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ISIJ International Vol. 63 (2023), No. 1

ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559
Publisher: The Iron and Steel Institute of Japan

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  1. Vol. 64 (2024)

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ISIJ International Vol. 63 (2023), No. 1

Effect of SiO2 Content and Mass Ratio of CaO to Al2O3 on the Viscosity and Structure of CaO–Al2O3–B2O3–SiO2 Slags

Yongpeng Wen, Qifeng Shu, Yong Lin, Timo Fabritius

pp. 1-9

DOI:

10.2355/isijinternational.ISIJINT-2022-288

Abstract

The development of mold fluxes for continuous casting is one of major challenges to produce high aluminum steel. The CaO–Al2O3–B2O3 based mold flux is one of the potential candidates for casting high aluminum steel but its composition and properties still need to be optimized. In this work, the effect of silica and mass ratio of CaO to Al2O3 on the viscosity and structure of slag are studied. The viscosity of CaO–Al2O3–B2O3–SiO2 slag with varying SiO2 content (3%, 5%, and 7%) and mass ratio of CaO to Al2O3 (0.8, 1, and 1.2) were measured by rotating cylinder method at temperatures between 1723 K and 1873 K. It was found that the addition of SiO2 leads to the increase of the slag viscosity and the activation energy increases from 178.6 to 203.4 kJ/mol. In contrast, the increase of mass ratio of CaO to Al2O3 will reduce the viscosity of slag and the activation energy decreases from 227.1 to 191.0 kJ/mol. The structures of glassy CaO–Al2O3–B2O3–SiO2 slags were investigated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Deconvolutions on Raman spectral reveal that silicon mainly exists as Q0(Si) and Q1(Si) in glasses. According to deconvolution results of XPS, as SiO2 content in glassy slag increases, the number of bridging oxygens increases, indicating a more polymerized structure. In contrast, the increase of the ratio of CaO to Al2O3 contributes to the depolymerization of glassy slag. The structural variations with different SiO2 contents and mass ratio of CaO to Al2O3 can be correlated to the viscosity variation of slag.

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Effect of SiO2 Content and Mass Ratio of CaO to Al2O3 on the Viscosity and Structure of CaO–Al2O3–B2O3–SiO2 Slags

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Decarburization Kinetics of Fe–C Melt with CO2–O2 Mixed Gas by Isotope Tracing Method

Yuewen Fan, Xiaojun Hu, Hiroyuki Matsuura, Kuochih Chou

pp. 10-19

DOI:

10.2355/isijinternational.ISIJINT-2022-321

Abstract

The partial substitution of O2 with CO2 in steelmaking process is an important technology to reduce CO2 emission and recycle. In order to improve CO2–O2 decarburization utilization, the decarburization kinetics of Fe–C melt with CO2–O2 mixed gas have been studied using 13CO2–18O2 dual isotope tracing method and established the decarburization kinetic model. The results show that less than 40% of the oxygen is partially replaced by CO2, which improves the O2 utilization involved in the decarburization reaction and the CO2 utilization is still more than 80%. For the rate limiting steps, regarding O2, it is governed by the mixed control mechanism involving gas-phase mass transfer and interfacial chemical reaction; regarding CO2, with the increase of CO2 partial pressure, the rate limiting step changes from the mixed control to gas-phase mass transfer control only. As bath temperature increase from 1723 to 1873 K, the overall decarburization rate increases; bath temperature mainly affects O2 decarburization rates, whereas, the rates of CO2 are not significantly affected. The apparent activation energy of CO2–O2 mixed gas decarburization is 21.5 kJ·mol−1.

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Decarburization Kinetics of Fe–C Melt with CO2–O2 Mixed Gas by Isotope Tracing Method

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Phase Equilibria in High Phosphate-Containing Slag without CaO Saturation at Elevated Temperature

Yu-ichi Uchida, Chiho Watanabe, Masakatsu Hasegawa

pp. 20-29

DOI:

