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ISIJ International Vol. 64 (2024), No. 6

ISIJ International
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Grid List Abstracts
オンライン版ISSN: 1347-5460
冊子版ISSN: 0915-1559
発行機関: The Iron and Steel Institute of Japan

Backnumber

  1. Vol. 64 (2024)

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  2. Vol. 63 (2023)

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キーワードランキング

23 Nov. (Last 30 Days)

ISIJ International Vol. 64 (2024), No. 6

Thermodynamic Analysis on Slag/Metal Reactions in Steelmaking Process Using Direct Reduced Iron and Steel Scraps

Kengo Kato, Hideki Ono

pp. 881-892

DOI:

10.2355/isijinternational.ISIJINT-2023-398

抄録

Hydrogen reduction processes of iron ores are being developed to achieve carbon neutrality. However, high-grade iron ore pellets used in the current direct reduction process will be depleted in the future. On the other hand, steel scraps recovered from society are usually contaminated with tramp elements, which are difficult to remove in the current steel refining processes. To produce high-quality steel from DRI and steel scraps, molten steel composition in the melting process should be optimized considering the impurities originating in iron resources and conditions such as temperature and oxygen potential. In this study, the equilibrium of slag/metal reactions in the steelmaking process using DRI and steel scraps were thermodynamically analyzed, and the effect of using scrap on the composition of molten steel and slag and the conditions to produce low-phosphorous molten steel from high-P content DRI and steel scrap were discussed. The use of steel scrap showed such advantages as a decrease in the concentrations of Si, S, and P originating from high-P DRI, a decrease in the amount of slag, and a reduction in the amount of limestone required to maintain slag basicity. Moreover, the P content of iron can be decreased to 13 mass ppm at 1873 K and PO2 = 10−10 atm even when the high-P DRI is used in combination with steel scrap. The thermodynamic analysis showed the potential for carbon-free steel by optimizing the hydrogen reduction process and the melting process of DRI with steel scraps.

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Activity of Chromium Oxide in CaO–SiO2–MgO–Al2O3–MnO–CaF2–CrOx Slag for Chromium Reducing Process

Chonglin Shi, Zhi Li, Yuxing Liu, Yoshinao Kobayashi

pp. 893-900

DOI:

10.2355/isijinternational.ISIJINT-2023-214

抄録

Thermodynamic data of chromium oxide activities in molten slags are important for improvement of the reduction treatment process of chromium oxides in stainless steel slags. The chemical equilibrium experiments were conducted in the present work to measure the activity coefficients of chromium oxides in the CaO–CaF2–MgO–Al2O3–SiO2–MnO–CrOx slags at 1823 K (1550°C) under oxygen partial pressure of 2.57×10−11 atm with different chromium oxides contents. It is found that no solid phase appears in the slag when the initial CrO1.5 mole fraction of the slag is no more than 0.00390 (0.5 mass%), which could ensure the accuracy of the chromium valence analysis. The activity coefficient of CrO keeps almost constant with the increase of mole fraction of total chromium oxides, which indicates that CrO obeys Henry’s law under the present conditions. The activity coefficient of CrO1.5 firstly levels off and then rises sharply when the mole fraction of total chromium oxides reaches 0.00198, beyond this point, activity coefficient of CrO1.5 keeps relatively constant again. Through the Raman spectroscopy analysis, the sharp increase of the activity coefficient of CrO1.5 is assumed to be caused by the transformation of CrO1.5 from network former to network modifier.

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Activity of Iron Oxide in Slag with Nepheline Syenite Added as a Flux

Yusaku Sakamoto, Keijiro Saito, Masakatsu Hasegawa

pp. 901-908

DOI:

10.2355/isijinternational.ISIJINT-2023-452

抄録

Although fluorspar has been widely used as a flux for steelmaking slag, there is a strong incentive to explore alternatives. As one of the candidates for such substances, “nepheline syenite” has been investigated in terms of slag fluidity and lime dissolution rate. The present study aimed at clarifying the homogeneous liquid region and FexO activities in the CaO–FexO slags with nepheline syenite added at 1673 K. When the molar ratio of nepheline syenite/CaO was below 0.658, the substitution of CaO with nepheline syenite raised the FexO activity as well as CaF2. The effect of the nepheline syenite addition on slag basicity was discussed by means of the reduction-oxidation reaction of Fe3+/Fe2+.

