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Metals
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Inclusion/Precipitate Engineering in Steels
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Inclusion/Precipitate Engineering in Steels

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Extractive Metallurgy".

Deadline for manuscript submissions: closed (15 January 2021) | Viewed by 55402

Special Issue Editors

Prof. Dr. Pär Jönsson

E-Mail Website
Guest Editor
Department of Materials Science and Engineering (MSE), KTH Royal Institute of Technology, Stockholm, Sweden
Interests: inclusion engineering; precipitate engineering; reactor design; process control; metallurgical process modeling; sustainable steelmaking
Prof. Dr. Keiji Nakajima

E-Mail Website
Guest Editor
Department of Materials Science and Engineering (MSE), KTH Royal Institute of Technology, Stockholm, Sweden
Interests: inclusion and precipitate engineering; metallurgical process modeling; microstructure control; solidification and casting process modeling; macro- and micro-segregation modeling; physical properties

Special Issue Information

Dear Colleagues,

Inclusion/precipitate particle behaviors in liquid steel and in solid steel strongly control both the cleanliness and the material properties of steel materials, such as their toughness. These fundamental techniques have traditionally been denoted “Clean Steel” and “Oxide Metallurgy”, respectively, and they have been utilized in practice. Today, these two research directions have been partially overlapped and combined. Thus, we suggest that they collectively be denoted “Inclusion/ Precipitate Engineering”.

The current issue focuses on presenting the latest research on the inclusion/precipitate engineering of steels, including the metallurgical processing of steels, the resulting microstructure, and the final material properties. Both experimental research carried out in laboratories and steel plants as well as modeling research will be considered. In addition, because inclusions/precipitates are complexes composed of oxides, sulfides, nitrides, and carbides, their composition control and consequent size control are also of interest.

Prof. Dr. Pär Jönsson
Prof. Dr. Keiji Nakajima
Guest Editors

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Keywords

  • inclusions
  • precipitates
  • modeling
  • laboratory trials
  • steel plant trials

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Published Papers (18 papers)

