ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 57 (2017), No. 11

  • Effect of MnO on High-Alumina Slag Viscosity and Corrosion Behavior of Refractory in Slags

    pp. 1887-1894

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    DOI:10.2355/isijinternational.ISIJINT-2017-120

    The influence of MnO on viscosities of CaO–SiO2–MgO–Al2O3–Cr2O3-based slags and the corrosion mechanism of carbon composite brick used in blast furnace hearth by slags was investigated in this work. From the viscosity experimental results, it was indicated that the viscosity decreased with the addition of MnO. The break point temperature decreases from 1655 to 1632 K and the apparent activation energy decreases from 217.54 to 185.90 kJ mol−1 with the increasing MnO content from 0 to 3 wt.%. The FTIR spectra analyses revealed that MnO exists as a network modifier and the polymerization degree of the slag decreases with the rising content of MnO. The corrosion of carbon composite brick by molten slag could be a consequence of dissolution, slag penetration and slag-refractory reaction, and the degradation of the brick becomes intenser with the addition of MnO.
  • Viscosity of Heterogeneous Silicate Melts: Assessment of the Measured Data and Modeling

    pp. 1895-1901

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    DOI:10.2355/isijinternational.ISIJINT-2017-288

    The measured viscosity data of solid-bearing silicate melts from low to high solid fractions in the last 50 years are reviewed. The compiling of these data and the examination of the structural evolution with increasing solid fraction indicate the existence of three rheological regimes: a gradual viscosity increase in the liquid-like regime, an accelerated viscosity increase in the transitional regime and a viscosity plateau in the solid-like regime. An empirical viscosity model based on the modification of the Avrami equation is proposed, enabling viscosity calculation of the solid-bearing silicate melt over the full solid fraction ranges from 0 to 100 vol.%.
  • Effect of Particle Penetration Depth on Solid/liquid Mass Transfer Rate by Particle Blowing Technique

    pp. 1902-1910

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    DOI:10.2355/isijinternational.ISIJINT-2017-336

    In this study, cold model experiments on particle blowing were carried out to clarify the effect of particle penetration depth on solid/liquid mass transfer rate. A comparison of penetration depth obtained by experiment and CFD calculation using commercially available software was also carried out. The penetration depth was measured by a visual observation whereas the solid/liquid mass transfer rate was obtained from the ion-exchanged reaction between Na+ on pearlite particles and H+ in HCl aqueous solution. Both of the penetration depth and solid/liquid mass transfer rate increased with the increase in particle feed rate and top blowing gas flow rate, and the decrease in lance height and particle diameter. The following non-dimensional equation of particle penetration depth was obtained by several non-dimensional numbers:
    [ This part of text is omitted ]
    where, ReP: particle Reynolds number, Fr: Froude number, We: Weber number, ρl and ρp: liquid and particle densities (kg/m3), respectively. A good agreement was confirmed by the experiment. The particle penetration depth was also calculated by a combination of VOF and DEM model and it was in good agreement with the experiment. The solid/liquid mass transfer coefficient calculated by the CFD simulation and Froessling equation increased with the increase in top blowing gas flow rate, particle feed rate and penetration depth. The solid/liquid interfacial area was expressed by a function of penetration depth.
  • CFD Study on the Heavy Oil Lance Positioning in the Blast Furnace Tuyere to Improve Combustion

    pp. 1911-1920

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    DOI:10.2355/isijinternational.ISIJINT-2017-213

    Auxiliary fuels are used to replace expensive coke in two ways, as a reducing agent for iron oxides and to provide energy for the blast furnace operation. Poor combustion of heavy oil produces soot and cenosphere, which plug the coke bed and lead to an increased pressure drop and lower the productivity of blast furnace. In the study a new combustion model for heavy oil in a blast furnace is explained. Droplet atomization is modelled with the wave breakup model and the combustion consists of droplet vaporization and gas phase combustion with a detailed combustion model. Three different lance positions were modelled to evaluate the effect of lance position on combustion and blast furnace operation. The study is limited to the tuyere-raceway area, where e.g. mixing between air blast and heavy oil, pressure drop and combustion have been investigated. The most promising position based on this study is to move the injection lance 10 cm downstream from the tuyere nose. The results show that the pressure drop increases when the lance is moved inside the tuyere, but the pressure drop growth is moderate until the lance is at least 10 cm downstream from the tuyere nose. According to the results the pressure drop versus lance position behavior is similar to an experimental study previously described in the literature. In addition the combustion behavior was found to be similar to the actual blast furnace.
  • Effect of Sulfur on Carburization and Melting Behavior of Iron by CO Gas

    pp. 1921-1927

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    DOI:10.2355/isijinternational.ISIJINT-2017-224

