| 1. |
- Bi, Yanyan, et al.
(författare)
-
Evolution of Different Inclusions during Ladle Treatment and Continuous Casting of Stainless Steel
- 2013
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:12, s. 2099-2109
-
Tidskriftsartikel (refereegranskat)abstract
- The inclusions and clusters in steel samples of two similar steel grades of high-silicon non-calcium treated (HSiNC) stainless steels were investigated and compared during ladle treatment and continuous casting. Samples of liquid steel and slag were taken at different stages of the ladle treatment and casting during two plant trials: Low Al steel (LAI) and High Al steel (HAI). After electrolytic extraction of the steel samples, characteristics of inclusions and clusters (such as morphology, composition, size and number) were investigated in three dimensions (3D) by SEM in combination with EDS. Moreover, the composition of typical inclusions and clusters was analyzed on a polished cross section of steel samples. Spherical (SP), irregular and regular (IR) inclusions and clusters (CL) were observed in the samples from both heats. It was found that the morphology and composition of inclusions and clusters in both heats were significantly changed during the ladle treatment and casting. Most of inclusions (44-98%) in a Low Al steel are MgO-CaO-SiO2-Al2O3 spherical inclusions. The compositions of IR inclusions and clusters in steel samples of a High Al steel were mostly MgO center dot Al2O3 spinet, but also the complex SP inclusions containing Al2O3-MgO-CaO-SiO2. In addition, phase stability diagram based on Darken's quadratic formalism and Redlich-Kister type polynomial was estimated for both heats at a non-infinite solution.
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| 2. |
- 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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| 3. |
- Bi, Yanyan
(författare)
-
Three Dimensional Determinations of Inclusions in Ferroalloys and Steel Samples
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As the requirements on material properties increase, there has been a demand on an additional knowledge on the effect of impurities in the ferroalloyson the steel cleanness. Thus, the number, morphology, size and composition of inclusions in sixdifferent ferroalloys (FeTi, FeNb, FeSi,SiMn, LC and HC FeCr) were investigatedin this study. This was done in three dimensions (3D) by using a SEM in combination with EDS after electrolytic extraction of the ferroalloy samples. Theresults show that thenon-metallic and metallic inclusions can besuccessfully analyzed on the surface of a film filterafter a separation of the inclusions from the matrix. Overall, the inclusions canbe divided into two categories depending on the melting point. Furthermore, the possible transformation of different kinds of inclusions after their addition to the liquid steel canalso be determined.The inclusions and clusters in steel samples of two similar steel grades of high-silicon non-calcium treated (HSiNC) stainless steels were also investigated and compared during ladle treatment and continuous casting. Samples of liquid steel and slag were taken at different stages of the ladle treatment and casting during two plant trials: a low Al steel (LAl) and a high Al steel (HAl). Spherical (SP), irregular and regular (IR) inclusions and clusters (CL) were observed in the samples from both heats. It wasfound that the morphology and composition of inclusions and clusters in both heats were significantly changed during the ladle treatment and casting. Most of inclusions (44-98%) in a low Al steel are MgO-CaO-SiO2-Al2O3spherical inclusions. The compositions of irregular and regularinclusions and clusters in steel samples of a high Al steel were mostly MgO·Al2O3spinel, but also complex sphericalinclusions containing Al2O3-MgO-CaO-SiO2. In addition, the phase stabilitydiagram based on Darken’s quadratic formalism and Redlich-Kister type polynomial was estimated for both heats at a non-infinite solution.It is known that clusters in liquid steel have a harmful effect on the casting process and the quality of the final steel product. Therefore, 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 differentholding times after the addition of a mischmetal. The morphology, composition, number and size of clusters in PT and IH steel samples were analyzed and compared as a function of the 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 μm. In addition, the size and number of most clusters in PT are larger than those in IH samples.Largesize inclusions are recognized to be crucially harmful for the mechanical properties of steel products. Therefore, predictionsof the maximum size of Al2O3-CaO spherical inclusions in an Fe-10 mass% Ni alloy have been examined based on two dimensional (2D) and three dimensional (3D) investigations. The effects of the number of measurements and unit volume on the estimated 3D results were also investigated.
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| 4. |
- Bi, Yanyan, et al.
(författare)
-
Three-dimensional determinations of the non-metallic inclusions in different ferroalloys
- 2014
-
Konferensbidrag (refereegranskat)abstract
- Ferroalloys are commonly used in the steel industry to alloy or deoxidize the steel during the secondary steelmaking process before casting. Depending upon the ferroalloy quality, the addition can also lead to a supply of deleterious inclusions to the liquid steel. Thus, the number, morphology, size and composition of inclusions in six different ferroalloys (FeTi, FeNb, FeSi, SiMn LCFeCr and HCFeCr) were investigated. This was done in three dimensions (3D) by using SEM in combination with EDS after electrolytic extraction of the ferroalloy samples. Moreover, statistics of extreme values (SEV) were used to determine the largest size of inclusions.
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| 5. |
- Bi, Yanyan, et al.
(författare)
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Three Dimensional Evaluations of REM Clusters in Stainless Steel
- 2014
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 54:6, s. 1266-1273
-
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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| 6. |
- Bi, Yanyan, et al.
(författare)
-
Three-dimensional investigations of inclusions in ferroalloys
- 2014
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 85:4, s. 659-669
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Tidskriftsartikel (refereegranskat)abstract
- As the requirements on material properties increase, there has been a demand on an additional knowledge on the effect of impurities in the ferroalloys on the properties. Thus, the number, morphology, size, and composition of inclusions in four different ferroalloys (FeTi, FeNb, FeSi, and SiMn) were investigated. This was done in three dimensions (3D) by using scanning electron microscopy in combination with energy dispersive spectroscopy after electrolytic extraction of the ferroalloy samples. The non-metallic and metallic inclusions were successfully analyzed on the surface of film filter. Thereafter, the particle size distribution was plotted for most of the non-metallic inclusions. The non-metallic inclusions were found to be REM oxides in FeTi, FeSi, and SiMn, Al2O3, Ti-Nb-S-O oxides in FeNb and silicon oxides in SiMn. Moreover, the intermetallic inclusions were found to be a Ti-Fe phase in FeTi, Ca-Si, and Fe-Si-Ti phases in FeSi and a Mn-Si phase in SiMn. In addition, the almost pure single metallic phases were found to be Ti in FeTi, Nb in FeNb, and Si in FeSi. As the requirements on material properties increase, the effect of impurities in ferroalloys on the steelmaking process is increasingly becoming more important. The characteristic of inclusions (morphology, number, size, and composition) in ferroalloys investigated in three-dimensional after electrolytic extraction is a good method for studying the evolution of inclusions during steelmaking.