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Liquid-Liquid Phase Separation and Phase Distribution in CaO–P2O5–FeO Slag for Phosphorus Recovery

Yu-ichi Uchida, Kenji Nakase, Katsunori Takahashi

pp. 909-919

DOI:

10.2355/isijinternational.ISIJINT-2023-476

抄録

Supposing to utilize the slag with high P2O5 content as a new phosphorus resource produced from a novel steelmaking process, a fundamental investigation was carried out with particular focus on spontaneous liquid-liquid phase separation occurring in the system CaO–P2O5–FeO for effective phosphorus recovery. At 1773 K, two types of phase separation, which is a double-layered or a dispersed structure of two liquid phases, were observed according to the bulk composition. The double layers separated vertically and consisted of the phase with higher P2O5 content over 40 mass%, and the phase with higher FeO content over 90 mass%. Such structure corresponds to the liquid-liquid separation in the compositional region which is located in higher P2O5 content (upper side) against the tie line between Ca3P2O8–FeO apex on the isothermal section of CaO–P2O5–FeO ternary system. At 1673 K, various separation was observed such as a double-layer or a dispersed structure of two liquid phases, and a coexistence of solid/liquid phases. The slag with the bulk composition lying in the upper two liquid region showed the double-layered structure, giving a promising result for phosphorus recovery through phosphate concentration. The condition for formation of double-layered structure was considered based on the index originally proposed for co-continuity in polymer blends processing, which consists of viscosity and volume fraction of the co-existing phases. The index was found to represent a specific condition for making co-continuous phases in this study and would be significant in view of effective phosphorus recovery.

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Precipitation Behavior of MnS Inclusion in Unidirectionally-Solidified Fe-18Mn-1Al-0.3C Steels

Yuewen Fan, Kouki Kameda, Xiaojun Hu, Hiroyuki Matsuura

pp. 920-927

DOI:

10.2355/isijinternational.ISIJINT-2023-323

抄録

In order to reasonably control the precipitation of inclusions during solidification in TWIP steels, the precipitation behavior of typical MnS inclusions in high manganese steel was investigated by unidirectional solidification experiments. Through the combined analyses using ASEM-EDS, optical microscope, and thermodynamic calculation, it was found that Mn concentration in the liquid metal region were higher than those in the solid metal region. Furthermore, closer to the inclusion the liquid phase was, higher its Mn content was. In Fe-18mass%Mn-1Al-0.3C, MnS inclusions can precipitate at the positions located in the junction of dendrites at the end of the solidification (solid fraction fs=0.96), Mn content reaching 34.88 mass%. Already existing Al2O3 particles could become the core of MnS to form composite inclusions to promote the MnS precipitation during the solidification process. When fs achieved 0.7 leading the Mn segregation in the liquid phase to 25 mass%, MnS starts to precipitate to attach the Al2O3 surface to form composite inclusion.

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Dissolution of Carbon-Containing Species in CaO–SiO2–Al2O3 Slag

Qiuju Li, Cong Liang, Bowen Han

pp. 928-934

DOI:

10.2355/isijinternational.ISIJINT-2023-353

抄録

The acceleration of the carburizing and melting processes in reduced iron is critical for reducing energy consumption and CO2 emissions produced by the steel industry. The aims of the study were to clarify the carbon dissolution reactions and diffusion processes in molten slag. A combined approach utilizing Raman spectroscopy and XPS was employed to investigate the relationship between carbon-containing species and slag composition in the CaO–SiO2–Al2O3 slag system. The Raman spectra indicated that carbon dissolved in slag in the form of carbides, carbonates, and graphitic structures. The proportion of carbide ions in the slag increased from 64.2% to 74.7%, and the proportion of graphitic structures decreased from 19.7% to 7.4% as the slag’s basicity increased. The carbon dissolution mechanism in slag involved the reaction of carbon with dissolved oxide ions and oxygen-containing anions in the slag. This formed carbon-containing species such as CO32−, C22−, and graphitic structures that diffused in the slag and subsequently underwent carburization and deposition at the iron interface.

