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Publications (4 of 4) Show all publications
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)000491547100001 ()2-s2.0-85074354022 (Scopus ID)
Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2020-06-01Bibliographically 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
Safara Nosar, N. & Olsson, M. (2013). Influence of tool steel surface topography on adhesion and material transfer in stainless steel/tool steel sliding contact. Wear, 303(1-2), 30-39
Open this publication in new window or tab >>Influence of tool steel surface topography on adhesion and material transfer in stainless steel/tool steel sliding contact
2013 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 303, no 1-2, p. 30-39Article in journal (Refereed) Published
Abstract [en]

Transfer of work material to the tool surface is a common problem in many metal forming and metal working operations, especially in the case of work materials with a high adhesion tendency e.g. stainless steel, aluminum and titanium. In many operations, material transfer occurs already during the initial contact and with time it may result in degradation and roughening of the tool surface which will affect the surface quality of the formed or machined work material surface, e.g. problems related to galling in sheet metal forming. In the present study, the mechanisms behind the initial stages of material transfer between stainless steel and tool steel have been investigated under well controlled laboratory conditions and analyzed using optical surface profilometry and scanning electron microscopy.The results show that, independent of tool surface topography, transfer of stainless steel occurs already after a very short sliding distance. Depending on the tool steel surface topography, initial transfer occurs on two different scales. For a fine polished tool steel surface, fine scale transfer occurs in connection to protruding hard phase particles (carbides and carbonitrides) while for a ground rough surface large scale transfer occurs in connection to grinding scratches, where these act to mechanically scrape off material resulting in lumps off stainless steel on the tool steel surface. Also, sliding perpendicular to the grinding scratches results in more severe material transfer as compared with sliding parallel to the grinding scratches. Finally, the present paper illuminates the usefulness of combining optical surface profilometry and scanning electron microscopy as a powerful analytical tool when it comes to understanding the mechanisms controlling material transfer in a sliding contact on a Όm-scale level. © 2013 Elsevier B.V.

Keywords
Controlled laboratories; Galling; Initial contact; Material transfers; Optical surfaces; Scanning electrons; Sliding contacts; Sliding distances, Adhesion; Carbides; Carbon nitride; Grinding (machining); Metal forming; Metal working; Profilometry; Scanning electron microscopy; Stainless steel; Surface properties; Surface topography, Tool steel
National Category
Materials Engineering
Research subject
Stålformning och ytteknik
Identifiers
urn:nbn:se:du-12194 (URN)10.1016/j.wear.2013.02.015 (DOI)000322422500004 ()
Available from: 2013-05-08 Created: 2013-05-08 Last updated: 2017-12-06Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3812-5285

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