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| 7. |
- Davydenko, Arkadiy, et al.
(författare)
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Characterization of Briquettes Used for Slag Foaming in the EAF during Stainless Steel Production
- 2014
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 86:2, s. 137-145
-
Tidskriftsartikel (refereegranskat)abstract
- The modern sustainable stainless steel making industry is characterized by different factors such as an efficient utilization of energy in the Electric Arc Furnace (EAF) by a slag foaming practice and an utilization of waste products from its own production facilities. In this study, the foaming briquettes applied for a combined slag foaming and waste product reduction in the EAF are characterized. The recipes of the briquettes were made based on a literature review and previous experience. Afterwards, the composition and density of briquettes were estimated and compared to calculated data. Moreover, weight reduction experiments were made on a laboratory scale at temperatures up to 1500-°C in an argon atmosphere in order to characterize the products (metal, slag, and gas). Based on these results, the calculations were compared with experimental data. The following main results were found: (i) the density of briquettes can be successfully verified, (ii) briquettes have different mechanical properties depending on the materials used for production of briquettes, and (iii) the briquettes yield in different amounts of metal and gas. Moreover, it was found that light briquettes (without FeCr) produced almost double the amount of gas in comparison with heavy briquettes (containing FeCr); valuable metals can be recovered from briquettes, and recipes of briquettes can be optimized based on the amount of metal droplets in briquettes and the total utilization of carbon. This study is focused on a characterization of briquettes, which are used for slag foaming and waste product reduction in the Electric Arc Furnace (EAF) during the stainless steel production. The experimental data is compared with calculations according to the obtained results.
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| 8. |
- Davydenko, Arkadiy
(författare)
-
Some aspects of recycling of rest products and slag foaming in the EAF during stainless steel production
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An efficient stainless steel making industry is defined by different factors such as an efficient utilisation of energy in the Electric Arc Furnace (EAF). This requires a good by slag foaming practice and an utilisation of waste products from own production facilities. In the following study, briquettes applied for a combined slag foaming and waste product recycling in the EAF were investigated in both laboratory and industrial scales. More specifically, briquettes were characterised and used for slag foaming in the EAF. The recipes of the briquettes were made based on a literature review and previous experience. Afterwards, the composition and density of briquettes were defined and compared to calculated data. Moreover, weight reduction experiments were made on a laboratory scale at temperatures up to 1500°C in an argon atmosphere in order to characterise the products (metal, slag and gas) produced by briquettes. The calculations were also compared to experimental data. Thereafter, briquettes with different densities and pet-coke addition were tested on an industrial scale to study slag foaming in the EAF process during a stainless steel production. The slag foaming tendencies were determined based on visual estimations of slag foaming, determinations of the slag density before and after additions of different briquettes, and by calculating a foaming index. Moreover, the influence of the main parameters of the briquettes (composition, density) and the furnace slag (composition, basicity and etc.) on slag foaming was studied. Investigation of briquettes made on laboratory and industrial scales provided the following main results: the density of briquettes can successfully be verified, briquettes have different mechanical properties depending on the materials used for production of briquettes, briquettes yield different amounts of metal and gas. Moreover, it was found that the heavy briquettes (containing FeCr) produce about half the amount of gas compared to the light briquettes (without FeCr). The main part of the gas was generated during the first 2-3 min. Also, the valuable metals can be recovered from briquettes; recipes of briquettes can be optimized based on the amount of metal droplets in briquettes and the total utilisation of carbon. In addition, it was found that both heavy and light briquettes can be used for slag foaming. The highest slag foaming rate was obtained for slags with a basicity in the range of 1.31-1.49.
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| 9. |
- Doostmohammadi, Hamid, et al.
(författare)
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A Comparison of a Two-Dimensional and a Three-Dimensional Method for Inclusion Determinations in Tool Steel
- 2010
-
Ingår i: STEEL RES INT. - : Wiley. - 1611-3683. ; 81:5, s. 398-406
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Tidskriftsartikel (refereegranskat)abstract
- To produce clean commercial tool steel the non-metallic inclusions characteristics have to be known, since they influence the mechanical properties of steel. In this work, inclusion characteristics in steel samples from plant trials were studied. The samples were collected in the steel plant according the two following methods: (a) 2D investigations of inclusions by a cross sectional method and (b) 3D investigations of inclusions collected on a film filter after electrolytic extraction. More specifically, the chemical composition, morphology, number and size distribution of inclusions in tool steel samples taken from ladle during melt treatment were determined by both methods. In both methods SEM equipped with EDS was used for compositional analysis of inclusions. In addition, in the cross sectional method an automated detection program called 'INCAFeature' was used to collect more statistics of non-metallic inclusions. The composition of inclusions larger than 5 mu m was found to contain 49% CaO based on the results from both methods. However, for smaller inclusions it was found that the accuracy of the 2D method was less than that of the 3D method due to the influence of the metal matrix on the results. In addition, it was found that a critical inclusion size of 4 mu m could be defined for the 3D method, above which the standard deviation in composition determination was very low.
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| 10. |
- Doostmohammadi, Hamid, et al.
(författare)
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Use of Computational Thermodynamic Calculations in Studying the Slag/Steel Equilibrium during Vacuum Degassing
- 2010
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Ingår i: STEEL RES INT. - : Wiley. - 1611-3683. ; 81:1, s. 31-39
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Tidskriftsartikel (refereegranskat)abstract
- The effectiveness of a ladle refining process for production of tool steel with focus on the top slag is studied using computational thermodynamic calculations. The theoretical assessment was based on compositional data of steel and slag samples collected during trials in a plant equipped with a 65-t EAF, a ladle furnace and a vacuum degasser The calculation of slag-metal equilibrium during ladle treatment was performed for top slag excluding (Case A) and including (Case B) slag carryover and deoxidation products. The predictions showed that slag carryover and deoxidation products in the ladle significantly affect the composition of the top slag. Thus, these conditions must be taken into consideration when predicting the actual top slag composition. It was also found that it is possible to predict the final aluminium and sulphur content in steel based on the same calculation approach.