    In-situ observation of carburization and melting behavior of sulfur saturated iron by CO gas and carbon concentration measurement were carried out to discuss the effect of sulfur. The time for starting the melt formation on the sulfur saturated iron is twice longer than that on iron without sulfur because the average carburization rate of former iron is very slow compared with that of latter one. On the other hand, the time from reaching the saturated carbon concentration to starting the melt formation is short. The reason may be that the carburization rate is large when the carbon concentration reaches to the saturated one and the critical energy for the melt formation is smaller. The carburization to sulfur saturated iron is mixed control of desorption reaction of oxygen and sulfur on the iron surface and diffusion of carbon and sulfur into iron.
  • Acceleration of Carburization and Melting of Reduced Iron in Iron Ore–Carbon Composite Using Different Types of Carbonaceous Materials

    pp. 1928-1936

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    DOI:10.2355/isijinternational.ISIJINT-2017-249

    In the ironmaking process, not only faster reduction of iron ore but also the acceleration of carburizing and melting of reduced iron is very important to save energy. In this study, the use of different types of carbonaceous materials having the superior functions for reducing and carburizing is suggested for the acceleration of carburization and melting of reduced iron in a iron ore–carbon composite.A tablet sample made of mixed powder of iron ore and carbonaceous materials such as coal, charcoal, coke, and graphite was heated up to 1573 K, and its reduction, carburization, and melting behaviors were evaluated. It was found that coal and charcoal, which generate reducing gases at lower temperature, are suitable for the reducing agents. On the other hand, graphite and coke should be used as carburizing agents because of their lower reactivity with CO2. Using coal and graphite for the reducing and carburizing agents, respectively, accelerates the carburization and melting of reduced iron in the composite unlike when only coal is used. The effect of the particle size of graphite on the carburization is strong. Carbon concentration in the reduced iron in the composite held at 1573 K for 1.8 ks increases with increasing particle size of graphite. Reduction of iron ore is accelerated by mix-grinding of the ore and reducing agent. The carburization is accelerated using charcoal as the reducing agent, whereas agglomeration of melted iron in the mixed grinding sample is inhibited when the reducing agent comprises coal and graphite.
  • Effect of Iron Ore Concentrate on Sintering Properties

    pp. 1937-1946

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    DOI:10.2355/isijinternational.ISIJINT-2017-276

    According to sinter pot experiments, with increases in coarser commercial concentrates (mean size 0.1–0.3 mm) in iron ore blends, the productivity of sinter decreased 5–7% for each 10 mass% concentrate increased. With increases in finer commercial concentrates (mean size 0.02 mm) of 10–30 mass%, the productivity did not alter significantly. With an increase in 10–20 mass% micro-particle concentrate (mean size 0.01 mm) pulverized from the coarser commercial concentrate, the productivity increased 3–11%. The portion of −20 µm in iron ore concentrate favoured the granulation and the productivity in conventional sintering, but the portion of +45 µm had the reverse effects.With increases in finer commercial concentrates (10–40 mass%) combined with low grade ore (10–20 mass%) in iron ore blends, the productivity also did not obviously change.Compared with conventional sintering process, using the intensive mixer in an intensive mixing process or a separate granulation process could improve the productivity of sinter around 2 or 3% respectively.
  • Impact of Potassium on Gasification Reaction and Post-Reaction Strength of Ferro-coke

    pp. 1947-1954

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    DOI:10.2355/isijinternational.ISIJINT-2017-292

