| 1. |
- Bai, Haitong, et al.
(författare)
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Experimental Validation and Numerical Analysis of the Swirling Flow in a Submerged Entry Nozzle and Mold by using a Reverse TurboSwirl in a Billet Continuous Casting Process
- 2016
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X.
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Tidskriftsartikel (refereegranskat)abstract
- As an alternative to some traditional methods to generate a swirling flow in the continuous casting process, the use of a new swirling flow generator, TurboSwirl, was studied. Specifically, a reversed TurboSwirl device was designed as part of a submerged entry nozzle (SEN) for a round billet continuous casting process. Mathematical modelling was used to investigate this new design and a water model experiment was carried out to validate the mathematical model. The predicted velocities by the turbulence models: realizable k-ε model, Reynold stress model (RSM) and detached eddy simulation (DES) were compared to the measured results from an ultrasound velocity profile (UVP) method. The DES model could give the best prediction inside the SEN and had a deviation less than 3.1% compared to the measured results. Moreover, based on the validated mathematical model and the new design of the SEN, the effect of the swirling flow generated by the reverse TurboSwirl on the flow field of the SEN and mold was compared to the design of the electromagnetic swirl flow generator (EMSFG). A very strong swirling flow in the SEN and a stable flow pattern in the mold could be obtained by the reverse TurboSwirl compared to the EMSFG.
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| 2. |
- Bergstrom, Jens, et al.
(författare)
-
Very High Cycle Fatigue of Two Ductile Iron Grades
- 2016
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 87:5, s. 614-621
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Tidskriftsartikel (refereegranskat)abstract
- Two ductile iron grades, EN-GJS-600-3 a ferritic-pearlitic grade, and EN-GJS-600-10 a silicon strengthened ferritic nodular iron grade, are studied in the very high cycle fatigue range using a 20kHz ultrasonic test equipment. Fatigue strengths and SN-curves are achieved, and fracture surfaces and microstructures are investigated. The ferritic grade with higher ductility displays a lower fatigue strength at 10(8) load cycles than the ferritic-pearlitic grade, 142 and 167MPa, respectively. Examination of fracture surfaces shows that fatigue failures are controlled by micropores in both of the ductile iron grades, while the graphite nodule distributions do not seem to influence the difference in fatigue strengths. Prediction of the fatigue strengths, using a model for ductile iron proposed by Endo and Yanase, indicates a large potential for improvement in particular for the ferritic grade.
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| 3. |
- Brämming, Mats, et al.
(författare)
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BOF Process Control and Slopping Prediction Based on Multivariate Data Analysis
- 2016
-
Ingår i: Steel Research International. - : Wiley-VCH Verlag. - 1611-3683 .- 1869-344X. ; 87:3, s. 301-310
-
Tidskriftsartikel (refereegranskat)abstract
- In a complex industrial batch processes such as the top-blown BOF steelmaking process, it is a complicated task to monitor and act on the progress of several important control parameters in order to avoid an undesired process event such as "slopping" and to secure a successful batch completion such as a sufficiently low steel phosphorous content. It would, therefore, be of much help to have an automated tool, which simultaneously can interpret a large number of process variables, with the function to warn of any imminent deviation from the normal batch evolution and to predict the batch end result. One way to compute, interpret, and visualize this "batch evolution" is to apply multivariate data analysis (MVDA). At SSAB Europe's steel plant in Luleå, new BOF process control devices are installed with the purpose to investigate the possibility for developing a dynamic system for slopping prediction. A main feature of this system is steelmaking vessel vibration measurements and audiometry to estimate foam height. This paper describes and discusses the usefulness of the MVDA approach for static and dynamic slopping prediction, as well as for end-of-blow phosphorous content prediction. Multivariate data analysis (MVDA) methods have been applied on the top-blown BOF steelmaking process, with the main aim to create industrially applicable static (i.e., prior to blow), as well as dynamic in-blow batch models for predicting the slopping probability. The MVDA approach has also been investigated in regard to in-blow prediction of end-of-blow phosphorous content.
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| 4. |
- Brämming, Mats, et al.
(författare)
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Characterization of Slag‐Metal Emulsion and Its Impact on Foaming Behavior and Slopping in the LD Process
- 2019
-
Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 90:2
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Tidskriftsartikel (refereegranskat)abstract
- In the Basic Oxygen Steelmaking (BOS) process, a heterogeneous emulsion‐solid mix will form, consisting of an emulsion of liquid slag and metal droplets, in which 2nd phase particles of undissolved fluxes and solid in‐blow precipitates are suspended. When the carbon in the metal droplets reacts with iron oxide, small bubbles of CO gas are formed. If the upward movement of these bubbles is obstructed by the physical properties of the emulsion‐solid mix, foaming will occur. Certain process conditions may lead to an excessive foam growth, in the worst case forcing foam out of the vessel. This undesired process event is known as “slopping”. Extensive studies during recent decades have shown that emulsion characteristics strongly connected to foaming are: viscosity, surface tension, and density. The extent of foaming is also dependent on bubble size; foaming increasing with smaller bubble size. However, investigations into the influence of the mineralogy and morphology of the emulsion‐solid mix on foaming in basic oxygen steelmaking are scarce. In this work, samples from trials in a 6‐tonne pilot plant BOS vessel are examined by XRD and with SEM for the determination of emulsion‐solid mix mineralogy and morphology at different stages of the oxygen blow. The study confirms the importance of tight process control in order to minimize the emulsion‐solid mix apparent viscosity and, hence, the foam height, but this without over‐oxidizing the liquid slag phase, which would result in increased gas generation within the slag‐metal emulsion.
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| 5. |
- Bölke, Kristofer, et al.
(författare)
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Physical Modeling Study on the Mixing in the New IronArc Process
- 2018
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Ingår i: Steel Research International. - : WILEY-V C H VERLAG GMBH. - 1611-3683 .- 1869-344X. ; 89:7
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Tidskriftsartikel (refereegranskat)abstract
- IronArc is a newly developed technology for pig iron production with the aim to reduce the CO2 emission and energy consumption, compared to a conventional blast furnace route. In order to understand the fluid flow and stirring in the IronArc reactor, water modeling experiments are performed. Specifically, a down scaled acrylic plastic model of the IronArc pilot plant reactor is used to investigate the mixing phenomena and gas penetration depth in the liquid bath. The mixing time is determined by measuring the conductivity in the bath, after a sodium chloride solution is added. Moreover, the penetration depth is determined by analyzing the pictures obtained during the experimental process by using both a video camera and a high speed camera. The results show that the bath movements are strong and that a circular movement of the surface is present. The mixing in the model for the flow rate of 282 NLmin(-1) is fast. Specifically, the average mixing times are 7.6 and 10.2s for a 95% and a 99% homogenization degree, respectively. This is 15% and 18% (per degree of homogenization) faster compared to the case when using 3 gas inlets and the same flow rate.
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| 6. |
- Condo, Adolfo Firmino Timoteo, et al.
(författare)
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Study on the Effect of Aging on the Ability of Calcium Carbide for Hot Metal Desulfurization
- 2016
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Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 87:9, s. 1137-1143
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Tidskriftsartikel (refereegranskat)abstract
- Industrial trials and laboratory study are carried out to investigate the effect of aging on the ability of CaC2 in hot metal desulfurization. The industrial trials indicate that the time of storage of calcium carbide within the limit of industrial practice has no appreciable effect on its ability of desulfurization. In the laboratory, samples of CaC2 are prepared by exposing them in air for different times to promote formation of a Ca(OH)(2) outer layer. The thickness of Ca(OH)(2) increases with exposing time. Thereafter, the aged CaC2 samples are employed for desulfurization at 1673 and 1773 K for 8 min. For all the samples after desulfurization, layers of graphite and CaO are found between the remaining CaC2 particles and the outer CaS layer. The desulfurization using CaC2 is found to proceed by the diffusion of calcium vapor through the product layers and then its reaction with dissolved sulfur in the hot metal at the surface. No appreciable difference in the thickness of the CaS layer is found with the samples exposed to air for different times. This finding explains well the industrial results.
