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

ISIJ International Advance Publication

  • Influence of H2–H2O Content on the Reduction of Acid Iron Ore Pellets in a CO–CO2–N2 Reducing Atmosphere

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    DOI:10.2355/isijinternational.ISIJINT-2019-734

    Using hydrogen as a reducing agent for iron production has been the focus of several studies due to its environmental potential. The aim of this work is to study the influence of H2–H2O content in the gas phase on the reduction of acid iron ore pellets under simulated blast furnace conditions. Temperature and gas compositions for the experiments were determined with multi-point vertical probes in an industrial blast furnace. The results of the reduction tests show that higher temperatures and H2 content increase the rate and extent of reduction. For all the gas and temperature combinations, morphological, mineralogical, and microstructure changes were observed using different characterization techniques. Microscopy images reveal that H2–H2O, in the gas phase, has a positive influence on reduction, with metallic iron forming at the pellet's periphery and core at lower temperatures compared to CO–CO2–N2 reducing gas. Porosity and surface area changes were determined using a gas pycnometer and the BET method. The results indicate that increasing the reduction temperatures and H2 content results in greater porosity and a larger surface area. Moreover, carbon deposition did not take place, even at lower temperatures. A rate minimum was detected for pellets reduced at 800°C, probably due to metallic iron formation, hindering the diffusion of reducing gases through the product iron layer.
  • Improvement in Reduction Behavior of Sintered Ores in a Blast Furnace through Injection of Reformed Coke Oven Gas

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    DOI:10.2355/isijinternational.ISIJINT-2020-063

    As an innovative route to mitigating CO2 emissions in ironmaking, increasing the hydrogen reduction in a blast furnace is promising. One possible method is the shaft injection or blast tuyere injection of coke oven gas (COG) with its hydrogen concentration enhanced by steam-reforming methane and tar. Therefore, the reduction behavior of sintered ores in a blast furnace by injecting reformed COG was investigated using a softening-melting tester and counter-current reaction simulator (BIS). The shaft injection of reformed COG promoted the reduction and improved the permeability of the ore layer, particularly in the wall area of the blast furnace. An injection rate larger than 200 Nm3/t-HM was required for reformed COG for a limiting intermediate distribution ratio of injection gas lower than 20% in a large blast furnace. Unchanged shaft temperature and increased hydrogen reduction were observed during the shaft injection of hot reformed COG in the BIS test. The water-gas shift reaction below the temperature of the thermal reserve zone was insignificant even for the shaft injection of reformed COG. As for tuyere injection, direct reduction was decreased by increasing the injection rate of reformed COG from tuyere. The injection of COG with or without reforming from tuyere reduced the carbon consumption of the blast furnace by 10 kg/t-HM. The influence of the composition of COG on carbon consumption was insignificant. Direct observation of hydrogen reduction revealed a decrease in flooding molten slag in the upper coke layer during reduction, thus explaining the improved permeability of the ore layers.
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  • Fundamentals of the Reduction of SFC in CO/CO2 Gas at 1000°C

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    DOI:10.2355/isijinternational.ISIJINT-2020-064

    SFC (Sillico-Ferrite of Calcium) is a kind of simplified SFCA (Sillico-Ferrite of Calcium and Aluminum) with no Al2O3. SFC and SFCA are believed to be the most desirable bonding phase in sinter. In order to better understand the fundamentals of the reduction of SFC, a series of experiments on the SFC reduction were carried out in the present work, including phase equilibria tested by XRD, morphology tested by SEM-EDS, and reduction pathway under the different CO/CO2 mixture gas at 1000°C. The experimental results indicated, (1) in the case of CO = 20% and 40%, most of Fe2O3 in SFC was reduced to FeO. The equilibrium phases were FeO, CaO·Fe2O3, and CaO·SiO2. (2) In the case of CO = 60%, CaO·Fe2O3 was reduced to generate FeO and 2CaO·Fe2O3. The equilibrium phases were FeO, 2CaO·Fe2O3, and CaO·SiO2. (3) In the case of CO = 80% and 90%, FeO was reduced to Fe, and 2CaO·Fe2O3 was reduced to generate Fe and CaO. The equilibrium phases were Fe, CaO, and CaO·SiO2. The findings from this work may provide guidelines for the improvement of sintering production and blast furnace performances.
  • Hydrogen Absorption Rate into Fe with Rust Layer Containing NaCl during Atmospheric Corrosion in Humidity-controlled Air

