| 1. |
- Li, Yan, et al.
(författare)
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Influence of Short Intercritical Annealing Times on the Microstructure and Tensile Properties of a Cold-rolled Medium Mn Steel
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This work studies the microstructure and tensile properties of a cold-rolled Fe–0.204C–4.86Mn (mass %) steel after short intercritical annealing (IA) times, i.e. 3 and 10 min. The short IA time is applied to represent the process characteristics of the industrial continuous annealing line. The microstructure evolution is studied using scanning and transmission electron microscopy, and the tensile properties are obtained using uniaxial tensile tests. The experimental results show that IA temperature (600–700 °C) has strong, while IA time has less, influence on the final microstructure and tensile properties. The fractions of retained austenite are much higher after IA at 650 and 675 °C (~ 10 vol. %) than the other IA temperatures, and thus result in improved elongation (~ 20–30 %). Simulations using the DICTRA software and constitutive modeling are further performed to assist the understanding of the microstructure evolution and stress-strain curves.
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| 2. |
- Huyan, Fei, et al.
(författare)
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Experimental Determination and Thermodynamic Modeling of Msσ for a Medium Mn Steel
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Medium Mn steels have attracted worldwide interests recent years due to their excellent mechanical properties and low cost. These steels contain large fraction (~30%) of metastable retained austenite and exhibit good elongation due to transformation-induced plasticity (TRIP). In order to obtain the highest elongation, the mechanical stability of austenite, quantified using Msσ, needs to be optimized. Msσ is defined as the highest temperature at which martensite can form under stress without austenite yielding by slip. The present work aims to formulate a model of Msσ which can be used to design medium Mn steels with optimized elongation. In the present work, an Fe–0.18C–5.08Mn (mass %) steel was intercritically annealed at 650 °C. Based on tensile tests at different temperatures using a single specimen method, the Msσ temperatures were experimentally determined to about 0 °C regardless of intercritical annealing time between 15 min and 3 h. Microstructure observations showed that large austenite grains with a globular shape are more transformed than thin-film ones, and thus the former probably governs the determined Msσ. Msσ was further predicted at the crossing point of yielding by martensite formation and by austenite slip; the former was modeled by expanding an existing model of martensite start temperature and the latter by a constitutive model. The predicted Msσ showed reasonable agreement with the determined values. The model also indicated that a large and a small austenite grain have similar Msσ, which could partly explain why the determined Msσ is rather constant regardless of IA time.
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| 3. |
- Huyan, Fei, et al.
(författare)
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Influence of Sub-micron Austenite Grain Size on Martensitic Transformation in a Medium Mn Steel
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Many previous studies suggest that austenite stability increases with decreasing grain size, i.e. the martensite start temperature, Ms, decreases. Therefore, the influence of small austenite grain size would be high for many modern steels containing fine austenite. Models from literature deviate severely from each other for grain sizes below 1 μm where there is a lack of experimental data. Besides, the experimental data are mostly obtained from a fully austenitic microstructure with equiaxed grains. This raises concerns about the applicability of these models to design medium Mn steels, where the austenite stability is essential for elongation via transformation-induced plasticity. The present work concerns the influence of grain size on martensitic transformation for thin-film austenite in a medium Mn steel. After IA, austenite grains exhibit two morphologies, thin-film like and globular, while the former is dominant. The globular austenite is less stable and responsible for the Ms measured by dilatometry. Similar to particles, the austenite grains are isolated and dispersed, and autocatalysis from surrounding austenite is minimized. Therefore in this work an approach to describe the transformation in small particles has been adopted, where the number fraction of partly or fully transformed austenite grains (F) is phenomenologically formulated as a function of temperature and grain size. Experimental data from the present work and from literature have been used to derive a model of Ms and grain size for thin-film austenite in medium Mn steels, using the cross-sectional area of austenite grain as a variable. The current model provides a practical and useful way of determining austenite stability from 2-dimensional micrograph, and can be used in designing medium Mn steels with optimized austenite stability.
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| 4. |
- Huyan, Fei, et al.
(författare)
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On the tuning of austenite stability in a medium mn trip steel
- 2015
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Ingår i: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015. - : International Conference on Solid-Solid Phase Transformations in Inorganic Materials. - 9780692437360 ; , s. 933-934
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Konferensbidrag (refereegranskat)
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| 5. |
- Huyan, Fei, et al.
(författare)
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Simulation of the Growth of Austenite from As-Quenched Martensite in Medium Mn Steels
- 2018
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 49A:4, s. 1053-1060
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Tidskriftsartikel (refereegranskat)abstract
- As part of an ongoing development of third-generation advanced high-strength steels with acceptable cost, austenite reversion treatment of medium Mn steels becomes attractive because it can give rise to a microstructure of fine mixture of ferrite and austenite, leading to both high strength and large elongation. The growth of austenite during intercritical annealing is crucial for the final properties, primarily because it determines the fraction, composition, and phase stability of austenite. In the present work, the growth of austenite from as-quenched lath martensite in medium Mn steels has been simulated using the DICTRA software package. Cementite is added into the simulations based on experimental observations. Two types of systems (cells) are used, representing, respectively, (1) austenite and cementite forming apart from each other, and (2) austenite forming on the cementite/martensite interface. An interfacial dissipation energy has also been added to take into account a finite interface mobility. The simulations using the first type of setup with an addition of interfacial dissipation energy are able to reproduce the observed austenite growth in medium Mn steels reasonably well.