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| 7. |
- Condo, Adolfo Firmino Timoteo, et al.
(författare)
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Study on the Equilibrium of Slag and Hot Metal at Tapping with Respect to Sulfur
- 2017
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Ingår i: Steel Research International. - : Wiley. - 1869-344X .- 1611-3683. ; 88:6, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- The blast furnace slag and hot metal were collected from the industrial trials. The collected slag and hot metal samples are re-melted in a graphite crucible and stirred to investigate the sulfur partition at different stirring times. The experimental oxygen potential is well controlled to simulate the blast furnace conditions. The results show evidently that sulfur is transferred from hot metal to slag, which led to an increase in the sulfur partition from its initial value (t=0 min) of 26 -33 at 1743 K, and from 23 to 37 at 1773 K after 30 min of slag-metal reaction. The results strongly indicate non-equilibrium between slag and hot metal at tapping. The sulfide capacities of the slag with typical composition of the slag at tapping are determined. On the basis of the sulfide capacity data, the theoretical sulfur partition is evaluated. The theoretically calculated partition further supports the finding obtained in the stirring experiments. This finding would suggest the possibility of improvement to increase the usage of blast furnace slag in desulfurization.
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| 8. |
- Condo, Adolfo Firmino Timoteo, 1976-, et al.
(författare)
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Sulfide Capacities in the Al2O3-CaO-MgO-SiO2 System
- 2018
-
Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 89:8
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, the sulfide capacities of the slags in the ternary Al2O3-CaO-SiO2 system at 1873K, and in the quaternary system Al2O3-CaO-MgO-SiO2 at 1823 and 1873K are experimentally measured using copper-slag equilibrium at controlled oxygen partial pressure. The experimental data, which has been unavailable, are needed for the improvement of a sulfide capacity model. An assessment of the available data for sulfide capacities in the Al2O3-CaO-MgO-SiO2 system and its sub lower-order systems are made. Based on this assessment and the present experimental results, the model parameters of the existing sulfide capacity model are re-optimized. The sulfide capacity model can be successfully used in the prediction of the sulfide capacities of multicomponent slags with satisfactory accuracy.
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| 9. |
- Davydenko, Arkadiy, et al.
(författare)
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Investigation of Slag Foaming by Additions of Briquettes in the EAF during Stainless Steel Production
- 2015
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 86:2, s. 146-153
-
Tidskriftsartikel (refereegranskat)abstract
- Nowadays, an effective application of energy required for stainless steel production in the electric arc furnace (EAF) by a slag foaming practice and recycling of waste products play two of the most significant roles for a sustainable steel production. In this study, briquettes were used to obtain a combined slag foaming and waste product reduction in the EAF process. Briquettes with different densities produced partly from waste products were tested in an industrial scale to study slag foaming in the EAF process during stainless steel production. The slag foaming tendency was determined based on visual estimations of slag foaming, evaluations of the slag density before and after addition of different briquettes, and by calculating a foaming index. The influence of the main parameters of briquettes (composition, density) and the furnace slag (composition, basicity, and, etc.) on slag foaming was studied. It was found that both heavy and light briquettes can be used for slag foaming. The heavy briquettes, with FeCr, produce about half the amount of gas compared to the light briquettes, without FeCr. The main part of the gas, >80%, was generated during the first 2-3min, Moreover, the highest slag foaming rate was obtained for slags with a basicity in the range of 1.31-1.49.
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| 10. |
- Deng, Zhiyin, et al.
(författare)
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Effects of Temperature and Holding Time on the Sintering of Ladle Filler Sand with Liquid Steel
- 2016
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 87:7, s. 921-929
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work the effects of temperature and holding time on the sintering of ladle filler sand are studied. Laboratory experiments are carried out using pellets made of chromite based filler sand and two steel grades containing different contents of Mn and Al. It is found that the liquid steel plays a major role in the sintering behavior. The results also show that the amount of liquid phase in the sintered sand pellets increases with the increase of temperature and holding time. The Al2O3 content increases substantially in the chromite phase (spinel), especially in the region close to the liquid phase, when the temperature is high enough or when the holding time is long enough. Higher content of dissolved Al would accelerate the formation of the alumina-rich chromite.
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| 11. |
- Deng, Zhiyin, et al.
(författare)
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Mechanism Study of the Blocking of Ladle Well Due to Sintering of Filler Sand
- 2015
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X.
-
Tidskriftsartikel (refereegranskat)abstract
- The present work is aimed at a mechanism study of blocking of ladle well by filler sand. Laboratory experiments are carried out using two different chromite-based filler sands. The interaction between the liquid steel and the sand is also studied by using steels containing different contents of Mn and Al. The reaction between the silica phase and the chromite phase is found to be the main mechanism for the sintering of sand. The reaction results in a liquid oxide phase, which becomes the binding phase between the solid oxide grains. The amount of silica phase and its grain size are found to have great impact on the formation of the liquid oxide phase. Faster formation of the liquid oxide phase leads to more serious sintering of the sand. It is found that liquid steel can hardly infiltrate into sand. On the other hand, the presence of steel considerably increases the amount of liquid phase and enhances the sintering of the sand.
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| 12. |
- Ersson, Mikael, et al.
(författare)
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Review on CFD Simulation and Modeling of Decarburization Processes
- 2018
-
Ingår i: Steel Research International. - : WILEY-V C H VERLAG GMBH. - 1611-3683 .- 1869-344X. ; 89:1
-
Forskningsöversikt (refereegranskat)abstract
- Over the last few decades, a number of CFD models have been dedicated to increasing the understanding of the decarburization processes in steelmaking. However, these processes are highly complex with large variations in time and length, and this makes the systems extremely demanding to simulate. Several reports have been published where parts of the processes have been investigated numerically, but to date no models have been presented that can handle the entire complexity of the processes. Here, a review of the research performed on the subject from 1998 to 2016 is given. A table summarizing the models used and the key focus of the studies is given, and it can be concluded that the effort put in so far to investigate the decarburization in steelmaking is substantial, but not complete. The currently available numerical models give an insight into process parameters such as reactions, mixing time, temperature distribution and thermal losses, off-gas post combustion and de-dusting, and also nozzle configuration. With the recent developments in numerical modeling and the increase in hardware capability, the future of simulation and modeling of the decarburization processes in steelmaking seems bright.
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| 13. |
- Forouzan, Farnoosh, 1985-, et al.
(författare)
-
Optimization of Quenching Temperature to Minimize the Micro Segregation Induced Banding Phenomena in Quenching and Partitioning (Q&P) Steels
- 2019
-
Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 90:1
-
Tidskriftsartikel (refereegranskat)abstract
- Mn, Cr, and Si are favorable elements for designing the quenching and partitioning (Q&P) steels while the microsegregation of them is a common phenomenon in the steels. This segregation makes the bands of enriched and depleted Mn–Cr regions, which affects the Ms temperature of the bands and consequently influence the volume fraction of initial martensite, retained austenite, and secondary fresh martensite in different bands. This issue leads to non-homogeneity in the microstructure and mechanical properties. In this study, the optimization method to minimize the inhomogeneity by selection of the quenching temperature is demonstrated.