    Ferro-coke is an advanced kind of coke, to clarify the behavior of its gasification affected by alkalis is very important for its practical use in blast furnace. In this paper, potassium was added to sample by soaking and boiling it in K2CO3 aqueous solution, the variation of coke weight loss vs time was measured with the thermogravimetry approach, the Tablets Coke Method was applied for measurement of the reactivity and post-reaction strength of cokes, and the gasification reaction mechanism was analyzed based on the Shrinking-Core Model (SCM). This work demonstrated that potassium had a catalytic effect on ferro-coke gasification in terms of a decrease in the starting reaction temperature and reaction activation energies. In comparison with traditional coke, when no K2O was added, the reactivity index of ferro-coke was higher and the post-reaction strength index of ferro-coke was lower, while as a same amount of K2O was added and in respect to these two indices, the direction of variation of ferro-coke was the same and the extent of variation of ferro-coke was slightly higher. Different from traditional coke, when temperature ranges from 950 to 1050°C and the degree of burning-off is within 50%, the reaction of ferro-coke is always mixed controlled by chemical reaction and inner diffusion.
  • Effect of Municipal Solid Waste Incineration Fly Ash Addition on the Iron Ore Sintering Process, Mineral Phase and Metallurgical Properties of Iron Ore Sinter

    pp. 1955-1961

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    DOI:10.2355/isijinternational.ISIJINT-2017-310

    Municipal solid waste incineration (MSWI) fly ash is well known as hazardous waste, for promoting its harmless treatment and resource utilization, a new process was proposed by utilizing the iron ore sintering process employed massively in iron and steel industry. In this article, the feasibility of this process was estimated from the point of the effects of MSWI fly ash addition on the iron ore sintering process, sinter mineral phase structure and metallurgical properties through the sintering pot experiments, the reduction and melt-dropping experiments at different temperature. Results show that, for the sintering process, the flame front speed, the sinter productivity, the drum index and the yield of sinter decrease with the increasing of MSWI fly ash addition; for the sinter metallurgical properties, with the increasing of MSWI fly ash addition, the lower temperature reduction property (RDI) is improved obviously, the soft-dropping property is worsened; but the effect of MSWI fly ash addition on the middle temperature reduction property (RI) is not obvious; for the sinter mineral phase, the phase fraction of the silico-ferrite of calcium and aluminum (SFCA) and the calcium silicate (CS) both increases with the increasing of MSWI fly ash addition. The complex of oxides, silicates and chlorides with lower melting point in the MSWI fly ash change the formation of sinter mineral phase and its composition essentially, which further effect the sintering process and the metallurgical properties.
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    Readers Who Read This Article Also Read

    1. Impact of Potassium on Gasification Reaction and Post-Reaction Strength of Ferro-coke ISIJ International Vol.57(2017), No.11
    2. Effect of Iron Ore Concentrate on Sintering Properties ISIJ International Vol.57(2017), No.11
    3. Effect of Particle Penetration Depth on Solid/liquid Mass Transfer Rate by Particle Blowing Technique ISIJ International Vol.57(2017), No.11
  • Modeling of Slag Entrainment and Interfacial Mass Transfer in Gas Stirred Ladles

    pp. 1962-1970

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    DOI:10.2355/isijinternational.ISIJINT-2016-589

    In gas stirred steelmaking ladles, entrainment of liquid slag into liquid steel and vice versa takes place. Qualitatively, slag entrainment is known to increase slag-metal interfacial reaction rates. However, it is unknown how the entrainment is quantitatively affected by gas stirring rate and the properties of the slag and metal. In this paper the modelling of slag entrainment is resolved into several sub-models to determine the interfacial reaction rates between slag and metal for the droplets and other interfaces. The model predictions are in line with literature values for refining rates and also rationalize the effects of ladle size and number of gas injection plugs.
  • Modeling of Gas-Steel-Slag Three-Phase Flow in Ladle Metallurgy: Part I. Physical Modeling

    pp. 1971-1979

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    DOI:10.2355/isijinternational.ISIJINT-2016-710

