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ISIJ International Vol. 59 (2019), No. 12

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 Dec. (Last 30 Days)

ISIJ International Vol. 59 (2019), No. 12

Development and Application of Thermo-mechanical Control Process Involving Ultra-fast Cooling Technology in China

Zhaodong Wang, Bingxing Wang, Bin Wang, Yong Tian, Tian Zhang, Guo Yuan, Zhenyu Liu, Guodong Wang

pp. 2131-2141

DOI:

10.2355/isijinternational.ISIJINT-2019-041

抄録

Thermo-mechanical control process (TMCP) is an important and effective rolling technology for microstructural control to obtain excellent mechanical properties, such as high strength, excellent toughness and other performances, which consists of controlled hot rolling and controlled cooling. RAL laboratory in China has been making efforts to develop ultra-fast cooling (UFC) technology, which is referred as the core technology for New Generation (NG)-TMCP. The ongoing development of UFC technology, with high cooling capacity and uniform cooling control, provides the effective control of cooling paths for a wide range of water-cooled steel strips and plates. Here, the development and characterization of UFC technology are introduced, and advanced cooling system (ADCOS) for the UFC equipment will be elucidated as well. Moreover, the superior mechanical properties can be obtained by inter-pass cooling technology during rolling processing, which is characterized by water-cooling between controlled rolling passes and further reheating due to the internal heat capacity of plate on its own. The resultant theory and technology can achieve resource conservation, energy saving and emission reduction for green products in the manufacturing process for upgrading of steel industry in China.

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Effect of Temperature and CO2 Concentration on Gasification Behavior of Carbon Fiber Containing Fine Iron Particles

Kazuto Nishihiro, Takayuki Maeda, Ko-ichiro Ohno, Kazuya Kunitomo

pp. 2142-2148

DOI:

10.2355/isijinternational.ISIJINT-2019-240

抄録

In direct reduced iron (DRI) process, CO–H2 gas mixture is used as a reducing agent, which may make the operation unstable owing to a carbon deposition reaction and metal dusting reaction through Fe3C. The Fe3C decomposition reaction forms iron particles which acts as a catalyst for a carbon fiber deposition reaction at around 600°C. Such a carbon fiber deposition not only causes the loss of the carbon but also decrease the reducibility of the gas. On the other hand, the carbon fiber is likely gasified by CO–CO2 gas mixture at around 1000°C. In the present study, the carbon fiber gasification was quantitative analyzed using thermobalance to clarify the mechanism of the carbon fiber gasification reaction. To prepare a carbon fiber sample, the carbon was deposited with a reduced iron catalyst at 600°C in 50vol%CO-50vol%H2. Carbon fiber containing fine iron particles was gasified with various compositions of CO–CO2 gas mixture at 1000°C. Further, the effect of temperature of the gasified reaction was also investigated at 800°C, 900°C and 1000°C in 100vol%CO2. According to XRD analysis of the sample after gasification, Fe3C in the sample before gasification decomposed to iron and a portion of iron was oxidized to Fe3O4 and FeO when gasification ratio was high. The transition of carbon fiber shape was confirmed by SEM observation. Fine iron particles located on the tip of carbon fiber were sintered during gasification of carbon fiber. The mechanism of carbon fiber gasification was evaluated considering crystalline size, such as La and Lc that show (002) and (110) determined by XRD analysis, respectively. It was found that the La decreased with gasification ratio at all temperatures. In addition, Lc decreased after gasification at 1000°C.

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Fuzzy Comprehensive Evaluation Model of Pulverized Coal Digestibility in Blast Furnace Raceway Based on the Fusion of Subjective and Objective Evidence

Guimei Cui, Yanqing Yao, Xiang Ma, Yong Zhang

pp. 2149-2155

DOI:

10.2355/isijinternational.ISIJINT-2018-738

抄録

In the blast furnace smelting process, the pulverized coal digestibility of the tuyere is an important indicator for studying the combustion status of tuyere. It is the basis for decision making and improvement of pulverized coal injection ratio. A correct and effective assessment is of great significance. In this paper, a fuzzy comprehensive evaluation model based on the fusion of subjective and objective evidence is proposed, which integrates the pulverized coal burnout rate, temperature gradient, combustion zone activity, and uniformity. Pulverized coal burnout rate in the raceway is calculated by the mathematical model. The temperature gradient is obtained by digitizing the tuyere image. The activity and uniformity of the combustion zone are defined by the required temperature for the active state of the blast furnace hearth and average temperature, respectively. Through the expert knowledge and principal component analysis to determine the weights of various indicators, a more accurate and comprehensive model of the pulverized coal digestibility of the raceway in the blast furnace is constructed. The evaluation model is applied to make the application analysis of actual blast furnace off-line data, and the evaluation results are consistent with the actual operation data analysis.

