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ISIJ International Vol. 63 (2023), 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

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キーワードランキング

21 Nov. (Last 30 Days)

ISIJ International Vol. 63 (2023), No. 6

Production and Technology of Iron and Steel in Japan during 2022

The Technical Society, The Iron and Steel Institute of Japan

pp. 951-969

DOI:

10.2355/isijinternational.63.951

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Formation Mechanism of Secondary Inclusions in Fe-36mass%Ni Alloy Using a Novel Combination Analysis Technique

Hiroshi Fukaya, Jonah Gamutan, Makoto Kubo, Shintaro Yano, Shigeru Suzuki, Takahiro Miki

pp. 970-980

DOI:

10.2355/isijinternational.ISIJINT-2022-433

抄録

Controlling the size, number, and composition of secondary inclusions is vital in the production of high-quality steels. In this study, experimental and computational investigation of the relationship between secondary inclusion formation in Fe-36mass%Ni alloy and cooling rate was carried out. Assuming the case of large ingots, solidification experiments using various cooling rates (0.17 to 128 K/min) were employed and the size, number, composition, and distribution of inclusions were analyzed by SEM-EDS automatic inclusion analysis. Like previous studies, inclusion number density increased with increasing cooling rate, while inclusion size decreased with increase of cooling rate. On the contrary, oxide inclusion area fraction was found to have little relationship with the cooling rate and was instead found related with oxygen content of the sample. As a new attempt to investigate the relationship between microsegregation and secondary inclusion formation, a combination of SEM-EDS analysis and EPMA mapping analysis was carried out. By superimposing information of microsegregation and inclusions, it was found that high-Al2O3 inclusions formed during the early stage of solidification, whereas low-Al2O3 inclusions formed during the later stage of solidification. These findings suggest that Al2O3 inclusions formed in the early stage of solidification reacted with the remaining Si-enriched liquid steel and changed into low-Al2O3 inclusions. Experimental results were also confirmed by thermodynamic calculations. Present work made it possible to understand deeper the relationship between microsegregation and secondary inclusion formation.

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Behavior of CaO Formation by Decomposition of Desulfurization Ash Considered under Minimum Energy Conditions

Xuecheng Peng, Yao Su, Jing Guo, Hanjie Guo, Sheng-chao Duan, Mingchun Zhang, Litao Zhang, Xiuyan Lu

pp. 981-992

DOI:

10.2355/isijinternational.ISIJINT-2022-457

抄録

The treatment of desulfurization ash (DA) by high-temperature can solve the increasingly environmental risk caused by the accumulation desulfurization ash on the one hand, and realize the reuse of Ca and S on the other. However, the understanding of the high-temperature reduction decomposition process of desulfurization ash is still vague. In this study, a multivariate and multiphase reaction mathematical model of the complex system of desulfurization ash, carbon, and gas is established by using the principle of minimum free energy. The modeling results show that the reductive decomposition of DA has four stages, and the decomposition products are different in each stage. This result confirms that the optimal thermodynamic conditions to obtain only CaO as a decomposed product are a temperature greater than 1400 K and a C/S molar ratio of 0.5. Further, the processes of CaO and CaS production are parallel competitive reactions, but are regulated by different factors at different stages. A micropositive pressure equilibrium reaction crucible was designed for laboratory DA decomposition experiments. The correctness of the calculation result of the minimum free energy mathematical model is proved by the high temperature reductive decomposition experiment. When the temperature and C/S molar ratio are 1500 K and 0.5, the DA decomposition rate can reach 100%. The main reaction product is spherical CaO, the minimum S content is approximately 1.5%, and the desulfurization rate can reach approximately 70%. The present strategy is highly promising for application in industrial DA recycling processes.