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Effect of Iron Oxide Dissolution on Thermochemical Property of Solid Solution between Ca2SiO4 and Ca3P2O8 at 1573 K

Keijiro Saito, Yoshiyuki Makino, Masakatsu Hasegawa

pp. 935-943

DOI:

10.2355/isijinternational.ISIJINT-2023-466

抄録

The key to a better understanding of phosphorus removal from hot metal is to know the thermochemical properties of solid solution between Ca2SiO4 and Ca3P2O8. Although the solid solutions would inevitably incorporate iron oxide in steelmaking slags, there is a still lack of knowledge about the solid solutions containing iron oxide. The present study focused on the effect of FeO dissolution on the activities of components in the Ca2SiO4–Ca3P2O8 solid solution. The P2O5 activities were measured in the solid solution containing FeO at 1573 K. Subsequently, the activities of Ca2SiO4, Ca3P2O8, and Fe2SiO4 were derived from the Gibbs-Duhem equation with the measured P2O5 activities and reported FeO activities. When iron oxide dissolved into the Ca2SiO4–Ca3P2O8 solid solution, the Ca3P2O8 activity decreased, while the Ca2SiO4 activity was insensitive. As a result, the dissolution of iron oxide into the solid solution caused a drastic decrease in the P2O5 activity.

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Direct Electrodeposition of High-Purity Iron from Fe2O3 in Molten Calcium Chloride

Zhongya Pang, Jinjian Li, Shun Chen, Xueqiang Zhang, Feng Tian, Guangshi Li, Shujuan Wang, Xing Yu, Chaoyi Chen, Qian Xu, Xionggang Lu, Xingli Zou

pp. 944-953

DOI:

10.2355/isijinternational.ISIJINT-2023-462

抄録

The low-cost production of high-purity metallic iron is of great practical importance. Herein, we report the direct production of high-purity metallic iron (99.92%) via a one-step electrochemical strategy in molten CaCl2–CaO–Fe2O3 system at 850°C. The involved CaO-assisted dissolution of Fe2O3 and electrodeposition mechanism were systematically studied, and the obtained iron products were characterized using scanning electron microscopy, inductively-coupled high-frequency plasma emission spectrometry, and glow discharge mass spectrometry. The results show that the crystalline iron products with tunable morphologies can be obtained in a controlled manner. The electrolysis parameters (voltage, current density, electrodeposition time and substrate material) have significant effects on the electrodeposition process and the characteristics of iron products. In particular, high-purity dense iron film can be directly electrodeposited at 15 mA∙cm−2, and its thickness increases considerably with increasing electrodeposition time. Furthermore, the as-deposited iron product can also be processed into bulk iron materials with high-purity of 99.995 wt.% by plasma melting for the potential applications. In general, this one-step electrodeposition process provides an acid-/alkaline-free strategy for the facile production of high-purity iron materials direct from Fe2O3.

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Development of Innovative Gasification Process of Used Plastic by Using Fluidized Bed

Koichi Momono, Jun Ishii, Seiji Hosohara, Hideo Kijima

pp. 954-963

DOI:

10.2355/isijinternational.ISIJINT-2023-479

抄録

Used plastic waste flowing into oceans has become a worldwide problem. Since international trade in used plastics has been regulated in recent years, a large amount of used plastic now requires domestic disposal. On the other hand, used plastics with a high calorific value could be used as an energy source. Therefore, the authors developed a new used plastic gasification process utilizing a fluidized bed. In this process, used plastics are decomposed in a fluidized bed reactor at around 600°C, which is a lower temperature than that used in current commercial processes. A higher calorific value gas could be obtained by gasification reaction control at the lower temperature. Hydrogen enriched gas generated by the water-gas shift reaction (WGSR) of basic oxygen furnace gas was used as the fluidizing or gasifying agent, since hydrogen was considered to have an effect of promoting the decomposition reaction of the hydrocarbons in used plastics. As the fluid medium in the reactor, catalysts were used to improve gasification efficiency. In this study, the effect of the gasification temperature and type of catalyst on the calorific value of the produced gas and gasification efficiency were investigated. High calorific value gas (LHV: 5000 kcal/Nm3) could be successfully produced by pyrolysis of used plastics by using an appropriate gasification temperature and catalyst.

