| 1. |
- Bi, Yanyan, et al.
(författare)
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Investigations of inclusions in ferrochromium alloys
- 2014
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Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 41:10, s. 756-762
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Tidskriftsartikel (refereegranskat)abstract
- Ferrochromium alloys are commonly added during different stages of steelmaking processes according to the specific steel grade being produced. Depending upon the ferrochromium quality, the addition can also lead to a supply of deleterious inclusions to the liquid steel. Therefore, the number, size, morphology and composition of inclusions in LCFeCr and HCFeCr alloys were investigated. The alloy samples were first treated with electrolytic extraction, followed by filtration to gather the inclusions on a film filter. Thereafter, the characteristics of the inclusions and clusters were investigated in three dimensions by SEM in combination with energy dispersive spectroscopy. The results show that the main inclusion types found in LCFeCr alloys are different to those found in HCFeCr alloys. More specifically, the inclusions in LCFeCr alloys were found to consist of Si-Cr-O and Cr-O oxides as well as intermetallic Cr-Fe inclusions. Moreover, the inclusions in HCFeCr alloys were found to consist of Cr-Mn-S, Cr-C-N, Si-Al-Ca-Mg-O and Ca-O-P inclusions. Overall, the inclusions can be divided into two categories depending on the melting point. Furthermore, the possible transformation of different inclusions after their addition to the liquid steel is discussed.
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| 2. |
- Bi, Yanyan, et al.
(författare)
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Three Dimensional Evaluations of REM Clusters in Stainless Steel
- 2014
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 54:6, s. 1266-1273
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Tidskriftsartikel (refereegranskat)abstract
- It is known that clusters in liquid steel have a harmful effect on the casting process and the quality of the final steel product. In this study, clusters. of rare earth metals (REM) were investigated in steel samples of a S30185 stainless steel grade from a pilot trial (PT, 250 kg) and from an industrial heat (IH, 100 t). Samples were taken from the liquid steel at different holding times after the addition of mischmetal. Thereafter, REM clusters collected on film filters after electrolytic extraction and filtration were investigated in three dimensions (3D) by SEM in combination with EDS. The morphology, composition, number and size of clusters in PT and IH steel samples were analyzed and compared as a function of holding time. It was found that typical clusters with regular and irregular inclusions were the main type of clusters (69%-98%) in all PT and IH steel samples. The composition of inclusions in clusters corresponded mostly to REM-oxides. The size of clusters that were observed in different samples varied mainly from 2 to 23 mu m. In addition, the size and number of most clusters in PT are larger than those in IH samples. Furthermore, the formation mechanisms and evolution of different type of REM clusters were discussed in both PT and IH heats.
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| 3. |
- Dahlin, Anders, et al.
(författare)
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Influence of ladle slag additions on BOF process performance
- 2012
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Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 39:5, s. 378-385
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Tidskriftsartikel (refereegranskat)abstract
- A plant trial has been performed, with recycling of ladle slag to the LD converter at SSAB EMEA, Lulea, Sweden. The effect of ladle slag addition on the slag and steel composition, together with the slag weight, was investigated with sampling both during the blow and at blow end. The addition of ladle slag resulted in an increase in slag weight between 1 and 2 t throughout the blow and an increase of 3 wt-% in the slag Al2O3 content. This indicated that the ladle slag melted during the initial stages of the blow and enhanced the early slag formation. Lime additions were reduced with 3.5 kg t(-1) liquid steel without drawbacks on the phosphorus or sulphur refining. Heats with added ladle slag had an increase in blowing time with similar to 4% and an increased tendency for slopping. However, this can be handled by different lance and addition programmes.
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| 4. |
- Dahlin, Anders, et al.
(författare)
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Influence of ladle slag additions on BOF process under production conditions
- 2012
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Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 39:5, s. 318-326
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Tidskriftsartikel (refereegranskat)abstract
- The influence of recycled ladle slag on the basic oxygen furnace (BOF) process under production conditions was investigated in plant trials. More specifically, 25 heats with ladle slag additions and 23 heats without ladle slag additions were studied. Both steel and slag samples were collected, from which the chemical compositions were determined. In addition, several process parameters were monitored. Overall, it was found that recirculation of ladle slag during normal production conditions works fine. On the positive side, it was seen that the steel quality concerning the phosphorus and sulphur contents of liquid steel has, in accordance with previous studies, not been affected by the ladle slag additions. Furthermore, no major differences in the slag composition occur when the recycling of ladle slag to BOF is performed. Finally, in comparison to previous studies, the increased tendency for slopping when adding ladle slag could be eliminated with a change in the lance schedule. However, on the negative side, it was seen that the addition of ladle slag leads to an increased blowing time due to lower iron ore additions. Moreover, the slag weight at tapping increased due to an increased weight of added slag formers.
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| 5. |
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| 6. |
- Karasev, Andrey, et al.
(författare)
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Three-dimensional investigation of large-size inclusions and clusters in steels by using the electrolytic extraction technique
- 2013
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Ingår i: AISTech 2013. - 9781935117339 ; , s. 1139-1145
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Konferensbidrag (refereegranskat)abstract
- It is well known that the non-metallic inclusions and clusters (especially, the large size inclusions and clusters) in steels have significant harmful effects on the mechanical properties of final products. Therefore, it is important to carry out a precise quantitative analysis of inclusion and cluster characteristics in metal samples at different stages of steel production. According to the obtained experimental results during the last years, it was found that the three-dimensional (3-D) investigation of inclusions and clusters on a film filter after electrolytic extraction of steel samples (EE) has a major advantageous in comparison to commonly used two-dimensional (2-D) observations on a polished cross section of metal samples. Experimental results focusing mainly on investigations of large size inclusions and clusters in different steels are discussed in this study.