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| 11. |
- Ericsson, Ola
(författare)
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An Experimental Study of a Liquid Steel Sampling Process
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the steelmaking process samples are taken from the liquid steel, mainly to assess the chemical composition of the steel. Recently, methods for rapid determination of inclusion characteristics (size and composition) have progressed to the level where they can be implemented in process control. Inclusions in steel can have either good or detrimental effects depending on their characteristics (size, number, composition and morphology). Thereby, by determination of the inclusion characteristics during the steelmaking process it is possible to steer the inclusion characteristics in order to increase the quality of the steel. However, in order to successfully implement these methods it is critical that the samples taken from the liquid steel represent the inclusion characteristics in the liquid steel at the sampling moment. The purpose of this study is to investigate the changes in inclusion characteristics during the liquid steel sampling process. Experimental studies were carried out at steel plants to measure filling velocity and solidification rate in real industrial samples. The sampling conditions for three sample geometries and two slag protection types were determined. Furthermore, the dispersion of the total oxygen content in the samples was evaluated as a function of sample geometry and type of slag protection. In addition, the effects of cooling rate as well as oxygen and sulfur content on the inclusion characteristics were investigated in laboratory and industrial samples. Possibilities to separate primary (existing in the liquid steel at sampling moment) and secondary (formed during cooling and solidification) inclusions depending on size and composition were investigated. Finally, in order to evaluate the homogeneity and representative of the industrial samples the dispersion of inclusion characteristics in different zones and layers of the samples were investigated. It was concluded that the type of slag protection has a significant effect on the filling velocity and the sampling repeatability. Furthermore, that the thickness of the samples is the main controlling factor for the solidification rate. It was shown that top slag can contaminate the samples. Therefore, the choice of slag protection type is critical to obtain representative samples. It was shown that the cooling rate has a significant effect on the number of secondary precipitated inclusions. However, the number of primary inclusions was almost constant and independent on the cooling rate. In most cases it is possible to roughly separate the secondary and primary oxide inclusions based on the particle size distributions. However, in high-sulfur steels a significant amount of sulfides precipitate heterogeneously during cooling and solidification. This makes separation of secondary and primary inclusions very difficult. Moreover, the secondary sulfides which precipitate heterogeneously significantly change the characteristics (size, composition and morphology) of primary inclusions. The study revealed that both secondary and primary inclusions are heterogeneously dispersed in the industrial samples. In general, the middle zone of the surface layer is recommended for investigation of primary inclusions.
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| 12. |
- Ericsson, Ola, et al.
(författare)
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Changes in inclusion characteristics during sampling of liquid steel
- 2012
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Ingår i: Ironmaking & Steelmaking. - 0301-9233. ; 39:1, s. 67-75
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Tidskriftsartikel (refereegranskat)abstract
- In order to improve the process control during the steelmaking process, it is essential to obtain knowledge, as well as interpret information, on the characteristics of non-metallic inclusions in liquid steel samples. The purpose of the present study is to evaluate the effect of different sampling conditions on the inclusion characteristics. The changes in number, size and composition of primary inclusions due to the precipitation of secondary inclusions are studied. This is investigated in laboratory scale samples from an Fe-10 mass-%Ni alloy as well as industrial steel samples with varying contents of oxygen and sulphur. The results show that in most cases, the inclusion population can be separated, using a size condition, into primary (>= 0.6 mu m) and secondary (< 0.6 mu m) inclusions. Overall, the Lollipop sample with a 6 mm thickness can be recommended, because most of the secondary inclusions in low sulphur steels can be removed from the total particle size distribution. However, during sampling of liquid steel containing high levels of sulphur, a significant amount of sulphides precipitate heterogeneously onto primary inclusions, making it impossible to use size or morphology to separate the population. Finally, the numbers of secondary inclusions in the steel samples were found to increase significantly with an increased sample cooling rate. However, the number of primary inclusions was found to be almost constant and independent of the sample cooling rate.
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| 13. |
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| 14. |
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| 15. |
- Ericsson, Ola, et al.
(författare)
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Effect of Slag Protection System and Sample Geometry on Homogeneity of Total Oxygen Content in Samples from Liquid Steel
- 2011
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Ingår i: Steel Research International. - : Wiley. - 1611-3683. ; 82:3, s. 222-229
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Tidskriftsartikel (refereegranskat)abstract
- Many kinds of disposable samplers are available for sampling of liquid steel during steelmaking. Depending on slag protection, they can be divided into two main groups: metal-cap-protected and argon-protected samplers. For high quality steels, a correct determination of inclusion characteristics in metal samples is important for an improved process control. This paper seeks to investigate the effect of slag protection system, and sample geometry, on deviation and total content of oxygen within samples from the ladle treatment of liquid duplex stainless steel. The homogeneity with respect to total oxygen content was determined for different zones in the body, pin and inlet part of Bjorneborg and Lollipop (6 and 12mm thickness) samples. The results showed low, and stable, contents of oxygen in the argon-protected samples. However, the total oxygen content, and deviation of oxygen, in metal-cap-protected samples was much higher, especially in the body part of the samples. Finally, it was found that the oxygen content heterogeneity in the metal-cap-protected samples increased with a decreased sample weight. Based on the obtained results, the 6mm thick Lollipop sample with argon-protection is recommended for determination of total oxygen content and oxide inclusion characteristics.
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| 16. |
- Ericsson, Ola, et al.