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Effect of Biocarbon Addition on Metallurgical Properties of Mill Scale-Based Auger Pressing Briquettes

Olli Vitikka, Mikko Iljana, Anne Heikkilä, Illia Tkalenko, Oleksii Kovtun, Nikita Koriuchev, Daniel Shehovsov, Timo Fabritius

pp. 964-977

DOI:

10.2355/isijinternational.ISIJINT-2023-417

抄録

This work focused on the usage of bio-based and secondary iron and steelmaking raw materials. Auger pressing briquettes, cold-bonded agglomerates made from by-products, mainly mill scale (80%), were successfully tested in industrial-scale blast furnace (BF) trials. The briquettes from industrial production were studied in two different laboratory-scale reduction experiments to compare them to laboratory-made briquettes. A blast furnace simulator (BFS) device was utilized in the simulations mimicking the temperature and gas profiles of an actual BF process. A reduction under load (RUL) device enabled the simulation of the physical load under reducing conditions. To determine how the high-temperature properties of the self-reducing briquettes depend on the amount of biocarbon, a bio-based reducing agent (2–10%) was added to the laboratory-scale briquettes that already contained 5.6% total carbon mainly originating from BF dust. For the recipes studied, a weight loss of about 30% under reducing conditions leads to the disintegration of a briquette under load. Based on the BFS experiments, adding biocarbon to the recipe was profitable in terms of a self-reducing effect up to 6% when the total carbon content was 11%. The RUL experiments showed that the structure of the briquette became extremely plastic with the addition of 4% biocarbon which covers 39% of the total carbon contained in the briquette. This was the upper limit for biocarbon addition due to telescoping and disintegration followed by the formation of fines. The industrial briquettes used in the BF corresponded well to the laboratory-made briquettes in terms of metallurgical properties.

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Comparison of Hydrochar and Anthracite as Reducing Agents for Direct Reduction of Hematite

Yu-Chiao Lu, Andrey Vladimirovich Karasev, Björn Glaser, Chuan Wang

pp. 978-987

DOI:

10.2355/isijinternational.ISIJINT-2023-436

抄録

The substitution of fossil coal with biocarbon in the metallurgical processes can help to decrease fossil CO2 emissions. Biocarbon’s characteristics, such as high volatile matter contents and high reactivities with CO2, are beneficial for increasing the reduction degrees and reduction rates of iron oxides in carbon composite agglomerates (CCA). This study compared the reduction of hematite by of two types of carbonaceous materials (CM): hydrochar (high-volatile biocarbon) and anthracite (a low-volatile coal) in the form of CCA. CM, hematite, and binder (starch) were mixed together to obtain mixtures with C/O molar ratios equal to 0.4–1.2. The mixtures were reduced non-isothermally in nitrogen atmosphere up to 1003 K or 1373 K. Up to 1003 K, the volatiles released from CMs and starch reduced hematite by 18–35%. Between 1003 K and 1373 K, both hydrochars (produced from lemon peels and rice husks) reacted with iron oxides more rapidly than anthracite below 1360 K, when the samples had C/O ratios in the range of 1.0–1.2. In this temperature range, rice husk hydrochar promoted a slower reaction with iron oxides than lemon peel hydrochar, which was possibly influenced by its higher ash content which decreased the rate of Boudouard reaction. Samples with C/O ≥ 1.0 achieved complete reduction at 1373 K, regardless of the type of CM used, whereas samples with C/O equal to 0.4–0.5 achieved 63–86% reduction. It can be concluded from this study that hydrochar can fully substitute anthracite for direct reduction of iron oxide to decrease fossil CO2 emissions during ironmaking processes.

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Isothermal Reduction Kinetics of the Mixture of Iron Carbon Agglomerates and Sinter

Jiwei Bao, Mansheng Chu, Jue Tang, Lifeng Zhang

pp. 988-999

DOI:

10.2355/isijinternational.ISIJINT-2023-448

抄録

The effect of iron carbon agglomerates (ICA) on the reduction of sinter is very important to blast furnace (BF) ironmaking. In this paper, the isothermal reduction kinetics of ICA-sinters mixture and the coupling synergistic mechanism between ICA and sinter are comprehensively studied. The results show that the early stage of isothermal reduction of ICA-sinters mixture is jointly controlled by the interfacial chemical reactions of FeO being reduced to Fe in sinter and gasification reaction in ICA, and the later stage is controlled by the internal diffusion. As the reactivity of ICA improves from 52.81% to 69.71%, the isothermal reduction reaction activation energy of ICA-sinters mixture decreases from 84.22 to 72.58 kJ/mol in early stage and decreases from 110.78 to 97.41 kJ/mol in late stage. Meanwhile, the activation energy of isothermal reduction reaction for the mixture of ICA and sinter with a higher reducibility is lower. There is a coupling synergistic effect between ICA and sinters, and ICA plays a continuous role in circulating CO and transferring oxygen during the reduction of sinter, which can significantly promote the reduction of iron oxides in sinter. The synergistic effect gradually increases with the improvement of the reactivity of ICA and the reducibility of sinter.