10.2355/isijinternational.ISIJINT-2022-344

Abstract

Japan relies on imports for almost the entire amount of phosphorus, which is indispensable for human life and industrial materials. Therefore it is required to recover phosphorus from dephosphorization slag and sewage sludge which are promising unutilized phosphorus resources. Aiming wholesale recovery of phosphorus from the slag and sludge, a fundamental study on condensation of phosphorus in solid phase through high temperature phase separation was carried out. The experiments at 1573 K on principal [CaO–SiO2–P2O5] ternary model sample and Al2O3 and Fe2O3 added therein showed unsaturation with CaO and precipitation of solid 3CaO·P2O5 as the phosphorus-concentrated phase in all the sample. The contamination of the other components in 3CaO·P2O5 was low, especially less than 1 mass% for Al2O3 added samples. The liquid phase was also formed with Al2O3 or Fe2O3 addition, and the liquidus composition in quaternary samples were consistent with those appeared in [CaO–SiO2–Fe2O3] and [CaO–SiO2–Al2O3] ternary diagram. P2O5 content in the quaternary liquid phases were lower in Al2O3 added samples than those in Fe2O3 added samples. Such difference was discussed in terms of optical basicity and CaO activity for liquid phase. Due to the coexistence of solid SiO2 phase at Fe2O3 addition, the SiO2 content in liquid phase became lower compared to Al2O3 addition, and led to higher optical basicity, which would allow higher P2O5 capacity in liquid phase. These considerations strongly suggest that an effective control of composition would be key technology for the phosphorus recovery through condensation and separation of phosphorus concentrated phase.

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Phase Equilibria in High Phosphate-Containing Slag without CaO Saturation at Elevated Temperature

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Preparation and Characterization of Al2O3-loaded Deacidification Agents for Blast Furnace Gas

Shu-hua Geng, Xin-qing Zou, Hui Dong, Zhu-ming Chen, Ming Zhang, Xing-li Zou, Yu-wen Zhang, Xiong-gang Lu

pp. 30-41

DOI:

10.2355/isijinternational.ISIJINT-2022-218

Abstract

A deacidification agent was prepared through incipient-wetness impregnation method, by using activated γ-Al2O3 as the carrier material to loaded Na2CO3, which can simultaneously remove HCl, H2S and carbonyl sulfur (COS) from blast furnace gas. The pretreatment at temperature of 550°C can improve the dechlorination performance. The maximum breakthrough time, penetration chlorine capacity, and the highest utilization rate of active component of deacidification agents were 47.5 h, 11.59%, and 75.6%, respectively. The deacidification agents can not only be used as active component to remove H2S from blast furnace gas, but also can act as a COS hydrolysis catalyst. HCl has no obvious effect on the desulfurization performance, while the sulfide gases inhibited the dechlorination process. The synergistic desulfurization and dechlorination experiment results show that the highest removal efficiencies for HCl, H2S and COS by the prepared deacidification agents were all above 99%.

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Preparation and Characterization of Al2O3-loaded Deacidification Agents for Blast Furnace Gas

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Experimental and Modeling Study on Reduction and Heat Transfer Characteristics of Single Iron Ore Pellet in H2/CO Atmospheres

Zhongjie Shen, Shuang Sun, Jianliang Xu, Qinfeng Liang, Haifeng Liu

pp. 42-53

DOI:

10.2355/isijinternational.ISIJINT-2022-280

Abstract

Experimental and modeling study was carried out for the reduction of single iron ore pellet in the H2/CO atmosphere with considering the porosity evolution and heat transfer characteristics of product layer, reaction layer, and unreacted layer. A mathematical model was proposed and validated with a good match to the experimental data. The experimental results showed that both porosity and effective diffusion coefficient increased with the reduction time, temperature, and H2 content in the gas mixtures. With the increase of temperature, the pore size presented multi-level distribution characteristics. Adding 20 vol.% CO in H2 as a threshold value (H2/CO = 8:2) proved to achieve higher reduction degree than other conditions. It was found that the addition of CO in H2 increased the temperature of the reaction layer by about 10 to 27°C higher than the initial temperature. Temperature profiles and temperature difference evolution of these three layers inside the pellet presented a first decrease, where the reduction degree was about 0.3, and then an increase during the reduction process. With more CO participated in the reaction, a delayed high-temperature reaction layer was presented from extra heat supply of CO reduction, owing to the low diffusion rate. The radiation heat was dominant for the heat transfer between the environment and iron ore pellet, while inside the pellet heat flux changed among three layers and verified with the temperature and gas atmosphere.