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    DOI:10.2355/isijinternational.ISIJINT-2020-018

    The research aimed to detect the rate of hydrogen absorption into Fe with rust layer during atmospheric corrosion in humidity-controlled air, and to realize the effect of relative humidity (RH) on hydrogen absorption rate. One side of an Fe plate specimen was covered by electrochemical Ni plate and the other side was covered with rust layer containing NaCl. The specimen was set between the double cells for electrochemical hydrogen permeation test. The cell for hydrogen detection was filled with 1 kmol·m-3 NaOH solution and the Ni side of the specimen was subjected to 0 VAg/AgCl in the solution. The cell for hydrogen absorption was filled with the air with a controlled RH to make the rust layer side corrode. During the corrosion, a hydrogen absorption current and an RH were continuously monitored. In the tests, the following results were obtained. In the region of RH between 42 and 74%, a hydrogen absorption rate increased with an increase in an RH. At an RH of 80%, a hydrogen absorption rate suddenly decreased. In the region of RH between 80 to 95%, a hydrogen absorption rate again increased with an increase in an RH. The pH in the rust layers during the corrosion under the tested RH range was estimated to be 4.2 and 4.3, slightly acidic.
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    1. A Review of the Twin-roll Casting Process for Complex Section Products ISIJ International Advance Publication
  • A Review of the Twin-roll Casting Process for Complex Section Products

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    DOI:10.2355/isijinternational.ISIJINT-2020-149

    Complex section products have significant lightweight and functional characteristics, and the twin-roll casting (TRC) is characterized by high efficiency and short flow. Hence, the TRC process for fabricating complex section products combines both advantages and will have a broader market demand and application prospect. In this paper, the research progress in recent years is reviewed, and novel TRC processes are divided into three categories according to the product section characteristics, namely transverse variable profiled strip, longitudinal variable profiled strip, and circular section products. The essence of the TRC process of complex section products is to change the steady-state characteristics in time series and the uniform characteristics in spatial distribution into transient or nonuniform. The technical principle, deformation characteristics, influence mechanism, are systematically analyzed. The current challenges and future directions of the TRC process are discussed.
  • Hydrogen-assisted Crack Propagation in Pre-strained Twinning-induced Plasticity Steel: from Initiation at a Small Defect to Failure

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    DOI:10.2355/isijinternational.ISIJINT-2019-510

    Hydrogen-assisted crack growth of pre-strained twinning-induced plasticity (TWIP) steel was investigated using artificial defects (micro-drilled holes), which acted as artificial crack initiation sites. Hydrogen was introduced into the specimens by electrochemical hydrogen charging during slow strain rate tensile test. The quasi-cleavage crack propagation observed was due to repeated crack initiation near the crack tip and subsequent coalescence. Crack initiation near the crack tip occurred after plastic deformation of the crack tip, and pre-straining facilitated plasticity-driven crack initiation. The early stage of plasticity-driven crack growth was sensitive to the crack length and remote stress level. Accordingly, the crack growth rate in the early stage increased with the increase in the initial defect size. In the following stage of the crack growth, the crack growth rate exhibited a complicated trend with respect to the crack length, which is possibly due to the plastic-wake-altered stress field around the crack tip, which depends on the initial defect size.
  • Development of a Prediction Method for Carbonitrided Surface Carbon and Nitrogen Contents by Computational Thermodynamics and Validation by Carbonitriding for Pure Iron

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    DOI:10.2355/isijinternational.ISIJINT-2020-050

    In this study, a new method for predicting carbon and nitrogen contents of a carbonitrided surface using computational thermodynamics with Thermo-Calc was developed. The nitrogen content of alloyed steel, which is in equilibrium between the steel surface and the atmosphere, was predicted using the nitriding potentials and Thermo-Calc, and the experimental and calculated results were compared using pure iron. For lower nitrogen levels, the accuracy of prediction was sufficient. However, for higher nitrogen levels, the experimental nitrogen content was lower than the calculated value, which was attributed to pore formation. Through a comparison of the described method with the conventional one, it was confirmed that our novel prediction method exhibits sufficient accuracy to predict the nitrogen content following carbonitriding.
  • Microstructure and Mechanical Properties of Simulated Heat Affected Zone of Laser Welded Medium-Mn Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-716