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Effect of Rare Earth La–Ce on Solidification Structure of 3.2%Si-0.9%Al Non-oriented Silicon Steel

Cheng Song, Li Xiang, Chao Shi, Jialong Qiao, Jianfeng Liu, Shengtao Qiu

pp. 1000-1009

DOI:

10.2355/isijinternational.ISIJINT-2023-394

抄録

The effect of rare earth on the solidification structure of 3.2%Si-0.9%Al non-oriented silicon steel was investigated using industrial trials. The outputs demonstrated that increasing rare earth content leads to a decrease in the average size of equiaxed crystals in the casting billets. In order to further understand the rare earth on the grain refinement of δ-ferrite, the conventional inclusion detection technology, was used to investigate the distribution characteristics of inclusions, together with theoretical calculation of the equilibrium partition coefficients, pinning forces and mismatch degrees. The detection results of inclusions and the calculation results of pinning force showed that the effect of rare earth on the pinning force of inclusions was marginal. Thermodynamic calculation indicated that Ce addition had negligible effect on the equilibrium partition coefficient of Si, Al and Mn. Combined with the calculation results of GRF model, it is reasonable to consider that the contribution of rare earth element to the refinement of equiaxed crystals can be ignored. Further, the outcomes obtained from the E2EM model calculations revealed that the principal mechanism responsible for the refinement of equiaxed crystals through rare earth treatment can be attributed to the heterogeneous nucleation effect of (La, Ce)2O2S.

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Effect of Submerged Entry Nozzle Structure on Fluid Flow, Slag Entrainment, and Solidification Process in a Slab Continuous Casting Mold

Rui Xu, Haitao Ling, Xiang Tian, Lei Ren, Lizhong Chang, Shengtao Qiu

pp. 1010-1018

DOI:

10.2355/isijinternational.ISIJINT-2023-407

抄録

The fluid flow and slag entrainment in a slab continuous casting mold were investigated by establishing a full-scale water model. Meanwhile, the heat transfer and solidification process of liquid steel in the mold were studied through numerical simulation. The effect of two different submerged entry nozzles (SENs) was compared and analyzed, named as original SEN and L1 SEN, respectively. The results indicate that the structure of the SEN has a significant influence on the fluid flow pattern and solidification process in the slab mold. For the original SEN, the liquid level in the mold fluctuated obviously and the slag phase was easily entrained into the mold. The percentage of ±3 mm level fluctuation was 57.2–74.3%. By enlarging the exit size, the L1 SEN considerably reduced the jet velocity at the nozzle exit and subsequently decreased the surface velocity at the top surface. The level fluctuation and slag entrainment in the mold have been effectively controlled. The percentage of ±3 mm level fluctuation was increased to 91.7–98.6%. Furthermore, under the condition of L1 SEN, the thickness of the solidifying shell at the mold outlet was increased from 13.5 mm to 16.4 mm, which was beneficial to decrease the risk of breakouts and quality problems.

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RDDPA: Real-time Defect Detection via Pruning Algorithm on Steel Surface

Kun Lu, Xuejuan Pan, Chunfeng Mi, Wenyan Wang, Jun Zhang, Peng Chen, Bing Wang

pp. 1019-1028

DOI:

10.2355/isijinternational.ISIJINT-2023-360

抄録

Real-time object detectors deployed on general-purpose graphics processing units (GPUs) or embedded devices allow their mass usage in industrial applications at an affordable cost. However, existing state-of-the-art object detectors are difficult to meet the requirements of high accuracy and low inference latency simultaneously in industrial applications on general-purpose devices. In this work, we propose RDDPA, a fast and accurate defect detection framework. RDDPA adopts a novel end-to-end pruning scheme, which can prune the detection network from scratch and achieve real-time detection on general-purpose devices. Additionally, we have developed a new training scheme to minimize the accuracy loss associated with the pruning process. Experimental results on a standard steel surface defect dataset indicate that our model achieves 79.2% mAP (mean Average Precision) at 103.7 FPS (Frames Per Second) on a single mid-end Titan X GPU as well as 40.1 FPS on a single low-end GTX 960M GPU, and outperforms the state-of-the-art defect detectors by about 20× speedup with considerable or higher accuracy.