    To obtain a better understanding the gas-steel-slag three-phase flow in ladle metallurgy with eccentric gas bubbling, both the single-plug-stirred and dual-plug-stirred water model systems were employed. The plume Froude number derived from the buoyancy of the bubble plume was used to characterize the plume two-phase flow. The elctrical conductivity measurement technique was applied to measure the mixing time. A video technique was used to monitor the slag eye and the open software called ImageJ was taken to quantify the slag eye area. Some experiments were carried out to determine the location of the probe in the ladle where the measured mixing times can be interpreted as the bulk mixing times. The eccentric gas injection in the ladle bottom can improve the mixing efficiency in the ladle. Shorter mixing times can be achieved by injecting gas through two porous plugs, located diametrically opposite at mid-bath radius position (α=180°). A critical gas flow rate is proposed based on the formation of slag eye. The mixing time will decreases sharply at the condition of slag eye formation and collapse alternately. The critical gas flow rate increases with increasing the slag layer thickness and decreasing the porous plug angles. Four fators effect on the slag eye area were investigated: the gas flow rate, slag layer thickness, porous plug locations and angles. A semi-empirical model was developed based on the experimental data of the present work to describe the slag eye area as a function of the heights of the two liquids and the gas flow rate. The present correlation for slag eye area was reviewed against many previous different liquid-liquid systems.
  • Modeling of Gas-Steel-Slag Three-Phase Flow in Ladle Metallurgy: Part II. Multi-scale Mathematical Model

    pp. 1980-1989

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    DOI:10.2355/isijinternational.ISIJINT-2017-069

    Gas stirring ladle is a complex three-phase reactor which contains phases whose interfaces are in different scales. The bubble-liquid interaction also leads to multi-scale eddy structures. The present work proposes a multi-scale mathematical model to simulate the multiphase flow in ladle, which directly captures large phase interfaces and eddies, while models sub-grid scale interfaces and eddies using respectively discrete bubble model (DBM) and one equation eddy viscosity model (OEEVM) in large eddy simulation (LES) approach. By this way, the mesh resolution can be defined relatively coarse to save computational resources. The volume of fluid (VOF) model coupled with the compressive interface capturing scheme for arbitrary meshes (CICSAM) is adopted for the slag surface, while the DBM is used for handling the dynamics of discrete bubbles. The bubble coalescence is considered using the O’Rourke’s algorithm to solve the bubble diameter redistribution and it is found that aggregation mostly occurs below 0.2 m from the inlet. Moreover, bubbles are removed after leaving the air-liquid interface and the mass is transferred to air. The flow with multi-scale eddies induced by bubble-liquid interaction is solved using LES. The slag droplet entrainment and the slag-eye size fluctuation related with the pressure fluctuation on gas inlet are well revealed. The time-averaged spout eye size and the bubble diameter evolution are validated against the experimental data. The results show that the multi-scale VOF-DBM-LES model provides an effective modeling framework to predict the intrinsically unsteady flow behaviors in ladle.
  • Effect of Tunnel Filters on Flow Characteristics in an Eight-strand Tundish

    pp. 1990-1999

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    DOI:10.2355/isijinternational.ISIJINT-2017-165

    Fluid flows in an eight-strand tundish with tunnel filters have been investigated with physical modeling and mathematical simulation methods. This paper mainly studies the effect of tunnel filters install location and turning corner angle on the flow characteristics. In 1/3 scale tundish model experiments, RTD curves were used to study the flow characteristics in tundish with different configurations. The molten steel flow velocity and temperature fields were calculated by the commercial CFD package FLUENT. The result shows that tunnel filters play an important role in promoting flow characteristics. Suppose the tundish was divided into two regions by baffles, defined as sub-tundish a and sub-tundish b. The tunnel filters distinguished and enhanced the metallurgical function of each region, that is sub-tundish a is the inclusion collision and aggregation region and the main metallurgical function of sub-tundish b is uniform the temperature and remove large inclusions. The corner angle of tunnel filters has a great influence on the dead volume fraction, and the install location plays a key role in the assignment proportion of plug volume between sub-tundish a and sub-tundish b. By overall evaluation and contrast analysis, the tundish equipped with 120° tunnel filters long distance to the pouring point, was identified as the optimal tundish configuration. Industrial experiment verified the simulation results and had proved that the tundish with tunnel filters can effectively improve the removal efficiency of small inclusion(>5 µm).
  • Morphology of Solidification Structure and MnS Inclusion in High Carbon Steel Continuously Cast Bloom

    pp. 2000-2009

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    DOI:10.2355/isijinternational.ISIJINT-2017-294

