| 1. |
- Atwell, D.L., et al.
(författare)
-
The effect of initial grain size and temperature on the tensile properties of magnesium alloy AZ31 sheet
- 2012
-
Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 549, s. s.1-6
-
Tidskriftsartikel (refereegranskat)abstract
- This research aimed to assemble and review data that are relevant to sheet metal formability of the magnesium alloy AZ31. Rolled sheets were processed to give four different grain sizes in the range from 2.9 to 47.1 μm. Similar basal textures were present in all these conditions. Tensile tests were carried out at various temperatures between 25 °C and 240 °C, with some additional tests also made below room temperature in dry ice. Results are presented and discussed relating to strength, ductility, strain rate sensitivity and anisotropy. An optimum grain size of about 7 μm applies for ductility over most of the temperature interval. Uniform elongation decreases steadily with increasing temperature whereas the post-necking and total elongation values increase markedly. Measurements of strength, anisotropy and strain rate sensitivity all indicate a significant role of grain boundary mediated deformation above room temperature. The plastic strain ratio, r, is high at room temperature but decreases considerably, especially for the fine grained conditions, at higher temperatures. Modifications to the active slip modes also occur over the same temperature interval but their effect on plasticity is probably less important than was previously believed. © 2012 Elsevier B.V.
|
|
| 2. |
- Barnett, M.R., et al.
(författare)
-
Role of grain boundary sliding in the anisotropy of magnesium alloys
- 2009
-
Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 61:3, s. 277-280
-
Tidskriftsartikel (refereegranskat)abstract
- The plastic anisotropy of magnesium alloy sheet drops rapidly with test temperature. It has previously been suggested that this may be due to an increase in the activity of 〈c+a〉 dislocations. The present note points out that the phenomenon may result, instead, from the action of grain boundary sliding. This can explain the strong effect of grain size on anisotropy. Furthermore, it points to a new avenue for alloy development. © 2009 Acta Materialia Inc.
|
|
| 3. |
- Bate, Pete, et al.
(författare)
-
Application of laser-ultrasonics to texture measurements in metal processing
- 2017
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 123, s. 329-336
-
Tidskriftsartikel (refereegranskat)abstract
- The paper describes in principle how information about textures can be obtained through the application of laser-ultrasonics (LUS) which can be carried out at elevated temperatures, for example in connection with hot rolling. The benefits from getting a measure of texture in this way are explained together with the proposed methodology which is based on the elastic anisotropic properties of the textured material. Measurements are made using only a single laser pulse and in real-time. Two approaches are presented to modelling the propagation of elastic waves, ray tracing and finite difference modelling. These give consistent results but the latter provides a more complete prediction of the ultrasonic spectrum that can be quantitatively related to measured signals through a cross-correlation procedure. Some experimental results are presented for room temperature measurements on a sheet of interstitial-free steel. Agreement between experimental data and modelling results is good and allows estimation of the 4th order coefficients of the orientation distribution function.
|
|
| 4. |
- Berg, Frenk van den, et al.
(författare)
-
How the EU project “Online Microstructure Analytics” advances inline sensing of microstructure during steel manufacturing
- 2023
-
Ingår i: Research and Review Journal of Nondestructive Testing (ReJNDT). - Lisabon : NDT.net GmbH & Co. KG. - 2941-4989. ; 1:1
-
Tidskriftsartikel (refereegranskat)abstract
- Weight savings in mobility and transport are mandatory in order to reduce CO2 emissions and energy consumption. The steel industry offers weight saving solutions by a growing portfolio of Advanced High Strength Steel (AHSS) products. AHSS owe their strength to their largely refined and complex microstructures, containing multiple metallurgical phases. Optimal control of the thermo-mechanical processing of AHSS requires inline sensors for real-time monitoring of evolution and consistency of microstructure and material properties.
|
|
| 5. |
- Gyhlesten Back, Jessica
(författare)
-
Modelling and Characterisation of the Martensite Formation in Low Alloyed Carbon Steels
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current work contains experimental and theoretical work about the formation of martensite from the austenitic state of the steel Hardox 450. Simulation of rolling and subsequent quenching of martensitic steel plates requires a model that can account for previous deformation, current stresses and the temperature history, therefore dilatometry experiments were performed, with and without deformation. Two austenitization schedules were used and in the standard dilatometry the cooling rates varied between 5-100 °C/s, in order to find the minimum cooling rate that gives a fully martensitic microstructure. Cooling rates larger than 40°C/s gave a fully martensitic microstructure. The cooling rate of 100 °C/s was used in the deformation dilatometry tests where the uniaxial deformation varied from 5-50 %. The theoretical work involved modelling of the martensite formation and the thermal/transformation strains they cause in the steel. Characterizations were done using light optical microscopy, hardness tests and electron backscatter diffraction technique. The parent austenite grains of the martensitic structure were reconstructed using the orientation relationship between the parent austenite and the martensite. Kurdjumov-Sachs orientation relationships have previously been proven to work well for low-carbon steels and was therefore selected.The standard implementation of the Koistinen-Marburger equation for martensite formation and a more convenient approach were compared. The latter approach does not require the storage of initial austenite fraction at start of martensite formation. The comparison shows that the latter model works equally well for the martensite formation. The results showed that the use of martensite start and finish temperatures calibrated versus experiments for Hardox 450 works better when computing thermal expansion than use of general relations based on the chemistry of the steel.The results from deformation dilatometry showed that deformation by compressive uniaxial stresses impedes the martensite transformation. The simplified incremental model works well for deformation with 5 % and 10 %. However, the waviness in the experimental curve for deformation 50 % does not fit the model due vi to large barrelling effect and the large relative expansion for the material that the sample holders are made of.Crystallographic reconstruction of parent austenite grains were performed on a hot-rolled as-received reference sample and dilatometry samples cooled with 60 °C/s and 100 °C/s. The misorientation results showed that the samples match with the Kurdjumov-Sachs orientation relationship in both hot rolled product and dilatometry samples. When misorientation between adjacent pixels are between 15° and 48°, then the boundary between them was considered as a parent austenite grain. The austenitic grain boundaries of the sample cooled at 100 °C/s is in general identical with the hot rolled sample when considering high angle boundaries (15°-48°). The results from the hardness tests showed that the rolled product exhibits higher hardness as compared to samples cooled by 100 °C/s and 60 °C/s. This can be attributed to the formation of transition-iron-carbides in the hot rolled product due to longer exposure of coiling temperature.