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Assessing the Banding Degree of Martensite in the Bainite Matrix through EPMA

Yang Meng, Chunlian Yan, Juan Wen, Xinhua Ju

pp. 1029-1036

DOI:

10.2355/isijinternational.ISIJINT-2023-333

抄録

Due to the difficulty of distinguishing the grain boundaries between martensite and bainite in fast-cooling microstructures, few good methods were reported to accurately assess the banding degree of martensite or bainite. In present work, a novel method has been developed to meet this challenge. The hot rolled bars of drill steel 23CrMoNi, which had martensite bands distributed in the bainite matrix, were used in this research. The banded structure in this hot rolled 23CrMoNi was closely related to the segregation of the alloying elements such as Cr, Ni and Mo. These alloying element mappings were first acquired by electron probe micro analyzer (EPMA). A new data processing method was developed to correlate the segregated element mapping with the banded structure. The banding assessment was conducted on the processed binary images of element mappings according to ASTM E1268-19. This method was well verified by assessing the banded pearlite in the ferrite matrix, whose banding degree can be easily accessed through microstructure difference. It was shown from the quantitative analysis results of the hot rolled 23CrMoNi that the banded distribution of martensite was greatly optimized by the adjustment of hot rolling process.

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Efficient Finite Element Simulation of Cold Rolled Strip Coiling Process Considering Additional Contact Deformation between Layers

Meng Dai, Shujie Liang, Ping Qiu, Hong Xiao

pp. 1037-1046

DOI:

10.2355/isijinternational.ISIJINT-2023-405

抄録

When analyzing the strip coiling process, the finite element (FE) method is closer to the actual working conditions compared to the analytical method. However, due to the large number of strip elements and contact elements, it often leads to problems such as long-time consumption and non-convergence. Meanwhile, traditional FE methods are still unable to solve the problem of additional contact deformation between layers. Therefore, in order to overcome the shortcomings of the above methods, the FE software MSC Marc is used to establish a strip coiling model. The distribution pattern of interlayer friction and contact stress are analyzed to propose a new step-by-step bonding FE model, which greatly reduces the computing time. Through laminated compression experiments, the variation curve between additional contact deformation and pressure is obtained. The curve is introduced into the gasket elements to consider the additional contact deformation between the layers, and the effect of additional contact deformation between the layers on the stress of the coil and the pressure on the mandrel is studied. Finally, the analytical solution is compared with the FE solution proposed in this paper, and the errors generated by the analytical method are analyzed.

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Effect of Nano-sized Cu-Rich Phase on Microbiological Corrosion Behavior of Cu and Ni-Added Steel for Oil Country Tubular Goods

Xianbo Shi, Yunpeng Zeng, Yi Ren, Wei Yan, Xu Yang, Guanghui Wu, Yiyin Shan, Ke Yang

pp. 1047-1056

DOI:

10.2355/isijinternational.ISIJINT-2023-445

抄録

The Cu-bearing antibacterial low-alloyed steel pipe is a new strategy to mitigate microbiologically influenced corrosion (MIC) for oil and gas industry. It can effectively alleviate the occurrence of bacterial corrosion, but cannot avoid the MIC totally. To enhance the resistance to MIC of Cu-bearing low-alloyed steel, the MIC behavior of a Cu and Ni-added experimental steel with different nano-sized Cu-rich precipitates was investigated. Results showed that the synergistic effect of antibacterial ability of nano-sized Cu-rich precipitates and protective Cu–Ni enrichment layer formed on the steel surface contributed to the good MIC resistance. Although the Cu-rich precipitates possessed antibacterial actively, they also increased the surface potential difference simultaneously, resulting in promoting MIC. The extremely fine and dispersed Cu-rich precipitates with high-density was the preferred microstructure to achieve better MIC resistance for the steel.

