:nbn:se:du-26645 (URN)10.1016/j.matchar.2017.11.046 (DOI)000423248200027 ()2-s2.0-85035068432 (Scopus ID)
Note

Open Access APC beslut 13/2018

Available from: 2017-11-30 Created: 2017-11-30 Last updated: 2018-08-17
Organisations

Search in DiVA

Show all publications