(författare)
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Experimental study of parameters for liquid steel sampling
- 2010
-
Ingår i: Steel Grips - Journal of Steel and Related Materials. - 1611-4442 .- 1866-8453. ; 8, s. 115-124
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Tidskriftsartikel (refereegranskat)abstract
- Sampling of liquid steel to control the steel making process is very important in the steel industry. However, numerous types of disposable samplers are available and no united standard for sampling exists today. The goal in this study is to investigate the effect of slag protection type and sample geometry on sampling parameters such as filling velocity and solidification rate. Three sample geometries were selected: i) Björneborg, ii) 6 mm thick Lollipop, and iii)12 mm thick Lollipop. These have been tested with two types of slag protection: metal-cap protection and argon protection. The filling velocity and solidification rate of steel samples, which are very important for inclusion characteristics and sample quality, have been experimentally measured during plant trials. The study shows that argon protected samples have lower, more even, filling velocities (0.19 ± 0.09 m/s) compared to metal-cap protected samples (1.77 - 2.08 m/s). Solidification rate results for a 304L stainless steel show that the 6 mm thick Lollipop sample solidifies at a rate of about 100 °C/s while the Björneborg and the 12 mm thick Lollipop sample solidifies at a rate of about 20 °C/s.
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| 17. |
- Janis, Diana, et al.
(författare)
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Application of Different Extraction Methods for Investigation of Nonmetallic Inclusions and Clusters in Steels and Alloys
- 2014
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Ingår i: Advances in Materials Science and Engineering. - : Hindawi Limited. - 1687-8434 .- 1687-8442. ; 2014, s. 210486-
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Tidskriftsartikel (refereegranskat)abstract
- The characterization of nonmetallic inclusions is of importance for the production of clean steel in order to improve the mechanical properties. In this respect, a three-dimensional (3D) investigation is considered to be useful for an accurate evaluation of size, number, morphology of inclusions, and elementary distribution in each inclusion particle. In this study, the application of various extraction methods (chemical extraction/etching by acid or halogen-alcohol solutions, electrolysis, sputtering with glow discharge, and so on) for 3D estimation of nonmetallic Al2O3 inclusions and clusters in high-alloyed steels was examined and discussed using an Fe-10 mass% Ni alloy and an 18/8 stainless steel deoxidized with Al. Advantages and limitations of different extraction methods for 3D investigations of inclusions and clusters were discussed in comparison to conventional two-dimensional (2D) observations on a polished cross section of metal samples.
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| 18. |
- 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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| 19. |
- 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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| 20. |
- 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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| 21. |
- 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
-
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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| 22. |
- Janis, Jesper, et al.
(författare)
-
Effects of Nitride-Oxide Particles on Solidified Structure inFe-20mass%Cr Alloy Deoxidised with Ti/M (M = Zr or Ce)
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The ratio of equiaxed grains on a cross section and average grain sizein Fe-20mass% Cr alloy deoxidised with Ti/M (M = Zr or Ce) were studiedas function of nitrogen content and particle characteristics such as sizedistribution, morphology and composition. Fe-20mass%Cr alloys weremelted at 1600ºC, deoxidised, cooled to 1400ºC followed by waterquenching. The particles were investigated on a surface of film filter afterelectrolytic extraction of metal samples with 10%AA electrolyte. It wasfound that the number of particles increases with increasing the N content.The as-cast solidification structure and grain size were clearly affected bythe number of oxide and oxide-nitride particles in Ti/Zr experiments. Theeffect in the Ti-Ce case was almost undetectable.
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| 23. |
- Janis, Jesper, et al.
(författare)
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Effects of Primary Oxide and Oxide-Nitride Particles on the Solidification Structure in a Fe-20 mass%Cr Alloy Deoxidised with Ti and M (M = Zr or Ce)
- 2013
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:2, s. 221-229
-
Tidskriftsartikel (refereegranskat)abstract
- The ratio of equiaxed grains on a cross section and the size of equiaxed grains in a Fe-20 mass% Cr alloy deoxidised with Ti/M (M = Zr or Ce) were studied as function of nitrogen content and particle characteristics such as size distribution, morphology and composition. Fe-20 mass% Cr alloys were melted at 1 600 degrees C, deoxidised, and cooled to 1 400 degrees C followed by water quenching. Thereafter, the particles were separated from the matrix using electrolytic extraction using a 10%AA electrolyte and collected on a film-filter surface. The inclusion characteristics were determined using SEM. It was found that the number of particles increases with an increased N content. Furthermore, that the solidification structure was clearly affected by the number of primary oxide and oxide-nitride particles in the Ti/Zr deoxidation experiments. However, a similar effect could not be detected in the Ti/Ce deoxidation experiments.
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| 24. |
- Kanbe, Yuichi, et al.
(författare)
-
Analysis of Largest Sulfide Inclusions in Low Carbon Steel by Using Statistics of Extreme Values
- 2011
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Ingår i: Steel Research International. - : Wiley. - 1611-3683. ; 82:4, s. 313-322
-
Tidskriftsartikel (refereegranskat)abstract
- The statistics of extreme values was applied for the determination of the largest sulfide inclusions with different morphology in low carbon steel samples by using both two-dimensional (2D) observations on the polished cross section and three-dimensional (3D) observations on a surface of a film filter after electrolytic extraction of the samples. It was found that the globular, rod-like and dendritic sulfides in the molten steel sample as well as the elongated sulfides in the rolled steel sample can be successfully extracted from the both samples, and analyzed precisely by using extreme value analysis in 3D. Based on the geometrical considerations of the probability for measurement of the true length of rod-like and elongated inclusions on a cross section, it was found that this probability for inclusions decreases dramatically with an increasing real aspect ratio value of them. Particularly for the determination of the true length for elongated inclusions in the rolled steel sample by 2D investigations on a metal cross section, it is required to be cut investigating section of steel sample within +/- 1 degree against rolling direction. Therefore, a 3D observation is considered to be more preferable and accurate than the conventional cross sectional observation in 2D, due to the possibility for the measurements of the real size of them.
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| 25. |
- Kanbe, Yoichi, et al.
(författare)
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Application of Extreme Value Analysis for Two- and Three-Dimensional Determinations of the Largest Inclusion in Metal Samples
- 2011
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 51:4, s. 593-602
-
Tidskriftsartikel (refereegranskat)abstract
- The maximum size of single inclusion particles and clusters in an Fe-10 mass% Ni alloy deoxidized with Al or Ti/Al were examined using extreme value analysis. The results obtained from conventional two-dimensional observations of inclusions on a polished cross section of metal sample (the CS-method) were compared to those from three-dimensional investigations of inclusions on a film filter after electrolytic extraction (the EE-method). It was found that the EE-method can successfully be used as a reference method for estimation of the probable maximum size of single inclusion particles and clusters by using an extreme value distribution (EVD). The EVD results for single inclusion particles obtained from the EE-method agreed satisfactorily well with those from a conventional CS-method. However, this required identification as well as neglect of pores on an investigated cross section of a metal sample. The predicted maximum size of single inclusion particles in a 1 mm(3) volume was confirmed by results from the EE-method.