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Hydrogen Trapping and Precipitation of Alloy Carbides in Molybdenum Added Steels and Vanadium Added Steels

Shunsuke Taniguchi, Miyuri Kameya, Yukiko Kobayashi, Kazuma Ito, Shingo Yamasaki

pp. 1057-1066

DOI:

10.2355/isijinternational.ISIJINT-2024-031

抄録

Martensitic steels of Fe-0.1%C-2%Mn-1.6%Mo and Fe-0.1%C-2%Mn-0.2%V alloys were subjected to tempering at 873 K to investigate the hydrogen trapping of Mo and V carbides. We analyzed the alloy carbides in detail via atomic-resolution scanning transmission electron microscopy and atom probe tomography, and evaluated hydrogen trapping energy via ab initio calculations. The hydrogen content of the Mo-added steel tempered for 1.8 ks increased from that of the quenched Mo-added steel, and the hydrogen content monotonically decreased as the tempering time increased. The hydrogen content of the V-added steels increased during tempering up to 7.2 ks and then remained almost constant. A plate-shaped B1-type Mo carbide with a chemical composition of MoC0.50 precipitated in the Mo-added steel tempered for 3.6 ks. Needle-shaped HCP Mo2C precipitated and the B1-type Mo carbide decreased in the Mo-added steel tempered for 14.4 ks. A plate-shaped B1-type V carbide with a chemical composition of VC0.75 precipitated in the V-added steel tempered for 14.4 ks. We found a positive correlation between the hydrogen content and the product of the interface area and the carbon vacancy fraction of the B1-type alloy carbide. The hydrogen trapping energy of the carbon vacancy at the interface between BCC-Fe and the B1-type Mo carbide was higher than that of the interstitial sites in BCC-Fe. These results suggest that the main trapping site in the tempered Mo-added steel was the carbon vacancy at the interface of B1-type MoC0.50, not HCP Mo2C.

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Dependence of Mechanical Properties and Deformation Behavior of TRIP-FeMnCoCrAl Dual-phase High-entropy Alloy on Grain Size and Strain Rate

Jie Li, Bo Zhang, Lichong Niu, Minghe Zhang, Yunli Feng

pp. 1067-1077

DOI:

10.2355/isijinternational.ISIJINT-2023-451

抄録

Fe50Mn30Co10Cr10 dual-phase metastable high-entropy alloys (HEAS) have gained significant attention for their outstanding mechanical properties. However, limited research has explored the relationship between grain size and strain rate sensitivity (SRS) in dual-phase HEAS. Current investigations primarily focus on pure metals and single-phase FCC HEAS. To address this gap, this study examines the impact of grain size on the deformation behavior and SRS of TRIP-(Fe50Mn30Co10Cr10)97Al3 dual-phase HEAS. Two variants of dual-phase HEAS were prepared, distinguished by their grain sizes (2.86 µm, labeled Fine Grain or FG, and 5.25 µm, termed Coarse Grain or CG), via the vacuum melting method. Subsequent tensile tests were conducted at varying strain rates, ranging from 0.001/s to 0.02/s. The findings unveil a robust grain size dependency in the phase transformation and deformation twinning of the (Fe50Mn30Co10Cr10)97Al3 dual-phase HEA during tensile deformation. Within the FeMnCoCrAl HEA system, characterized by a dual-phase structure, both TRIP (Transformation-Induced Plasticity) and TWIP (Twinning-Induced Plasticity) effects intensify with increasing grain size. Additionally, as the strain rate increases, the TRIP effect gradually diminishes while the TWIP effect strengthens. Notably, the strain rate sensitivity index ‘m’ exhibits a downward trend with an increase in grain size, distinguishing it from the behavior observed in single-phase FCC HEAS. This study conducts an in-depth analysis of grain size’s impact on the SRS of (Fe50Mn30Co10Cr10)97Al3 dual-phase HEA, scrutinizing micro-level aspects encompassing phase transformation, deformation twinning, and grain boundary slip. The findings provide essential theoretical insights for designing HEAS tailored for applications requiring high strain rates.