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Research

16 pages, 11116 KiB  
Article
Evaluation of Sulfide Inclusions before and after Deformation of Steel by Using the Electrolytic Extraction Method
by Shuo Guo, Andrey Vladimirovich Karasev, Anders Tilliander and Pär Göran Jönsson
Metals 2021, 11(4), 543; https://doi.org/10.3390/met11040543 - 26 Mar 2021
Cited by 4 | Viewed by 2344
Abstract
The characteristics of elongated MnS have a critical effect on fatigue anisotropy and all mechanical anisotropies. A comparative investigation of nonmetallic inclusions in both stainless steels and tool steels has been carried out in this study. The inclusion characteristics were investigated using electrolytic [...] Read more.
The characteristics of elongated MnS have a critical effect on fatigue anisotropy and all mechanical anisotropies. A comparative investigation of nonmetallic inclusions in both stainless steels and tool steels has been carried out in this study. The inclusion characteristics were investigated using electrolytic extraction (EE) followed by scanning electron microscopy combined with energy-dispersive spectroscopy (SEM-EDS). Overall, three types of MnS inclusions (type I (regular), type II (irregular) and type III (Rod)) were found in tool steels in as-cast samples, which had not been heat-treated. Furthermore, three types of MnS inclusions (Rod-like sulfide (RS), Plate-like sulfide (PS) and Oxysulfide (OS)) were found in samples taken after rolling. Based on the breakability of the elongated MnS, three types of inclusions, Type UU, UB and BB, where U represents the undamaged or unbroken edge of an inclusion and B represents the fragment or broken edge of an inclusion, were studied in both stainless steels and tool steels both before and after additional heat treatment. The effect of heat treatment and dissolving the metal layer during the EE process is also discussed. The results show that both processes have a limited effect on the breakability of inclusions in steels with carbon contents <0.42 mass%. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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16 pages, 5785 KiB  
Article
Application of Some Modern Analytical Techniques for Characterization of Non-Metallic Inclusions in a Fe-10mass%Ni Alloy Deoxidized by Ti/Zr and Ti/Mg
by Andrey V. Karasev, Dmitry Gorkusha, Konstantin V. Grigorovich and Pär G. Jönsson
Metals 2021, 11(3), 448; https://doi.org/10.3390/met11030448 - 9 Mar 2021
Cited by 1 | Viewed by 1943
Abstract
In this study, a complete and comprehensive analysis of non-metallic inclusions (NMI) in an Fe-10%Ni alloy was done by using two modern analytical methods that complement each other: Electrolytic Extraction (EE) of inclusions from metal samples followed by investigations by using Scanning Electron [...] Read more.
In this study, a complete and comprehensive analysis of non-metallic inclusions (NMI) in an Fe-10%Ni alloy was done by using two modern analytical methods that complement each other: Electrolytic Extraction (EE) of inclusions from metal samples followed by investigations by using Scanning Electron Microscopy (SEM) and Fractional Gas Analysis (FGA). The composition, morphology, size and number of different NMIs and clusters were investigated in metal samples taken after deoxidation by additions of Ti, Ti/Zr and Ti/Mg. The obtained results were discussed with respect to formation, modification and removal of NMIs and clusters depending on the type of deoxidations and the holding time. It was found that the peaks of oxygen reduced from different oxide inclusions obtained by the FGA measurements corresponded well to the main types of inclusions and clusters observed by using the EE + SEM method. More specifically, the total O content in oxide inclusions (ONMI) increases by 10% after a Zr addition and then decreases linearly by 40% during 5 min of holding due to flotation of NMIs and clusters. However, after a Mg addition in the melt deoxidized by Ti, the ONMI content decreases drastically by 63% during 5 min of holding, due to a fast floatation of NMIs caused by bubbles of vaporized Mg. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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13 pages, 9459 KiB  
Article
Effects of Induction Heating in the ESP Line on Microstructural Evolution and Nb Dissolution Behavior of Nb-Ti Micro-Alloyed Steel
by Qibo Tang, Gang Niu, Huibin Wu, Lixiong Xu and Rui Yuan
Metals 2021, 11(2), 251; https://doi.org/10.3390/met11020251 - 2 Feb 2021
Cited by 2 | Viewed by 2056
Abstract
The thermo-mechanical control processing of Nb-Ti micro-alloyed steel by induction heating in the endless strip production (ESP) line was analyzed to better understand the microstructural evolution and Nb precipitation and dissolution behavior in austenite during rapid heating to high temperatures. The Nb-Ti micro-alloyed [...] Read more.