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| 14. |
- Hou, Ziyong, 1986-, et al.
(författare)
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Enhanced Grain Growth Behavior of Ferritic Steel during Continuous Cyclic Annealing
- 2018
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 89:11
-
Tidskriftsartikel (refereegranskat)abstract
- Microstructural characterization as well as mechanical property determination of a cold-rolled ferritic steel subjected to isothermal and cyclic non-isothermal annealing, has been carried out by utilizing comprehensive experimental analysis. The findings show that the variables of cyclic annealing, that is, amplitude, ramp rate, and intermediate holding time exhibit a great effect on the grain growth kinetics and the evolution of grain boundaries. The resulting grain size of the cyclic annealed steel is mainly attributed to the following factors: 1) the accelerating effect in the grain growth behavior caused by the additional driving force available during cyclic annealing, which increases with increasing amplitude; 2) the retarding effect due to the low equivalent isothermal temperature. Furthermore, the formation of low sigma- coincidence site lattice (sigma CSL) boundaries and the strength of gamma-fiber texture are enhanced through the cyclic annealing compared to the isothermal annealing. The potential advantages of continuous cyclic annealing in the steel industry are explored, in comparison with the conventional isothermal and cyclic annealing with an intermediate soaking time.
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| 15. |
- Hou, Zi Yong, et al.
(författare)
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Effect of Holding Temperature on Microstructure and Mechanical Properties of High-Strength Multiphase Steel
- 2016
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 87:9, s. 1203-1212
-
Tidskriftsartikel (refereegranskat)abstract
- Isothermal holding following intercritical annealing is usually used in microstructure control, e.g., fractions and stabilities of retained-austenite (RA). Fe-0.22C-2.5Mn-0.47Si-0.41Cr-0.02Nb (mass%) steel is subjected to intercritical annealing and isothermal treatment at 250, 300, 350, and 400 degrees C to elucidate the impact on microstructures and mechanical properties by means of electron microscopy and uniaxial tensile test, respectively. The results show that the isothermal holding temperature is vital for the formed phases, including the morphology, volume fraction, and carbon content of RA in the processed steels. The tensile test results indicate that the mechanical properties including Ultra-tensile strength (UTS), Yield strength (YS), as well as Total Elongation (TEL) are attributed to the synthetic action of all constituents of phase morphology and corresponding fractions, e.g., hard-to-soft phase ratio, morphology and fraction of RA, dispersed precipitates. An excellent combination of strength-ductility of the present multiphase steel has been explained in terms of their specific microstructure.
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| 16. |
- Hu, Xianfeng, et al.
(författare)
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Direct Alloying Steel with Chromium by Briquettes Made from Chromite Ore, Mill Scale, and Petroleum Coke
- 2017
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Ingår i: Steel Research International. - : Wiley-VCH Verlag. - 1611-3683 .- 1869-344X. ; 88:5
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, the effectiveness of using briquettes made from chromite ore, mill scale, and petroleum coke for direct chromium alloying is tested by induction furnace trials carried out in three different scales. The experimental results show that steel scrap can be alloyed with chromium by the chromite ore in the briquettes and the Cr yield from the chromite ore increases with the increase in mill scale addition to the briquettes: the more mill scale is added to the briquettes, the lower the mass ratio of Cr to (Cr + Fe) would be, leading to a higher Cr yield from the chromite ore. Specifically, the maximum Cr yield from the chromite ore is 99.9% when the mass ratio of Cr to (Cr + Fe) in the briquettes is 0.05, and being 93.0% when the ratio is 0.10. However, when the ratio of Cr to (Cr + Fe) in the briquettes reaches 0.20, the maximum Cr yield is only 67.1%. The reduction of chromite ore under the present experimental conditions is promoted by a solid-state reduction mechanism.
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| 17. |
- Hu, Xianfeng, et al.
(författare)
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Thermal Analysis Study on the Carbothermic Reduction of Chromite Ore with the Addition of Mill Scale
- 2016
-
Ingår i: Steel Research International. - : Wiley-VCH Verlag. - 1611-3683 .- 1869-344X. ; 87:5, s. 562-570
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a fundamental study on the carbothermic reduction of chromite ore with the addition of mill scale, which forms the basis for designing an alloying precursor, "chromite ore + mill scale + carbon," for direct chromium alloying. The reduction of chromite ore by petroleum coke with or without the addition of mill scale is investigated by Thermogravimetric Analysis (TGA) under non-isothermal conditions (from room temperature to 1823 K) in the argon atmosphere; the fractional reduced samples were characterized by SEM/EDS and XRD analyses. The experimental results show that the mill scale in the alloying mixture is reduced to high active iron first and disseminated around the chromite ore particles; the reduction of chromite ore is enhanced with the addition of mill scale especially at temperatures higher than 1623 K, and the enhancing effect increased with increasing mill scale addition. The enhancing effect is attributed to the presence of molten Fe-C alloy in the vicinity of chromite ore, which can decrease the thermodynamic activity of chromium by having chromium in situ dissolve into the melt. In this paper, the effect of mill scale addition on the reduction of chromite ore is investigated on the samples with three different amounts of mill scale addition (78 wt%, 38 wt%, and 0 for the samples #1b, #2b, and #3b, respectively) by thermogravimetric technique. The fractional reduced samples are characterized by SEM/EDS and XRD analyses. The mechanism of mill scale addition on the reduction of chromite ore is discussed and the industrial implications of the experimental results are also presented.
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| 18. |
- Janis, Diana, et al.
(författare)
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A Study of Cluster Characteristics in Liquid Stainless Steel and in a Clogged Nozzle
- 2015
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Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 86:11, s. 1271-1278
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Tidskriftsartikel (refereegranskat)abstract
- Clusters of Al2O3 inclusions in a liquid stainless steel (18/8) and in a clogged ZrO2 nozzle after casting were studied during a pilot plant trial. Samples were taken from the melt at different holding times after an addition of 0.1 mass% Al. The characteristics (composition, size, number, and morphology) of clusters and clustered inclusions in the steel samples and in the clogged nozzle were investigated after electrolytic extraction and etching by using SEM. It was found that the Al2O3 inclusions in the clusters are transformed from a spherical into irregular and regular (with sharp edges) shape during the holding time. Most of the inclusions in the clusters (>80%) after a 6 min holding time are regular inclusions, which have sharp edges and flat faces. The size of the inclusions in clusters in the melt increased on average from 1.0 μm at a 1 min to 5.2 μm at a 12 min holding time. While the sizes of different types of inclusions in the clogged nozzle correspond to those present in the liquid steel at respective time, the frequency of spherical inclusions in the clogged nozzle is about 2–4 times larger (particularly near the nozzle wall) compared to that in the melt. Growth and transformation of Al2O3 clusters in the liquid steel at different holding times after an addition of Al and during casting were considered based on the obtained results.
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| 19. |
- Jiang, Liang, et al.
