| 1. |
|
|
| 2. |
|
|
| 3. |
- Offerman, S. E., et al.
(författare)
-
Ferrite formation during slow continuous cooling in steel
- 2007
-
Ingår i: Fundamentals of Deformation and Annealing. - Stafa : Trans Tech Publications Inc.. - 0878494340 - 9780878494347 ; , s. 357-362
-
Konferensbidrag (refereegranskat)abstract
- Ferrite formation during austenite decomposition in carbon-manganese steel is studied during slow continuous cooling by three-dimensional x-ray diffraction microscopy at a synchrotron source. The ferrite fraction and nucleation rate are measured simultaneously and independently in real time in the bulk of the specimen. Thermodynamic calculations involving both ortho - and para -equilibrium have been performed to determine the driving force for nucleation. From the experiments and thermodynamic calculations the activation energies are estimated for nucleation and the transfer of iron atoms across the interface of the cluster during ferrite nucleation in steel.
|
|
| 4. |
- Amirthalingam, M., et al.
(författare)
-
Synchrotron diffraction analysis of retained austenite in welded transformation induced plasticity (TRIP) steels
- 2012
-
Ingår i: Science and Technology of Welding and Joining. - 1362-1718. ; 17:2, s. 146-154
-
Tidskriftsartikel (refereegranskat)abstract
- A quantitative analysis of the retained austenite (RA) fractions in gas tungsten arc welded silicon and aluminium containing transformation induced plasticity steels was carried out by synchrotron X-ray diffraction measurements. The variation in RA transverse to the weld line was measured to study the effect of weld thermal cycles on the stabilisation of austenite in the heat affected zone (HAZ) and the fusion zone (FZ). The results showed that the FZ of silicon based steels contained a higher amount of RA (similar to 7%) than aluminium based steels, which contained only similar to 4%. During the solidification of the weld pool, aluminium was found to partition to solidifying delta-ferrite and to stabilise the soft delta-ferrite grains at the fusion boundaries. Owing to this partitioning, the HAZ was enriched in carbon and the RA content was found to increase with distance from the fusion boundaries. In contrast, this partitioning behaviour was not present in silicon based transformation induced plasticity steels and a lesser amount of RA was found in the coarse grained HAZ than in the FZ.
|
|
| 5. |
- Ohlund, Carin Emmy Ingrid Christersdotter, et al.
(författare)
-
A Comparison between Ultra-high-strength and Conventional High-strength Fastener Steels: Mechanical Properties at Elevated Temperature and Microstructural Mechanisms
- 2016
-
Ingår i: ISIJ International. - 0915-1559. ; 56:10, s. 1874-1883
-
Tidskriftsartikel (refereegranskat)abstract
- A comparison is made between the mechanical properties of the ultra-high-strength steel KNDS4 of fastener grade 14.9 and of conventional, high-strength steels 34Cr4 of fastener grade 12.9 and 33B2 of grade 10.9. The results show that the ratio of the yield strength at elevated temperatures to the yield strength at room temperature is higher for the ultra-high-strength steel than for both conventional high strength steels, especially at 500 degrees C. Moreover, the results show a trend in which the nano-indentation creep rate is lower as the strength of the steels is higher. The improved mechanical properties of the KNDS4 steel compared to the conventional high-strength steels are related to the smaller size of the alloy carbides in the KNDS4 steel. Furthermore, the effect of an alternative (industrial) heat-treatment on the evolution of the microstructure and hardness of the KNDS4 steel was investigated. Changing the industrial heat treatment can increase the hardness of KNDS4 by about 8%, since more alloy carbides can nucleate and grow. However, the standard industrial heat treatment results in a refinement of the martensite microstructure (grain size), which might be more beneficial for the toughness of the steel. Independent of the heat treatment, the mechanical performance of KNDS4 fasteners at elevated temperature and the low nano-indentation creep rates are two strong indicators that fasteners made from KNDS4 steel might be used at higher service temperatures than traditional high strength fasteners.
|
|
| 6. |
- Ohlund, Ceic, et al.
(författare)
-
Effect of Ti on Evolution of Microstructure and Hardness of Martensitic Fe-C-Mn Steel during Tempering
- 2014
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 54:12, s. 2890-2899
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of the addition of 0.042 wt.% of titanium on the relation between the evolution of the microstructure and the softening kinetics of quenched martensite in high-purity Fe-C-Mn steel has been studied during tempering at 300 and 550 degrees C. The evolution of the microstructure is characterized by measuring the cementite particle size, the martensite block size, the area fraction of martensite regions which contain a high dislocation density, the macroscopic hardness, the nano-hardness of martensite blocks boundaries, the nano-hardness of the matrix and the TiC-precipitate size during tempering. Nucleation of TiC-precipitates take place during annealing at 550 degrees C and starts earlier in regions close to the block boundaries, after 5-10 minutes, and thereafter in the matrix, after 10-30 minutes, due to the higher dislocation density in the regions close to the block boundaries. The TiC-precipitates slow down the recovery in regions of high dislocation density compared to the alloy without TiC-precipitates. The TiC-precipitates increase the macroscopic hardness of the steel after 30 minutes annealing at 550 degrees C. The growth of TiC-precipitates in martensite is simulated in good agreement with experimental observations by a model that takes into account: 1) capillarity effects, 2) the overlap of the titanium diffusion fields between TiC-precipitates, and 3) the effect of pipe diffusion of titanium atoms via multiple dislocations. The average, experimentally-observed, TiC-precipitate size is 69 +/- 48 Ti atoms.
|
|
| 7. |
- Ohlund, Ceic, et al.
(författare)
-
Modelling the Evolution of Multiple Hardening Mechanisms during Tempering of Fe-C-Mn-Ti Martensite
- 2015
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 55:4, s. 884-893
-
Tidskriftsartikel (refereegranskat)abstract
- We model the hardness evolution of martensite during tempering as a linear addition of multiple hardening mechanisms that is combined with a microstructural Kampmann-Wagner-Numerical (KWN) model to simulate the nucleation and growth of TiC-precipitates during tempering. The combined model is fitted to the measured hardness evolution during tempering at 300 degrees C and 550 degrees C of martensitic steels with and without the addition of titanium. The model predicts TiC-precipitate sizes in agreement with experimental observations and generates fitting parameters in good agreement with literature. The microstructural components that give the highest contribution to the overall hardness are Fe3C precipitates (88 HV) and dislocations (54 HV). Both Fe3C- and dislocation-strengthening decreases rapidly during the initial stage and stabilise after 10 minutes of tempering. The model shows that the decrease in dislocation density due to recovery is slowed down due to the presence of TiC-precipitates. Titanium atoms in solid solution give a stable hardness contribution (25 HV) throughout the tempering process. TiC-precipitate strengthening generates a minor contribution (3.5 HV). The model shows that less than 1% of the equilibrium volume fraction of TiC-precipitates forms during isothermal tempering at 550 degrees C due to the large misfit strain (1.34 GJ/m(3)) and a limited density of potential nucleation sites in the martensite. The model shows that the hardness of tempered martensitic steels could potentially be increased by increasing the TiC-precipitate density by reducing the misfit strain.
|
|