The thermo-mechanical control processing of Nb-Ti micro-alloyed steel by induction heating in the endless strip production (ESP) line was analyzed to better understand the microstructural evolution and Nb precipitation and dissolution behavior in austenite during rapid heating to high temperatures. The Nb-Ti micro-alloyed steel consisting of 0.05 wt% C and 0.05 wt% Nb was processed through simulated rough rolling at 1050 °C followed by rapid isothermal reheating at 1150 °C. The austenite coarsening behavior and the Nb dissolution behavior at different holding times were compared, and the coarsening kinetics of austenite grains and the dissolution kinetics of precipitates were investigated. It was found that during induction heating, the size of austenite grains gradually increased with the isothermal time, and the amounts of precipitates were greatly reduced. Round precipitates of (Ti, Nb) (C, N) and square precipitates of Ti (C, N) gradually dissolved into the austenite matrix with the holding time. The Nb content in the solution increased from 0.0137 to 0.0299 wt% as the holding time increased from 1 to 40 s; therefore, about 59.8% of the total Nb content dissolved into the austenite matrix during the induction heating process. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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14 pages, 5778 KiB  
Article
Effects of High Temperature Aging Treatment on the Microstructure and Impact Toughness of Z2CND18-12N Austenitic Stainless Steel
by Hui Zhang, Yanfeng Liu, Xian Zhai and Wenkai Xiao
Metals 2020, 10(12), 1691; https://doi.org/10.3390/met10121691 - 18 Dec 2020
Cited by 5 | Viewed by 2586
Abstract
During the casting cooling process or the forging process, austenitic stainless steel will remain at around 800 °C for some time. During this period, precipitate particle behaviors in austenitic stainless steel (containing ferrite) will cause a reduction in ductility, which can lead to [...] Read more.
During the casting cooling process or the forging process, austenitic stainless steel will remain at around 800 °C for some time. During this period, precipitate particle behaviors in austenitic stainless steel (containing ferrite) will cause a reduction in ductility, which can lead to material cracking. In this study, the effects of aging at 800 °C on the microstructure, impact toughness and microhardness of Z2CND18-12N austenitic stainless steel were systematically investigated. The precipitation processes of the χ and σ phases were characterized by color metallography and back scattered electron (BSE) signals. The toughness was investigated by the Charpy impact test. After the aging treatment, the χ and σ phases precipitated successively in the ferrite, and as the aging duration increased, the χ-phase dissolved and the σ-phase precipitated along the austenite grain boundaries. These all lead to a decrease in toughness and an increase in microhardness. Finally, the relationship between fracture morphology and aging time is discussed herein, and a crack mechanism is given. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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16 pages, 5894 KiB  
Article
Origin of the Inclusions in Production-Scale Electrodes, ESR Ingots, and PESR Ingots in a Martensitic Stainless Steel
by Ewa Sjöqvist Persson, Andrey Karasev, Alec Mitchell and Pär G. Jönsson
Metals 2020, 10(12), 1620; https://doi.org/10.3390/met10121620 - 2 Dec 2020
Cited by 10 | Viewed by 2921
Abstract
The focus of the study was to define the origin of the inclusions in production-scale electro-slag remelting, (ESR) and electro-slag remelting under a protected pressure controlled atmosphere, (PESR), ingots. The inclusion characteristics in production samples were studied using both polished sample surfaces (two-dimensional [...] Read more.
The focus of the study was to define the origin of the inclusions in production-scale electro-slag remelting, (ESR) and electro-slag remelting under a protected pressure controlled atmosphere, (PESR), ingots. The inclusion characteristics in production samples were studied using both polished sample surfaces (two-dimensional (2-D) investigations) and inclusions extracted from steel samples by electrolytic extraction (three-dimensional (3-D) investigations) using SEM in combination with EDS. The results were compared to results from previously reported laboratory-, pilot-, and production-scale trials including electrode, remelted, and conventional ingots. The results show that primary, semi-secondary, and secondary inclusions exist in the remelted ingots. The most probable inclusion to survive from the electrode is a MgO-Al2O3 (spinel). It was also found that the ESR/PESR process slag acts in a similar way to a calcium treatment modification of alumina inclusions. On the whole, the most significant finding is that the overall cleanliness of the electrode including the inclusions in the electrode has an influence on the inclusion content of the ESR and PESR ingots. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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16 pages, 6004 KiB  
Article
Influence of Manufacturing Conditions on Inclusion Characteristics and Mechanical Properties of FeCrNiMnCo Alloy
by Nuri Choi, Nokeun Park, Jin-kyung Kim, Andrey V. Karasev, Pär G. Jönsson and Joo Hyun Park
Metals 2020, 10(10), 1286; https://doi.org/10.3390/met10101286 - 25 Sep 2020
Cited by 18 | Viewed by 2691
Abstract