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A Prediction System of Burn through Point Based on Gradient Boosting Decision Tree and Decision Rules

Song Liu, Qing Lyu, Xiaojie Liu, Yanqin Sun, Xusheng Zhang

pp. 2156-2164

DOI:

10.2355/isijinternational.ISIJINT-2019-059

抄録

According to the characteristics of sintering process, a sintering end-point prediction system based on gradient boosting decision tree (GBDT) algorithm and decision rules is proposed in this paper. The on-line parameters of the sintering machine, which can characterize the change of the properties of the sintered raw materials in real time, were selected as the input of the model. The soft measurement results of the burn-through point position and temperature were selected as the output. The problem of establishing a system model based on the data collected in the sintering process to dynamically predict the state of burn through point (BTP) was solved. With the combination of process knowledge and several feature selection methods, the important characteristic variables related to the BTP were screened out. the algorithm of GBDT was used to establish the prediction model of BTP and burn through temperature (BTT). The parameters of the ensemble algorithm were optimized by using the methods of grid search and cross-validation, and the system model based on training data was established. On this basis, the corresponding decision model was added to the output of the prediction model, and the prediction accuracy of the system was improved. The establishment process of system model is introduced in detail. The operation results show that the system has better performance.

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Effect of Natural Gas Injection Point on Combustion and Gasification Efficiency of Pulverized Coal under Blast Furnace Condition

Akinori Murao, Kiyoshi Fukada, Michitaka Sato, Hidetoshi Matsuno, Yasuhiro Saito, Shota Akaotsu, Yohsuke Matsushita, Hideyuki Aoki

pp. 2165-2173

DOI:

10.2355/isijinternational.ISIJINT-2019-154

抄録

The reduction of CO2 emission from the ironmaking process is an important issue from the view of environmental problems typified by global warming in recent years. Low RAR (reducing agent rate) operation of the blast furnace is one of effective methods for reducing CO2 emission. Injection of HRA (hydrogenous reducing agents) from the tuyere (where is the lower part of a blast furnace) is also effective measure. In this study, the influence of HRA injection point on combustion and gasification efficiency of pulverized coal (PC) in the case of simultaneous injection of HRA and PC from double-channel lance was examined by small scale combustion furnace and three-dimensional numerical simulation for permeability in the blast furnace. Combustion experimental conditions were in three cases, case 1: injected HRA from the outer side and PC from the inner side of double-channel lance, case 2: injected HRA from inner side and PC from outer side of double-channel lance and case 3: injected HRA and PC premixed. As a result, the combustion and gasification efficiency was increased in the order of case 1, case 2 and case 3. The rate of combustion and gasification of PC was investigated in case1. Not only the oxidation reaction was also accelerated CO2 and H2O gasification reaction in the case of simultaneous injection HRA and PC. A three-dimensional numerical simulation of the experimental furnace was conducted, we confirmed the increase of combustion temperature, the acceleration of oxygen consumption and gasification reaction as with the experimental results in the case of simultaneous injection HRA and PC.

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Reaction Behavior of Coke in a High Alumina Slag

Renze Xu, Jianliang Zhang

pp. 2174-2181

DOI:

10.2355/isijinternational.ISIJINT-2019-180

抄録

The reaction behaviors between coke and CaO–SiO2–MgO–Al2O3–Cr2O3 slag at different immersion time, temperature and rotation speeds were studied in this work. The diameter decrement of the coke increased as increasing the immersion time, temperature and rotation speed. When the coke was in contact with the molten slag, the slag could infiltrate into the coke and further flow to the interior of the coke through pore channels, which will fill up the coke pores. During the penetration process of slag into the coke, the carbon could be oxidized by Cr2O3 and SiO2 in the slag. Furthermore, the penetrated slag could also dissolve the coke ash minerals and react with that to form new phase. The comprehensive effects of slag penetration, slag-carbon reaction and slag-mineral reaction eventually resulted in the coke degradation.