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Thermodynamic Formation and Three-dimensional Characterization of MnS–MgAl2O4 Composite Inclusions in Steel

Qian Meng, Liying Ju, Tao Li, Min Tan, Xiaopei Guo, Henan Cui, Peidong Xu, Han Guo

pp. 993-1001

DOI:

10.2355/isijinternational.ISIJINT-2022-329

抄録

The distribution and morphology of inclusions in steel have an important effect on the quality of steel. It has been proved that the oxide inclusions can be modified into small and dispersed spinel inclusions by adding proper amount of Mg in steel. The MnS–MgAl2O4 composite inclusions are formed with the core of MgAl2O4 inclusions during the solidification process of molten steel, which has deforming ability and can improve the properties of materials steel. However, the investigation of the control of the composite inclusions is limited by the lack of understanding structure of the inclusions. In this study, the Mg treated steel samples were prepared by induction furnace in this study. In the experiment, SEM-EDS was used to characterize the samples, and thermodynamic calculations were used to describe the evolution mechanism of inclusions and MnS–MgAl2O4 composite inclusions formed in steel samples with different Mg contents. The atomic mismatch calculated between MnS and MgAl2O4 proves that they can nucleate effectively. The three-dimensional (3D) morphology of the composite inclusion of MnS–MgAl2O4 in steel samples were observed by using the X-ray Micro-CT in the beamline of BL16U2 at Shanghai Synchrotron Radiation Facility (SSRF). It is proved that MnS and MgAl2O4 phases exist in the form of co-associated, which is valuable for the control of composite inclusions in steel. The current work provide a powerful method to analyze the detailed structure of the composite inclusions in the steel.

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Effect of Re-ignition Method on Sinter Yield Through Improving Carbon Combustion Ratio at Upper Layer of Sinter Packed Bed

Masaru Matsumura, Ryota Kosugi, Yuichiro Yamamoto, Junji Nagata, Kenichi Higuchi

pp. 1002-1010

DOI:

10.2355/isijinternational.ISIJINT-2022-485

抄録

Conventionally, it has been known that the product yield of the upper part of the sintering layer is extremely low, because of the heat loss caused by transferring heat toward the space above sintering layer, and of the large amount of unburned carbon in upper sintering layer.

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A Thermo-gravimetric Approach for Quantification of Carbon Sources from Coal-char and Coke Mixture of Interests

Rajeswar Chatterjee, Chalumuri Sivananda, Manisha Sahoo, Dibyajyoti Behera, Samik Nag, Padma Pal

pp. 1011-1016

DOI:

10.2355/isijinternational.ISIJINT-2022-563

抄録

Blast furnace sludge contains carbon, which can originate from both coal-char and coke. Naturally, it becomes difficult to assign this unutilized carbon to a specific source. Conventional chemical analysis can only predict the total carbon content. This work therefore focuses on the quantification of carbon from the mixture of two different carbon sources using thermo-gravimetric methodology. To establish the methodology, synthetic char has been prepared under different conditions and suitably chosen for this study. Prepared char and coke fines have been heated separately to understand their individual performance. Further, coal-char and coke are mixed in known proportions (wt.%) and subjected to controlled heating under combination of synthetic air and inert atmosphere. Optimized heating profile consists of heating the mixture under inert environment, followed by an isothermal zone of around 12 hrs. Subsequently, the mixture is heated again in inert condition and followed by an isothermal zone of around 4 hrs. The controlled heating and holding time ensure weight loss of known carbon sources occurring separately. Weight loss of the mixture at lower isotherm is solely from carbon from coal-char, and at higher isotherm it is due to coke fines. The ratio of measured weight loss due to carbon sources has been agreed well with the known proportion inside the mixture. This derived process parameters have been found to be equally applicable for the complete range of mixing proportion. Subsequently, developed methodology is applied for different blast furnace sludge samples for quantification of carbon sources.