    In this study, a new generation automobile Medium-Mn steel (0.1C-5Mn-Fe) was welded by fiber laser and regional thermal cycle experiment was performed on a thermo-mechanical simulator. The microstructure, microhardness, and tensile properties of both base metal (BM) and simulated heat-affected zone (HAZ) were investigated. The results show that the peak temperature (PT) of different regions in HAZ results in differences of microstructure and mechanical properties. The microstructural analysis indicates that BM is comprised of an ultrafine-grained (UFG) duplex microstructure of ferrite and austenite. The change of PT has significant influence on microstructure and mechanical properties of HAZ. At the PT of 1350°C, the microstructure consists mainly of martensite and austenite film. At the PT of 900°C, the microstructure consists mainly of martensite packet with high density dislocations. At the PT of 700°C, the microstructure corresponding to the inter-critical HAZ (ICHAZ) consists of ferrite, austenite, and carbides. At the PT of 500°C, the microstructure corresponding to the sub-critical HAZ (SCHAZ) consists of ferrite and austenite. The volume fraction of austenite and ferrite increased sharply and the content of martensite decreased with decreasing PT. Tensile strength and yield strength decreased with decreasing PT due to martensite content reduction. Static toughness of ICHAZ is 343.4 MJ/m3 due to good balance of ductility and strength of metastable austenite. CGHAZ has the lowest static toughness of 196.4 MJ/m3 due to the lower ductility for martensite.
  • Enhancement of Wear and Corrosion Resistance of M2052 Damping Alloys by Electroless Plating Ni–P Coating

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    DOI:10.2355/isijinternational.ISIJINT-2019-797

    M2052 is a famous high damping Mn–Cu alloys with good strength, but lack of well corrosion and wear resistance. In this study, we expect to enhance the wear and corrosion resistance of M2052 damping alloys by electroless plating Ni–P coating. Successfully, a high phosphorus amorphous Ni–P coating with thickness about 15 µm plated on M2052 substrate. After electroless plating Ni–P coating, the roughness of samples surface decreased and the microhardness increased. Thus, the coated sample featured better wear resistance, and attributed to adhesive wear mechanism. By contrast, the friction coefficients of uncoated samples presented a high value with great fluctuations, which due to low hardness, high roughness, and easier to be oxidized. This leads to the dominant wear mechanisms are abrasive and corrosive wears. Ni–P coating significantly improved the corrosion resistance, because it has lower Icorr, higher Ecorr, and higher impedance than M2052 substrate. Surface morphologies after electrochemical tests were also observed: the uncoated samples had been corroded severely with a fibrous corrosion product layer dispersing cracks and pits. However, coated samples had not been corroded and remains intact. Furthermore, Mott–Schottky plots inferred that the sample surface after plating Ni–P coating performed an excellent passivation behavior in NaCl solution.
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  • Electroplating of Copper on Low Carbon Steel from Alkaline Citrate Complex Baths

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    DOI:10.2355/isijinternational.ISIJINT-2019-747

    The use of alkaline electroplating baths is the essential requirement to deposit Cu directly onto steels because of non-adherent Cu formation by replacement reaction between Cu2+ and Fe in acidic solution. For the development of such an electroplating bath, complexing agents to form soluble Cu complex in alkaline pH is necessary at first. Secondary, the soluble Cu complex must be reduced electrochemically. Cyanide-based baths meet these requirements, but the bath is toxic. In this study, the survey of complexing agents revealed that citric and tartaric acids form soluble copper complex solutions in alkaline pH, and electroplating is possible. The cathodic current density range to obtain smooth and adhesive electroplating with citrate complexed bath was extensive than that with a tartrate bath. It was found that 0.1 mol dm-3 CuSO4 - 0.5 mol dm-3 citric acid baths with pH of 9–11 are optimum to obtain adhesive and uniform Cu layer. Copper electroplating with an acidic CuSO4–H2SO4 bath was possible on 1 μm Cu layer with the alkaline citrate bath. Because the plating rate is high with the acidic bath, the multilayer Cu electroplating from the citrate bath and then an acidic sulfate bath gives a reasonable way for Cu coating onto steels. Elongation test of the steel sheet electroplated with the multilayer Cu showed that detachment of the Cu layer was limited in the vicinity of the broken part of the sheet. It is concluded that the toxic cyanide Cu plating bath can be replaced with a citrate bath.
  • Effect of the Moisture Content of Coal Blends on Coke Structure and its Apparent Gasification Kinetics with CO2