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| 6. |
- Kristan, Matej, et al.
(författare)
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The Visual Object Tracking VOT2015 challenge results
- 2015
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Ingår i: Proceedings 2015 IEEE International Conference on Computer Vision Workshops ICCVW 2015. - : IEEE. - 9780769557205 ; , s. 564-586
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Konferensbidrag (refereegranskat)abstract
- The Visual Object Tracking challenge 2015, VOT2015, aims at comparing short-term single-object visual trackers that do not apply pre-learned models of object appearance. Results of 62 trackers are presented. The number of tested trackers makes VOT 2015 the largest benchmark on short-term tracking to date. For each participating tracker, a short description is provided in the appendix. Features of the VOT2015 challenge that go beyond its VOT2014 predecessor are: (i) a new VOT2015 dataset twice as large as in VOT2014 with full annotation of targets by rotated bounding boxes and per-frame attribute, (ii) extensions of the VOT2014 evaluation methodology by introduction of a new performance measure. The dataset, the evaluation kit as well as the results are publicly available at the challenge website(1).
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| 7. |
- Kristan, Matej, et al.
(författare)
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The Visual Object Tracking VOT2016 Challenge Results
- 2016
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Ingår i: COMPUTER VISION - ECCV 2016 WORKSHOPS, PT II. - Cham : SPRINGER INT PUBLISHING AG. - 9783319488813 - 9783319488806 ; , s. 777-823
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Konferensbidrag (refereegranskat)abstract
- The Visual Object Tracking challenge VOT2016 aims at comparing short-term single-object visual trackers that do not apply pre-learned models of object appearance. Results of 70 trackers are presented, with a large number of trackers being published at major computer vision conferences and journals in the recent years. The number of tested state-of-the-art trackers makes the VOT 2016 the largest and most challenging benchmark on short-term tracking to date. For each participating tracker, a short description is provided in the Appendix. The VOT2016 goes beyond its predecessors by (i) introducing a new semi-automatic ground truth bounding box annotation methodology and (ii) extending the evaluation system with the no-reset experiment.
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| 8. |
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| 9. |
- Yan, Jiayi, et al.
(författare)
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Configurational thermodynamics of C in body-centered cubic/tetragonal Fe : A combined computational study
- 2018
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Ingår i: Computational materials science. - : ELSEVIER SCIENCE BV. - 0927-0256 .- 1879-0801. ; 147, s. 293-303
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Tidskriftsartikel (refereegranskat)abstract
- Configurational thermodynamics of C in body-centered cubic (bcc) or tetragonal (bct) Fe is investigated combining several computational techniques. Pairwise CAC interaction energies in bcc Fe are calculated by density functional theory (DFT) and embedded atom method (EAM) potential respectively. The interaction between C atom and homogeneous strain is calculated assuming C acts as force dipoles in linear elastic medium of Fe. The CAC and C-strain interactions are input into Monte Carlo (MC) simulations to find equilibrium C configuration on octahedral interstitial sublattices (OISs) in bcc/bct Fe and corresponding thermodynamic properties. In bcc Fe, DFT-MC and EAM-MC both give a single-phase region with C distributed with disorder on all the three OISs (alpha) at high temperature, and a two-phase region with ferrite and an ordered compound (alpha''') at low temperature. The compound is Fe16C1 according to DFT or Fe16C2 according to EAM inputs, both having two OISs occupied. When a homogeneous tetragonal lattice strain is applied, the disordered phase exhibits a preferential sublattice occupation (Zener ordered alpha'), which is primarily caused by C-strain interaction and is mitigated by CAC interactions. The ordered compound may also have two (alpha''') or one (alpha '') OIS occupied. C clustering in bcc/bct Fe follows a conditional spinodal mechanism, namely long-range order being a prerequisite of spinodal decomposition. This is verified by the difference in solution thermodynamics of alpha/alpha' (ordering-type) and a'''/a '' (clusteringtype), as well as kinetic Ising model simulations which reveal a temporal sequence of short-range ordering, long-range ordering, and eventually C clustering.
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| 10. |
- Yan, Jiayi, et al.
(författare)
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Molar volumes of bcc, hcp, and orthorhombic Ti-base solid solutions at room temperature
- 2016
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Ingår i: Calphad. - : Elsevier. - 0364-5916 .- 1873-2984. ; 52, s. 152-158
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Tidskriftsartikel (refereegranskat)abstract
- The roomerature molar volumes of bcc (β), hcp (equilibrium α or martensitic α′), and orthorhombic (martensitic α′′) phases are modeled for a number of Ti-base solid solutions in the CALPHAD framework. The martensitic molar volume is continuous at the α′/α′′ transition composition. Hcp and orthorhombic structures are modeled separately, and the predicted martensitic structure is taken as the denser one.
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