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Reduction and Gasification Characteristics of A Unique Iron Ore/carbon Composite Prepared from Robe River and A Coal Tar Vacuum Residue

Kouichi Miura, Jingchong Yan, Hideaki Ohgaki, Ryuichi Ashida, Kazuhira Ichikawa

pp. 2182-2192

DOI:

10.2355/isijinternational.ISIJINT-2019-048

抄録

We have prepared a unique iron ore/carbon composites (IOC) from a low grade iron ore called Robe River and a thermoplastic carbonaceous material. When Robe River which contains iron as goethite, FeOOH, is heated up to 250 to 300°C, the OH groups are removed as H2O, leaving flat pore spaces of 0.8 nm wide between 2.0 nm thick Fe2O3 layers. The pore spaces are, however, closed over 300°C by the sintering of the Fe2O3 layers. The idea proposed is to insert the thermoplastic carbonaceous material into the pore space of 0.8 nm wide while the pore spaces are opened and to carbonize it to form carbon in the pore space below 500°C. The iron oxide in the IOC thus prepared is reduced very rapidly in inert atmosphere and the carbon retained in the pore space is gasified by CO2 very rapidly also. In this work the reaction characteristics of the unique iron ore/carbon composite prepared from Rove River and a coal tar vacuum residue, CTVR, were examined for its direct reduction, indirect reduction in a H2 atmosphere, and coke gasification in a CO2 atmosphere from the viewpoints of reaction enthalpies and rate parameters. The examinations clarified that the carbonaceous material retained as coke in the pore space of iron ore are very reactive and show reaction characteristics different from bulk carbon.

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Numerical Analysis of Effect of Water Gas Shift Reaction on Flash Reduction Behavior of Hematite with Syngas

Xingnan Wang, Guiqin Fu, Wei Li, Miaoyong Zhu

pp. 2193-2204

DOI:

10.2355/isijinternational.ISIJINT-2019-215

抄録

The water gas shift reaction (WGSR) is the most important side reaction in direct iron reduction processes in syngas. In this study, an Euler-Lagrange model has been developed to simulate the flash reduction behavior of hematite with syngas in a drop tube reactor. Based on model validation, the effect of WGSR on the flash reduction is investigated by comparing results predicted by models with and without WGSR. Results indicate that the WGSR has a minor effect in CO–H2 system while a major effect in H2–CO–CO2–H2O system. The difference of gas composition caused by WGSR leads to a difference of gas reduction capacity, which results in different reduction behavior. The relationship between the composition of gas mixture and the equilibrium constant of WGSR determines the direction of WGSR and thus determines the positive or negative effect of WGSR on the reduction process. The higher oxygen partial pressure and temperature, the stronger influence of WGSR can be considered to have.

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Characterization and Properties of Scaffold in a Dissected Blast Furnace Hearth

Fan Xiaoyue, Jiao Kexin, Zhang Jianliang, Wu Senran, E Dianyu, Yan Bingji

pp. 2205-2211

DOI:

10.2355/isijinternational.ISIJINT-2019-199

抄録

The blast furnace scaffold can only be obtained while the blast furnace shut down after operating for many years. Its characteristics and properties are important for the blast furnace campaign life. The key to delaying the carbon brick corrosion in blast furnace hearth is the scaffold formed between the melt and the carbon brick. In an emergency shutdown blast furnace, the scaffold in hearth is completely preserved, and the scaffold on the surface of the carbon brick above and below the taphole in hearth are sampled. The purpose of this study is to describe the characterization and properties of the scaffold in hearth. The paper presents results from investigations using electron imaging techniques such as Transmission Electron Microscopy (TEM), Optical Microscope (OM), Scanning Electron Microscope combined with Energy Dispersive Spectrometer (SEM-EDS), Raman analysis and X-ray Diffraction (XRD). The main component of the slag skull above the taphole is similar to the final slag and is rich in harmful elements. The thermal conductivity of the scaffold is about 2 W/(m·K) and the viscosity as well as the solidus temperature are higher than the final slag. The slag skull acts to isolate and contain harmful elements. The phase on the hot surface of the carbon brick below the taphole is mainly consist of graphite and the large-grained graphite phase has a random spatial network distribution in the iron matrix. The slag skull and the graphite serves to segregate the melt and harmful element, thereby protecting the carbon brick and extending hearth life.