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| 26. |
- Kanbe, Yuichi, et al.
(författare)
-
Application of Statistics of Extreme Values for Inclusions in Stainless Steel on Different Stages of Steel Making Process
- 2011
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 51:12, s. 2056-2063
-
Tidskriftsartikel (refereegranskat)abstract
- A statistics of extreme values was applied to determine the largest inclusion sizes in the Type 304 stainless steel. The samples taken from a tundish, slab and hot rolled steel in one heat were examined by using a two dimensional observation of inclusions on a metal cross section. It was found that the molten steel sample contained two different types of inclusions, which were deoxidation products (SiO(2)-CaO-MgO-Al(2)O(3)) and reoxidation products (SiO(2)-MnO-Cr(2)O(3)). As a result, the extreme value distribution (EVD) for different types of inclusions in the melt has two different slopes. Meanwhile, the inclusions in the slab sample provided a good linearity in one EVD. Moreover, the correlation coefficients of the regression lines for both the slab and rolled steel samples increased significantly with an increased number of measurements from 40 to 80 unit areas. It was found also that the EVD data for fractured inclusions on a parallel cross section of rolled steel agreed satisfactorily well with that for the initial spherical inclusions in the slab sample. Based on the geometrical considerations of inclusion deformation and fracture during hot-rolling, the maximum length of fractured inclusions in rolled steel can be estimated reasonably well from the EVD for initial undeformed inclusions in the slab sample.
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| 27. |
- Kanbe, Yuichi, et al.
(författare)
-
Application of Statistics of Extreme Values for the inclusions in Type 304 Stainless Steel throughout the Steel Making Process
- 2010
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Application of statistics of extreme values was applied to determine the inclusion sizes in Type 304 stainless steel. The samples taken from a tundish, slab and hot rolled steel in one heat were examined by using a cross sectional observation. In the molten steel sample, the extreme value distribution (EVD) containing two different types of inclusions, which are deoxidation products (SiO2-CaO-MgO-Al2O3) and reoxidation products (SiO2-MnO-Cr2O3), resulted in two different slopes in one EVD. Meanwhile, the inclusions in the slab sample provided a good linearity with respect to the EVD. The correlation coefficients of the regression lines for both the slab and rolled steel samples were found to increase with an increased number of measurements between 40 and 80. Based on the EVD data obtained from the slab and rolled steel samples, it was found that the EVD data for the area of fractured inclusions on a parallel cross section of rolled steel agrees well with that for the initial undeformed inclusions area in a slab sample. According to the geometrical considerations of morphological change of inclusion during the hot rolling, the EVD for the length of fractured inclusions after the rolling is possible to estimate from their initial sizes in the case of the fracture into the equivalent particle size.
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| 28. |
- Kanbe, Yuichi, et al.
(författare)
-
Determination of Size Distribution and Probable Maximum Size of Inclusions in AISI304 Stainless Steel
- 2013
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:11, s. 1968-1973
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Tidskriftsartikel (refereegranskat)abstract
- The probable maximum sizes (PMS) of inclusions in AISI304 stainless steels were predicted by two methods of the statistics of extreme values (SEV) and the particle size distributions (PSD). Firstly, the PMS of inclusions in the molten steel taken from a tundish agreed well with those in the slab sample. The particle size distributions (PSD) of inclusions almost obeyed exponential functions. The results of comparison between the two methods showed that the PMS by the SEV analysis agreed with that by the PSD approximation in the case of the steel with the higher oxygen content. However, in the case of the steel with the lower oxygen content, the PMS by the PSD approximation overestimated the predicted size with the reference to the SEV analysis. In this case, the approximations with elimination of some largest inclusions which were deviated from an exponential distribution were found to be effective to predict the probable largest size in a reference area. This above result suggests that it is necessary to decide if some largest inclusions are employed for adequate predictions. It is considered that necessity of this operation increases with decreasing oxygen content.
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| 29. |
- Karasev, Andrey, et al.
(författare)
-
Three-dimensional investigation of large-size inclusions and clusters in steels by using the electrolytic extraction technique
- 2013
-
Ingår i: AISTech 2013. - 9781935117339 ; , s. 1139-1145
-
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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| 30. |
- Karasev, Andrey Vladimirovich, 1962-, et al.
(författare)
-
Application of Laser Ablation ICP Mass Spectrometry for Analysis of Oxide Particles on Cross Section of Alloys and Steels
- 2011
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 51:12, s. 2042-2049
-
Tidskriftsartikel (refereegranskat)abstract
- Some aspects for the application of Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) are considered and discussed from the viewpoint of the rapid analysis of oxide inclusions in metal samples. The inclusion characteristics in Fe-10% Ni alloy samples such as number, size and particle size distribution obtained by LA-ICP-MS method are compared with those from three-dimensional observation of particles on a film filter after electrolytic extraction. Though some limits had to be considered regarding to the content of soluble elements, the number and dispersion of analyzed inclusions in metal matrix, it was found that the LA-ICP-MS technique can be successfully applied for the rapid analysis of oxide inclusions containing Al2O3, MgO and others.
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| 31. |
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| 32. |
- Karasev, Andrey Vladimirovich, et al.