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    DOI:10.2355/isijinternational.ISIJINT-2020-009

    In this work, the influences of moisture content of coal on the structure and reactivity of cokes were investigated by blending different proportion of dry coal (with < 2 wt.% moisture) and wet coal (with ~10 wt.% moisture) and analyzing the gasification of the produced coke. The results indicated the coke formed from dry coal has the highest specific surface area and thinner pore walls. The results of isothermal thermogravimetric method show that the order of gasification reactivity of bulk coke from different proportion of wet coal is: 0 wt.% wet coal, 100 wt.% wet coal, 60 wt.% wet coal and 30 wt.% wet coal. In order to eliminate the influence of diffusion on the gasification reaction, coke with a particle size fraction of less than 48 µm was used for the non-isothermal gasification reaction. Results show that the gasification reaction curves of four samples are similar in the gasification process. It was concluded from kinetics analysis that the volume reaction model is well fitted with the experimental data. The activation energy with the volume reaction model is 191.9, 203.1, 190.1, and 190.8 kJ/mol. It was concluded that the moisture content of coal has little effect on the activation energy of the gasification, while the coke gasification kinetics is mainly determined by the coke pore structures which influence reaction surface.
  • Thermodynamic Properties and Viscosities of High-Titanium Slags

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    DOI:10.2355/isijinternational.ISIJINT-2020-004

    The influence of TiO2, binary basicity and Al2O3/TiO2 ratio on the heat capacity, enthalpy and slag fluidity of CaO–SiO2–MgO–Al2O3–TiO2-based slag at 1693 K, 1723 K, and 1753 K (1420°C, 1450°C, and 1480°C) was investigated in this work. From the calculation results, it was found that the heat capacity of the slag increased with the increasing of TiO2 content and the Al2O3/TiO2 ratio and with the decreasing of basicity in the experimental temperature range. Enthalpy change increased with the increasing Al2O3/TiO2 ratio and the decreasing of TiO2 content. With the increasing of basicity, the slag temperature rises slightly and the viscosity decreases along with it. Additionally, the larger the basicity, the smaller the viscosity fluctuation under heat decrement. Therefore, a proper increase in basicity contributes to reduce viscosity fluctuation, for the current slag system, the appropriate basicity should be 1.15–1.20. Besides, the fluctuation of the temperature reaches a small value around the Al2O3/TiO2 ratio is 0.6, and in metallurgical production, the heat input should be adjusted in time according to titanium content charge fluctuations, thus ensuring good fluidity and an adequate reaction between the slag and metal. The above experimental results can provide a reference for ironmaking enterprises using more vanadium–titanium magnetite ore.
  • Comprehensive Recovery of Multisource Metallurgical Wastes: Recycling Nickel Slag by Aluminum Dross with Converter-Slag Addition

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    DOI:10.2355/isijinternational.ISIJINT-2019-670

    Recovery of multisource metallurgical wastes can facilitate the recovery of valuable metals, and achieve the full utilization of slag. Recycling nickel slag by aluminum dross with converter-slag addition was studied. Based on the element mapping of slags, mineral phases in the modified slag were reconstructed under the interaction of nickel and converter slags, and ‘FeO' could be separated from the relevant structures of the two slags. Element mapping and chemical analysis of the metal phase after reduction indicated that the reduced product was Fe–Cu-based alloy, element mapping and XRD detection of the secondary slag indicated a complex characterization. The influence of factors, including the basicity of the modified slag, the reduction temperature and the Al/‘FeO' ratio on the recovery degree of Fe, Cu, Mn and P, was discussed and the optimal technical parameter was determined as 1.0, 1773 K and 0.67, respectively.
  • Effects of Strain Rate on the Deformation Mechanism of Ultra-high Strength TWIP Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-714