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Efficiency of Biomass Use for Blast Furnace Injection

Alexander Babich, Dieter Senk, Jon Solar, Isabel de Marco

pp. 2212-2219

DOI:

10.2355/isijinternational.ISIJINT-2019-337

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Numerous studies and available experience proved the feasibility and benefits of the biomass usage in various metallurgical applications, particularly, by its injection into the blast furnace (BF). This contribution focuses on three aspects, which could increase the economic efficiency of this technology.The first one is related to the thermal treatment of biomass. Woody biomass were pyrolysed using a laboratory pyrolysis plant under different conditions resulting in various amounts and properties of solid, liquid and gaseous constituents. Co-injection of the produced charcoal and biogas into the BF was proposed. Mathematical modelling using the experimental data of mentioned biomass product characteristics was undertaken to examine the effect of this technology on the BF operation results.The second aspect is related to the optimisation of grain size and size distribution of injected solid biomass products. Tests using a laboratory injection rig allowed for recommendation of the coarser grinding of charcoal than that for fossil coal applied for the BF injection. This could lead to the additional energy and cost saving.The third aspect concerns the improvement of the BF control. It is proposed a new BASE1 method for the BF thermal state control by adaption of the pyrolysis parameters while injecting pyrolysed biomass and coupling the blast furnace with a pyrolysis reactor.1Babich-Senk

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Solubility of Nitrogen in Liquid Ni, Ni–Nb, Ni–Cr–Nb, Ni–Fe–Nb, and Ni–Cr–Fe–Nb Systems

Kun Qian, Bo Chen, Pengxiang Zhao, Mengshu Zhang, Kui Liu

pp. 2220-2227

DOI:

10.2355/isijinternational.ISIJINT-2019-187

抄録

By means of sampling methods, we have determined the solubility of nitrogen in liquid Ni, Ni–Nb, Ni–Cr–Nb, Ni–Fe–Nb, and Ni-18Cr-17Fe-5.2Nb systems within the temperature range from 1773 K to 1873 K and with the niobium content from 5 to 20 mass%. It has been found that Sieverts’ formalism successfully describes the solubility of nitrogen in all these liquid alloys up to 7 atm of the nitrogen partial pressure. Niobium addition increases the nitrogen solubility and its effect to increase nitrogen solubility is only second to chromium. Furthermore, we have derived the enthalpy and entropy of dissolution of nitrogen in these liquid alloys, determining the first order interaction parameter, = –0.0785, up to 20 mass% Nb in nickel between nitrogen and niobium. In addition, the effects of alloying elements on the activity coefficient of nitrogen have been further investigated and the second order cross-interaction parameters between nitrogen and chromium or iron with niobium at 1873 K have been determined as = 0.0256 and = 0.0115.

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Numerical Simulation of Multiphase Flow and Mixing Behavior in an Industrial Single Snorkel Refining Furnace: Effect of Bubble Expansion and Snorkel Immersion Depth

Weixing Dai, Guoguang Cheng, Shijian Li, Yu Huang, Guolei Zhang

pp. 2228-2238

DOI:

10.2355/isijinternational.ISIJINT-2019-280

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A coupled mathematical model is used to simulate the multiphase flow in an industrial Single Snorkel Refining Furnace (SSRF). Based on the present model, the evolution characteristics of bubble size, density, and velocity are analysed during the long-distance rising process. The comparative studies indicate that the expansion of bubbles has an enormous impact on the circulation rate and free surface in the vacuum chamber. Furthermore, the effect of snorkel immersion depth (SID) on the circulation rate, mixing time, and fluid flow are investigated. The results indicate that the circulation rate decreases with the increase of SID, while the mixing time shows an uptrend with the increase of SID. Particularly, when the SID exceeds 0.4 m, the scope of dead zone around the snorkel dramatically increases, which further decreases the flow velocity of slag layer in the ladle.

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Evaluation of Solidified Shell Thickness by Thermocouple in Mold

Yoichi Ito, Seiji Nabeshima, Yuji Miki, Jun Kubota, Katsuaki Matsuoka

pp. 2239-2246

DOI:

10.2355/isijinternational.ISIJINT-2019-221

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High speed continuous casting technology has been developed to improve productivity. In this study, the method of real-time calculation of the solidified shell thickness by using multiple thermocouples embedded in the mold copper plates was tested at JFE Steel Kurashiki No. 4CCM, and the possibility of detecting various types of breakouts in high-speed casting was demonstrated. The main results are summarized as follows.(1) Real-time calculation of the solidified shell thickness at the mold outlet position was successfully achieved on the basis of the local heat flux calculated by two thermocouples installed 5 mm apart in the copper plate depth direction.(2) The calculated solidified shell thickness was in good agreement with that observed by FeS addition.(3) Retardation of solidification was evaluated by a calculation in consideration of the heat input caused by the impingement of the steel stream from the submerged entry nozzle. The index on the narrow face increased under the condition of high speed casting of narrow width slabs.(4) An instantaneous local heat flux drop in the thermocouple measurements was observed when slag rim or scum entrapment in the solidified shell occurred. The calculated solidified shell thickness at the mold outlet position was reduced to about 2/3 in this case.