(författare)
-
Effects of Soluble Ti and Zr Content and Austenite Grain Size on Microstructure of the Simulated Heat Affected Zone in Fe-C-Mn-Si Alloy
- 2011
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 51:9, s. 1524-1533
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of soluble Ti and Zr contents on the microstructure in a simulated heat affected zone of a Fe-0.05mass%C-1.5mass%Mn-0.20mass%Si alloy was studied. This was done as a function of the austenite grain size as well as the number and size of TiN, Ti(2)O(3), MgO(+Ti(2)O(3)), TiN(+MgO) and ZrO(2)(+Ti(2)O(3)) particles under different peak temperature (1 300 and 1 400 degrees C), peak holding time (0, 60 and 600 s) and a constant time of cooling (70 s) from 800 to 500 degrees C. The effectiveness of inclusion phases for intragranular ferrite (IGF) formation was studied from the area fraction of IGF for a given austenite grain size and soluble Ti content. For a given austenite grain size, the primary ferrite decreases and the IGF increases with an increased soluble Ti content up to about 100 ppm. After going through a maximum the replacement of IGF by lath bainitic ferrite occurs with an increased soluble Ti content. It is found that the effect of soluble Zr content on the microstructure is much stronger than that of a soluble Ti content. The area fraction of IGF decreases gradually with an increase in the austenite grain size (50-1 000 mu m) for a given soluble Ti content (50-400 ppm). By using the hardenability parameter based on the non-equilibrium grain-boundary segregation model, it is observed that the IGF formation is encouraged in the following order: TiN>{Ti(2)O(3), MgO(+Ti(2)O(3))}>ZrO(2)(+Ti(2)O(3)).
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| 33. |
- Malmberg, Kristofer, et al.
(författare)
-
Influence of final stirring treatment on inclusion number in tool steel
- 2013
-
Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 40:6, s. 407-412
-
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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| 34. |
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| 35. |
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| 36. |
- Malmberg, Kristofer, et al.
(författare)
-
Optimisation of stirring conditions during vacuum degassing in order to lower inclusion content in tool steel
- 2013
-
Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 40:3, s. 231-237
-
Tidskriftsartikel (refereegranskat)abstract
- In the production of tool steel, the control of secondary metallurgy plays an important role to meet the rapidly increasing demands for clean steel, as impurities and non-metallic inclusions can reduce its mechanical properties. This study focuses on the influence of stirring rate during the vacuum degassing of liquid steel on the inclusion characteristics. During this treatment, both gas and induction stirring are used; thus, fluid flow simulations were made for the vacuum treatment of melts at high (900 A + 100 L min(-1) Ar) and low (700 A + 10 L min(-1) Ar) stirring rates. By decreasing the Weber number to a value smaller than the critical value (We(crit)=12.3) at a lower stirring rate, the probability for dispersion and entrapping of slag inclusions into the liquid steel significantly decreases. Five plant heats were carried out with different rates of induction stirring and argon flow in the ladle during vacuum treatment. The results gained by light optical microscopy investigation show that the total amount of large size single inclusions (>11.3 mm) in steel samples after vacuum treatment and in the final product decreases considerably with a lowered stirring rate. Thus, the experimental results support the theoretical results based on the Weber number.
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| 37. |
- Muwanguzi, Abraham Judah Bumalirivu
(författare)
-
Characterisation of Muko iron ores (Uganda( for defferent routes of iron production
- 2010
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Iron and its products, especially the various forms of steel, have been and still are a vital material in many sectors of life. It is utilized in many industrial activities ranging from production of heavy duty mechanical equipment to light electrical appliances and home appliances. With the world‟s iron ore consumption estimated to stand at 1.3 billion tonnes by 2025, exploitation of any existing natural deposits is of increasing importance to meet the demands of the expanding world economy. Large deposits of iron ore exist in Uganda in the eastern (Tororo) regions and south-western (Kisoro-Kabale) regions of the country. The ore deposits of Kisoro-Kabale consist of an iron-rich hematite grade with less deleterious impurities as compared to that of Tororo. Prospective quantification puts the deposits at 30-50 million tonnes of raw-ore reserves. To date the deposits lay unexploited, with small holder black smith activities taking place in the area. This work involves understanding the occurrence, quantity and quality of the ore plus its properties and characteristics in a bid to pave way for its exploitation for economic use in Uganda and beyond. Characterisation was done on the samples collected from the deposits, to establish its physical, chemical and metallurgical properties. Literature detailing the natural occurrence of the deposits plus the genesis of the parent rocks and ore and the prospective tonnage is included. The economic situation in Uganda as far as demand and consumption of iron and steel is concerned is also briefly highlighted. The chemical, physical and metallurgical characteristics that could facilitate the initial exploitation of the ore are examined with conclusive results from the representative samples examined. The results present Muko ore as a high grade of hematite with an Fe content averaging 68%. The gangue content (SiO 2+Al2O3) of 5 of the 6 samples investigated is < 4%, which is within the tolerable limits for the dominant iron production processes, with its S and P contents being < 0.1% and 0.07% respectively. Thus, Muko iron ore can be reduced in the furnace without presenting major difficulties. With respect to mechanical properties, Muko ore was found to have a Tumble Index value > 85 wt%, an Abrasion Index value < 4 wt% and a Shatter Index value < 2.5 wt%. This implies that the ore holds its form during the processes of mining, transportation, screening and descent when loaded in the furnace for reduction. Its reducibility index was found to be 0.868%/min. This is well within the desired reduction limits for the major iron reduction processes. It implies that a high productivity (in terms of iron reduced) can be realised in the reduction processes in a given period of time. Muko iron ore was found to meet most of the feed raw material requirements (physical, chemical and metallurgical) for the blast furnace and the major direct reduction processes (Midrex, HYL III and SL/RN). Furthermore, for those desired for sinter and pellet making. It can thus serve well as a feed raw material for smelting reduction and direct reduction processes.
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| 38. |
- Muwanguzi, Abraham Judah Bumalirivu, et al.
(författare)
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Characterisation of the Physical and Metallurgical Propertiesof Natural Iron Ore for Iron Production
- 2012
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Ingår i: ISRN Materials Science. - : Hindawi Publishing Corporation. - 2090-6080 .- 2090-6099. ; 2012, s. 9-
-
Tidskriftsartikel (refereegranskat)abstract
- The blast furnace is still the dominant form of iron production, but over the years, direct reduction methods have increased due to a number of reasons. Overall, iron production methods have optimal requirements with respect to the feed materials especially iron ore. In this study, tests were carried out on Muko iron ore from Uganda to analyse its suitability to meet the feed requirements of today's dominant iron production methods. More specifically, the Tumbler, Abrasion, and Shatter Indices of the ore were determined. In addition, porosity, thermoanalysis, and reducibility tests were performed. Overall, the Muko ore was found to have good mechanical properties exemplified with tumble and shatter index data >89.0 wt% and <2.5 wt%, respectively. Furthermore, its reducibility at 0.87%/min is within the acceptable range as a natural material feed for blast furnace and direct reduction furnaces. Also, the energy requirement for heating the ore to 1100°C was found to be higher in the samples containing a wider size range of irregular grains and the largest contaminations. In summary, it is concluded that the Muko iron ore has good physical and metallurgical properties to serve as a natural material for the blast furnace and direct reduction furnaces.