    Present study was undertaken to investigate the characteristics of solidification structure and sulfide inclusions in the rail steel U75V continuously cast bloom using various methods, including the metallographic examination, traditional 2D optical microscopy, 3D electrolytic extraction, SEM detection with EDS analysis, and thermodynamic calculation for MnS inclusion precipitation. Metallographic examination shows that the area ratio of chill zone, columnar zone, mixed zone and equiaxed zone in the cast bloom are 5.3%, 43.1%, 21.5% and 30.1%, respectively. 2D/3D investigations on the morphology and distribution of sulfide inclusions reveal that the sulfide inclusions in the subsurface region with smaller equivalent diameter and lower aspect ratio are more fine and rounded compared with those in the bulk, and more complex sulfide inclusions consisting of MnS and TiS with the nuclei of Al2O3 particle are observed in the bloom centre. Moreover, the size and distribution of MnS inclusion precipitation in the rail steel U75V continuously cast bloom was numerical predicted, using the heat transfer model for continuous casting coupled with thermodynamic model for MnS inclusion precipitation, and the parametric study show that sulfide inclusions are much larger in size for the continuously cast bloom with high sulfur content and coarse cast structure.
  • Evaluation Method for Low Temperature Toughness of Weld Seam of HFW Pipe Based on the Distribution of Scattered Type Penetrator

    pp. 2010-2015

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    DOI:10.2355/isijinternational.ISIJINT-2017-092

    We found the correlation between low temperature toughness of the weld seam and the echo level from a scattered-type penetrator consisting of micro oxides in high frequency welding pipes. Conventionally, the low temperature toughness is evaluated by Charpy impact test. The factors that affect the quality of the weld seam were investigated by using an ultrasonic C-scan with a focused probe and samples sliced from the weld seam. As a result, it was found a scattered-type penetrator consisting of micro oxides is a key factor affecting low temperature toughness. Absorbed energy obtained by Charpy impact test can be evaluated by the ultrasonic echo amplitude with the optimized focused beam size (about 1 mm2) to detect the scattered-type penetrators.
  • Mold Oscillation Feedforward Control Algorithm for Sinusoidal Oscillation of Various Asymmetries

    pp. 2016-2021

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    DOI:10.2355/isijinternational.ISIJINT-2017-215

    A feedforward control algorithm for the mold oscillators of a continuous casting process is proposed for both sinusoidal and non-sinusoidal oscillations. As steel industries grow, processes allowing for faster continuous casting are required in order to keep up with production demands. To achieve a quicker, continuous casting process, while maintaining slab quality, requires mold oscillations that make use of improved powder consumption rate and reduced friction force. Recently, non-sinusoidal oscillations have been researched owing to their advantages in regards to lubrication and friction. There have been several mechanical approaches but no algorithmic approaches. In this paper, a feedforward control algorithm consisting of embedded input shape and feedforward velocity control algorithms is proposed. Although conventional feedback controls have been commercialized for technical applications, the input shape control algorithm can prevent the non-negligible phase delays or amplitude reduction problems caused by a slow response of systems. In addition, the proposed feedforward velocity control algorithm is derived from the relationship between the valve input and mold velocity, and it allows the mold to correctly follow the non-sinusoidal oscillation. To determine the feasibility of the proposed algorithm, a Matlab Simulink model is derived from the mathematical model. Additionally, 1/100 scale specimen of a typical industry mold oscillator is used. The tests on the specimen showed that the proposed feedforward control algorithm could achieve precise control for both sinusoidal and non-sinusoidal oscillations.
  • Ensemble Non-Gaussian Local Regression for Industrial Silicon Content Prediction

    pp. 2022-2027

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    DOI:10.2355/isijinternational.ISIJINT-2017-251

    Due to the complicated characteristics of modeling data in industrial blast furnaces (e.g., nonlinearity, non-Gaussian, and uneven distribution), the development of accurate data-driven models for the silicon content prediction is not easy. Instead of using a fixed model, an ensemble non-Gaussian local regression (ENLR) method is developed using a simple just-in-time-learning way. The independent component analysis is utilized to handle the non-Gaussian information in the selected similar data. Then, a local probabilistic prediction model is built using the Gaussian process regression. Moreover, without cumbersome efforts for model selection, the probabilistic information is adopted as an efficient criterion for the final prediction. Consequently, more accurate prediction performance of ENLR can be obtained. The advantages of the proposed method is validated on the online silicon content prediction, compared with other just-in-time-learning models.
  • Small-angle X-ray Scattering Studies on Aging Precipitation of High-strength Soft-magnetic Stainless Steels

    pp. 2028-2033

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    DOI:10.2355/isijinternational.ISIJINT-2017-170