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| 7. |
- Kasimagwa, I., et al.
(författare)
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Slag corrosion of MgO-C refractories during secondary steel refining
- 2014
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Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 41:2, s. 121-131
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Tidskriftsartikel (refereegranskat)abstract
- Studies of the reactions between the MgO-C refractory and a CaO-Al2O3-SiO2-MgO slag system have been carried out through thermodynamic simulations, laboratory experiments and microscopy studies of the microstructure of the refractory samples after the experimental procedures. Corrosion experiments were conducted using the rotating immersion method of the MgO-C refractory rods in a liquid slag: in the temperature range of 1773-1923 K, revolution speed of 200 rev min(-1), with varying slag compositions and times ( 2700-8100 s). Laboratory experiments have shown that the time during which the ladle lining is exposed to a liquid slag with high stirring and slag composition are two important parameters which have large effect on the kinetics of the refractory wear. The rate constants calculated in the present work are in the range of 4 x 10(-7) to 1 x 10(-6) ms(-1). The estimated activation energy from the experimental results is 26 kJ mol(-1)
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| 8. |
- Malmberg, Kristofer, et al.
(författare)
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Influence of final stirring treatment on inclusion number in tool steel
- 2013
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Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 40:6, s. 407-412
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Tidskriftsartikel (refereegranskat)abstract
- The focus was to study the elimination of non-metallic inclusions during the final part of the ladle refining of tool steel (AISI H13). More specifically, the final stirring treatment in a ladle before casting was modified to study how the number of inclusions could be decreased. The following three stirring treatments were tested: a conventional induction stirring with a 650 A current for 20 min, a short induction stirring with a 650 A current during 10 min, and a combined gas and induction stirring during 20 min (no open eye and a 600 A current). Steel samples were collected from the ladle before and after the final stirring period of the ladle treatment. Thereafter, the numbers of inclusions in steel samples were determined using a light optical microscope based on a classification according to the Swedish standard SS111116 (JK Scale II). Overall, the results showed that a combined gas and induction stirrings was the most efficient way of decreasing the number of DM, DH and DP inclusions. The decrease in the inclusion number in four heats was the following for the different size classes for a combined stirring procedure: 15-40% for DM type inclusions, 30-61% for DH type inclusions and 50-100% for DP inclusions. In addition, it should be mentioned that a stirring practice with induction stirring during 10 min resulted in a 67-100% decrease in the DH type inclusions. However, the results for a combined stirring case for DH type inclusions were more stable than those for a shorter induction stirring time.
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| 9. |
- Memarpour, Arashk, et al.
(författare)
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Post-mortem study of the internal coated SENs (Submerged Entry Nozzle) respecting clogging phenomena
- 2011
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Konferensbidrag (refereegranskat)abstract
- A large number of accretion samples formed inside alumina/graphite clogged Submerged Entry Nozzles (SEN) were examined using FEG-SEM-EDS and Feature analysis. The SENs were used for continuous casting of stainless steel grades alloyed by Rare Earth Metals (REM). The internal surfaces of the SENs were coated by a glass/silicon powder layer to prevent the SEN decarburization during the preheating process. The results indicated a harmful effect of the SENs decarburization on the accretion thickness. In addition, the post-mortem results clearly revealed the formation of a multi-layer accretion. Also, the study indicated the penetration of the protecting glaze into the Alumina/graphite refractory materials. The interaction of the penetrated glaze with alumina in the SEN refractory materials leads to formation of high viscous alumina-rich glaze during the SEN preheating process. This interaction may lead to formation of an uneven surface inside the SEN. These areas consist of alumina particles, silica particles and the penetrated glaze in between. The results showed that these areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. Furthermore, the penetration of the glaze may lead to reactions between alkalines in the glaze and the graphite. This leads to a supply of oxygen at the interface between the SEN and the molten steel. This, in turn, may lead to reoxidation of the REM alloying elements in molten steel under the formation of “in situ” REM oxides. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the SEN´s uneven inside surface, may create a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxides inclusions on the SEN internal surface and thereafter the clogging.
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| 10. |
- Pirouznia, Pouyan, et al.
(författare)
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An investigation of the temperature distribution of a thin steel strip during the quenching step of a hardening process
- 2019
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 9:6, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- The dimension quality of the strip within the hardening process is an essential parameter, which great attention needs to be paid. The flatness of the final product is influenced by the temperature distribution of the strip, specifically across the width direction. Therefore, based on physical theories, a numerical model was established. The temperature of the strip for the section before the martensitic transformation was objected in the predicted model by using a steady state approach. In addition an infrared thermal imaging camera was applied in the real process in order to validate the results and to improve the boundary conditions of the numerical model. The results revealed that the temperature of strip decreased up to 250 degrees C within the area between the furnace and the quenching bath. This, in turn, resulted in significant temperature difference across the width of the strip. This difference can be up to 69 degrees C and 41 degrees C according to the numerical results and thermal imaging data, respectively. Overall, this study gave a better insight into the cooling step in the hardening process. In addition, this investigation can be used to improve the hardening process as well as an input for future thermal stress investigations.
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