Three CoCrFeMnNi high-entropy alloys (HEAs) were produced by vacuum induction melting, induction melting under inert gas atmosphere, and melting under inert gas atmosphere followed by air exposure, respectively. The different manufacturing conditions for the three investigated alloys resulted in different levels and types [...] Read more.
Three CoCrFeMnNi high-entropy alloys (HEAs) were produced by vacuum induction melting, induction melting under inert gas atmosphere, and melting under inert gas atmosphere followed by air exposure, respectively. The different manufacturing conditions for the three investigated alloys resulted in different levels and types of inclusions. The alloys melted under vacuum or inert gas contained Al2O3 inclusions formed by impurity Al, due to its high oxidation tendency. The molten alloy exposed in air showed an excessive oxidation. During oxidation of the molten alloy in air, impurity Al was initially oxidized, and fine MnCr2O4 inclusions were formed rather than pure Al2O3 inclusions. This difference was analyzed based on thermodynamic calculations. Specifically, the influence of impurity content on the inclusion characteristics was investigated for the three HEAs. Moreover, the inclusion characteristics were found to have an influence on mechanical properties of the alloys also. In air-exposed HEA, smaller inclusions were formed, resulting in a higher dislocation density at the matrix/inclusion interface and thus strengthening of the HEA. Thus, it is proposed that atmospheric conditions could be an important factor to control the inclusion characteristics and to form fine inclusion particles, which could improve the mechanical properties of HEAs. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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9 pages, 10463 KiB  
Article
Effect of Zr Additions on Non-Metallic Inclusions in X11CrNiMo12 Steel
by Jaka Burja, Mitja Koležnik, Barbara Šetina Batič and Jožef Medved
Metals 2020, 10(9), 1183; https://doi.org/10.3390/met10091183 - 2 Sep 2020
Cited by 3 | Viewed by 2884
Abstract
The production of clean steel is associated with high-quality steel grades for demanding applications. The formation of oxide inclusions mainly depends on the deoxidation practice; it is usually carried out through Al additions, but alumina inclusions can have detrimental effects. An alternative zirconium [...] Read more.
The production of clean steel is associated with high-quality steel grades for demanding applications. The formation of oxide inclusions mainly depends on the deoxidation practice; it is usually carried out through Al additions, but alumina inclusions can have detrimental effects. An alternative zirconium inclusion modification was used in a creep-resistant steel to improve the cleanliness of laboratory-made steel. The thermodynamics behind the inclusion modification are presented, the reaction products are identified and the steel cleanliness improvement is quantified. The resulting influence of zirconium addition on non-metallic inclusions and mechanical properties is discussed. While the Zr additions drastically reduce the non-metallic inclusion size and area, additions above a certain amount result in the formation of zirconium nitrides that ultimately soften the martensitic steel due to the depletion of nitrogen in solid solution. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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13 pages, 11699 KiB  
Article
Effect of Inclusions on the Corrosion Properties of the Nickel-Based Alloys 718 and EP718
by Ekaterina Alekseeva, Andrey Karasev, Pär G. Jönsson and Aleksey Alkhimenko
Metals 2020, 10(9), 1177; https://doi.org/10.3390/met10091177 - 1 Sep 2020
Cited by 10 | Viewed by 3911
Abstract
Inclusions in steels and alloys are known to lower the resistance to deformation, as well as to lower the mechanical, corrosion and other properties. Studies of inclusions in nickel-based alloys are important since these materials could suffer from corrosion degradation in harsh operational [...] Read more.
Inclusions in steels and alloys are known to lower the resistance to deformation, as well as to lower the mechanical, corrosion and other properties. Studies of inclusions in nickel-based alloys are important since these materials could suffer from corrosion degradation in harsh operational conditions. This, in fact, could lead to a pitting initiation around the inclusions. Two industrial Ni-based alloys (alloy 718 and EP718) were investigated to determine the harmful effects of different inclusions on the corrosion resistance of Ni-based alloys. Specifically, the inclusion characteristics (such as composition, morphology, size, number and location) were determined for inclusions collected on film filters after electrolytic extraction and dissolution of a metal matrix around different inclusions on surfaces of metal samples after electrolytic extraction (EE). It was found that both Ni-based alloys contain various inclusion types: carbides (large size NbTi-C and small multicomponent carbides), nitrides TiNb-N and sulphides (TiNb-S in EP718 alloy). The most harmful effects on the corrosion resistance of metal were detected around sulphides and small carbides containing Mo, W, Cr. Dissolution effects were also observed around large carbides and nitrides, especially around inclusions larger than 10 µm. Moreover, the dissolution of a matrix around inclusions and clusters located on the grain boundaries were found to be 2.1–2.7 times larger compared to inclusions found inside of grains of the given alloy samples. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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18 pages, 7131 KiB  