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Effect of Na2O on the Interfacial Reaction between CaO–Al2O3 based Mold Fluxes and High-Al Steel at 1500°C

Jian Yang, Hongji Cui, Jianqiang Zhang, Oleg Ostrovski, Chen Zhang, Dexiang Cai

pp. 2247-2255

DOI:

10.2355/isijinternational.ISIJINT-2019-257

抄録

The use of traditional CaO–SiO2-based mold fluxes for the continuous casting of high-Al steel is problematic due to the reaction between [Al] from liquid steel and SiO2 from the CaO–SiO2-based fluxes. CaO–Al2O3-based mold fluxes were proposed to mitigate the interfacial reaction. However, these fluxes contain fluxing agents, such as Na2O, B2O3, etc., which react with [Al] in liquid steel. This article investigates the effect of Na2O content in CaO–Al2O3-based mold fluxes on the reaction between high-Al steel and mold fluxes at 1500°C. The flux-steel reaction led to the accumulation of Al2O3 and reduction of SiO2, Na2O and B2O3 in the fluxes. The increase of the initial Na2O concentration enhanced the rates of Al2O3 accumulation and Na2O reduction; the [Al] concentration in liquid steel also decreased with the increase of initial Na2O content. In the early stage of the reaction, emulsification was observed at the flux-steel interface, which was affected by the precipitation of solid phases along the reaction interface.

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Simulation for Mass Transfer Kinetics at Slag-Steel Interface during High Al Steel Continuous Casting

Kai-tian Zhang, Jian-hua Liu, Heng Cui

pp. 2256-2263

DOI:

10.2355/isijinternational.ISIJINT-2019-291

抄録

A series of laboratory-scale experiments were carried out in order to elucidate the relationship between the flow field and slag-steel reaction in mold, which could provide a theoretical fundamental of for controlling the slag-steel reaction by kinetics during high alumina steel continuous casting process. The similarity of slag-steel interface mass transfer behavior between simulated experiment and actual continuous casting process was determined through theoretical derivation, and the mold water model was established. Simultaneously, a mathematical model for predicting the composition of mold slag was established according to the principle of slag-steel reaction, and the predicted results were consistent with the results of slag-steel reaction in an actual continuous casting and laboratory experiments. The effects of mold casting speed, SEN (Submerged Entry Nozzle) outlet angle and submerged depth on slag-steel reaction rate were also investigated by water model. The simulated continuous casting results reflected that the slag-steel reaction rate can be controlled by controlling the mold surface velocity and fluctuation. On the one hand, reducing the mold surface velocity could slow down the replenishment rate of “fresh” molten steel, then the concentration gradient of [Al] between the liquid-steel and slag-steel interface was decreased, leading to a slower reaction rate. On the other hand, weak surface fluctuation could reduce the slag-steel interface area, thus reducing the capacity mass transfer coefficient of interfacial mass transfer, as well as the reaction rate.

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Physical Modeling of Asymmetrical Flow in Slab Continuous Casting Mold due to Submerged Entry Nozzle Clogging with the Effect of Electromagnetic Stirring

Bin Li, Haibiao Lu, Zhe Shen, Xiaohui Sun, Yunbo Zhong, Zhongming Ren, Zuosheng Lei

pp. 2264-2271

DOI:

10.2355/isijinternational.ISIJINT-2018-866

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Submerged Entry Nozzle (SEN) clogging is a serious problem for continuous casting process and slab quality. In order to investigate the impact of the SEN clogging rate on the flow field and the optimization effect of electromagnetic stirring (EMS) on the asymmetrical flow due to the SEN clogging, a 1:5 scaled mercury model, with various SEN clogging rates and different electromagnetic stirring currents was established and the flow velocity was measured by means of Ultrasonic Doppler Velocimetry (UDV). S index is introduced to judge quantitatively whether the horizontal flow pattern is symmetrical or not. The results show that the symmetry of the flow pattern in the mold becomes broken with the increase of the SEN clogging rate. In this study, EMS is an effective method to increase S index and active the free surface flow when the SEN clogging rate is under 50%. However, the stirring current of EMS should be controlled to avoid the adverse surface flow which may induce slag entrapment.