(författare)
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Formation of Spinel Phases in Oxidized BOF Slag under Different Cooling Conditions
- 2017
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Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 88:11
-
Tidskriftsartikel (refereegranskat)abstract
- To enhance utilization of wastes generated from steelmaking, a BOF slag sample from Ning Steel group in China is treated by oxidizing at 1500 °C for 30 min and then cooled by different methods. The treated samples are characterized, in combination with calculations using FactSage 6.4. XRD results show that iron oxides in BOF slag are converted largely by the oxidation to spinel phases, Fe3O4 and MgFe2O4, which also eliminates free CaO and MgO. EDS analyses show Fe element existing in di-calcium silicate and glass phase, which are Fe3+ ions formed by oxidation. An incorporation of Fe3+ ions into crystal structures has stabilized high temperature polymorph of C2S, β-C2S, and α’-C2S, in the treated slag samples. Fe3+ ions may also act as a network former to facilitate glass formation. This may make it possible for the glass and α’-C2S phase to complement each other, leading to a higher hydraulicity, while the BOF slag, after the spinel separation, is blended in cements. Some suggestions are proposed, based on the present and early studies, to enhance hydraulicity for the BOF slag, as well as grain sizes of spinel phases, which may result in economic and environmental benefits for steel and cement industries.
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| 20. |
- Karasev, Andrey, et al.
(författare)
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Estimation of non-metallic inclusions in industrial Ni based alloys 825
- 2017
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 88:4
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that inclusions affect the properties of the steel and other alloys. The importance of understanding the behavior of the inclusions during production can never be overstated. This study has examined the main types of big size (>10μm) inclusions that exist in Ni-based Alloy at the end of ladle treatment and after casting during industrial production of Ni based Alloys 825. Sources, mechanisms of formation and behavior of different type large size inclusions in Alloy 825 are discussed based on 2 and 3D investigations of inclusion characteristics (such as, morphology, composition, size, and number) and thermodynamic considerations. The large size inclusions found can be divided in spherical (Type I and II) inclusions and in clusters (Type III-V). Type I-A inclusions (Al2O3-CaO-MgO) originate from the slag. Type I-B inclusions and Type II inclusions consist of CaO-Al2O3-MgO and Al2O3-TiO2-CaO, respectively. Both types originate from the FeTi70R alloy. Type III clusters (Al2O3-MgO-CaO) are formed during an Al deoxidation of the Ni-based alloy. Type IV clusters (Al2O3-TiO2-CaO) formed from small inclusions, which are precipitated in local zones which contain high Ti and Al levels. These clusters are transformed to Type III clusters over time in the ladle. Finally, Type V clusters are typical TiN clusters.
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| 21. |
- Kellner, Hans E O, et al.
(författare)
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Evolution of Non-Metallic Inclusions from FeTi70R Alloys during Alloying of Fe-40Ni-20Cr Steels
- 2016
-
Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X.
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the composition, size, and number of large non-metallic inclusions (>20μm) are investigated in a commercial refined FeTi70R alloy, which is used for deoxidation and alloying of different industrial high-quality steels. It is found that this ferroalloy contains different complex oxide inclusions, which sizes vary from 20 to 260μm. These different complex inclusions contain mostly CaO, SiO2, and TiOx. When adding FeTi70R alloy in the steel during the final stage of ladle treatment, these large size inclusions can significantly decrease the cleanliness and mechanical properties of steel. Therefore, the evolution and behavior of these inclusions after addition of this ferroalloy into the liquid iron or Fe-40Ni-20Cr steel are investigated in laboratory experiments. In addition, the results from the laboratory scale experiments are compared to results obtained from industrial heats using Alloy 825. A consideration of the evolution mechanism of large inclusions after an addition of a FeTi70R alloy helps to understand their behavior in the melt. It also helps to estimate their possible harmful effects on the quality of this steel grade during commercial production.
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| 22. |
- Kellner, Hans, 1989-, et al.
(författare)
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Effect of the Stirring Mode on the Behavior of Al2O3–MgO Particles and Clusters during Ladle Treatment of Ni-based Alloy 825
- 2017
-
Ingår i: Steel Research International. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 87
-
Tidskriftsartikel (refereegranskat)abstract
- It is well known that inclusions affect the properties of alloys. Therefore, the importance of understanding what inclusions exist and how they behave cannot be overstated. This study has examined the behavior of Al2O3–MgO particles and clusters in the melt during the ladle treatment of Alloy 825, who is a Ni-based Alloy. The effect of different stirring directions of electromagnetic stirring in combination with gas stirring is discussed based on three-dimensional investigations of the clustered particles. More specifically, the composition, size, and number of particles and clusters are determined after electrolytic extraction of metal samples by using SEM in combination with EDS. The results show that the agglomeration of Al2O3–MgO particles in the melt is faster for an upward induction stirring combined with a gas stirring in comparison to a downward stirring combined with a gas stirring. However, the total removal of clusters from the melt is more effective when using a downward induction stirring compared to when using an upward induction stirring, especially for large size clusters (>11.2 mm). The effect of the different stirring modes on the behavior of the Al2O3–MgO particles and clusters in the melt for the ladle treatment experiments agree with the theoretical predictions based on Stokes’, Brownian, and Turbulent collisions.
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| 23. |
- Kumar, T K Sandeep, 1986-, et al.
(författare)
-
Establishing a Novel Methodology to Correlate the Macroscopic and Microscopic Degree of Sintering inMagnetite Pellets during Induration
- 2018
-
Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 89:3
-
Tidskriftsartikel (refereegranskat)abstract
- The quality of product pellets is a result of the physico-chemical phenomenainvolved in the induration process. Sintering is the primary phenomenon,and its degree or extent contributes substantially to the evolution of themetallurgical and mechanical properties of a pellet. During the induration ofmagnetite pellets, sintering proceeds through the oxidized and non-oxidizedmagnetite phases. Sintering of these phases has been previously studied ona single pellet at the macroscopic scale using an optical dilatometer. Adeeper understanding requires corroboration of these studies throughcharacterization at the microscopic scale. In the present work, the observationsrecorded at the microscopic scale are quantified using image processingtechniques to correlate them to the macroscopic measurements. Distancetransformation, which is an image processing principle, is adapted in a novelway to digitize the microstructures and to determine the degree of sinteringin a pellet quantitatively. This methodology has potential applications as ageneric tool to follow the sintering phenomenon and process kinetics at anystage during induration.
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| 24. |
- Lindell, David, et al.
(författare)
-
Fast and Efficient Annealing of Stainless Steel Strip Using Oxyfuel Burners
- 2015
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 86:5, s. 557-566
-
Tidskriftsartikel (refereegranskat)abstract
- Pilot plant and annealing experiments have been conducted to study the effect of the higher water content in oxyfuel annealing on oxidation and pickling of cold rolled stainless steel. The experiments were conducted on the austenitic grade AISI 304 in a propane-fired furnace using air and pure oxygen as oxidizers. The experiments were conducted at 1050-1200 degrees C for typically less than 60 s, in order to simulate industrial annealing of thin strip. Supplementary laboratory annealing trials were made to study the evolution of the microstructure during fast heating rates and short hold times. Increasing the water content from 15 to 50 mol% did not alter the oxidation kinetics or the chemistry of the oxide. Since the oxidation is not altered significantly, the pickling performance of the material remains unchanged. The presence of spalled areas increased the pickling efficiency significantly but this was only seen for material annealed at higher temperature compared to industrial practice. Oxyfuel combustion allows higher heat input and therefore faster heating. The 304 grade recrystallizes readily even at moderate cold rolling reductions so the total annealing time can be reduced substantially if the heating rate can be increased. The present work suggests that this can be done without any downstream effects.
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| 25. |
- Lindström, David, 1981-, et al.