Article
Characterization of Coarse-Grained Heat-Affected Zones in Al and Ti-Deoxidized Offshore Steels
by Henri Tervo, Antti Kaijalainen, Vahid Javaheri, Satish Kolli, Tuomas Alatarvas, Severi Anttila and Jukka Kömi
Metals 2020, 10(8), 1096; https://doi.org/10.3390/met10081096 - 13 Aug 2020
Cited by 2 | Viewed by 3444
Abstract
Deterioration of the toughness in heat-affected zones (HAZs) due to the thermal cycles caused by welding is a known problem in offshore steels. Acicular ferrite (AF) in the HAZ is generally considered beneficial regarding the toughness. Three experimental steels were studied in order [...] Read more.
Deterioration of the toughness in heat-affected zones (HAZs) due to the thermal cycles caused by welding is a known problem in offshore steels. Acicular ferrite (AF) in the HAZ is generally considered beneficial regarding the toughness. Three experimental steels were studied in order to find optimal conditions for the AF formation in the coarse-grained heat-affected zone (CGHAZ). One of the steels was Al-deoxidized, while the other two were Ti-deoxidized. The main focus was to distinguish whether the deoxidation practice affected the AF formation in the simulated CGHAZ. First, two different peak temperatures and prolonged annealing were used to study the prior austenite grain coarsening. Then, the effect of welding heat input was studied by applying three cooling times from 800 °C to 500 °C in a Gleeble thermomechanical simulator. The materials were characterized using electron microscopy, energy-dispersive X-ray spectrometry, and electron backscatter diffraction. The Mn depletion along the matrix-particle interface was modelled and measured. It was found that AF formed in the simulated CGHAZ of one of the Ti-deoxidized steels and its fraction increased with increasing cooling time. In this steel, the inclusions consisted mainly of small (1–4 μm) TiOx-MnS, and the tendency for prior austenite grain coarsening was the highest. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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13 pages, 5620 KiB  
Article
Effect of Cerium Content on the Evolution of Inclusions and Formation of Acicular Ferrite in Ti-Mg-Killed EH36 Steel
by Zhen Liu, Bo Song, Zhanbing Yang, Xiaokang Cui, Longfei Li, Lei Wang and Zirui Song
Metals 2020, 10(7), 863; https://doi.org/10.3390/met10070863 - 29 Jun 2020
Cited by 16 | Viewed by 2655
Abstract
Ce has been widely used in oxide metallurgy for modifying inclusions and refining microstructure. Effect of Ce contents on the evolution and characteristics of non-metallic inclusions and the formation of acicular ferrite (AF) in Ce-treated Ti-Mg-killed EH36 steel was investigated. The results showed [...] Read more.
Ce has been widely used in oxide metallurgy for modifying inclusions and refining microstructure. Effect of Ce contents on the evolution and characteristics of non-metallic inclusions and the formation of acicular ferrite (AF) in Ce-treated Ti-Mg-killed EH36 steel was investigated. The results showed that the main type of inclusions in Ti-Mg deoxidized steel was MgO·Al2O3-MnS. After 0.014%, 0.024% and 0.037% Ce were added into the steels, dominant inclusions became CeAlO3-MgO-MnS, Ce2O2S-MgO-MnS and Ce2O2S-MnS, respectively. The precipitation of pure MnS was suppressed in the steel with 0.024% Ce, while the number density of total inclusions increased significantly in the steel with 0.037% Ce, causing the inclusions distributing densely. Ce addition refined the microstructure of tested steels by promoting AF formation and polygonal ferrite distributing evenly. Dispersive distribution, low lattice mismatch against α-Fe, as well as lower number density of pure MnS caused the highest number density of effective inclusions (nucleus of AF formation) in 0.024% Ce-treated steel. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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16 pages, 4476 KiB  
Article
Study on the Possible Error Due to Matrix Interaction in Automated SEM/EDS Analysis of Nonmetallic Inclusions in Steel by Thermodynamics, Kinetics and Electrolytic Extraction
by Alexander Mayerhofer, Dali You, Peter Presoly, Christian Bernhard and Susanne K. Michelic
Metals 2020, 10(7), 860; https://doi.org/10.3390/met10070860 - 29 Jun 2020
Cited by 10 | Viewed by 3214
Abstract
Up to now, the Fe content of nonmetallic particles has often been neglected in chemical evaluations due to the challenging analysis of matrix elements in nonmetallic inclusions (NMI) in steel by scanning electron microscope and energy dispersive spectroscopy analysis (SEM/EDS). Neglecting matrix elements [...] Read more.