    The deformation mechanism of Fe-20Mn-0.6C twinning-induced plasticity (TWIP) steel was studied with respect to different strain rates ranging from 10-4 to 103 s-1. Moreover, the microstructure of the ultra-high strength TWIP steel at each strain rate was characterized by transmission electron microscopy (TEM). The TWIP steel exhibits three distinct strain hardening stages with increasing true strain. In stage II, dσ/dε shows a plateau at the strain rates of 10-3 to 10-1 s-1, while dσ/dε continuously decreases in the other stages with increasing strain rate. The deformation mechanism of TWIP steel under the high strain rate was a process in which the deformation twin and the dislocation slip promoted and restricted each other. When the strain rate is higher than 102 s-1, the increase in the adiabatic heating temperature (approximately 143°C) suppresses the secondary twinning and enhances the softening effect.
  • Modeling and Analysis of Heat Transfer in Deforming Packed Bed

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    DOI:10.2355/isijinternational.ISIJINT-2019-825

    The cohesive zone of the blast furnace is one of the most important zones because it deeply relates to the furnace stability and efficiency. It is considered that the thickness of the cohesive zone increases with decreasing the reducing agent rate and increasing the usage of the low grade raw materials in future. The thickness of the cohesive zone should be decreased or permeability of the cohesive zone should be improved to keep the furnace stability and production efficiency. Heat transfer in the cohesive zone is a quite important issue to control the cohesive zone because it determines the temperature rise of this zone namely softening and melting rate of the burden materials. In this study, a mathematical simulation model for the fluid flow and heat transfer in the packed bed of the deforming particles was developed. This model combined the discrete element method for bed deformation and the computational fluid dynamics for the gas flow. Additionally, the inter-particle heat exchange in the deforming packed bed was newly formulated and linked with the discrete element analysis. This mathematical model successfully revealed the variation of the heat transfer mechanism with the deformation of the packed bed. The simulation results could give the useful information for designing the burden distribution under the low carbon and high low-grade material operation of the blast furnace.
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    1. Influence of Understanding of Physical Phenomena in Materials on Supply Chain Patterns of Steel Products ISIJ International Advance Publication
  • New Method for Preparation of Coke Analogues and Comparability for Industrial Metallurgical Coke

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    DOI:10.2355/isijinternational.ISIJINT-2020-079

    To better understand metallurgical coke behavior in blast furnace, the preparation of coke analogues was improved by using demineralized coke powder. Scanning electron microscope, Raman spectroscopy, mercury intrusion method, and CO2 gasification reactivity test were used to establish the representativeness relation between different coke analogues and metallurgical cokes. The results show that the coke analogues prepared by graphite powder and demineralized metallurgical coke powder were in general representative of industrial coke. With the controlled and reproducible pore characteristic, the average pore diameter of coke analogues is smaller and the average pore area is bigger, while the pore connectivity of metallurgical coke is stronger. Analogue prepared from demineralized coke has a slight superiority over that prepared from graphite in carbon structure and gasification reaction with CO2. In general, the coke analogue made from demineralized coke has higher comparability to industrial metallurgical coke and are more suitable for laboratory research.
  • Influence of Understanding of Physical Phenomena in Materials on Supply Chain Patterns of Steel Products

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    DOI:10.2355/isijinternational.ISIJINT-2020-033