(författare)
-
Study on Desulfurization Abilities of Some Commonly Used Desulfurization Agents
- 2015
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 86:1, s. 73-83
-
Tidskriftsartikel (refereegranskat)abstract
- The desulfurization abilities of some commonly used agents, namely fluidized CaO, CaC2, commercial-CaO, Mg, MgO, CaO center dot MgO, and mixtures of commercial-CaO-Mg were studied and compared under the same experimental conditions in a laboratory furnace at 1773 K. The desulfurization mechanisms of CaO center dot MgO, commercial-CaO, and mixtures of commercial-CaO and Mg were also studied. While fluidized CaO showed the best performance, commercial-CaO mixed with 20 mass% Mg achieved the second best desulfurization. Mg-granules performed slightly better than CaC2 and commercial-CaO, but somewhat less satisfactory compared to fluidized CaO and commercial-CaO-Mg mixtures. Since only the CaO portion in CaO center dot MgO functioned to take up sulfur, additional 70% mass had to be added to achieve the same desulfurization level. The poor ability of commercial-CaO in comparison to fluidized CaO powder was due to both its less reactive surface and agglomeration of the particles.
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| 26. |
- Liu, Yu, et al.
(författare)
-
Comparison of Euler-Euler Approach and Euler–Lagrange Approach to Model Gas Injection in a Ladle
- 2019
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 90:5
-
Tidskriftsartikel (refereegranskat)abstract
- The gas injection in a ladle using a porous plug is simulated using both the Euler-Euler and Euler-Lagrange approaches. The effects of various forces, bubble sizes, and bubble injection frequencies on the flow pattern are modeled. For predicting axial velocity and turbulent kinetic energy, the Euler-Lagrange approach fits better than Euler-Euler approach with the measured data. In the Euler-Euler approach, differences in axial velocities and turbulent kinetic energies for various bubble sizes mainly appears in the plume zone. In the Euler-Lagrange approach, different bubble sizes with the same injection frequency have a small impact on the turbulence dissipation. Furthermore, the turbulent dispersion from the gas phase to the liquid phase has an important effect on the plume structure and spout eye formation. For both modeling, the smaller the bubble diameter is, the larger the axial velocity and turbulent kinetic dissipation are in the central zone. For the bubble coalescence and breakup, according to the comparison of two modeling approaches, the Euler-Lagrange approach is more accurate in predicting the flow pattern for gas injection with a porous plug in the ladle.
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| 27. |
- Lundkvist, Nicholas, et al.
(författare)
-
A Physical Modeling Study on Slag Behavior in the AOD Converter Process
- 2018
-
Ingår i: Steel Research International. - : WILEY-V C H VERLAG GMBH. - 1611-3683 .- 1869-344X. ; 89:6
-
Tidskriftsartikel (refereegranskat)abstract
- A water/oil physical model is built up to investigate the slag behavior under the side gas-blowing condition of an AOD process. The critical side-blowing air flow rates for the top oil entrainment and emulsification are investigated. In addition, the oil entrainment with the existence of solid particles is studied. Specifically, the influences of the tuyere size, oil viscosity, oil thickness, and volume fraction of solid particles in oil on the mixing phenomena are studied. It is found that oil viscosity is an important factor for the initial oil entrainment and emulsification. Oil thickness only has a slight influence on these phenomena. The critical air flow rate for both initial oil entrainment and emulsification increases slightly with an increased tuyere size from 2.0 to 3.2 mm. Empirical equations have been proposed to predict the critical air flow rate for the initial oil entrainment and emulsification. Furthermore, solid particles in oil are found to increase the critical air flow rate for an initial entrainment. This may be due to the increase of oil viscosity when solid particles exist in oil. In addition, a new model is developed to predict the oil viscosity when solid particles exist inside it.
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| 28. |
- Martinsson, Johan, et al.
(författare)
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Study on Apparent Viscosity of Foam and Droplet Movement Using a Cold Model
- 2016
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 87:6, s. 712-719
-
Tidskriftsartikel (refereegranskat)abstract
- The apparent viscosities of foams generated by passing argon through silicone oil are measured. The foams are found to be non-Newtonian flows having apparent viscosities 4-5 times higher than the dynamic viscosity of the origin fluid. The movements of different particles and droplets and their residence times are studied. The measured average velocities of the particles/droplets are substantially lower than the values estimated based on the dynamic viscosities. For both mechanical and gas stirrings, the flows of the foam are very different from pure liquid. The movement of the bar and stirring gas bubbles only pushes a limited number of bubbles which are very close to them to move. No bulk flow as in pure liquid is generated by the stirring. The apparent viscosities of foams generated by passing argon through silicone oil are measured. The foams are found to be non-Newtonian flows and have apparent viscosities about 4-5 times higher than the dynamic viscosity. The average velocities of the particles/droplets moving in the foam are substantially lower than the values estimated based on the dynamic viscosities of the oils.
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| 29. |
- Médioni, Charlotte, et al.
(författare)
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Effect of Stirring Practice on Sulphur and Nitrogen Refining as well as Inclusion Removal in Ladle Treatment
- 2015
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 86:12, s. 1498-1507
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of different stirring conditions during ladle treatment on the steel cleanliness was studied in the steel plant of SSAB Special Steels in Oxelosund, Sweden. The cleanliness was examined with regards to the contents of sulfur, nitrogen, and large inclusion (>10 mu m). The results showed that vacuum degassing increased the amount of inclusions larger than 10 mu m and that subsequent induction stirring suggested a possible positive effect on the inclusion removal. A shortening of the vacuum degassing time from 24 to 15 min did not affect the nitrogen or sulphur refining. Overall, all heats reached the desired composition and cleanliness levels regardless of the treatment time.
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| 30. |
- Mu, Wangzhong, et al.
(författare)
-
Combination of in situ microscopy and calorimetry to study austenite decomposition in inclusion engineered steels
- 2015
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X.
-
Tidskriftsartikel (refereegranskat)abstract
- In situ high-temperature confocal laser scanning microscopy and differential scanning calorimetry studies of ferrite formation in inclusion engineered (Ti2O3 and TiN) steels have been performed. The applied methodology allows distinction between intragranular ferrite, grain boundary ferrite, and pearlite. The effect of the inclusions and cooling rates on the initiation of phase transformation and the final microstructure is discussed. It is concluded that the applied hybrid methodology could provide vital details of solid-state phase transformations within the field of inclusion engineering.
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| 31. |
- Mu, Wangzhong, et al.
(författare)
-
Effect of Carbon Content on the Potency of the Intragranular Ferrite Formation
- 2016
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 87:3, s. 311-319
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of the carbon content on the potency of the intragranular ferrite (IGF) formation for each inclusion size is investigated in the present work. The TiN inclusion was detected to be the effective nucleation site for the IGF formation in the Fe-0.2 mass% C alloy and the Fe-0.4 mass% C alloy. It is noted that the potency of the IGF formation for each inclusion size is decreased with the increase of carbon content. Moreover, the critical diameters of the TiN, TiO, and VN inclusions in the steels with different carbon contents are calculated based on the classical nucleation theory. The calculated critical diameter is also found to be decreased with the increase of carbon content. This is in agreement with the experiment results. Finally, the decrease of the potency of IGF formation for each inclusion size is due to a larger amount of pearlite formation in the steel containing a higher carbon content, which is detected by differential scanning calorimetry (DSC) measurements.
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| 32. |
- Mu, Wangzhong, et al.
(författare)
-
Effect of Carbon Content on the Probability of the Intragranular Ferrite Formation
- 2015
-
Ingår i: Steel Research International. - Wiley. - 1611-3683 .- 1869-344X.