Up to now, the Fe content of nonmetallic particles has often been neglected in chemical evaluations due to the challenging analysis of matrix elements in nonmetallic inclusions (NMI) in steel by scanning electron microscope and energy dispersive spectroscopy analysis (SEM/EDS). Neglecting matrix elements as possible bonding partners of forming particles may lead to inaccurate results. In the present study, a referencing method for the iron content in nonmetallic inclusions in the submicrometer region is described focusing on the system Fe-Mn-O. Thermodynamic and kinetic calculations are applied to predict the inclusion population for different Fe/Mn ratios. Reference samples containing (Fe,Mn)-oxide inclusions with varying Fe ratios are produced by manganese deoxidation in a high-frequency induction furnace. Subsequent SEM/EDS measurements are performed on metallographic specimens and electrolytically extracted nonmetallic inclusions down to 0.3 µm. The limits of iron detection in these particles, especially for those in the submicrometric regime, as well as the possible influence of electrolytic extraction on Fe-containing oxide particles are examined. The measured inclusion compositions correlate well with the calculated results regarding segregation and kinetics. The examinations performed are reliable proof for the application of SEM/EDS measurements to evaluate the Fe content in nonmetallic inclusions, within the physical limits of polished cross-section samples. Only electrolytic extraction ensures the determination of accurate compositions of dissolved or bonded matrix elements at smallest particles enabling quantitative particle descriptions for submicrometric (particles ≤ 1 µm) steel cleanness evaluations. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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15 pages, 7483 KiB  
Article
Effect of Ti Content on the Behavior of Primary Carbides in H13 Ingots
by Yu Huang, Guoguang Cheng and Meiting Zhu
Metals 2020, 10(6), 837; https://doi.org/10.3390/met10060837 - 24 Jun 2020
Cited by 4 | Viewed by 2528
Abstract
The Ti element plays a role in pinning grain boundaries but also has a good binding ability to C and N, forming large primary carbides. Therefore, the effect of Ti content on primary carbides’ behavior in H13 ingots was comprehensively studied. A non-aqueous [...] Read more.
The Ti element plays a role in pinning grain boundaries but also has a good binding ability to C and N, forming large primary carbides. Therefore, the effect of Ti content on primary carbides’ behavior in H13 ingots was comprehensively studied. A non-aqueous electrolysis method was used to determine the three-dimensional (3D) characteristics of primary carbides. We found a great difference between the two-dimensional (2D) and the three-dimensional characteristics of primary carbides. When performing 2D analyses, the density of the primary carbides appeared high, while their size was small. The actual characteristics of primary carbides can be obtained only by 3D observation. The primary carbide showed a typical dendritic structure, whose center consisted of Ti–V-rich carbide wrapped by V-rich carbide. As the Ti content increased, the size of the primary carbide increased from 24.9 μm to 41.3 μm, and the number density increases from 25.6 per/mm2 to 43.9 per/mm2. The Ti4C2S2 phase precipitated first, then changed into Ti–V-rich carbide, and finally further partly transformed into V-rich carbide. The addition of elemental Ti promoted the precipitation and transformation of primary carbides, resulting in an increase of the number density and size. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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13 pages, 19006 KiB  
Article
Effect of Heterogeneous Nucleation on Removal of Arsenic from Molten Steel by Rare Earth Addition
by Hongpo Wang, Peng Yu, Silu Jiang and Yu Wang
Metals 2020, 10(5), 664; https://doi.org/10.3390/met10050664 - 20 May 2020
Cited by 9 | Viewed by 2340
Abstract
Cleanliness control is an eternal theme to improve the properties of steel products. With the increasing recycling rates of scrap steel, the removal and stabilization of residual elements have become a vital issue for improving the performance of steel products. Thermodynamic and mismatch [...] Read more.
Cleanliness control is an eternal theme to improve the properties of steel products. With the increasing recycling rates of scrap steel, the removal and stabilization of residual elements have become a vital issue for improving the performance of steel products. Thermodynamic and mismatch calculations plus laboratory experiments were carried out to study the heterogeneous nucleation phenomena of inclusions when lanthanum was employed to remove arsenic from molten steel and stabilize arsenic in solid steel. The effect of heterogeneous nucleation on the mechanism of arsenic removal was discussed. A series of heterogeneous nucleation phenomena of inclusions in the La-O-S-As system were discovered, and the heterogeneous nucleation among the inclusions turned out to be selective. As the vital product of arsenic removal, La-S-As is most likely to generate with LaS as heterogeneous nucleation cores, and its possible chemical formula turned out to be 3LaS⸱LaAs. Sulfur plays an essential role in removing arsenic from molten steel by adding lanthanum. It needs to control the initial sulfur content in an appropriate range, because the high initial content causes too much loss of rare earth, and the low initial content cannot produce LaS and La-S-As. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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13 pages, 3890 KiB  