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Experimental and Modeling Study on Reduction and Heat Transfer Characteristics of Single Iron Ore Pellet in H2/CO Atmospheres

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Soft Sensors and Diagnostic Models Using Real Time Data of Blast Furnaces at Tata Steel

Adity Ganguly, Kanak Das, Goutam Kumar Raut, A Srinivasa Reddy

pp. 54-62

DOI:

10.2355/isijinternational.ISIJINT-2022-246

Abstract

A huge amount of real time data of blast furnace process and quality are getting captured and analyzed for an in-depth understanding of phenomena resulting in better control and improved performance. This paper describes how process visualization and diagnostic models are helping to generate additional insights and becoming useful tool for identification of factors for process efficiency improvement. These tools are important enabler for faster process performance diagnosis and for early indicator of performance deterioration. In earlier paper of this journal, few models and their usage in process analysis were discussed and, in this document, additional diagnostic tools viz. burden descent index, sounding ore by coke etc. are explained.10)

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Soft Sensors and Diagnostic Models Using Real Time Data of Blast Furnaces at Tata Steel

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Effect of Converter Dust on Phosphorus Migration Behavior in Molten Iron

Chaogang Zhou, Qinggong Chen, Yi Ji, Shuhuan Wang, Dingguo Zhao, Liqun Ai, Dongsheng Shi, Xiangdong Shi

pp. 63-73

DOI:

10.2355/isijinternational.ISIJINT-2022-249

Abstract

In order to make better use of converter dust to achieve effective pre-dephosphorization of molten iron, the influence of the addition ratio of dedusting ash and oxide scale on dephosphorization of molten iron was compared, so as to reveal the reasons for the decrease of dephosphorization rate caused by dust. Through theoretical analysis, XRD, SEM-EDS, Raman and infrared spectroscopy, the influence of mineral phase structure, polymerization degree and phosphorus structure of pre-dephosphorization final slag on pre-dephosphorization was studied. The results show that when the proportion of dedusting ash in the oxidant increases from 0 to 25%, the dephosphorization rate decreases from 50.8% to 38.71%, and the dephosphorization rate increases to 50% after adding fluorite. The increase in the proportion of dedusting ash will lead to the decrease of phosphorus-rich phase and the increase of RO phase and iron-rich phase, which will affect the dephosphorization effect. When the dedusting ash ratio increased from 0% to 25%, the proportion of Q0(Si), Q0(P), Q1(P) and [FeO6]9− structures in the pre-dephosphorization final slag increased, which was beneficial to the diffusion in the slag, but unfavorable to the migration of phosphorus. In addition, by adding fluorite in the experiment with 25% dedusting ash, it was found that the molar fractions of Q1(Si), Q3(Si), Q0(P) and Q2(P) in the pre-dephosphorization final slag increased, and the phosphorus migrating into the silicon-oxygen network structure gradually increased. This study can provide reference for iron and steel enterprises to realize the secondary utilization of dedusting ash.

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Effect of Converter Dust on Phosphorus Migration Behavior in Molten Iron

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Effect of Converter Shape on Reaction Rate between Slag and Metal in a Combined Blowing Converter with Inert Gas Bottom Blowing

Hironori Yoshida, Shota Amano, Yoshie Nakai, Yukio Takahashi, Naoki Kikuchi

pp. 74-82

DOI:

10.2355/isijinternational.ISIJINT-2022-334

Abstract

The peroxidation of molten steel is a problem that occurred in a combined blowing converter with inert gas bottom blowing. It was caused by the relatively weak stirring power of the bottom blown inert gas compared with that of bottom blown oxygen gas. Although several methods for optimizing the combined blowing conditions have been developed in an attempt to resolve this problem, the effect of equipment conditions such as the converter shape on metallurgical characteristics has not been investigated sufficiently. In this study, the effect of H/D (ratio of bath depth H to bath diameter D) on the reaction rate between slag and metal and furnace body vibration was investigated by water model experiments. It was found that the apparent reaction rate constant kA/Vw increased with increasing H/D, except for the case of H/D = 0.85. The change of kA/Vw with increasing H/D appeared to be related to water bath vibration behavior. An analysis based on a bath surface vibration model indicated that the change of H/D affects bath surface vibration behavior and slag emulsion formation behavior, and these effects increase the reaction interface between the slag and the metal.

