| 1. |
- Andersson, Margareta, et al.
(författare)
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Some Aspects on Grain Refining Additions with Focus on Clogging during Casting
- 2006
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 46:6, s. 814-823
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Tidskriftsartikel (refereegranskat)abstract
- Some ideas of how to study optimum conditions for implementation of grain refining in liquid steel processing with focus on how to avoid clogging are discussed. It is assumed that the inclusions most beneficial for grain refining are known from studies by physical metallurgists. The challenge for a process metallurgist is how to provide a homogeneous distribution of grain refiners at the onset of solidification. Four different ways of providing information to succeed with this are discussed. Thermodynamic modeling can be used to predict what additions to make to create potential grain refiners, if relevant thermodynamic data is available. Mathematical fluid-flow modeling can be used to study where to add potential grain refiners. It is discussed that the tundish is the most appropriate reactor to add grain refiners, since enough time is given to a complete mixing of the grain refiner into the steel before the steel enters the mold. By using the scanning laser microscopy technique it is possible to study which potential grain refiners has the lowest attraction forces between each other. This is important in order to minimise growth of inclusions when they collide during transport in the tundish, which can lead to the formation of larger inclusions that do not serve as useful grain refiners. Finally, it is suggested that laboratory experiments are carried out in order to study the tendency for nozzle clogging, before the use of grain refiners is tested in industrial scale.
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| 2. |
- Appelberg, Jesper, et al.
(författare)
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In situ studies of misch-metal particle behavior on a molten stainless steel surface
- 2008
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 495:1-2, s. 330-334
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Tidskriftsartikel (refereegranskat)abstract
- The use of misch-metal is widely spread among the stainless steel producers. Casting problems like clogging are common when using these additions. Information about Ce-La-Al-O particles formed due to the addition of misch-metal in the ladle is scarce in the open literature. The aim of this study is to increase the knowledge of the particle behavior and the particle characteristics in two stainless steels resulting from the addition of misch-metal. The in situ particle behavior has been studied using a Confocal Laser Scanning Microscope.
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| 3. |
- Chen, J., et al.
(författare)
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Criterion for dendrite fragmentation of steel under imposition of linear traveling EMS
- 2011
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Ingår i: 2010 International Conference on Advances in Materials and Manufacturing Processes, ICAMMP 2010. - 9780878492015 ; , s. 84-91
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Konferensbidrag (refereegranskat)abstract
- In the fragmentation theory of T. Campanella et al, the local remelting of dendrite arms is induced by the solute-rich fluid flow. Based on this theory, the effects of linear EMS intensity and solute content on CET of steel are investigated. The conclusions are as follows: The criterion for dendrite fragmentation under linear EMS is derived based on dendrite fragmentation theory by T. Campanella et al. And the criterion is verified with steel experiments. It is valid for steel under the Linear EMS. Investigation is carried out on relation between critical volume fraction of solid and solute content at the time of dendrite fragmentation (CET occurrence). It is concluded that critical volume fraction of solid is small with low EMS intensity and it decreases with the increase of solute content (C, Mn). The reason is that it causes that flow in the mushy zone becomes small which leads to CET occurrence difficult.
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| 4. |
- Chen, J., et al.
(författare)
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Critical conditions for dendrite fragmentation of low carbon steel in travelling electromagnetic field
- 2010
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Ingår i: Dongbei Daxue Xuebao/Journal of Northeastern University. - 1005-3026. ; 31:12, s. 1717-1720+1732
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the effect of travelling electromagnetic field on dendrite fragmentation in solidification process, the 0.22 wt%~0.34 wt%C steel was tested for its solidifying behavior in travelling electromagnetic field. Observing the solidification structures of casting blanks under different magnetic flux density, the distributions of secondary dendrite arm spacing were investigated and the functional relationship between secondary dendrite arm spacing and cooling rate in solidification was discussed, as well as the effect of travelling electromagnetic field on the columnar-to-equiaxed transition (CET) position. The solidification rate and solid fraction when CET occurs were calculated. The critical conditions for dendrite fragmentation in travelling electromagnetic field is derived and verified by the testing results of low carbon steel. Thus, the relationship between the average velocity of the liquid-phase and the critical solid volume fraction when CET occurs was obtained.
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| 5. |
- Janis, Jesper, et al.
(författare)
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An experimental study on the influence of particles on grain boundary migration
- 2010
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 45:8, s. 2233-2238
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Tidskriftsartikel (refereegranskat)abstract
- The pinning effect of particles on grain boundary migration was studied in a Fe-20 mass % Cr alloy deoxidised with Ti and Zr. The different nitrogen contents (65, 248 and 490 ppm) were used to vary the number of precipitated inclusions. The specimens from equiaxed zones of metal samples with different particle densities were examined by in situ observations during a 60-min holding time at 1200 and 1400 degrees C in a Confocal Scanning Laser Microscope. The change of particles pinning effect on the grain growth was described by an average grain size, (D) over bar (A), and the ratio between the perimeter and area of grains, P-GB/A(G). It was found that the pinning effect of particles (mostly complex Ti-Zr oxynitrides) on grain growth decreased with a decreased nitrogen content in the metal. Furthermore, the effect of particles decreased with an increased temperature of treatment, due to the reduction of the number of particles on the grain boundaries.
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| 6. |
- Janis, Jesper, et al.