    In this study, supply chain patterns of steel products are investigated from the viewpoints of quality assurance responsibility and understanding of physical phenomena in steel. This study focuses on the differences in supply chain patterns between steel nails for common use and valve springs for the automotive industry. In the supply chain of steel nails for common use, which takes a conventional pattern from raw materials to final products, the quality of each supplier's product is guaranteed just by the Japanese Industrial Standards (JIS), and no supplier takes quality assurance responsibilities beyond its business range. By contrast, in the supply chain of valve springs for automotive use, each supplier takes quality assurance responsibilities for the final product beyond its business range, and the suppliers cooperate with one another to fulfill stringent quality requirements by automotive manufacturers. Therefore, the supply chain pattern of valve springs is different from the conventional pattern of common use steel products like steel nails. It was also found that the supply chain pattern of valve springs can be caused by the insufficient understanding of physical phenomena in steel, martensitic transformation and hardening in this case. This study suggests that the conditions that determine the supply chain pattern of a steel product could be business practices for quality assurance, namely based on standard specifications or users' requirements, and the natural scientific understanding level about physical phenomena in steel. Although this study focuses on steel nails and valve springs, this finding is applicable to other steel products.
  • Effect of Nickel Addition on the Corrosion Resistance of Steel in a Subtropical Seashore Environment

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    DOI:10.2355/isijinternational.ISIJINT-2019-658

    This study investigated the effects of Ni addition on the corrosion resistance of steel in subtropical seashore environments. Carbon steel and 3, 5, and 7% Ni steels were exposed in such an environment for a year. Addition of Ni depressed the corrosion rate of steels and number of cracks in the rust layer. Quantitative and three-dimensional measurement of the cracks with a wide range of widths and volumes in the rust layer was carried out for the exposed steel specimens using the mercury intrusion method. The total crack volume in the rust layers on 5% Ni steel was 60% lower than that for the carbon steel. It is considered that rust layers with less crack volume suppressed Cl migration through the rust layer. The Cl concentration near the metal interface was relatively lower in the 5% Ni steel by EPMA analysis. And the rust layer on 5% Ni steel also showed a higher permeation resistance than that formed on carbon steel. Considering the formation of rust layers with less volume crack on Ni-added steel based on Morcillo's model, it is concluded that the Ni addition promoted the formation of a-FeOOH and suppressed the reduction of γ- and β-FeOOH, thus resulting in a more intact rust layer.
  • Composition Changes of Inclusions by Reaction with Slag and Refractory: A Review

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    DOI:10.2355/isijinternational.ISIJINT-2019-695

    Precise control on inclusions is of great importance for improving steel quality. In secondary refining, three types of inclusion are generally observed in Al-killed steel: Al2O3, MgO·Al2O3 spinel, and CaO–Al2O3 type. Many researchers have reported on inclusions transformed in the routine of Al2O3 → MgO·Al2O3 spinel → CaO–Al2O3 during secondary refining in Al-killed steel. The deoxidizer of Al is intentionally added to the steel, and Al2O3 inclusions are formed as a deoxidation product. However, MgO·Al2O3 spinel and CaO–Al2O3-type inclusions have been observed even without any intentional Mg or Ca addition. Therefore, it is important to clarify the source of Mg and Ca causing MA spinel and CaO–Al2O3-type inclusions formation, in order to control the compositions of the inclusions. Regarding to this phenomenon, a good review was published by Park and Todoroki in 2010. Several studies have since been conducted. This paper summarized the research activities on the composition changes of inclusions during secondary refining from the aspect of thermodynamics and kinetics.
  • Effect of Lattice Defects on Tribological Behavior for High Friction Coefficient under TCP Added PAO Lubrication in Nanostructured Steels

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    DOI:10.2355/isijinternational.ISIJINT-2019-707

    The effect of lattice defects on the tribological behavior under tricresyl phosphate (TCP) added poly-α-olefin (PAO) lubrication was investigated in the nanostructured steels produced by heavy plastic deformation processes. In surface-nanostructured SUJ2-bearing steel, tribological behavior with high friction coefficient was observed in ball-on-disk tests when compared to non-deformed steel. In addition, a similar phenomenon was observed in ultra-low carbon (ULC) steel with a high density of lattice defects (grain boundary, dislocation and so on). By increasing the density of lattice defects, a higher friction coefficient was observed. The reason for the tribological behavior with high friction coefficient seems to be that the compound film of Fe–O–P system formed in the ball-on-disk test was worn down.
  • A CFD Study on Refractory Wear in RH Degassing Process

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    DOI:10.2355/isijinternational.ISIJINT-2019-768