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Effects of Entrained Slag Droplets on Slag-Metal Interface in A Gas-Stirred Ladle

Yong Liu, Shusen Cheng, Tong Liu

pp. 1017-1024

DOI:

10.2355/isijinternational.ISIJINT-2022-164

抄録

This study explores the underlying mechanism between secondary refining efficiency, gas flow rate, and slag properties. The secondary refining efficiency is directly affected by the slag-metal interface area. Traditionally, the slag-metal interface has been limited to the liquid-liquid interface of the ladle cross-section and does not include the interface area between the entrained slag droplets and metal. To investigate the interface area with different slags and metals under various bottom blow rates, a physical model of a single-nozzle gas-stirred ladle was established using oil to simulate slag and water to simulate metal. The roles of relevant variables that affect the volume of entrained oil, the diameter of entrained droplets, and interface area were studied, as well as oil viscosity, interfacial tension, and oil thickness. Experimental data were collected using colorants and image processing techniques. Based on these findings, the increase in gas flow rate and oil layer thickness increased the volume of entrained oil and interface area, while the increase in oil viscosity and interfacial tension decreased these parameters. When the gas flow rate increased, the mean diameter of droplets first increased and then decreased. However, the specific surface area of droplets revealed the opposite trend. Furthermore, the mean diameter and specific surface area increased and decreased with increasing oil-layer thickness.

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Optimal Control of Inclusions to Prevent “Sand-Hole” Surface Defects in Deep Cold-Drawn Battery Cups for Electrical Vehicles

Min Jiang, Rui-Gang Wang, Jia Guo, Xinhua Wang

pp. 1025-1035

DOI:

10.2355/isijinternational.ISIJINT-2022-491

抄録

The present work was conducted to elucidate the influence of inclusionson surface quality of deep cold-drawn battery cups for electrical cars. The obtained results revealed that, to prevent the surface defects of sand-holes in battery cups in deep cold-drawing process, attentions should be paid to steelmaking and casting process for optimal control of inclusions. Because sand-holes were often caused by large Al2O3 clusters and CaO–Al2O3 particles. Most important, a worthy finding was that these inclusions were not safe when they were over 100 µm and bigger than 27 µm, respectively, which was important for process optimization. By reducing (FeO) contents in ladle slag and tundish covering flux to about 5% or lower, together with optimal fluid flow of molten steel in tundish, such large inclusions can be well decreased to prevent the occurrences of sand-holes in battery cups in industrial production.

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Vibration Sensor in Multiphase Flow Measurement

Tathagata Ray, Moni Sinha, Aditya Sarda, Ashish Mukherjee, Prateek Jivrajka, Pradeep Chaudhary, Surajit Sinha, Siriniwasagan Balamurugan

pp. 1036-1043

DOI:

10.2355/isijinternational.ISIJINT-2022-501

抄録

The solid waste generated in the steel industry are predominantly recycled via the agglomeration making route. In recent times, the amount of fines percentage has increased in sinter making, thereby affecting the bed permeability which eventually affects sinter quality. Hence, sinter bed permeability is to be monitored continuously. Currently the conventional infrared based velocity measurement is being used for this purpose. The permeability is being calculated based on the flow velocity of flue gases. The current paper is focused on the development of low cost novel vibration sensor for flow measurement to monitor permeability. The measurements are showing with good accuracy (96%) in comparison with the conventional technique. The design and development along with the results are discussed in detail in this paper.

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Quantitative SAXS Analysis of Precipitate Characteristics Limiting Hot Ductility in HSLA Steels Containing V, Nb & NbTi

Alyssa Stubbers, T. John Balk

pp. 1044-1053

DOI:

10.2355/isijinternational.ISIJINT-2022-540

抄録

Hot ductility behavior between 700 and 1050°C is governed by precipitation and phase transformation, which can cause cracking and limit steel processing in other ways. Characterization of this precipitation with conventional microscopy techniques is difficult due to the limited particle size, usually occurring on the nanometer scale. Casting simulation and hot tension testing were performed using a Gleeble 3500 to generate a property profile for high-strength low alloy (HSLA) steels containing Nb, Ti, V, and N. Small-angle X-ray scattering (SAXS) was then used to characterize precipitates in Gleeble-tested samples in order to evaluate relationships between hot ductility measurements and precipitate size, spacing, and volume fraction. SAXS results showed that interparticle spacing and volume fraction were the most significant factors influencing ductility in all tested grades. Specimens with reduction-in-area measurements ranging from 3–90% exhibited a range of particle spacing data from 5–80 nm and precipitate volume fraction from 0.001–0.03%. It was observed that particle spacing of 10–20 nm and a volume fraction of 0.01% were the most detrimental to hot ductility. Significant outcomes of the current study are that precipitate density may be the most significant factor limiting ductility and that laboratory-scale SAXS measurement represents a viable method for bulk precipitate characterization.