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of the carbon content on the probability of the intragranular ferrite (IGF) formation was investigated in the present work. The TiN inclusion was detected to be the effective nucleation site for the IGF formation in the Fe-0.2 mass.% C alloy and the Fe-0.4 mass.% C alloy. It is noted that the probability of the IGF formation for each inclusion size is decreased with the increase of carbon content. Moreover, the critical diameters of the TiN, TiO and VN inclusions in the steels with different carbon contents were calculated based on the classical nucleation theory. The calculated critical diameter was also found to be decreased with the increase of carbon content. This is in agreement with the experiment results. Finally, the decrease of the probability of IGF formation for each inclusion size is due to a larger amount of pearlite formation in the steel contains a higher carbon content, which was detected by differential scanning calorimetry (DSC) measurements.
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| 33. |
- Mu, Wangzhong, et al.
(författare)
-
Inclusion and Microstructure Characteristics in Steels with TiN Additions
- 2016
-
Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 87:3, s. 339-348
-
Tidskriftsartikel (refereegranskat)abstract
- The quantitative analysis of inclusion and microstructure characteristics in the steels with TiN additions has been studied. The typical inclusion was detected to be a TiN+Mn-Al-Si-Ti-O+MnS phase. This identification was based on the measurements of scanning electron microscopy with energy-dispersive X-ray spectrometer (SEM-EDS), electron probe microanalysis (EPMA), which equipped wavelength-dispersive X-ray spectroscopy (WDS), and equilibrium calculations by using the commercial software Thermo-Calc. TiN was found to be the effective nucleation site for the formation of intragranular ferrite (IGF). Furthermore, the increased inclusion size led to the increased probability of IGF nucleation. In addition, this probability of IGF nucleation was slightly decreased with the increased sulfur content. This tendency could fit the tendency of the area fraction of IGF in the steels containing different sulfur contents.
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| 34. |
- Nabeel, Muhammad, et al.
(författare)
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Characterization of Dust Generated during Mechanical Wear of Partially Reduced Iron Ore Pellets
- 2017
-
Ingår i: Steel Research International. - : WILEY-V C H VERLAG GMBH. - 1611-3683 .- 1869-344X. ; 88:9
-
Tidskriftsartikel (refereegranskat)abstract
- During reduction in a blast furnace (BF), the iron ore pellets undergo structural changes, which facilitate dust generation due to the mechanical wear/disintegration of the pellets. The generated dust decreases the permeability and productivity of the BF process. Thus, this study investigates the mechanical wear of iron ore pellets reduced at 500 degrees C (P500) and 850 degrees C (P850) and compares the results to the wear of unreduced pellets (P25). Moreover, the dust generated during the wear experiments is also characterized. It is found that pellets reduced at 500 degrees C exhibit a approximate to 16-35% higher wear rate than reference unreduced pellets. For the pellets reduced at 850 degrees C, the mechanical wear is inhibited by a formation of a metallic layer at the outer surface of the pellets. Further, the dust generated due to mechanical wear of reduced pellets contain 3-6 times higher amount of coarse particles (>20m) as compared to the dust from unreduced pellets. The obtained results are explained on the basis of the structural changes, which take place during the reduction of pellets.
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| 35. |
- Ni, Peiyuan, et al.
(författare)
-
Non-Metallic Inclusion Behaviors in a New Tundish and SEN Design Using a Swirling Flow during Continuous Casting of Steel
- 2016
-
Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X.
-
Tidskriftsartikel (refereegranskat)abstract
- The behaviors of non-metallic inclusions in a new tundish and SEN design enabling a swirling flow are investigated by using a Lagrangian particle tracking scheme. The results show that 99% of both Al2O3 and Ce2O3 inclusions are removed from both the top surface and the other tundish walls with a "trap" boundary condition, while only around 60% are removed from the top surface of tundish for a "reflect" boundary condition at the other tundish walls. Large size non-metallic inclusions of different densities show a large difference under a "reflect" boundary condition at tundish walls, due to a high buoyancy of light inclusions. In the swirling flow SEN, a much smaller number of large Al2O3 inclusions touches the wall compared to Ce2O3 inclusions. This is due to that they have larger deviations from the steel flow path compared to heavy Ce2O3 inclusions, due to the centripetal force. For small size inclusions, the centripetal separation is not effective neither for the light Al2O3 inclusions nor for the heavy Ce2O3 inclusions in the current swirling flow SEN with a swirl number of 0.4. Light Al2O3 inclusions larger than 40μm can be influenced by the current centripetal force.
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| 36. |
- Ni, Peiyuan, et al.
(författare)
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Study on Slopping Prevention in the BOF Steelmaking Process
- 2017
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 88:8
-
Tidskriftsartikel (refereegranskat)abstract
- A new method of preventing slopping is proposed in this paper, by simply blowing gas at the top of the foam surface. The physical experiment results show that the foam height can be effectively decreased by the top blowing air. The maximum decrease of the foam height can reach around 70 mm with an initial foam height of 145 mm in the current setup, around a 48% decrease. The first 40 mm of the foam height is easy to destroy with a low flow rate from the top. However, it is increasingly difficult for a further decrease in the foam height. Different types of nozzles show a large difference in the role of destroying the foam. The air flow velocity from the nozzle outlet is found to be the key factor for a decreased foam height. Overall, three foam destruction mechanisms are proposed. When the top air flow velocity is small, the drag and pressure destruction mechanisms are the main reasons for the decrease in foam height. However, when a large top air flow velocity is used, the coalescence and breakup mechanisms due to a high turbulence and the shear force on gas bubble shape deformation become important.
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| 37. |
- Ni, Peiyuan, et al.
(författare)
-
Transport and Deposition of Non-Metallic Inclusions in Steel Flows- A Comparison of Different Model Predictions to Pilot Plant Experiment Data
- 2017
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 88:12
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusion behavior during a ladle teeming process is investigated. A Lagrangian method is used to track different-size inclusions and to compare their behaviors in steel flows, solved by the realizable k-epsilon model with SWF (Standard Wall Function), realizable k-epsilon model with EWT (Enhanced Wall Treatment), and RSM (Reynolds Stress Model). The results show that inclusion tracking based on the realizable k-epsilon model with SWF to predict the steel flow does not agree with the data fromplant experiments. The predicted number of inclusions touching the wall shows almost no dependence on inclusion size. This is due to that the boundary layer is not resolved. The inclusion deposition predicted using the realizable k-epsilon model with EWT and the RSM model to predict the steel flow generally agrees with the experimental observations. However, the large size inclusion deposition is over-predicted when using the realizable k-epsilon model with EWT. More specifically, the prediction for 20 mu m inclusions is three times larger than that with the RSM. This is due to that this model cannot calculate the anisotropic turbulence fluctuations. In summary, the turbulence properties in the near-wall boundary layer are found to be very important for a good prediction on inclusion deposition.
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| 38. |
- Nilsson, Peter, et al.
(författare)
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A New Tundish Design to Produce a Swirling Flow in the SEN During Continuous Casting of Steel
- 2016
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X.
-
Tidskriftsartikel (refereegranskat)abstract
- A new tundish is designed with the aim to produce a swirling flow in a tundish SEN by an economical way of using the steel flow potential as the required power. This design is easily obtained by adding a cylindrical part of the tundish onto a traditional tundish. The results show that a swirling flow in the SEN of the new tundish is successfully obtained, also, that the tangential velocity in the SEN can reach around 1.6ms-1. The installation of weirs in the cylindrical tundish can contribute to stabilize the steel flow at the top of the tundish. However, this reduces the swirling flow intensity in the SEN around 30%. In addition, the possibility of slag entrainment at the top of the tundish is analyzed. The calculated Weber Number is around 5.0 for no weir case and 2.8 for the weir case, which means that the risk of slag entrainment is small. A high value of shear stress is found on the SEN wall due to the swirling flow in SEN. A further investigation shows that a smooth transition of SEN inlet can reduce the maximum shear stress level in the SEN, without decreasing the swirling flow intensity.