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Effect of Converter Shape on Reaction Rate between Slag and Metal in a Combined Blowing Converter with Inert Gas Bottom Blowing

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Natural Convection on Dendrite Morphology: A High–performance Phase–field Lattice Boltzmann Study

Tomohiro Takaki, Shinji Sakane, Takayuki Aoki

pp. 83-90

DOI:

10.2355/isijinternational.ISIJINT-2022-146

Abstract

Numerical study on the effect of liquid flow on three-dimensional dendrite growth is still a challenging topic. Herein, high-performance phase–field lattice Boltzmann (PF-LB) simulations were performed to investigate the effect of natural convection on dendrite morphology and the possibility for causing fragmentation. Parallel computing in multiple graphics processing units (GPUs) with dynamic load balancing for the block-structured adaptive mesh refinement (AMR) scheme (parallel-GPU AMR) was applied to the PF-LB simulations as a high-performance computing tool in a GPU supercomputer. Parallel-GPU AMR PF-LB simulations showed that the growth of dendrites with natural convection in two and three dimensions were quite different. The dendrite tip velocity increased in the following order: upward buoyancy, no gravity, and downward buoyancy. Downward and upward buoyancy enhanced and restricted the growth of the secondary arms, respectively. The root size of the secondary arms growing from the bottom was drastically affected by the flow direction. However, the dendrite fragmentations were not observed in the present simulations.

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Natural Convection on Dendrite Morphology: A High–performance Phase–field Lattice Boltzmann Study

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Application of Mean Age Theory in Multi-strand Tundish

Dong-Yuan Sheng

pp. 91-101

DOI:

10.2355/isijinternational.ISIJINT-2022-286

Abstract

The mean age theory has recently been used to analyze the mixing efficiency in a single-strand tundish. The spatial distribution of the mean age was obtained by using a steady-state calculation. By applying the new theory of mean age, the computing cost was two orders of magnitude lower than when using the conventional theory of residence time distribution (RTD). This study aimed at extending the application of the mean age theory to a multi-strand tundish. Theoretical relations between the mean age and RTD were analyzed and compared for the tundish applications. A new criterion, the standard deviation of flow-weighted mean age at the multiple outlets, was applied focusing on the consistency of the flow in the multi-strand tundish. A five-strand tundish was selected as a benchmark case. The feasibility of applying the mean age theory in the multi-strand tundish was confirmed through the benchmarking results. Thus, the proposed method can be adopted as an effective tool in finding the optimal geometry of multi-strand tundish equipped with flow control devices (FCD).

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Application of Mean Age Theory in Multi-strand Tundish

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Effect of Uneven Distribution of Material Property on Buckling Behavior of Strip during Hot Finishing Rolling

Chao Liu, Hairui Wu, Anrui He, Fengwei Jing, Wenquan Sun, Jian Shao, Chihuan Yao

pp. 102-110

DOI:

10.2355/isijinternational.ISIJINT-2022-221

Abstract

Unlike traditional austenitic rolling, there is phase transformation during hot finishing rolling for thin gauge and high strength steel or non-oriented electrical steel. The transverse differences of temperature and asynchronous phase transformation result in uneven distribution of material property of rolled strip, further change the buckling behavior of strip during hot finishing rolling. By replacing the elastic modulus constant in the traditional buckling model with the distribution function of tangent modulus obtained by multiphase compression experiments and multifield coupling simulation, the effect of uneven distribution of material property on the critical buckling stress and buckling wave length are analyzed. The results show that for the global longitudinal wave, the critical buckling stress at the exit of stand is greater than that at the entry. But the opposite is true for the local longitudinal wave. Under the effect of uneven distribution of material property, the critical buckling stress and buckling wavelength of global and local center waves change little. The critical buckling stress of global edge wave is almost unchanged, but the buckling wavelength decreases slightly. The critical buckling stress and buckling wavelength of local edge wave are reduced obviously, and the buckling wavelength is decreased by about 10%. It means that the existence of soft ferrite at the strip edge easily makes the wave mode develop to “fragmented edge wave”, which is consistent with the actual phenomenon.

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Effect of Uneven Distribution of Material Property on Buckling Behavior of Strip during Hot Finishing Rolling

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Analytical Model to Predict the Free Surface Profile of Outgoing Material in Oval-to-round Pass Rolling when Cross-section of Incoming Material is not Circular and Roll Gap Changes

Chang Ho Moon, Youngseog Lee

pp. 111-119

DOI:

10.2355/isijinternational.ISIJINT-2022-248

Abstract

There is a strong demand for the development of an analytical model that is necessary to quickly perform the roll pass design of hot rod (or bar) rolling process. In line with this, this study proposes an analytical model that predicts the free surface profile (FSP) of outgoing material in oval–to–round pass rolling sequence even when the cross-section of incoming material is not circular and roll gap changes. The separation angle and point were calculated by interpolating the intersection angle and the groove angle. FSP passing through the maximum spread of outgoing material and the separation point is calculated based on a weighting function depending on the geometry of incoming cross-section and roll groove. The performance of the proposed model was verified by finite element analysis that simulated 10-pass continuous bar rolling process. FSPs predicted by the analytical model and those by FE simulation were in good agreement. In addition, the proposed analytical model was applied to other 4-pass continuous rolling. It has been shown that it is possible to quickly calculate the amount of roll gap adjustment in each pass that improves the roundness of the material (from 83.57 to 98.65) in the final pass without the time-consuming FE analysis.

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Analytical Model to Predict the Free Surface Profile of Outgoing Material in Oval-to-round Pass Rolling when Cross-section of Incoming Material is not Circular and Roll Gap Changes

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Laser Cladding Strengthening Test on the Surface of Flatness Rollers

Shuai Zhang, Huaxin Yu, Shan Li, Shuang Liao, Tongyuan Zhang, Hongmin Liu

pp. 120-127

DOI:

10.2355/isijinternational.ISIJINT-2022-262

Abstract

Contact-type flatness meters are the key detection equipment in the production of high-end cold-rolled thin strips. The surface performance of a flatness meter roller is very important to improve its service life and ensure the surface quality of strip products. To improve the surface wear resistance and prolong the service life of a seamless flatness meter roller, it was subjected to a surface strengthening treatment by laser cladding an Fe-based wear-resistant alloy. The performance of the flatness meter roller strengthened by laser cladding and quenching was determined by tests. The results show that the laser cladding-strengthened layer forms a solid metallurgical bond with the roller matrix. When the laser cladding-strengthened surface meets the surface strength, hardness and thickness requirements of the cladding-strengthened layer, the average width of wear marks in the 30-minute sliding friction wear test is only 1.43 mm. The wear resistance of the cladding-strengthened layer is approximately 24% higher than that of the quenching-strengthened layer. This paper proposes a new approach for the research and development of the surface strengthening technology of cold-rolled strip seamless flatness meter rollers.

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Laser Cladding Strengthening Test on the Surface of Flatness Rollers

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Comparison of Fatigue Crack Propagation Behavior of Additive-Manufactured Zero Thermal Expansion Alloy with Forged and Casted Materials

Toshihiro Shimizu, Hiromasa Ikuta, Tatsuya Kato, Toshiharu Tanaka, Nobuyuki Oyama, Mitsuki Asahina, Yuji Hasumi, Yuki Nakamura

pp. 128-134

DOI:

10.2355/isijinternational.ISIJINT-2022-243

Abstract

This study examined the fatigue crack propagation (FCP) behavior of three kinds of zero thermal expansion (ZTE) alloys. The specimens were manufactured by one of three processes, (casting, forging, and laser additive manufacturing: selective laser melting (SLM)). The FCP rates in the casted alloy were similar to SS400, which was used for comparison. In the SLM product, the FCP rates were higher than the casted alloy and slightly higher than forged alloy, particularly in the low ΔK region. The fracture surfaces were examined by scanning electron microscopy. A rough crack surface was observed in the casted alloy, but small marks along the crack propagation direction were observed in the SLM specimen. The crack opening load was measured to estimate the FCP behavior and consider the effective stress intensity factor range. In an evaluation by the effective stress intensity factor range, the FCP rates of the specimens produced using the three manufacturing processes were similar. Overall, the ZTE alloy manufactured by SLM showed good FCP behavior compared to the forged alloy. The difference in the results between the two products was attributed to the difference in the fracture surface due to the different microstructures.

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Comparison of Fatigue Crack Propagation Behavior of Additive-Manufactured Zero Thermal Expansion Alloy with Forged and Casted Materials

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Fatigue Behavior of Resistance Spot Welded Steel Sheets Fabricated Using Electrodes with Different Tip Diameters

Yoshihiko Uematsu, Nao Kawabe, Yasuaki Okita, Hiroshi Matsuda, Toshifumi Kakiuchi, Takumi Igarashi

pp. 135-142

DOI:

10.2355/isijinternational.ISIJINT-2022-278

Abstract

Tensile shear test specimens were fabricated by a resistance spot welding (RSW) procedure using electrodes with two different tip diameters. The tip diameter was changed to adjust the corona bond length with keeping the nugget sizes the same. Furthermore, the nugget sizes were changed by controlling the welding process parameters, resulting in the nugget sizes of 3√t, 4√t and 4.7√t, where t was the sheet thickness. Microstructural analyses revealed that the corona bond length increased with increasing tip diameter at a given nugget size. Subsequently, tensile shear static and fatigue tests were conducted to investigate the effects of corona bond lengths and nugget sizes on the mechanical properties of the welds. The tip diameter had little effect on the tensile strength of the welds, while the strength increased with increasing nugget size and the strength level of steel sheet. However, the effects of the tip diameters, nugget sizes and strength levels of steel sheets on the fatigue strengths were hardly seen. That was because the fatigue crack propagation life was dominant in the total fatigue life of the welds. Under fatigue loading condition, fatigue crack tended to grow along the corona bond, which could be attributed to the lower bonding strength along the corona bond in the high strength steel. However, the fatigue crack propagation life along the corona bond was negligible in comparison with the total fatigue life.

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Fatigue Behavior of Resistance Spot Welded Steel Sheets Fabricated Using Electrodes with Different Tip Diameters

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Effects of Mo and Cu Contents on Sigma Phase Precipitation in 25Cr-5Ni-Mo-Cu-1Mn-0.18N Duplex Stainless Steel

Kenta Yamada, Takahiro Osuki, Kazuhiro Ogawa, Briony Holmes, Kasra Sotoudeh, Hongbiao Dong

pp. 143-149

DOI:

10.2355/isijinternational.ISIJINT-2022-361

Abstract

Recently, a new duplex stainless steel UNS S82551 (25Cr-5Ni-1Mo-2.5Cu-0.18N) has been developed to overcome the drawbacks in super martensitic stainless steel, conventional 22Cr and 25Cr super duplex stainless steels in terms of the productivity and the cost. The characteristic of the alloy design of S82551 is to use Cu, instead of Mo, addition to ensure the corrosion resistance and strength. In addition, S82551 is expected to be less sensitive to sigma phase precipitation during single or multi-pass welding compared with conventional duplex stainless steels and super duplex stainless steels due to the significant decrease in Mo content. There is a trade-off relationship between achieving better properties and avoiding sigma phase precipitation when increasing alloying elements such as Mo, Cr and Cu. In order to utilize the new material S82551 in industry by welding in a similar manner to conventional and super duplex stainless steels, the prevention of sigma phase precipitation is an important subject.This work investigated the effects of Mo and Cu contents on sigma phase precipitation in S82551 using time-temperature-precipitation (TTP) diagram generated by experimental work and calculation. The effects of Mo and Cu contents on the nose temperature and time of C-curve were clarified and compared with S31803 (22Cr-5Ni-3Mo) and S32750 (25Cr-7Ni-4Mo), which indicates the critical heating condition to be free from sigma phase precipitation in duplex stainless steels.

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Effects of Mo and Cu Contents on Sigma Phase Precipitation in 25Cr-5Ni-Mo-Cu-1Mn-0.18N Duplex Stainless Steel

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Dissolution Behavior of Ferritic Stainless Steel in Liquid Magnesium

Yu-ki Taninouchi, Tsubasa Yamaguchi, Toru H. Okabe, Hiroaki Nakano

pp. 150-158

DOI:

10.2355/isijinternational.ISIJINT-2022-232

Abstract

Steel containers and equipment are used to handle Mg and Mg-alloy melts in industrial processes such as Mg casting and Ti smelting. In this study, the dissolution behavior of SUS430 ferritic stainless steel in liquid Mg was quantitatively evaluated in order to obtain fundamental information on the contamination of Mg with steel materials in these industrial processes. Pure Mg was sealed in a SUS430 crucible and melted at 1073–1273 K for 24–96 h. In addition to Fe and Cr, some minor elements in the SUS430 (Mn, Ni, and Cu) were evaluated as impurity elements dissolved in liquid Mg. The concentrations of Fe and Cr in liquid Mg reached a steady state within 24 h, and the empirical equations describing their temperature dependence were obtained. In contrast, the concentrations of Mn, Ni, and Cu in Mg increased with increase in melt holding time. With the dissolution of these elements, a region with Mn concentration lower than that of the original composition was formed on the inner wall of the SUS430 crucible. The validity of the experimental values of impurity concentration in Mg was discussed based on the thermodynamic data of Mg–i (i = Fe, Cr, Mn, Ni, and Cu) binary systems and SUS430. Furthermore, impurity uptake through liquid Mg during Ti production using the Kroll process was preliminary discussed. The findings of this study provide important and beneficial information for improving impurity control in the melting and casting of Mg and in Ti smelting using Mg as a reductant.