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Effects of States of Carbon and Solute Nitrogen on Toughness of Ferritic Steel

Nobuyuki Yoshimura, Kohsaku Ushioda, Hiroyuki Shirahata, Manabu Hoshino, Genichi Shigesato, Masaki Tanaka

pp. 1054-1065

DOI:

10.2355/isijinternational.ISIJINT-2023-027

抄録

To develop microstructure control concepts for ensuring the toughness of high-strength steel plates, basic research was conducted using ferrite single-phase steels with different amounts of C, and the effects of the states of C were investigated along with those of solute N. In this study, Fe-0.017C (mass%) alloy, wherein the state of C was changed to a solid solution, intragranular cementite, and intergranular cementite, were used for microstructural observation, Charpy testing, and fracture surface investigation. The results reveal that the toughness of the intragranular cementite steel was the best, followed by that of solute C steel and intergranular cementite steel. In intergranular cementite steel with significantly inferior toughness, the coarse intergranular cementite leads to dislocation pile-up, initial crack formation, and macroscopic brittle fracture. The brittle fracture of intragranular cementite steel was caused by the deformation twins. It is thought that the fine intragranular cementite only had a minor effect on the crack initiation and dislocation mobility. Twin was also confirmed at the initiation point of brittle fracture in the solute C steel. Hence, it was deduced that the deterioration of toughness caused by solute C resulted from the promotion of twinning, which replaced the dislocation movements. However, the deterioration of toughness caused by solute C was smaller compared with that caused by solute N, which partly caused intergranular fracture. This is attributed to the suppression of intergranular fracture by the presence of a small amount of solute C.

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Effect of Nb on Grain Growth Behavior in the Heat Affected Zone of Linepipe Steels

Daichi Izumi, Nobuyuki Ishikawa, Pello Uranga, Nerea Isasti, Jose Maria Rodriguez-ibabe, Douglas Stalheim, David Jarreta, David Martin

pp. 1066-1074

DOI:

10.2355/isijinternational.ISIJINT-2022-556

抄録

Recrystallization and grain growth during plate rolling are prevented by Nb addition both with the solute drag and the Nb carbide precipitation. Although a fine microstructure is achieved in the base material, welding heat completely changes the microstructure in the heat affected zone (HAZ). In this study, laboratory simulation of the coarse grain HAZ (CGHAZ) thermal cycle of double submerged arc welded linepipe was carried out using low carbon steels containing different Nb contents. Extraction residue analysis of the simulated CGHAZ samples revealed that almost all the Nb remained in solid solution. To clarify the interaction of Nb carbide dissolution and grain growth on overall simulated HAZ microstructure evolution, additional weld HAZ thermal simulations were performed. It was found that Nb carbides remain undissolved at HAZ peak temperatures up to 1200°C and showed significant pinning effect to prevent austenite grain growth. Significant grain growth was seen after continuous fast heating to 1350°C peak temperature, while the higher Nb added steel showed a slower overall austenite grain growth rate, suggesting that grain growth in the HAZ at higher temperature was suppressed by the combined effects of slower coarse Nb carbide dissolution providing some pinning, and the solute drag effect of higher amounts of Nb in solid solution. A pronounced retardation of longer-term isothermal grain growth was identified at 1350°C at higher levels of solute Nb, confirming the influence of Nb solute drag on high temperature resistance to austenite grain coarsening.

