| 1. |
- Calmunger, Mattias, et al.
(författare)
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Mechanical Behaviours of Alloy 617 with Varied Strain Rate at High Temperatures
- 2014
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Ingår i: Materials Science Forum. - : Trans Tech Publications Ltd. - 0255-5476 .- 1662-9752. ; 783-786, s. 1182-1187, s. 1182-1187
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Tidskriftsartikel (refereegranskat)abstract
- Nickel-base alloys due to their high performances have been widely used in biomass and coal fired power plants. They can undertake plastic deformation with different strain rates such as those typically seen during creep and fatigue at elevated temperatures. In this study, the mechanical behaviours of Alloy 617 with strain rates from 10-2/s down to 10-6/s at temperatures of 650°C and 700°C have been studied using tensile tests. Furthermore, the microstructures have been investigated using electron backscatter detection and electron channeling contrast imaging. At relatively high strain rate, the alloy shows higher fracture strains at these temperatures. The microstructure investigation shows that it is caused by twinning induced plasticity due to DSA. The fracture strain reaches the highest value at a strain rate of 10-4/s and then it decreases dramatically. At strain rate of 10-6/s, the fracture strain at high temperature is now smaller than that at room temperature, and the strength also decreases with further decreasing strain rate. Dynamic recrystallization can also be observed usually combined with crack initiation and propagation. This is a new type of observation and the mechanisms involved are discussed.
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| 2. |
- Gärdsback, Magnus, et al.
(författare)
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Influence of Strain Path on Work Hardening and Texture in an Austenitic Stainless Steel
- 2014
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Ingår i: THERMEC 2013. - : Trans Tech Publications Inc.. - 9783038350736 ; , s. 2567-2572
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Konferensbidrag (refereegranskat)abstract
- The effect of strain path on work hardening and texture for a super austenitic stainless steel was investigated using both experiments and modeling. Compression deformation tests by stepwise changing loading direction in two and three dimensions were performed on cubic specimens at room temperature. The results were compared to uniaxial compression with equal accumulative strain, up to 20%, and uniaxial tension with equal final strain, up to 10% elongation of the longest side. The textures in all samples were analyzed using pole figures from EBSD analysis. Because of the high stacking fault energy of this super austenitic stainless steel, the texture was dominated by <110>-fiber texture in the compressive direction for the uniaxial compression, <111>- and <100>-fiber texture in the tensile direction for the uniaxial tensile test, and a combination of all these for the cube deformation. The density of the texture was much weaker for samples where the loading direction altered, if samples with equal accumulated strain were compared. The cube deformation was also modeled using a crystal plasticity model. The crystal plasticity model consists of a representative volume element (RVE) containing crystal grains with random orientations. The Taylor assumption was used for homogenization between the macro-and subscale. The material parameters in the crystal plasticity model were determined by calibration of its macroscopic response to experimental data. The simulated textures correspond rather well to the experimental results, but the work hardening should be completed to take into account kinematic hardening.
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| 3. |
- Johnsson, Andreas, et al.
(författare)
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Predicting the microstructural evolution of an austenitic stainless steel by hybrid modeling
- 2014
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Ingår i: Materials Engineering Forum. - : Trans Tech Publications Ltd. - 9783038350736 ; , s. 2154-2159
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Konferensbidrag (refereegranskat)abstract
- During the annealing heat treatment following cold rolling of a 304L austenitic stainless steel sheet material, the material goes through changes in microstructure and mechanical properties. The cold rolling history together with the time/temperature trajectory in the annealing furnace can be used to model the final microstructure. In this work, physically based models for recrystallization and the following grain growth was created for the prediction of the microstructure evolution- both grain size and grain size distribution-, and an artificial neural network, ANN, was added for secondary effects. This is more commonly referred to as a hybrid model. The microstructure hybrid model was tested and validated against cold rolled and annealed production sheet material of various thicknesses and reductions, where the grain size and grain size distribution was measured by Electron Back Scatter Diffraction, EBSD. The recrystallization and grain growth parameters and functionality were fitted for non-isothermal conditions, against experimental tests of cold rolled material. Given process history and time/temperature data from the annealing heat treatment, the model can predict the microstructure, average grain size and grain size distribution with high accuracy and the executing time is short which makes it suitable for in-line use. © (2014) Trans Tech Publications, Switzerland.
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| 4. |
- Kahrimanidis, Alexander, et al.