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Influence of Ambient and Oxygen Temperatures on Fluid Flow Characteristics Considering Swirl-type Supersonic Oxygen Jets

Lingzhi Yang, Zeshi Yang, Guangsheng Wei, Yufeng Guo, Feng Chen, Fuqiang Zheng

pp. 2272-2282

DOI:

10.2355/isijinternational.ISIJINT-2019-030

抄録

In vanadium extraction converter steelmaking, the swirl-type oxygen lance has been applied to improve the dynamic condition of the molten bath reaction to achieve a higher oxidation rate of vanadium and better vanadium slag quality, because the swirl-type jet can generate not only axial and radial forces but also tangential ones. Recently, the swirl-type supersonic jet with preheated oxygen was proposed to further enhance the agitation ability of the oxygen jet on the molten bath. In this study, the effects of the ambient temperature and oxygen temperature on the swirl-type supersonic jet behavior were analyzed to achieve better formulation and optimization of the process parameters. The flow characteristics of swirl-type oxygen jets were simulated by computational fluid dynamics software at 300 K, and 1700 K ambient and 300 K, 450 K and 600 K oxygen temperature, and partial results were validated against data from a preheating jet experiment. An analysis of the results shows that the centerline jet velocity was increased by preheated oxygen, and at higher ambient temperature, a longer core length was formed and the velocity fluctuation was aggravated. The influence of the preheating temperature on the core length was more evident at lower ambient temperature. From a dynamic perspective, the molecular motion was improved and with respect to energy, the internal energy of the oxygen jets could be preserved at higher ambient temperature.

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Effect of a Novel Hot-core Heavy Reduction Rolling Process after Complete Solidification on Deformation and Microstructure of Casting Steel

Hai-jun Li, Tian-xiang Li, Rui-hao Li, Mei-na Gong, Zhao-dong Wang, Guo-dong Wang

pp. 2283-2293

DOI:

10.2355/isijinternational.ISIJINT-2019-125

抄録

Hot-core Heavy Reduction Rolling (HHR2) is a novel technology designed for eliminating center defects of casting steel by using the large temperature gradient, which performed heavy reduction to bloom or slab with rolling mill after the position of solidification end of the strand. This works mainly focus on the effect of HHR2 process on the shrinkage elimination and microstructure evolution. Firstly, bonding plate rolling experiment were carried out, which proved HHR2 process with large temperature gradient in thickness direction could improve the internal deformation of workpiece. Meanwhile, the deformation permeability was beneficial to the microstructure refinement of center layer. Secondly, the HHR2 process was studied by analysis of the results of FEM to explore the influence of some process parameters on shrinkage closure. In this study, the Gm index and volumetric residual percentage V/V0 were used as evaluation index in mechanical analyses and quantitative comparison, the results reflected the void tend to closing with the reduction ratio and roll diameter increasing, as well as with the reduction position moving towards the solidification end after complete solidification. Finally, the pilot plant trail of HHR2 was carried out before industrial application, and the results reflects the HHR2 process can eliminate the large central shrinkage cavity and refine the center microstructure.

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Effect of Laminated Structure on Mechanical Properties of Composition-modulated Co–Ni Laminated Plating

Kohei Ishida, Takayuki Nagataki, Takuo Nakade, Tsutomu Morikawa, Masao Miyake, Tetsuji Hirato

pp. 2294-2301

DOI:

10.2355/isijinternational.ISIJINT-2019-293

抄録

A composition-modulated Co–Ni laminated plating has been developed to prolong the lifetime of molds to be employed in continuous steel casting. We have investigated the relationship between the laminated structure and the mechanical properties of the plating films. The tensile strength of as-plated film was enhanced by the thinned thickness of the constituent layers, while the elongation received no effect of the thickness change of the constituent layer and remained almost stable in the range from 3 to 5%. Heat treatment at 400°C have brought about the improvement both in the tensile strength and the elongation. The improvement in the elongation was as remarkable as reached 13% in the film composed of layers with a thickness of 0.8 µm. The layer with low Ni content had an hcp structure, and that with high Ni content produced two phases of the hcp and fcc structures in the as-plated state. By the heat treatment, the high Ni-content layer turned into the single fcc phase, while the low Ni-content layer kept the hcp phase, and accordingly, the film structure changed into the one where the lamination of the hcp and fcc layers was distinct. The fact that the fcc layers, which was easily deformed, were formed continuously in the lateral direction, was seemed to contribute to the significant improvement in the elongation after heat treatment.