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Age-hardening Behavior in γ′-phase Precipitation-hardening Ni-based Superalloy

Fumitaka Ichikawa, Masayoshi Sawada, Yusuke Kohigashi

pp. 1075-1083

DOI:

10.2355/isijinternational.ISIJINT-2022-555

抄録

Dislocations are often introduced in Ni-based superalloys to impart sufficient strength at both room temperature and high temperatures prior to their use in automobile exhaust gaskets. However, the interaction between the representative γ′ (Ni3(Al, Ti))-phase precipitates and dislocations in high temperature remains unclear. Therefore, this study examined the effect of cold rolling on age-hardening behavior and microstructure evolution, focusing on the formation of γ′-phase Ni3Ti during aging at 700°C for up to 400 h after 60% cold rolling of solution-treated specimens. During the early stage of aging, at 0.03 h, the hardness rapidly increased from 401 HV to 496 HV. Age-hardening continued until 3 h and reached its peak of 536 HV, followed by gradual decrease with aging time. 3D atom probe investigation revealed that the γ′-phase was confirmed after 0.3 h of aging. However, the composition-modulated structure speculated to be caused by spinodal decomposition was observed in the 0.03 h aged specimen. The change in strength with aging time was considered by calculating the contribution of each strengthening mechanism. In the initial stage of aging (0–3 h), dislocation and solid-solution strengthening dominated along with spinodal strengthening. Strengthening by spinodal decomposition in the 0.03 h aged specimen is presumptively accelerated by the introduced dislocations, which is followed by further precipitation strengthening caused by γ′-phase precipitates. In the later stage of aging (3–400 h), precipitation strengthening became dominant and reached its peak at 20 h aging, while dislocation strengthening decreased with aging time.

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Microstructures and Tensile Properties of Friction Stir Welded 0.2%C-2%Si-Cr Steels

Zexi Wu, Tomoya Nagira, Kohsaku Ushioda, Goro Miyamoto, Hidetoshi Fujii

pp. 1084-1095

DOI:

10.2355/isijinternational.ISIJINT-2023-047

抄録

The 0.2C-2Si (mass%) steels with the addition of 0–4 mass% Cr were prepared by hot rolling followed by subsequent annealing for normalization. The steels were subjected to friction stir welding (FSW) conducted above A3 temperature. For all the steels, sound FSWed joints were obtained. Microstructures and tensile properties using small tensile specimens were investigated for both base materials and stir zones. The base materials showed a relatively good balance of strength and ductility when the Cr content is over 3 mass% presumably owing to the relatively fine microstructures of ferrite and martensite. The tensile properties of stir zones were substantially enhanced by FSW, and the stir zone of the 0.2C-2Si-4Cr joint with fully martensitic structure exhibited the surprisingly high tensile strength of 1720 MPa compared with that of the conventional martensitic steel of 0.2 mass%C together with the excellent balance of ductility. This is assumed to be caused by the refinement of block size in the fresh lath martensite and/or the formation of ausformed martensite induced by the dynamically recrystallized fine austenite grains by FSW of the Cr added steels.

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Hydrogen Embrittlement Mechanism of Ultrafine-grained Iron with Different Grain Sizes

Satoshi Mitomi, Hideaki Iwaoka, Shoichi Hirosawa

pp. 1096-1106

DOI:

10.2355/isijinternational.ISIJINT-2022-562

抄録

To investigate the effect of grain sizes on hydrogen embrittlement of 4N-purity iron, miniature tensile tests were conducted after hydrogen charging for the ultrafine-grained specimens produced by high-pressure torsion and subsequent annealing. Hydrogen embrittlement indexes defined from reduction of area were increased with decreasing grain size, and shear-type fracture occurred with fine dimples on the fracture surface of the diagonally raptured tensile specimen with a smaller grain size. The formation and growth of microvoids at triple junctions of grain boundaries ahead of propagated cracks were responsible for such earlier shear-type fracture because necking between adjacent microvoids more likely and extensively occurred. In the specimens with larger grain sizes or without hydrogen charging, on the other hand, local coalescence and growth of microvoids were predominant due to longer distances between triple junctions, resulting in void coalescence-type fracture with coarser dimple patterns. Therefore, hydrogen atoms introduced by hydrogen charging are considered to enhance the formation of deformation-induced vacancies in ultrafine-grained iron, resulting in shear-type fracture with finer dimple patterns.

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