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| 39. |
- Muwanguzi, Abraham Judah Bumalirivu, et al.
(författare)
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Characterization of chemical composition and microstructure of natural iron ore from Muko deposits
- 2012
-
Ingår i: ISRN Materials Science. - : Hindawi Publishing Corporation. - 2090-6080 .- 2090-6099. ; 2012, s. 9-
-
Tidskriftsartikel (refereegranskat)abstract
- The study aimed at investigating the chemical composition and microstructure of raw iron ore from the deposits in Muko area (south-western Uganda). The quality of this iron ore was evaluated to establish its suitability to serve as a raw material for iron production. Samples were taken from the six hills of Muko ore deposits and tests carried out to establish their composition and properties. X-ray diffraction and scanning electron microscopy were employed in the investigation and chemical analysis performed to determine the compounds constituting the ore. The quality of this ore was compared to generalized world market standards and ores from other nations. It was found that Muko ore is a rich hematite grade with Fe content above 65%. It has little gangue (<6% SiO2 and 3-4% Al2O3) and low contents of the deleterious elements (P ~ 0.02% and S < 0.006%), which correspond to acceptable levels for commercial iron ores.
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| 40. |
- Muwanguzi, Abraham Judah Bumalirivu, et al.
(författare)
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Effect of different factors on low temperature degradation of hematite iron ore during reduction
- 2014
-
Ingår i: Metallurgical Research and Technology. - : EDP Sciences. - 2271-3646 .- 2271-3654. ; 111:1, s. 57-66
-
Tidskriftsartikel (refereegranskat)abstract
- Low temperature degradation (LTD) of iron oxides was investigated with the aim of understanding how natural iron ores degrade under different conditions. Minimisation of this degradation would increase the acceptance level of natural iron ores as feed materials without prior beneficiation. In addition to temperature and reduction gas composition, sample positioning in the reduction furnace and sample's original weight were also found to influence LTD. Samples placed in the top reaction zone of the furnace, which have the first contact with the reducing gas, were found to degrade 1.5 times more than those in the middle and bottom reaction zones. In addition, they presented a wide range of size in the disintegrated particles than those in the middle and bottom reaction zones. Furthermore, the samples with an original weight equal to or greater than 5 g, had a disintegration extent of less than 10%. Therefore, if the reduction gas comes into contact with a certain material first, before contacting the iron oxide, it may serve to reduce on LTD during reduction. Furthermore, in laboratory conditions, the occurrence of low temperature breakdown of the natural iron oxides can be minimised by using samples with an original weight equal to or greater than 5 g.
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| 41. |
- Muwanguzi, Abraham Judah Bumalirivu
(författare)
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Investigating the parameters that influence the behaviour of natural iron ores during the iron production process
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the iron production processes, sinters and pellets are mostly used as raw materials due to their consistency with respect to physical and chemical properties. However, natural iron ores, as mined, are rarely used directly as a feed material for iron processing. This is mainly due to the fact that they have small contents of iron and high concentration of impurities. Moreover, they swell and disintegrate during the descent in the furnace as well as due to low melting and softening temperatures. This work involves an investigation of the parameters that influence the use of natural iron ores as a direct feed material for iron production. Furthermore, it points out ways in which these can be mitigated so as to increase their direct use in iron production.Natural iron ore from Muko deposits in south-western Uganda was used in this study. Initially, characterisation of the physical and chemical properties was performed, to understand the natural composition of the ore. In addition, investigations were done to study the low temperature strength of the ore and its behaviour in the direct reduction zone. Also, simulations were performed with three models using the experimental data from the direct reduction experiments in order to determine the best model for predicting the direct reduction kinetics of natural iron ores.Chemical analyses showed that the Muko ore represents a high grade of hematite with an Fe content of 68% on average. The gangue content (SiO2+Al2O3) in 5 of the 6 investigated iron ore samples was < 4%, which is within the tolerable limits for the dominant iron production processes. The S and P contents were 0001-0.006% and 0.02-0.05% respectively. These can be reduced in the furnace without presenting major processing difficulties. With respect to the mechanical properties, the Muko ore was found to have a Tumble Index value of 88-93 wt%, an Abrasion Index value of 0.5-3.8 wt% and a Shatter Index value of 0.6-2.0 wt%. Therefore, the ore holds its form during the handling and charging processes.Under low temperature investigations, new parameters were discovered that influence the low temperature strength of iron oxides. It was discovered that the positioning of the samples in the reduction furnace together with the original weight (W0) of the samples, have a big influence on the low temperature strength of iron oxide. Higher mechanical degradation (MD) values were obtained in the top furnace reaction zone samples (3-25% at 500oC and 10-21% at 600oC). These were the samples that had the first contact with the reducing gas, as it was flowing through the furnace from top to bottom. Then, the MD values decreased till 5-16% at a 500oC temperature and 6-20% at a 600oC temperature in the middle and bottom reaction zones samples. It was found that the obtained difference between the MD values in the top and other zones can be more than 2 times, particularly at 500oC temperature. Furthermore, the MD values for samples with W0 < 5 g varied from 7-21% well as they decreased to 5-10% on average for samples with W0 ≥ 5 g. Moreover, the MD values for samples taken from the top reaction zone were larger than those from the middle and bottom zones.During direct reduction of the ores in a H2 and CO gas mixture with a ratio of 1.5 and a constant temperature, the reduction degree (RD) increased with a decreased flow rate until an optimum value was established. The RD also increased when the flow rate was kept constant and the temperature increased. An optimum range of 3-4g was found for natural iron ores, within which the highest RD values that are realised for all reduction conditions. In addition, the mechanical stability is greatly enhanced at RD values > 0.7. In the case of microstructure, it was observed that the original microstructure of the samples had no significant impact on the final RD value (only 2-4%). However, it significantly influenced the reduction rate and time of the DR process.The thermo-gravimetric data obtained from the reduction experiments was used to calculate the solid conversion rate. Three models: the Grain Model (GM), the Volumetric Model (VM) and the Random Pore Model (RPM), were used to estimate the reduction kinetics of natural iron ores. The random pore model (RPM) provided the best agreement with the obtained experimental results (r2 = 0.993-0.998). Furthermore, it gave a better prediction of the natural iron oxide conversion and thereby the reduction kinetics. The RPM model was used for the estimation of the effect of original microstructure and porosity of iron ore lumps on the parameters of the reduction process.