Article
Revolution and Control of Fe-Al-(Mg, Ti)-O Oxide Inclusions in IF Steel during 260t BOF-RH-CC Process
by Rijin Cheng, Renchun Li, Di Cheng, Junshan Liu, Qing Fang, Jian'an Zhou, Wenliang Dong, Hua Zhang and Hongwei Ni
Metals 2020, 10(4), 528; https://doi.org/10.3390/met10040528 - 19 Apr 2020
Cited by 4 | Viewed by 2756
Abstract
The evolution of inclusions that contain Al, Mg, and Ti was studied through industrial-grade experiments. Field emission scanning electron microscopy, energy dispersive spectrometry, inductively coupled plasma atomic emission spectrometry, and FactSage software were used to analyze the evolution mechanisms of inclusions in [...] Read more.
The evolution of inclusions that contain Al, Mg, and Ti was studied through industrial-grade experiments. Field emission scanning electron microscopy, energy dispersive spectrometry, inductively coupled plasma atomic emission spectrometry, and FactSage software were used to analyze the evolution mechanisms of inclusions in Al-killed titanium alloyed interstitial free (IF) steel. The research found that the evolution of inclusions during the smelting process of IF steel is results in ‘large sphere-like SiO2-CaO-FeO-MgO-MnO’ and ‘small cluster spherical FeO-MnO’ change to cluster-like Al2O3 and irregular MgO·Al2O3, then change to Al2O3·TiOx and Al2O3, and finally change to Al2O3. It is difficult for Al2O3·TiOx to stably exist in the IF molten steel. It is the key to extend the holding time properly after Ruhrstahl Heraeus (RH) to ensure the removal of Al2O3 inclusion. With the increase of Mg content, the change path of MgAl2O4 inclusion in IF steel is that Al2O3 changes to MgO·Al2O3, and finally changes to MgO. It is difficult to suppress MgO·Al2O3 spinel formation by controlling the oxygen in the steel, but Ca can modify part of the MgO·Al2O3 spinel inclusions during RH refining. In order to ensure the removal of 6–10 μm inclusions, the holding time is suitable for 19–42 min. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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13 pages, 2649 KiB  
Article
Methods to Determine Characteristics of AOD-Converter Decarburization-Slags
by Patrik Ternstedt, Gunilla Runnsjö, Anders Tilliander, Jesper Janis, Nils Å. I. Andersson and Pär G. Jönsson
Metals 2020, 10(3), 308; https://doi.org/10.3390/met10030308 - 26 Feb 2020
Cited by 3 | Viewed by 3738
Abstract
Argon Oxygen Decarburization (AOD) converter slags are known to consist of both liquid and solid phases, but limited information on the slag characteristics has been published in the open literature. Therefore, a new methodology to study the characteristics of slag samples taken from [...] Read more.
Argon Oxygen Decarburization (AOD) converter slags are known to consist of both liquid and solid phases, but limited information on the slag characteristics has been published in the open literature. Therefore, a new methodology to study the characteristics of slag samples taken from the AOD converter process during production was developed based on petrography. The results show that the preparations of the slag samples using the borax method are suitable to use when determining the chemical composition of AOD slag samples using the X-ray fluorescence (XRF) method. The results also showed that both the light optical microscopy (LOM) method and a method combining scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) can be used to characterize the slag samples and that the correlation between the methods was found to be good. This means that it is possible to use the faster LOM method instead of the more complicated SEM-EDS method to characterize AOD slag samples. Finally, the results show that the difference between calculated values based on stoichiometry and measured data for Ca and Cr in AOD slags are 11.7 mass% and 11.3 mass%, respectively. This is considered to be a good agreement for industrial samples. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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11 pages, 5108 KiB  
Article
Evolution of Inclusions in Steelmaking Process of Rare Earth Steels Containing Arsenic with Alumina Crucibles
by Hongpo Wang, Peng Yu, Silu Jiang, Bin Bai, Lifeng Sun and Yu Wang
Metals 2020, 10(2), 275; https://doi.org/10.3390/met10020275 - 20 Feb 2020
Cited by 20 | Viewed by 3132
Abstract
In order to determine strategies for removing arsenic from rare earth arsenic-containing steels, the evolution of inclusions in the whole steelmaking process with alumina crucibles was investigated. It has been proven that adding lanthanum has a significant effect on both the existing state [...] Read more.