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Roles of Inclusion, Texture and Grain Boundary in Corrosion Resistance of Low-Nickel Austenite Stainless Steel Containing Ce

Guojun Cai, Yuting Pang, Yanru Huang, Raja Devesh Kumar Misra

pp. 2302-2310

DOI:

10.2355/isijinternational.ISIJINT-2019-248

抄録

The roles of inclusion, texture and grain boundary in corrosion resistance of low-nickel austenite stainless steel containing Ce was investigated by using SEM, TEM, EBSD, XRD and testing technology of electrochemistry. The results revealed that the variation in corrosion resistance of 205 stainless steels containing Ce was higher than specimen without Ce, which depended on ∑3n boundaries and Ce modifying inclusion treatment. Ce addition to steels was prone to forming fine and dispersive Ce multi-phase inclusions containing CeAlO3, CeS and Ce2O2S. When addition of Ce was up to 0.016 wt.%, its textures were characterized by pronounced γ-fiber textures comprising {111} <110> and {111} <112> components, as well as the frequency of ∑3n boundaries related to {111} <112>, {111} <110> and {112} <110> components was significantly improved, which was in favor of corrosion resistance improvement. While adding 0.023 wt.%Ce element was detrimental to corrosion resistance of stainless steel.

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A Non-steady State Model for the Austenite-to-ferrite Transformation Kinetics under the Non-partition Condition in Fe–C–Mn Alloys

Akira Seki, Kotarou Hayashi, Takafumi Amino, Genichi Shigesato, Takayuki Nozaki, Masafumi Azuma, Masayoshi Suehiro

pp. 2311-2318

DOI:

10.2355/isijinternational.ISIJINT-2019-216

抄録

A non-steady state model describing the transition from the para-equilibrium to the local equilibrium under the non- or negligible-partition condition is proposed to investigate the austenite to ferrite transformation kinetics in Fe–C–Mn steels. The present model has been developed based on the quasi-steady state model used for calculating the solute drag force by the segregated solute within the ferrite/austenite interface, although the solute-drag force is not calculated in the present model. The calculated Mn profiles are compared with the STEM-EELS observation reported previously by some of the present authors. The temporal evolution of the Mn profiles during PE to NPLE is shown. Combining a simple C diffusion model, the transition path from PE to NPLE on the C–Mn isothermal section of an Fe–C–Mn alloy is also presented.

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Cracking Process Related to Hydrogen Behavior in a Duplex Stainless Steel

Afshin Yousefi, Goroh Itoh, Zoha Ghorani, Shigeru Kuramoto

pp. 2319-2326

DOI:

10.2355/isijinternational.ISIJINT-2019-159

抄録

Cracking process in hydrogen embrittlement (HE) of a duplex stainless steel (DSS) was investigated. Annealed DSS (SUS329J4L) specimens with phase volume fraction of about 50:50 were electrolytically hydrogen-charged and deformed in ambient atmosphere at a strain rate of 1.38×10−4 s−1. Microcracks were observed mostly to start and pass in the ferrite phase in the course of the deformation. In contrast, austenite phase acted as an obstacle against crack propagation. Delamination was also observed in accord with the authors’ previous study, and the delamination crack also initiated and propagated in ferrite phase. Hydrogen microprint technique (HMPT) revealed that hydrogen atoms migrate mainly in ferrite phase over the distance of the sample thickness. Considering this long diffusion distance of hydrogen, dimpled area observed around the center of the fracture surface was attributable to the sharp increase in the strain rate because of the localized deformation arising from the major crack propagation. HMPT also revealed a marked effect of elastic stress on the acceleration of hydrogen diffusion. Thermal desorption spectroscopy (TDS) confirmed that some of the hydrogen diffuses out during keeping the specimen in the ambient atmosphere, which was accelerated by deformation during keeping presumably by the mechanism of hydrogen transport with gliding dislocations. Furthermore, TDS results demonstrated that the majority of the hydrogen migrated and was trapped by a site with lower binding energy during the deformation.

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Hydrogen Embrittlement Induced by Hydrogen Charging during Deformation of Ultra-high Strength Steel Sheet Consisting of Ferrite and Nanometer-sized Precipitates

Katsutoshi Takashima, Ruoyu Han, Ken’ichi Yokoyama, Yoshimasa Funakawa

pp. 2327-2333

DOI:

10.2355/isijinternational.ISIJINT-2019-219

抄録

The hydrogen embrittlement behavior of an ultra-high strength steel sheet consisting of ferrite and nanometer-sized precipitates has been investigated by a tensile test and sustained tensile-loading test. The amount of absorbed hydrogen of the present ferritic steel is significantly larger than that of the conventional martensitic steels. Hydrogen thermal desorption analysis indicates that a large amount of diffusible hydrogen exists and the nanometer-sized precipitates act as trap sites of hydrogen. In a tensile test in air after the saturation amount of hydrogen charging, the fracture strain decreases slightly. However, in a tensile test during hydrogen charging, the fracture strain decreases markedly despite a small amount of absorbed hydrogen, and the morphology of the fracture surface exhibits a unique brittle mode. Upon pre-straining, the saturation amount of hydrogen is more than doubled and the tensile properties deteriorate further. In the sustained tensile-loading test during hydrogen charging, no delayed fracture occurs even under high applied stress. No effects of hydrogen charging on stress relaxation are observed. The results of the present study imply that the increase in the hydrogen content enhances the degradation of tensile properties, but the hydrogen content is not necessarily an index of the hydrogen embrittlement of the ferritic steel. The dynamic interactions between hydrogen and deformation, and particularly, the continuous interactions during hydrogen charging, play important roles in hydrogen embrittlement.

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EBSD- and ECCI-based Assessments of Inhomogeneous Plastic Strain Evolution Coupled with Digital Image Correlation

Ryohei Kakimoto, Motomichi Koyama, Kaneaki Tsuzaki

pp. 2334-2342

DOI:

10.2355/isijinternational.ISIJINT-2019-232

抄録

We measured the local grain orientation gradient and dislocation density using electron backscatter diffraction (EBSD) measurement and electron channeling contrast imaging (ECCI) to obtain strain maps near a stress concentration source in pure nickel (Ni) as a face-centered cubic (FCC) model sample. In particular, we obtained the relationship amongst the grain orientation spread (GOS), dislocation density, and equivalent plastic strain on the sample surface, which were obtained by EBSD, ECCI, and digital image correlation (DIC), respectively. After obtaining the GOS-strain and dislocation density-strain relationships, the strain distribution in the interior of the sample was also determined by measuring the GOS and dislocation density, which were linearly correlated. The dislocation density-strain relationship exhibited a relatively small deviation.

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Atomic and Effective Pair Interactions in FeC Alloy with Point Defects: A Cluster Expansion Study

Tien Quang Nguyen, Mary Clare Sison Escano, Kazunori Sato, Yoji Shibutani, Tamio Oguchi, Tetsuo Mohri

pp. 2343-2351

DOI:

10.2355/isijinternational.ISIJINT-2019-019

抄録

The Cluster Expansion Method (CEM) is used to investigate the pair interactions in body centered cubic (BCC) FeC alloy in the presence of vacancies. Within the CEM framework, the relation of cluster (point and pair) probabilities and set of independent correlation functions are derived. These are then applied to calculate the effective cluster interaction and atomic pair interaction energies for Fe, C and vacancy in FeC system. We found that, in this alloy, the interaction mostly comes from the first nearest neighbor pairs, and, to some degree, from the third nearest neighbor pairs. Detailed analysis shows that, within the first nearest neighbor pair interactions approximation, the C–C and Fe–C pair interactions are repulsive where the former one is more dominant. This is attributed to the local stress field formed in the vicinity of C atoms which pushes the first nearest neighbor atoms away to maintain the equilibrium distances. Moreover, there is an attractive interaction between C and vacancy which implies the possibility of C atoms to be trapped at vacancy site.

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Fabrication of Iron Oxide Nanoparticles via Submerged Photosynthesis and the Morphologies under Different Light Sources

Lihua Zhang, Melbert Jeem, Kazumasa Okamoto, Seiichi Watanabe

pp. 2352-2358

DOI:

10.2355/isijinternational.ISIJINT-2019-188

抄録

Recently, metal oxide nanocrystallites have been synthesized through a new pathway, i.e., the submerged photosynthesis of crystallites (SPSC), and flower-like ZnO and CuO nanostructures have been successfully fabricated via this method. In this work, the SPSC process was applied for the fabrication of iron oxide and hydroxide nanoparticles. The experiments were conducted under visible light, ultraviolet light, and gamma-ray irradiation conditions and the morphologies of the obtained nanoparticles were observed and compared with that obtained without illumination. Then, the mechanism of the SPSC process for the fabrication of iron oxide nanoparticles was discussed. The results show that various kinds of morphologies of nanocrystallites were obtained on the Fe plate surface and the main morphologies are different under different conditions. For example, most FeOOH with the morphologies of nanorod and nanofiber exist by visible light irradiation; most faceted crystals of FeOOH and Fe2O3 with the morphologies of nanograular and nanorod exist by ultraviolet irradiation. In the SPSC process, light irradiation generates ·OH at the crystal tips and promote the crystallization in apical growth of FeOOH.

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