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| 42. |
- Muwanguzi, Abraham Judah Bumalirivu, et al.
(författare)
-
Investigation of direct reduction of lumps from natural hematite iron ore
- 2013
-
Ingår i: Research and Application of Material. - : Sciknow Publications. - 2328-5079.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The effects of the main characteristics of hematite natural ore lumps such as weight and microstructure and the parameters of the direct reduction process (gas flow rate and temperature) on the reduction degree and thermo-mechanical degradation of iron ore lumps were investigated. Lumps from Muko deposit were used for direct reduction with H2/CO, ratio of 1.5. The temperature and gas flow rate ranged from 700-900°C and 0.25-1.0 L/min, respectively. The highest reduction degree (0.88-0.91) was obtained by direct reduction of 3-4 g samples at 900°C and 0.5 L/min. The effects of the flow rate of the reduction gas in the furnace and the carbon deposited on a sample surface on the accuracy of the weight measurement and the reduction degree by using the thermal gravimetric technique were estimated and discussed. It was further discovered that the natural microstructure of a lump iron ore has an effect on the reduction time.
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| 43. |
- Roos, Erik, et al.
(författare)
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An Experimental and Thermodynamic Study of Non-Metallic Inclusions in High Si Stainless Steels Regarding Clogging During Casting
- 2014
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 85:10, s. 1410-1417
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Tidskriftsartikel (refereegranskat)abstract
- Clogging of high Si-containing stainless steel grades was studied by metallographic examinations of steel samples from clogged and non-clogged heats as well as by thermodynamic modeling using Thermo-Calc and FactSage. Morphology, composition, number and size of inclusions and clusters in the steel samples were determined on a polished surface of the steel samples by using a scanning electron microscope equipped with energy-dispersive X-ray spectrometer. The results showed that the content of Al in ferroalloys added during ladle treatment should be controlled to avoid a formation of spinel MgO-Al2O3 inclusions in liquid steel and a resulting clogging during casting. The thermodynamic calculations showed that the Al content in a melt during ladle treatment and casting should not be larger than 0.003% to obtain < 1% of MgO-Al2O3 inclusions in the liquid steel for a 1.9% silicon content. Moreover, calculations also showed that if the Si content increased from 1.9% (non-clogging heats) to 2.65% (clogging heats), the number of MgO-Al2O3 inclusions decreased slightly. Moreover, it was found that an increased amount of FeSi additions for correction of Si content in the melt increase the Al content. As a result, the number of spinels and clusters increases, which is the primary cause for clogging during casting of these steel grades.
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| 44. |
- Suito, Hideaki, et al.
(författare)
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Influence of Oxide Particles and Residual Elements on Microstructure and Toughness in the Heat-Affected Zone of Low-Carbon Steel Deoxidized with Ti and Zr
- 2011
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 51:7, s. 1151-1162
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and toughness in Fe-0.04%C-1.85%Mn-0.03%Si-0.018%Nb steel deoxidized with Ti and Zr have been studied as functions of particle characteristics, austenite grain size and soluble Ti and Zr contents using a simulated HAZ (heat affected zone) thermal cycle (peak temperature, 1 400 degrees C; peak holding time, 60 s; time of cooling from 800 to 500 degrees C, 70 s) and submerged arc welding (heat input of 15 kJ/mm), respectively. Microstructures were studied in samples containing 1.0 to 1.5 mu m-diameter oxide particles numbering 500 to 2 000 mm(-2) and with a soluble oxygen content of 10 to 30 ppm (measured before casting) and soluble Ti and Zr contents of 50-150 ppm. The gamma grain size after HAZ thermal cycle in the range between 200 and 600 mu m is controlled by pinning and solute drag. Small gamma grain size below 300 mu m was obtained with high soluble Ti and Zr contents of 110-160 ppm, whereas large gamma grain size above 300 mu m was obtained with low soluble Ti and Zr contents of 60-110 ppm. Two types of microstructures that showed high Charpy absorbed energy (vE(-10 degrees C)= 150-250 J and vE(-50 degrees C)= 50-150 J) were observed independent of gamma grain size: One is acicular ferrite and a small amount of grain boundary ferrite (GBF) and ferrite side plate (FSP) and the other is GBF, FSP and granular bainitic ferrite. It was observed that low vE(T) values are attributed to the formation of porosity, large-size particles, carbides (+nitrides) and lathe bainitic ferrite.
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| 45. |
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| 46. |
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| 47. |
- Zhang, Zhi, et al.
(författare)
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Simulation of the Steel Sampling Process
- 2010
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 50:12
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a theoretical study of the liquid steel sampling process in the iron &steel industry. As a continuous research with the previous work, the initial solidification duringthe sampler filling was taken into account. The liquid steel sampling procedure, which ismainly used to monitor whether the steel is at the correct composition during the steelmaking,can also be applied to examine the inclusion size characteristics. Focus was on the influence ofthe initial solidification on the inclusion concentrations. The whole sampling system wasmodeled in order to obtain a simulation result which is realistic from an industrial perspective.Argon-protected sampling was the focus in the simulations. A discrete phase model was usedto simulate the movement of inclusions in the liquid steel. Inclusions were injected from theinlet pin of the lollipop-shaped sampler. Some selected different sized primary inclusions thatexist in the ladles during a steelmaking process were simulated. The conclusion from this workis that turbulent flow patterns within the sampler mold will change because of the spaceshrinkage due to the solidification. This, in turn, will also affect the inclusion dispersions. Itconcludes that the preferred position for detecting inclusions is the bottom region, except thebottom surface. It estimates that the mean deviation between the calculated result and the initialconcentration for all inclusions in these regions is within 10%.
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