    We investigated the effect of alloying elements Ni, Al, and Mo on the mechanical properties of precipitation-hardened soft-magnetic stainless steels, whose aging condition and chemical composition were varied. Thermodynamic calculations suggested that the aging treatments led to precipitation of a β-NiAl compound with B2 structure and Fe2Mo-type Laves phases. Although coarse precipitates, which are less effective for precipitation hardening, were observed in bright-field images obtained by transmission electron microscopy (TEM), the B2-type precipitates were detected in TEM electron diffraction patterns. By changing the concentration of the alloying elements, the B2-type β-NiAl precipitates were mainly responsible for the precipitation hardening, and the Vickers hardness was hardly affected by the Mo content. Small-angle X-ray scattering analysis was used to determine the size and number density of the fine β-NiAl precipitates, which contributed to the hardening. The high-density β-NiAl precipitates grew to a few nanometers in radius after an adequate period of aging, suggesting that the β-NiAl precipitates were responsible for the precipitation-hardening characteristics. On the other hand, the size of the precipitates was less affected by the amounts of Ni and Al, and the number density decreased with decreasing Ni and Al content. The improvement in hardness resulting from the β-NiAl precipitates had a linear relationship with the square root of the product of the precipitate size and number density.
  • Effect of Cold Rolling before Hydrogen Reduction on Reduction Behavior and Morphologies of Oxide Scale on Hot-rolled Low-carbon Steel

    pp. 2034-2041

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    DOI:10.2355/isijinternational.ISIJINT-2017-266

    A new ‘acid-free picking’ method that adding cold rolling prior to hydrogen-reduction descaling was put forward in this study. The purpose of cold rolling was to break the completeness of oxide scale and increase reduction efficiency. Subsequently, the high-temperature reduction behavior of oxide scale on the surface of hot-rolled low carbon steel, which reacted with hydrogen after 10% deformation of cold rolling in 20%H2-Ar at the temperature range of 400–850°C, was investigated to validate the feasibility. The mass loss of specimens in the non-isothermal and isothermal reduction experiment was clearly measured by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) was used to observe surface morphology and cross-section microstructure of reduction products. The phase composition of reduction products was identified by X-ray diffraction (XRD). The experimental results indicated that the reduction reaction degree can be controlled by three main factors: reduction temperature, time and cold rolling. After 10% deformation of cold rolling, the completeness of original oxide scale was broken and then a large amount of micro-cracking appeared in oxide scale and the gap formed at oxide/substrate interface. The reduction rate of broken oxide scale was significantly faster than that of original oxide scale when the reduction temperature achieved more than 700°C. The effect of micro-cracking and gap on the mechanism of reduction process were clarified based on reaction of gas (H2) – solid (iron oxides) interface.
  • An Online Rolling Model for Plate Mill Using Parallel Computation

    pp. 2042-2048

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    DOI:10.2355/isijinternational.ISIJINT-2017-299

    A new online rolling model of the draft schedule setup for a plate mill has been developed. This model comprises plate temperature, rolling force function and flow stress calculations and their coupling for the roll separating force estimation. The roll separating force calculation is also used when the work roll gap control is made realising a precise plate thickness control for each rolling pass, which is often referred to as an adaptive control. The temperature model and roll separating force model, as well as its inverse calculation (calculate entry thickness from exit thickness and given roll separating force), are involved in the draft schedule setup calculations. Plate rolling is carried out according to the setup calculation results and thus the product plate quality is largely attributable to the setup calculation preciseness. In this model, a one dimensional finite element model is employed to the temperature calculation that enables a precise temperature control which is necessary for the Controlled Rolling (CR) technology. Another development includes the rolling force function model; a new mathematical model which takes the peening effect into account, derived from the three-dimensional rigid-plastic finite element calculations. Finally, a flow stress model is developed taking into account the metallurgical nature such as work hardening, recrystallization and recovery. The coupling of these models allows to a physical based precise model without unnecessary artificial fitting parameters.In addition, for eliminating the convergence loop, an attempt has been made introducing a multi thread computing using General Purpose computing on Graphic Processing Unit (GPGPU). Thanks to this parallel computing technique, the computational time was remarkably reduced. The model was installed in a process computer and some trial rolling tests were conducted.
  • Effect of Microstructural Features on Mechanical and Magnetic Properties of Austempered High-silicon Ductile Irons

    pp. 2049-2057

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    DOI:10.2355/isijinternational.ISIJINT-2017-167