In order to determine strategies for removing arsenic from rare earth arsenic-containing steels, the evolution of inclusions in the whole steelmaking process with alumina crucibles was investigated. It has been proven that adding lanthanum has a significant effect on both the existing state and content of arsenic in steel. The content of arsenic steeply decreased after adding 0.148% lanthanum by generating La–S–As inclusions. The addition of 0.054% lanthanum did not dramatically affect the content of arsenic. Both 0.148% and 0.054% additions of lanthanum modified the existing Si–Mn–Al–O inclusions, making them first change to La-containing inclusions, and then change back to Si–Mn–Al–O inclusions. During this process, the compositions of inclusions changed from (SiO2–MnO)-rich to Al2O3-rich ones, owing to the reactions between lanthanum and alumina crucibles. The addition of 0.148% lanthanum resulted in a relatively severe reaction with the alumina crucible. This led to the decomposition of a part of the existing La–S–As inclusions and a slight increase in the arsenic content. Therefore, it is noted that choosing an appropriate holding time after adding rare earth elements to molten steel has a significant effect on the arsenic removal and saving the consumption of rare earth elements. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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15 pages, 6752 KiB  
Article
Transformation of Oxide Inclusions in Stainless Steel Containing Yttrium during Isothermal Heating at 1473 K
by Xueliang Zhang, Shufeng Yang, Jingshe Li and Jinqiang Wu
Metals 2019, 9(9), 961; https://doi.org/10.3390/met9090961 - 1 Sep 2019
Cited by 11 | Viewed by 3899
Abstract
To provide fundamental information on the control of rare earth inclusions in solid steel, two 18 mass% Cr-8 mass% Ni stainless steels with different yttrium additions were prepared using an electric resistance furnace and the evolution of yttrium-based oxide inclusions during heat treatment [...] Read more.
To provide fundamental information on the control of rare earth inclusions in solid steel, two 18 mass% Cr-8 mass% Ni stainless steels with different yttrium additions were prepared using an electric resistance furnace and the evolution of yttrium-based oxide inclusions during heat treatment of the steels at 1473 K was investigated. In both as-cast steels, homogeneous spherical Al-Y-Si(-Mn-Cr) oxide inclusions were observed; however, the steel with larger yttrium additions also had some heterogeneous oxide inclusions with double phases. After heating, a new oxide phase with higher yttrium content precipitated from the original inclusions and resulted in partitioning to Y-rich and Al-rich parts in both steels. The average size and number density of inclusions slightly increased, and the morphology of inclusions changed from spherical to irregular. The transformation mechanism during isothermal heating was proposed to be the mutual effects of (i) internal transformation of the yttrium-based inclusions owing to crystallization of glassy oxide and (ii) interfacial reaction between inclusions and the steel matrix. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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16 pages, 8722 KiB  
Article
An Investigation of Non-Metallic Inclusions in Different Ferroalloys using Electrolytic Extraction
by Yong Wang, Andrey Karasev and Pär G. Jönsson
Metals 2019, 9(6), 687; https://doi.org/10.3390/met9060687 - 15 Jun 2019
Cited by 10 | Viewed by 4590
Abstract
Ferroalloys are integral constituents of the steelmaking process, since non-metallic inclusions (NMIs) from ferroalloys significantly influence the transformation of inclusions present in liquid steel or they are directly involved in casted steel. In this study, the characteristics of inclusions (such as the number, [...] Read more.
Ferroalloys are integral constituents of the steelmaking process, since non-metallic inclusions (NMIs) from ferroalloys significantly influence the transformation of inclusions present in liquid steel or they are directly involved in casted steel. In this study, the characteristics of inclusions (such as the number, morphology, size, and composition) in different industrial ferroalloys (FeV, FeMo, FeB, and FeCr) were investigated using the electrolytic extraction (EE) technique. After extraction from the ferroalloy samples and filtration of the solution, the inclusions were investigated on a film filter. The three-dimensional (3D) investigations were conducted using a scanning electron microscopy in combination with energy dispersive spectroscopy (SEM-EDS). The characteristics of inclusions observed in the ferroalloys were compared with previous results and discussed with respect to their possible behaviors in the melt and their effects on the quality of the cast steels. The particle size distributions and floatation distances were plotted for the main inclusion types. The results showed that the most harmful inclusions in the ferroalloys investigated are the following: pure Al2O3 and high Al2O3-containing inclusions in FeV alloys; pure SiO2 and high SiO2-containing inclusions in FeMo alloys; Al2O3 and SiO2-containing inclusions in FeB alloys; and MnO-Cr2O3, Al2O3, and Cr2O3-based inclusions in FeCr alloys. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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