(författare)
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Formation of Multiple Twinned Structural Units in Electrodeposited Nickel after Annealing
- 2014
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Ingår i: Materials Science Forum. - 1662-9752 .- 0255-5476. - 9783038350736 ; 783-786, s. 2573-2578
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Konferensbidrag (refereegranskat)abstract
- Electrodeposition is an advanced synthesis technique which involves the creation of acoating or free-standing material through an electrolytic process. Organic additives such assaccharin have been frequently used in electroplating operations to moderate deposit growth ratesand to control film quality. In the present study, plating of Nickel without additives has resulted in asub-microcrystalline microstructure and a -fibre texture in growth direction. Structural unitsin form of groups of grains possessing a common -zone axis in growth direction and low-Sigmarelationships between them have been found in the microstructure by use of EBSD. Uponannealing, grain growth sets in. However, the structural units and the texture are preserved up to550°C. This means that the structural units stabilize the microstructure; there is no orientationchange when grain growth occurs (e.g. by twinning). The low-Sigma boundaries of the structural unitsare described in detail and texture development upon annealing is discussed in connection withresults from previous studies on Ni and Ni-alloys of different initial texture.
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| 5. |
- Karlberg, Mats
(författare)
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Thermo-mechanically coupled modeling of cooling temperature history effects on precipitation hardening in hot strip coiled products
- 2014
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Ingår i: Advanced Materials Research. - : Trans Tech Publications. - 9783038350736 ; , s. 2160-2165
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Konferensbidrag (refereegranskat)abstract
- When producing hot strip, HSLA(High Strength Low Alloyed) products the coiling temperature and the subsequent coil cooling is of great importance for the final mechanical properties. A thermo-mechanically coupled model has been developed where the anisotropic stress dependent thermal properties caused by the layered structure and the asymmetric cooling are included. Additionally the precipitation hardening effect on the yield strength, influenced by the thermal history during cooling was compared with mechanical tensile testing along the strip length at SSAB EMEA works in Borlänge, Sweden. Good agreement between measured and predicted yield stress variations in head and tail was obtained. © (2014) Trans Tech Publications, Switzerland.
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| 6. |
- Karlberg, Mats
(författare)
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Thermo-mechanically coupled modeling of cooling temperature history effects on precipitation hardening in hot strip coiled products
- 2014
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Ingår i: Materials Engineering Forum. - : Trans Tech Publications Ltd. - 9783038350736 ; , s. 2160-2165
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Konferensbidrag (refereegranskat)abstract
- When producing hot strip, HSLA(High Strength Low Alloyed) products the coiling temperature and the subsequent coil cooling is of great importance for the final mechanical properties. A thermo-mechanically coupled model has been developed where the anisotropic stress dependent thermal properties caused by the layered structure and the asymmetric cooling are included. Additionally the precipitation hardening effect on the yield strength, influenced by the thermal history during cooling was compared with mechanical tensile testing along the strip length at SSAB EMEA works in Borlänge, Sweden. Good agreement between measured and predicted yield stress variations in head and tail was obtained. © (2014) Trans Tech Publications, Switzerland.
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| 7. |
- Sidestam, Patrik, et al.
(författare)
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Modeling of hydrogen diffusion in piled slabs
- 2014
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Ingår i: Advanced Materials Research. - : Trans Tech Publications. - 9783038350736 ; , s. 2201-2206
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Konferensbidrag (refereegranskat)abstract
- Hydrogen is harmful in steel which makes it important to reduce the hydrogen content. Piling slabs after casting gives a slow cooling which increases the diffusion out of the steel. Finite element modeling has been used to simulate this process where hydrogen solubility and phase dependent diffusivity can be taken into account. The hydrogen diffusion model is using STEELTEMP® 2D for the thermal analysis. Measurements of temperature and hydrogen content in piled slabs have been done and the calculations are in good agreement. © (2014) Trans Tech Publications, Switzerland.
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| 8. |
- Sidestam, Patrik, et al.
(författare)
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Modeling of hydrogen diffusion in piled slabs
- 2014
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Ingår i: Materials Engineering Forum. - : Trans Tech Publications Ltd. - 9783038350736 ; , s. 2201-2206
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Konferensbidrag (refereegranskat)abstract
- Hydrogen is harmful in steel which makes it important to reduce the hydrogen content. Piling slabs after casting gives a slow cooling which increases the diffusion out of the steel. Finite element modeling has been used to simulate this process where hydrogen solubility and phase dependent diffusivity can be taken into account. The hydrogen diffusion model is using STEELTEMP® 2D for the thermal analysis. Measurements of temperature and hydrogen content in piled slabs have been done and the calculations are in good agreement. © (2014) Trans Tech Publications, Switzerland.
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