    In this study, mechanical and magnetic properties of high silicon ductile irons (GJS 500-14- and GJS 600-10) with fully ferritic initial microstructures were investigated after being austempered at 270–390°C for 60 min. Results showed that hardness and strength as well as ductility are mainly controlled by morphologies and volume fractions of the phases in the austempered microstructures. More silicon in the chemical composition results in a significant decrement in ductility and toughness. For this reason, when high toughness is concerned, GJS 600-10 grade ductile iron containing more silicon should not be a preferred grade for austempering. In the view point of magnetic properties, saturation magnetization strongly depends on the austempering temperature, whereas remenance and coercivity are somewhat related to mean ferritic cell size and the solute atoms in the chemical composition.
  • Molecular Statics Simulation of the Effect of Hydrogen Concentration on {112}<111> Edge Dislocation Mobility in Alpha Iron

    pp. 2058-2064

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    DOI:10.2355/isijinternational.ISIJINT-2017-172

    To clarify the whole picture of hydrogen embrittlement (HE), an understanding of the elementary processes occurring during the fracture process is important. As one of the most important elementary processes of HE crack growth, the role of dislocation motion has been intensively studied. In this study, we performed molecular statics calculations to simulate the dislocation velocity in the presence of absorbed hydrogen atom from a gaseous hydrogen atmosphere. The dislocation motion was assumed to be a stress-dependent thermal activation process, and the energy barriers were investigated using the nudged elastic band method for the {112}<111> edge dislocation in alpha iron. In addition to the energy barrier for dislocation motion, those for hydrogen diffusion were also computed to evaluate the competitive motion of dislocations and hydrogen atoms. The hydrogen concentration was also evaluated using the hydrogen trap energy concept. The results indicate that an extremely low hydrogen concentration yields contradictory results such as softening or hardening depending on the applied stress. In contrast, with increasing hydrogen concentration, the dislocation velocity always decreases and results in hardening independent of the applied stress. Focusing on the dislocation motion, we propose a simplified classification map of hydrogen embrittlement mechanisms, which suggests the importance of the environment and stress conditions on the dominant mechanism of HE.
  • <110> Dislocation Junction Formation via the Coalescence between Nanoscale 1/2<111> Prismatic Dislocation Loops in Iron

    pp. 2065-2069

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    DOI:10.2355/isijinternational.ISIJINT-2017-173

    Accurate knowledge of dislocation reactions is crucial for understanding and controlling the macroscopic mechanical properties of α-iron and its alloys. A dislocation reaction: 1/2[111]+1/2[111]→[110] has never been observed. However, using in-situ transmission electron microscopy, we demonstrate that the two nanoscale 1/2<111> prismatic dislocation loops that undergo 1D glide motion approach and collide with each other to form a “high-energy” [110]-dislocation junction. This anomalous reaction cannot be understood within the framework of the elasticity.
  • Influence of Heat Collection Plate Structure on Thermoelectric Generation Unit Performance for Radiant Waste Heat Recovery in Continuous Casting Process

    pp. 2070-2079

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    DOI:10.2355/isijinternational.ISIJINT-2017-058

    In recent years, environmental issues such as global warming and the energy resource depletion have become serious matters. Waste heat recovery can be one of the key technologies to solve these issues. Thermoelectric generator (TEG) is one of the promising technologies expected to play an important role for steel plant’s waste heat recovery, particularly radiant heat from steel products which had not been used yet efficiently. Despite the improved performances of thermoelectric materials, more effort on a TEG unit is needed to maximize TEG system performance. In optimizing the TEG unit performance, the influence of the surface shape of the TEG units has been investigated. Two types of the heat collection plate have tested. The first one was with a fin structure and the second one was with plain plate structure. Based on the results of the simulation and the experiments, it can be concluded that a better performance will be achieved by the TEG unit which has plain type heat collection plate because of larger total heat flux input to TEG modules of the TEG unit with plain type heat collection plate structure compared to the fin type heat collection structure.

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