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Effect of Rolling and Alloying Elements on the Impact Properties of Hypereutectoid Steels

Toko Tokunaga, Yoritoshi Minamino, Koji Yamamoto, Toshiyuki Sugimoto, Koji Hagihara

pp. 1078-1088

DOI:

10.2355/isijinternational.ISIJINT-2023-453

抄録

In this study, to develop steel with high strength and ductility, steels are designed based on JIS-SUJ2 hypereutectoid steel by controlling the contents of the alloying elements Cr and Mn. The steels are subjected to two types of specially designed heat treatment, i.e., “grain boundary amelioration (GBA)” treatment, with and without rolling. The effects of the alloy type and rolling on the microstructure and impact properties are investigated. High impact values over 50 J/cm2 were achieved compared to those of conventional steels by the significant refinement of γ grains with GBA treatment. All the steels exhibit transgranular fracture, and no intergranular fracture was observed. This indicates that the proposed heat treatment achieved the suppression of intergranular fracture by inhibiting the formation of θ particles on the grain boundaries and by refining the prior γ grains. Moreover, it has been suggested that the impact values were strongly affected by the C content in the matrix which is controlled by the alloying element and by the heat treatment. As the C content increases, hardness and fraction of the retained γ phase increase, which leads to the decrease in impact value. In samples where prior γ grains were extremely fine and θ particles were fine, area fraction and circularity of the θ particles did not have a significant effect on the impact values.

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Effect of Glycerol Mechanical Excitation on the Phase Evolution and Hydration Activity of Steel Slag

Peng Yao Liu, Jun Guo Li, Guo Peng Li, Meng Jie Tao, Xi Zhang, Shuai Chao, Ya Ling Zhang, Yi Ming Duan, Xin Ning, Chong Yu Niu, Guo Zhang Tang

pp. 1089-1100

DOI:

10.2355/isijinternational.ISIJINT-2023-424

抄録

During the slow cooling process of steel slag, the crystals of inert mineral phases (C2F, RO phases) and active mineral phases (C2S, C3S) adhere and grow, and the irregular interlocking, embedding, filling, stacking, and coating between mineral phases seriously affect the hydration activity of active mineral phases in steel slag. Therefore, this article selects glycerol (C3H8O3) as a grinding aid to mechanically excite steel slag, exploring the mineral phase evolution and hydration activity excitation mechanism of steel slag under different process parameters. C3H8O3 mechanical excitation refined the steel slag particles, increased porosity, increased specific surface area, and caused peeling behavior between the rough surface active mineral phases (C2S, C3S) of the steel slag particles and the smooth surface inert mineral phase C2F with sharp angular protrusions. When the addition amount of C3H8O3 is 0.24 wt% and the ball milling time is 90 minutes, the mechanical excitation effect of steel slag is the best. The total mass fraction of C2S and C3S increases by 14.3 wt%, while the mass fraction of C2F decreases by 19.3 wt%. The mechanical excitation of C3H8O3 can cause the steel slag to germinate cracks at the interface of each phase, and a porous honeycomb structure composed of calcium hydroxide (CH) and calcium silicon hydrogel (C-S-H) appears during the hydration process, producing a large number of acicular ettringite (AFt), effectively improving the early hydration activity of steel slag.

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Kinetics Analysis of Iron Oxide Reduction by Solid Carbon in HIsmelt Ironmaking Slag

Zhenyang Wang, Ruishuai Si, Jing Pang, Jixiang Han, Wei Ren, Ziluo Chen, Jianliang Zhang, Shushi Zhang, Dewen Jiang, Song Zhang

pp. 1101-1105

DOI:

10.2355/isijinternational.ISIJINT-2023-306

抄録

The HIsmelt process is a new molten reduction ironmaking technology with lower energy consumption and carbon emissions than the traditional blast furnace ironmaking route. In the HIsmelt smelting process, the reaction process between solid carbon and iron-bearing slag has its own characteristics. To investigate the kinetic mechanism of iron oxide reduction in slag, the degree of conversion was characterized by measuring the change of CO content of the generated gas during the experiments and analyzed by combining the model fitting method. The experimental results showed the highest agreement with the Avrami-Erofeev equation. The rate-controlling mechanism for the reduction of iron oxides in the slag was judged to be the random nucleation and subsequent growth of the products. In the study, the rate-controlling mechanism and the kinetic parameters of the reduction reaction of iron oxide in slag have been obtained.

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