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| 39. |
- Ono, Hideki, et al.
(författare)
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Formation Conditions of Ti2O3, MgTi2O4, Mg2TiO4, and MgAl2O4 in Ti-Mg-Al Complex Deoxidation of Molten Iron
- 2015
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 86:3, s. 241-251
-
Tidskriftsartikel (refereegranskat)abstract
- The relationships of the compounds in the Mg-Ti-Al-O system in equilibrium with molten iron are investigated at temperatures ranging from 1873 to 1973 K, and the thermodynamic calculations are conducted in avoiding Al2O3 or spinel MgAl2O4 formation and for inclusion control. The equilibrium relations between the compounds (Mg2TiO4, MgTi2O4, or MgAl2O4) and the composition of solutes in steel are clarified. The conditions are shown that the transformation of the stable compound from Mg-Ti spinel to Mg-Al spinel occurs at Mg contents ranging from 1 to 10 ppm by mass. It is also found, on the Mg-Ti spinel, the stable compound is transformed from inverse-spinel Mg2TiO4 to normal-spinel MgTi2O4 at Ti = about 60 ppm by mass. In addition, the stable compound is transformed from MgTi2O4 to Ti2O3 at Ti about 1000 ppm by mass.
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| 40. |
- Rehan, Arbab, et al.
(författare)
-
Effect of Austenitization and Tempering on the Microstructure and Mechanical Properties of a 5 wt% Cr Cold Work Tool Steel
- 2016
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 12:1 December, s. 1609-1618
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of austenitization and tempering temperatures for a 5 wt% Cr cold work tool steel are studied with an aim of understanding the influence on microstructure and mechanical properties. Microstructures are characterized with scanning electron microscopy and light optical microscopy. Retained austenite contents and martensite start temperatures are measured by X-ray diffraction and dilatometry, respectively. Hardness, impact toughness, and compressive yield strength are also determined. When the austenitization temperature is increased from 1020 or 1050 to 1075 °C, followed by tempering at 525 °C, significant hardness is gained while there is no increase in compressive yield strength. Higher austenitization temperatures also produce larger amounts of retained austenite. At the same time, the impact toughness is reduced due to coarsening of the martensitic microstructure. When the steel is tempered at 200 °C, a higher impact toughness and a higher volume fraction of retained austenite are observed. Retained austenite is not found after tempering at temperatures of 525 °C or above. It is concluded that the best combination of mechanical properties is achieved by austenitization at 1020 or 1050 °C followed by tempering at 525 °C.
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| 41. |
- Roos, Erik, et al.
(författare)
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Effect of Si and Ce Contents on the Nozzle Clogging in a REM Alloyed Stainless Steel
- 2015
-
Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 86:11, s. 1279-1288
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of the cerium and silicon contents on the castability of a REM-alloyed stainless steel was investigated by using pilot scale experiments. The trials were carried out with three different silicon concentrations: i) low (LSi; Si < 0.5%); ii) middle (MSi; Si approximate to 0.8-1.4%); and iii) high (HSi; Si approximate to 1.5-1.9%). During the casting, the liquid steel was teemed out through a zirconia nozzle located at the bottom of the furnace. The results showed that the nozzle clogging did drastically increase with increasing concentrations of Si and Ce up to levels larger than the critical contents (>= 1.5% Si and >= 0.05% Ce) in the cast HSi steel. In addition, the Ce content in a cast steel was found to increase linearly with an increased concentration of Si, due to the determinant effect of the Si content on an initial content of O in the melt before an addition of mischmetal. Finally, it was found that the concentration of insoluble Ce (Ce-insol.) determines the amount of inclusions and clusters in steel samples. Overall, soluble Ce concentrations larger than 250 ppm were found to be an important reason for fast nozzle clogging during casting.
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| 42. |
- Siafakas, Dimitrios, 1982-, et al.
(författare)
-
Particles Precipitation in Ti- and Al-Deoxidized Hadfield Steels
- 2016
-
Ingår i: Steel Research International. - : Wiley-VCH Verlag. - 1611-3683 .- 1869-344X. ; 87:10, s. 1344-1355
-
Tidskriftsartikel (refereegranskat)abstract
- The characteristics and precipitation mechanism of particles in titanium- and aluminum-treated Hadfield steel casted during pilot-scale experiments have been studied. Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) are utilized for the particle analysis and characterization. Additionally, thermodynamic equilibrium calculations are performed using Thermo-Calc software. Aluminum oxides, titanium carbon nitrides, titanium carbides, and manganese sulfides are the main types of particles found. The order of precipitation during solidification and chemical composition range of each type of particle are determined. Aluminum oxides are found to act as nucleation sites for titanium carbon nitrides. Thermodynamic equilibrium calculations for particles characteristics are in good agreement with the experimental findings. Titanium carbides are found to form during initial stages of the ferro-titanium additions dissolution.
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| 43. |
- Smeets, Stef, et al.
(författare)
-
Quantitative Phase Analysis for Carbide Characterization in Steel Using Automated Electron Diffraction
- 2019
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 90:1
-
Tidskriftsartikel (refereegranskat)abstract
- Carbides are critical to many different properties in a steel. In this paper, the quantification of a carbide powder extracted from a stainless steel analyzed with profile refinement of X-ray powder diffraction patterns, is compared to a novel technique for automated electron diffraction pattern collection with a transmission electron microscope. The automated analysis has the advantage of collecting patterns from individual particles, hence avoiding issues such as overlapping reflections in powder diffractograms. Electron diffraction patterns with satisfactory quality are selected through a deep convoluted neural network and matched to a library of pre-calculated diffraction patterns, corresponding to a set of selected carbide crystal structures. The quantitative results from the automated particle analysis are in good agreement with the phases identified by powder profile refinement.
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| 44. |
- Strandkvist, Ida, et al.
(författare)
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Effect of FeO/MgO Ratio on Dissolution and Leaching of Magnesiowüstite
- 2017
-
Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X. ; 88:6
-
Tidskriftsartikel (refereegranskat)abstract
- If slag is to be used as construction material, the leaching of some elements, such as chromium must be limited. The leaching of slag depends on the leaching properties of the minerals in the slag. However, the leaching/dissolution properties of individual slag minerals are usually not studied. One common slag mineral that can contribute to the leaching of chromium is magnesiowüstite. The object of this study is to determine whether magnesiowüstite can be modified to avoid chromium leaching. Magnesiowüstite samples with different FeO/MgO ratios with and without chromium content are manufactured. The dissolution is evaluated at pH 7 and 10 using the magnesiowüstite samples without chromium, at size fraction 20–38 μm, by measuring the acid consumption required to maintain constant pH level. The magnesiowüstite samples with chromium content are leached at pH 10; the leachate is analyzed for chromium. The results are unanimous, with increasing FeO content the dissolution of magnesiowüstite and leaching of chromium decrease. At pH 10 the magnesiowüstite, with ≥60 wt% FeO show no sign of dissolution and no chromium leaching could be detected with ≥70 wt% FeO. The results prove that the FeO content can stabilize magnesiowüstite and, thereby, prevent chromium leaching
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| 45. |
- Sui, Y., et al.
(författare)
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Optimization of Slag Chemistry Toward Inclusion Control for 28CrMo47 Drill Pipe Steel Based on Viscosity and Equilibration Studies
- 2015
-
Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X.