|
|
| 6. |
- Hutchinson, Bevis, et al.
(författare)
-
A minimum parameter approach to crystal plasticity modelling
- 2012
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 60:15, s. 5391-5398
-
Tidskriftsartikel (refereegranskat)abstract
- Plastic deformation processes in hexagonal metals are complex and are best analyzed using procedures such as visco-plastic self-consistent crystal plasticity modelling. These involve a large number of adjustable parameters and make limited use of independent input data. Using physical arguments, the authors show that several of the parameters can be replaced by experimentally measured values of critical resolved shear stresses from the literature. A further simplification derives from the argument that all deformation modes interact with the same substructure, and so a common work-hardening behaviour can be assumed as a reasonable first approximation. Furthermore, many microstructural contributions to the strength can be introduced through a single constant term. In these ways, the twelve or more adjustable parameters in the model are reduced to only three. This new approach is tested critically by applying it to a sheet magnesium alloy for which the plastic strain ratio varies markedly during the test. Its complex plastic behaviour, which arises from changes among the active deformation modes, is successfully predicted. A benefit of the present approach is that the effect of metallurgical variables such as grain size or precipitation strengthening can be readily investigated. Although tested here for a magnesium alloy, the same principles should be applicable to other hexagonal close-packed materials.
|
|
| 7. |
- Hutchinson, Bevis, et al.
(författare)
-
Anomalous ultrasonic attenuation in ferritic steels at elevated temperatures
- 2016
-
Ingår i: Ultrasonics. - : Elsevier B.V.. - 0041-624X .- 1874-9968. ; 69, s. 268-272
-
Tidskriftsartikel (refereegranskat)abstract
- An unexpected peak in attenuation has been observed at ∼800 °C when heating low carbon steels in a laser-ultrasonic instrument. An explanation is given in terms of enhanced crystalline anisotropy with increasing temperature in the bcc ferrite range combined with subsequent transformation to austenite at still higher temperatures. An analysis based on theoretical models of attenuation in the Rayleigh regime is in good agreement with the experimental observations.
|
|
| 8. |
- Hutchinson, Bevis
(författare)
-
Critical assessment 16 : Anisotropy in metals
- 2015
-
Ingår i: Materials Science and Technology. - 0267-0836 .- 1743-2847. ; 31:12, s. 1393-1401
-
Tidskriftsartikel (refereegranskat)abstract
- Sources of anisotropy in metals are discusssed as well as ways of interpreting and modelling this behaviour. A number of case studies are presented relating to mechanical and magnetic properties.
|
|
| 9. |
- Hutchinson, Bevis, et al.
(författare)
-
Deformation modes and anisotropy in magnesium alloy AZ31
- 2009
-
Ingår i: International Journal of Materials Research - Zeitschrift für Metallkunde. - : Walter de Gruyter GmbH. - 1862-5282 .- 2195-8556. ; 100:4, s. 556-563
-
Tidskriftsartikel (refereegranskat)abstract
- A strongly textured sheet of magnesium alloy AZ31 has been subjected to tensile testing at temperatures between ambient and 300 °C. Structures have been examined by optical and transmission electron microscopy and also by atomic force microscopy to quantify surface displacements seen at grain boundaries. Plastic anisotropy varies strongly with test temperature as was observed previously by Agnew and Duygulu. The present findings do not support the view that crystallographic becomes a major contributor to deformation at higher temperatures. Rather, the material behaviour reflects an increasing contribution from grain boundary sliding despite the relatively high strain rate (10-3 s-1 ) used in the mechanical tests. © Carl Hanser Verlag GmbH & Co. KG.
|
|
| 10. |
- Hutchinson, Bevis, et al.
(författare)
-
Elasticity and wave velocity in fcc iron (austenite) at elevated temperatures – Experimental verification of ab-initio calculations
- 2018
-
Ingår i: Ultrasonics. - : Elsevier. - 0041-624X .- 1874-9968. ; 87, s. 44-47
-
Tidskriftsartikel (refereegranskat)abstract
- High temperature crystal elasticity constants for face centred cubic austenite are important for interpreting the ultrasonic properties of iron and steels but cannot be determined by normal single crystal methods. Values of these constants have recently been calculated using an ab-initio approach and the present work was carried out to test their applicability using laser-ultrasonic measurements. Steel samples having a known texture were examined at temperatures between 800 °C and 1100 °C to measure the velocity of longitudinal P-waves which were found to be in good agreement with modelled values.
|
|