    In order to assess the wear damage of the lining refractory in the RH degasser, a transient 3D numerical model has been established using volume of fluid approach-discrete phase model (VOF-DPM) technology. The gas-oil-water three-phase flow in a RH degasser water model was evaluated. The breakup and coalescence of gas bubble was taken into account, and moreover the bubble diameter changed with static pressure. The wall shear stress and turbulence intensity were employed to predicate the erosion rate of the lining refractory, while the diffusion coefficient of the refractory material and the slag property at high temperature were used to consider the corrosion rate. The effects of the operational parameters on the refractory wear rate were clarified. A careful comparison between the experimental and the numerical results was conducted for the model validation. The results show that the wear behavior of the lining refractory at the up snorkel wall is the most severe due to the rapidly rising bubble. The vacuum chamber wall that near the up snorkel is also subjected to a serious wear damage. Besides, a higher wear rate is observed at the ladle wall that close to the oil/water interface, since both the physical erosion and chemical corrosion contribute to the wear damage of the lining refractory here. The developed model could help smelters to estimate the remaining thickness of the refractory in the RH degasser under different operational conditions.
  • Effect of Addition ZrO2 Nanoparticles on Inclusion Characteristics and Microstructure in Low Carbon Microalloyed Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-785

    The inclusion characteristics and microstructure in the low carbon microalloyed steel with addition ZrO2 nanoparticles were investigated by high temperature experiment and metallurgical analysis. The results showed that after ZrO2 nanoparticles were added, a large number of Zr–Al–Si–O+MnS inclusion, ZrO2+Al–Si–O+MnS inclusion, and ZrO2+MnS inclusion appeared in the steel, and these Zr-containing inclusions were effective to induce acicular ferrite (AF) formation. With the amount of added ZrO2 nanoparticles increased from 0.013% to 0.054%, the inclusions types had no significant effect, but the inclusions size distribution, number density and average diameter were affected. When the addition amount of ZrO2 nanoparticles was 0.027%, the proportion of large inclusions (larger than 5.0 μm), the inclusions number density and average diameter all were reached the extremum values, respectively 10.81%, 111/mm2, 2.62 μm. Moreover, as ZrO2 nanoparticles adding into steel, the majority solidification microstructure changed from bainitic ferrite (BF) to AF. With the adding amount of nanoparticles increase, the proportion of AF first increased and then decreased, also reached the maximum of 67.65% as the addition amount was 0.027%. Finally, Mn-depletion zone (MDZ) in the vicinity of Zr-containing inclusion was observed, and the MDZ was believed to be one of the possible mechanisms of Zr-containing inclusions inducing AF formation.
  • Multi-step Simulation of Vacuum-carburizing Reactor Based on Kinetics Approach

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    DOI:10.2355/isijinternational.ISIJINT-2019-815

    A novel and efficient simulation technique for the purpose of optimization of vacuum-carburizing process was proposed. This method consists of three steps: calculation of gas convection and diffusion, calculation of only gas diffusion, and calculation of carbon diffusion in steel. The first step provides the gas convection velocity that is employed in the second step. Adsorption rate of carbon on the steel surface is obtained in the second step, and carbon concentration in the steel is calculated in the third step based on the adsorption rate of carbon.Experiments were conducted to verify the proposed method in both laboratory- and industrial-scale reactors. Comparison of the computational predictions to the experimental data revealed that the proposed simulation technique enabled accurate prediction of the adsorption rate of carbon on the steel surface at various temperature conditions, the amount of carburized carbon at each operating time, and the profile of carbon concentration in the steel that is, in other words, the carburized depth. In addition, the calculation of the industrial-scale reactor, whose simulation model consisted of approximately seven million computational meshes, was completed within about two days. Therefore, the proposed simulation technique could be used to control and optimize the process in industrial vacuum-carburizing reactors.
  • Precipitation Characterization and Creep Strength at 600°C for Creep Resistant Cr–Mo Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-682