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Tidskriftsartikel (refereegranskat)abstract
- During the refining of 28CrMo47 drill pipe steel, it is found that the product often has internal defects and cracks. The present work is initiated with a view to examine if these problems could be solved by optimizing the slag chemistry of the refining slag. Three series of slags, namely, slag A (57.09%CaO-15.74%SiO2-16.35%Al2O3-5.35%MgO, original slag in the steel plant), slag B (55%CaO-21%SiO2-12%Al2O3-7%MgO-5%CaF2), and slag C (51%CaO-17%SiO2-25%Al2O3-7%MgO) are designed and their viscosities are measured. The effect of Al2O3 content on viscosity of the slag C is also investigated as part of the slag optimization. Slag-steel equilibrium experiments are subsequently carried out in order to understand the effect of the slag chemistry, especially the variation in the Al2O3 content in the same on the inclusions in drill pipe steel. It is concluded that both increasing Al2O3 content of the slag used in the refining unit in the plant and addition of CaF2 could decrease effectively the slag viscosity. Inclusions in steel equilibrated with slag C1, corresponding to 51%CaO-7%MgO-25%Al2O3-17SiO2, consisted mainly of low melting point CaO-Al2O3 complex, which did not have any negative effect on the steel quality.
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| 46. |
- Tofique, Muhammad Waqas, 1986-, et al.
(författare)
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Fatigue strength, crack initiation, and localized plastic fatigue damage in VHCF of duplex stainless steels
- 2016
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Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 87:7, s. 899-910
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Tidskriftsartikel (refereegranskat)abstract
- The fatigue strength of two-duplex stainless steel grades, 2304 SRG and LDX 2101, with austenitic–ferritic microstructure is tested using ultrasonic fatigue testing equipment operating at 20 kHz. The testing is conducted in tension-compression mode with the load ratio R=-1. The fatigue strength is evaluated at 107, 108, and 109 load cycles and the estimates of fatigue strength are higher for the LDX 2101 grade. The fatigue crack initiation mechanisms are analyzed using a scanning electron microscope. The fatigue cracks, in all cases, appear to initiate due to accumulation of plastic fatigue damage at the surface. In the 2304 SRG grade, accumulation of fatigue damage occurs at the external surface of fatigued specimens in the form of extrusions at the grain/phase boundaries and in the form of individual slip lines in the austenite phase. Meanwhile, in the LDX 2101 grade accumulation of plastic fatigue damage in the form of extrusions and intrusions occurs mainly within the ferrite grain. When the crack is microstructurally short, the crack growth appears to be crystallographic in nature and the crack appears to change its direction propagating from one grain into another.
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| 47. |
- Wang, Haijuan, et al.
(författare)
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Determination of Vanadium Oxidation States in CaO-MgO-Al2O3-SiO2-VOx System by K Edge XANES Method
- 2016
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Ingår i: Steel Research International. - : Wiley-VCH Verlag. - 1611-3683 .- 1869-344X. ; 87:2, s. 199-209
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation states of vanadium in the CaO-MgO-Al2O3-SiO2-VOx slag system are investigated with the initial V2O5 concentration in the range of 1-10 mole fraction, in the temperature range, 1823-1923K, partial pressures of oxygen from 10(-5) to 10(3)Pa, and with the basicities in the range of 0.85-2.20. The valance states of vanadium are determined by the X-Ray Absorption Near-Edge Structure (XANES) method. The results indicates that, for the oxide VOx, at a given temperature, and basicity, x is found to increase slightly with increase of initial V2O5 concentration. With the increase of slag basicity, x is increased. It is also found that x in VOx decreases with the increase of temperature, whereas, at constant basicity, the value of x increases with the increased oxygen partial pressure. The present results are useful in the quantification of V3+/V4+ and V4+/V5+ ratios for a given slag as functions of basicity, temperature, and oxygen partial pressure.
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| 48. |
- Wessman, Sten, 1967-, et al.
(författare)
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Application of computational thermodynamics to predict growth of intermetallic phases in superduplex stainless steels
- 2015
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 86:11, s. 1339-1349
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Tidskriftsartikel (refereegranskat)abstract
- Computational thermodynamics were used to predict the growth of intermetallic phases in superduplex stainless steels, assuming that it is the ferrite which primarily decomposes during heat treatments below 1000°C. Sigma and chi phase were modeled to form at the edge of a 10μm ferrite unit and the time from 0.1s to the development of a 100nm layer of the phase in question was evaluated. This approach encompasses thermodynamics and kinetics of growth of the intermetallic phases but omits nucleation. Nevertheless the calculations accurately predict the classic C-shaped TTT curves, in which "nose" the growth is most rapid with a critical combination of precipitation, diffusion, and driving force. Verification of the relevance of the model was done by comparison with a publication with experimental studies of molybdenum and tungsten alloyed superduplex stainless steel weld metals, showing that partial substitution of Mo of by W does cause a more rapid growth of intermetallic phases. In addition the effect of the partial substitution of nickel by copper was examined and showed that copper decreases the amount of sigma phase and also reduces its growth rate. The results also suggest that the time for nucleation is of less importance in this context than previously suggested and thermodynamics and kinetics are sufficient to give an adequate explanation to the experimental results.
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| 49. |
- Xu, Yonggui, et al.
(författare)
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Numerical Simulation of Single Argon Bubble Rising in Molten Metal Under a Laminar Flow
- 2015
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Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 86:11, s. 1289-1297
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Tidskriftsartikel (refereegranskat)abstract
- The fundamental aspects of rising argon bubbles in molten metal for a laminar flow were investigated by numerical simulations. The Volume-of-Fluid (VOF) model was used to track the interface between argon and liquid metal. The process of a bubble rising in the molten metal includes two steps, one is the bubble rising inside the liquid, and the other one is the bubble rising across the liquid surface. The bubbling dynamics inside the liquid phase was studied in terms of the bubble's trajectory, shape and terminal velocity over a wide range of bubble diameters. It shows that ≈3–10mm bubbles rise in a spiral way with strong instabilities by changing their instantaneous shapes, while ≈10–20mm bubbles rise rectilinearly and their shapes are kept almost steady. All these bubbles' terminal velocities are around 0.3 m s−1, which are in accordance with literature data. For a bubble with a specific size, small metal droplets can be formed due to the bubble bursting on the free surface. In a situation when the top surface of the bubble is ruptured, the remains of the bubble will collapse and jet droplets can be formed. Simulations of jet droplets were qualitatively analyzed. It shows that when the surface tension is 1.4 N m−1, the critical bubble size is 9.3 mm. Also, the ejection is found to increase with an increased surface tension value, unless a critical bubble size is reached.
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| 50. |
- Xuan, Changji, et al.
(författare)
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Attraction Force Estimations of Al2O3 Particle Agglomerations in the Melt
- 2016
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Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X.
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the van der Waals force, wettability of Al2O3 by liquid iron, and solid phase sintering on the Al2O3 agglomeration is studied. By using Fowkes module, the function of Hamaker constant of liquid iron changes with the surface tension of liquid iron, γFe (l), at temperature 1873K is created. For the agglomeration behavior of Al2O3 in the deoxidation case, the difference between the cavity bridge force and van der Waals force is smaller than seven times. It means that even though van der Waals force is weaker, it still can attract the inclusions to some extent. In the reoxidation case, the influence of the cavity bridge force decreases, and becomes similar to that of the liquid-capillary force. In this case, both attraction forces play important roles in the Al2O3 cluster formation. Moreover, for the solid phase sintering, the apparent self-diffusion coefficient, Dv, of Al2O3 at temperature 1873K in liquid Fe-10 mass%Ni alloy is found to have a value of 1.95×10-14m2s-1.
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