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Dissolution Behavior of Ferritic Stainless Steel in Liquid Magnesium

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Effect of Pro-eutectoid Cementite on Fatigue Crack Growth Behavior of Pearlitic Steels

Keisuke Ando, Hirofumi Ohtsubo, Tetsuya Tagawa

pp. 159-169

DOI:

10.2355/isijinternational.ISIJINT-2022-325

Abstract

The influence of pro-eutectoid cementite (θ) on fatigue crack growth behavior was investigated using various pearlitic steels containing from 0.64 to 1.21 mass% C. The fatigue crack growth rates of the hypo-eutectoid and eutectoid pearlitic steels hardly changed, while that of the 1.21 mass% C steel having a large amount of pro-eutectoid θ was accelerated, especially in the high stress intensity factor region. Scanning electron microscope (SEM) observation revealed that the fatigue fracture surface of the 1.21 mass% C steel more frequently contained islanded brittle fracture surfaces than that in other steels. In the 1.21 mass% C steel, the total area fraction of brittle fracture surfaces was notably increased with an enhancement in maximum stress intensity factor (Kmax) due to crack extension. More detailed SEM fractographies were performed comparing between before and after etching were performed in order to identify microstructures beneath the brittle fracture appearances on the fatigue fracture surface of the 1.21 mass% C steel. As a result, it was suggested that pro-eutectoid θ was involved in the formation of brittle fracture. Based on these investigations, the accelerated fatigue crack growth behavior of hyper-eutectoid steel was discussed in terms of static brittle fracture induced by pro-eutectoid θ near the crack tip.

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Effect of Pro-eutectoid Cementite on Fatigue Crack Growth Behavior of Pearlitic Steels

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Anomaly Detection in Rails Using Dimensionality Reduction

Shingo Mitsui, Toshihiko Sasaki, Masayoshi Shinya, Yasuo Arai, Ryutaro Nishimura

pp. 170-178

DOI:

10.2355/isijinternational.ISIJINT-2022-279

Abstract

As railroad rails are an important social infrastructure, monetary and human resources are spent on their maintenance and inspection for people’s safety and security. In particular, rails are uniformly ground periodically to reduce noise and vibration during railroad operations and avoid damage to the rail tops. However, due to cost reduction and lack of human resources, the damage mechanism of rails is being elucidated for more efficient grinding. Factors such as passing tonnage, transit speed, and weather conditions affect rail damage; however, the details of the damage mechanism are not clear. In this study, we measured a large amount of residual stresses and the full width at half maximum (FWHM) of the diffraction rings using a high-speed X-ray residual stress measurement system and explored the possibility of detecting abnormal areas of rails and diagnosing the signs of damage using statistical analysis methods and machine learning.For verification, 2D mapping measurements of the x-axis component of the vertical stress σx, shear stresses τxy, τxz, and τyz, and FWHM of the diffraction ring at the head of a cracked rail were used. The data were subjected to dimensionality reduction by principal component analysis, kernel principal component analysis, and an autoencoder. These normal models were built using the data of the normal areas without cracks. The anomaly score was defined as the differences from the normal models, and the detection accuracies of the models were compared using the area under the receiver operating characteristic curve; the autoencoder showed the best performance.

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Anomaly Detection in Rails Using Dimensionality Reduction

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Permanent Strength of Interstitial-free Steel Processed by Severe Plastic Deformation and Subsequent Annealing

Takayuki Koizumi, Tomoki Takahashi, Mitsutoshi Kuroda

pp. 179-189

DOI:

10.2355/isijinternational.ISIJINT-2022-328

Abstract

The permanent strengths of interstitial-free (IF) steels with different grain sizes and dislocation densities processed by severe plastic deformation (SPD) and subsequent annealing are systematically investigated. Permanent strength, which is athermal and time-independent, corresponds to the fundamental capability to bear stresses caused by external forces. Sufficiently long-time (24 h) stress relaxation tests were carried out and experimental stress–relaxation time relationships were extrapolated to estimate the permanent strength that remained after an infinite time passed. The flow stresses observed in standard uniaxial tension tests increased with repeated SPD processes, and the fraction of permanent strength to the observed flow stress was mostly above 65%. The permanent strength also increased with repetition of SPD processes, and subsequent low-temperature annealing further augmented the permanent strength. During SPD processes, the dislocation-related strengthening was dominant, while the grain-size-related strengthening was minor, i.e., the Hall–Petch relation does not hold. On the other hand, after low-temperature annealing, the grain-size-related strengthening became dominant, quickly replacing the dislocation-related strengthening. In a coarse-grain region, the grain-size-related strength was consistent with the classical Hall–Petch relation. It was confirmed that the original Hall–Petch relation holds only in the coarse-grain region and it indicates “softening with grain coarsening due to annealing”, not “strengthening by grain refinement due to SPD”.

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Permanent Strength of Interstitial-free Steel Processed by Severe Plastic Deformation and Subsequent Annealing

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CO2 Adsorption on a CaO–Ca12Al14O33 Composite Synthesized from a Blast Furnace Slag and its Regenerative Ability

Zaza Hazrina Hashim, Yasutaka Kuwahara, Abdul Rahman Mohamed, Hiromi Yamashita

pp. 190-196

DOI:

10.2355/isijinternational.ISIJINT-2022-310

Abstract

Utilizing a reversible reaction between CaO and CO2, namely the calcium looping (CaL) process, is among the CO2 adsorption and sequestration techniques that have been intensively studied over the years. While CaO-based sorbents offer numerous advantages, such as broad accessibility, low cost, and relatively high theoretical CO2 uptake (0.78 gram of CO2 per gram of CaO), its CO2 capture capability during cyclic operation degrades substantially, which has remained an important issue for commercial CaL process applications. To address the aforementioned problem, in this study, we synthesized a CaO–Ca12Al14O33 (BFS-CaO-CAO) composite from blast furnace slag (BFS) by using two types of inorganic acid, nitric acid, and hydrochloric acid. Acid-leaching and the subsequent separation of SiO2 content from BFS resulted in a formation of Ca–Al-based layered double hydroxide, which was then transformed into a mixed oxide of CaO and Ca12Al14O33 via thermal decomposition. According to the TGA study, the synthesized adsorbent produced with nitric acid (BFS-CaO-CAO(NO3)) had better adsorption of CO2 (13 wt% per mass of adsorbent) and regenerative ability compared to an analog synthesized with hydrochloric acid (BFS-CaO-CAO(Cl)). Moreover, the presence of mayenite (Ca12Al14O33) in the adsorbent, which acted as an inert binder, effectively prevented the sintering and agglomeration of CaO particles. A low-cost, ecologically viable regenerative CO2-adsorbent synthesized from BFS is advantageous for lowering CO2 emissions.

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CO2 Adsorption on a CaO–Ca12Al14O33 Composite Synthesized from a Blast Furnace Slag and its Regenerative Ability

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Thickness Classifier on Steel in Heavy Melting Scrap by Deep-learning-based Image Analysis

Ichiro Daigo, Ken Murakami, Keijiro Tajima, Rei Kawakami

pp. 197-203

DOI:

10.2355/isijinternational.ISIJINT-2022-331

Abstract

Avoiding the contamination of tramp elements in steel requires the non-ferrous materials mixed in steel scrap to be identified. For this to be possible, the types of recovered steel scrap used in the finished product must be known. Since the thickness and diameter of steel are important sources of information for identifying the steel type, in this study, the aim is to employ an image analysis to detect the thickness or diameter of steel without taking measurements. A deep-learning-based image analysis technique based on a pyramid scene parsing network was used for semantic segmentation. It was found that the thickness or diameter of steel in heavy steel scrap could be effectively classified even in cases where the thickness or diameter of the cross-section of steel could not be observed. In the developed model, the best F-score was around 0.5 for three classes of thickness or diameter: less than 3 mm, 3 to 6 mm, and 6 mm or more. According to our results, the F-score for the class of less than 3 mm class was more than 0.9. The results suggest that the developed model relies mainly on the features of deformation. While the model does not require the cross-section of steel to predict the thickness, it does refer to the scale of images. This study reveals both the potential of image analysis techniques in developing a network model for steel scrap and the challenges associated with the procedures for image acquisition and annotation.

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Thickness Classifier on Steel in Heavy Melting Scrap by Deep-learning-based Image Analysis

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Editorial Board, Copyright Page and Announcements

pp. Editorial-

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Editorial Board, Copyright Page and Announcements

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