(författare)
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Characteristics of Ti-Ce Complex Deoxidation Products in a Fe-20mass%Cr Alloy
- 2009
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Ingår i: STEEL RES INT. - 1611-3683. ; 80:6, s. 450-456
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Tidskriftsartikel (refereegranskat)abstract
- The particle characteristics such as size distribution, composition and morphology have been studiedin an Fe-20mass%Cr alloy as a function of holding time at 1600°C. The alloy was deoxidised with Tiand Ce, followed by holding at 1600°C and cooling to 1400°C and quenching. The inclusion particleswere investigated on a surface of film filter with an open pore size of 0.05 or 5 μm after electrolyticextraction of the metal samples. Different electric charge and electrolytes (2%TEA and 10%AA) werecompared for extraction of the Fe-20mass%Cr alloy. 300 Coulombs with 10%AA was found mostsuitable for the electrolytic extraction of particles to determine the particle composition and sizedistribution. Most of the particles were found to be complex oxides containing Ti, Ce and Cr.Furthermore, the composition of the particles was found to change from a high Ce-content to a highCr-content with longer holding time at 1600°C.
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| 7. |
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| 8. |
- Janis, Jesper, et al.
(författare)
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Dissolution of Nitrides and Precipitation of an AusteniticPhase on the Surface of Fe-20%Cr alloys
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- New phases have been observed on surfaces of metal specimens duringcooling after heat treatment at 1200, 1300 and 1400 °C of an Fe-20mass% Cr alloywith different nitrogen contents (65, 248 and 490 ppm) and deoxidised by Ti andZr. These phases were assumed to be related to a phase transformation. Theanalysis of nitrogen content in matrix metal and new phase crystals was carried outbased on point analysis of nitrogen using SEM. According to obtained results itwas concluded that the nitrogen had been dissolved from the nitrides during 60minutes of heat treatment at high temperature and diffused in to the matrix. Theseareas of enriched nitrogen content were then transformed to a new phase duringcooling. This new phase was assumed to be austenite because the nitrogen is a wellknown element for promotion of austenite formation. The possibility of austeniteformation in Fe-20mass% Cr alloys with different nitrogen content was consideredand confirmed thermodynamically by using the Thermo-Calc software.
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| 9. |
- Janis,, Jesper, et al.
(författare)
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Effect of Primary and Secondary Particles on Grain Sizein a Fe-20mass% Cr Alloy Deoxidised with Ti and Zr
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Because of the high and volatile Ni price in recent times, it becomesmore important to develop ferritic stainless steels with low level of Ni. Here,it is known that these steel grades usually contain oversized grains, which asa consequence leads to poor mechanical properties. One way to deal withthis problem is to control the microstructure and the size of grains in ferriticstainless steels. This would also make ferritic stainless steels morecompetitive in comparison to the more commonly used austenitic stainlesssteels. This study focuses on the grain refining effect of particles present in aferritic stainless steel. The particles were created by additions of Ti and Zr into a liquid Fe-20mass% Cr alloy, before the start of solidification. Aconstant O content (150 ppm) together with varying N contents (65, 248 and490 ppm) in the metal samples were used to vary the number, compositionand location of the precipitated particles. The grain sizes and particles werestudied in as-cast samples as well as for specimens heat treated for 60minutes at 1200 and 1400°C. It was found that the formation of particles isenhanced by an increased N content in the alloy. Based on SEMdeterminations, the precipitated particles were divided as primary (mainlyZr-oxides and Zr-nitrides) and secondary (mainly Ti-nitrides) particles andthe effect was studied for each of the types. An increased content of primaryparticles as “nucleators” for precipitation of α-ferrite during solidification ofthe melt lead to an increased formation of equiaxed small-size grains. Inaddition, an increased N content in the metal samples resulted in anincreased number of secondary particles, which are located near the grainboundaries. Therefore, the pinning effect of these particles on grain growthincreased at a holding temperature of 1200oC. However, most of the nitrideswere found to dissolve during heating and holding at a 1400 °C temperature.Thus, as a consequence, the pinning effect of these particles on grain growthdecreased rapidly with the holding time.
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| 10. |
- Janis, Jesper, et al.
(författare)
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Effect of Secondary Nitride Particles on Grain Growth in a Fe-20 mass% Cr Alloy Deoxidised with Ti and Zr
- 2013
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:3, s. 476-483
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Tidskriftsartikel (refereegranskat)abstract
- The pinning effects of different particles on grain growth were investigated in Fe-20 mass% Cr alloys deoxidised with Ti and Zr. More specifically, in-situ observations of the specimen surface were made during heat treatment at 1 200 and 1 400 degrees C in a High Temperature - Confocal Scanning Laser Microscope (HT-CSLM). Initially, primary and secondary particles were investigated using thermodynamic equilibrium calculations and the SEM/EDX observations. Thereafter, the pinning effect of secondary nitride particles on grain boundary migration and the kinetics of the grain growth process were investigated. It was found that secondary nitride particles generally have a considerable effect on the pinning of grain boundary migration during heating treatment. This is especially true for heat treatment at 1 400 degrees C. Despite that the pinning effect of TIN particles decreases due to dissolution of these particles, the implicit pinning effects of ZrO2, ZrO2-ZrN and ZrO2-ZrN-TiN particles appear. Thus, despite that TIN individually is ineffective in causing grain-boundary pinning at high-temperature, TiN is effective as a compound with ZrO2 and ZrN in pinning grain-boundaries at high temperatures. The changing of the uniformity of grain size distributions during grain growth at different N contents and temperatures was discussed based on the consideration of the geometric standard deviation of the grain size distribution (sigma(g)).
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