    The creep strength of 5Cr-0.5Mo steel was determined at 600°C and 78–170 MPa, as well as its relation to the microstructural changes during the creep tests. The microstructural characterization showed that the creep tests were conducted under the presence of a mixture of both intergranular and intragranular M7C3 and M23C6 carbides dispersed in the ferrite matrix. The n exponent of Norton-Bailey law suggested that the creep deformation process occurred through the ferrite grains, which conducted to a transgranular ductile- fracture mode after creep testing. The creep strength of this steel is directly related to the average radius and number density of carbides present during the test. The ferrite grain size of 5 µm seemed to cause an enhancement of the creep strength for this steel in comparison to that of other similar steels reported in the literature.
  • Mechanism of Improved Ductility of 1500 MPa-class Ultra-high Strength Cold-rolled Steel Sheet Produced by Rolling and Partitioning Method

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    DOI:10.2355/isijinternational.ISIJINT-2020-027

    By using a steel with standardized chemical composition and conventional manufacturing processes for flat-rolled steel strip, a 1500 MPa class stainless steel sheet, whose product of yield strength (YS) and total elongation (El) exceeds 30000 MPa%, was developed and its mass production was established. Besides the excellent YS–El balance, the developed steel sheet has excellent performance for not only an anti-secondary work embrittlement but also high cycle fatigue endurance.Core technology of the developed method is composed of a combination of high precision cold-rolling and isothermal partitioning treatment in a batch furnace, named as a rolling and partitioning (R&P) method. By the R&P method, the microstructure of steel is controlled to the mixture of a strain-induced martensite as the matrix phase, and an optimum amount of retained austenite as the second phase which is dispersed in isolation and surrounded by the transformed martensite.In this paper, the microstructure formation during the R&P process and the deformation mechanism that would bring about the excellent strength–ductility balance are discussed based on the results obtained from the in situ neutron diffraction measurement. The results have revealed that the typical Lüders-like stress–strain curve of R&P steel is caused by competitive plastic flow between austenite and martensite, and an effective transformation induced plasticity phenomenon.
  • Strain Distribution and Deformation-induced Martensitic Transformation in Tension for a TRIP Steel Plate

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    DOI:10.2355/isijinternational.ISIJINT-2019-497

    Digital image correlation was applied to analyze the strain distribution and deformation-induced martensitic transformation of retained austenite in a low alloy transformation-induced plasticity (TRIP) steel plate under tension. The distribution of strain instilled by tensile deformation was inhomogeneous at a microscopic scale. Strain generated by deformation-induced martensitic transformation was successfully visualized and it led to a homogeneous strain distribution. The retained austenite in the high strain region transformed to martensite preferentially, which demonstrates that inhomogeneous strain distribution affects the stability of retained austenite. The high resolution strain distribution exhibited that a certain amount of strain instilled into retained austenites and there are a lot of strain concentration sites at ferrite/austenite interfacial boundaries in high strain region. Therefore, the stress concentration at the ferrite/retained austenite interfacial boundary occurs due to the difference of strain between the ferrite matrix and retained austenite. These strain accumulation in a retained austenite and/or stress concentration at ferrite/retained austenite interfacial boundary may induce martensitic transformation in high strain regions.
  • Development of a Method for Evaluating Microstructurally Small Fatigue Crack Initiation and Growth by Using an Automatic System for In Situ Observation in Conjunction with a Digital-Image Correlation Technique

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    DOI:10.2355/isijinternational.ISIJINT-2019-823

    We have constructed an automatic in situ observation system for monitoring the behavior of small fatigue cracks at the microstructural level that, when used in conjunction with a digital-image correlation (DIC) technique, permits the continuous and automatic tracking and recording of microscopic deformation behavior. To verify the effectiveness of this system, we applied it to the evaluation of small fatigue cracks in heat-treated low-carbon steel. The results confirmed that our system can be used in the automatic tracking and recording of the initiation and early growth behavior of microstructurally small fatigue cracks. By the use of DIC analysis, we also succeeded in visualizing the opening-and-closing behavior of small fatigue cracks as well as the behavior of microscopic microstructural deformations, such as inhomogeneous strain concentrations, that caused the fatigue cracks. Although the early-stage growth of fatigue cracks propagates faster than that of long cracks, it is consistent with long-crack data if the effective stress intensity factor range ΔKeff which calculated by crack opening stress measured by DIC is used.
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    1. Numerical Simulation on Influence of Coke Oven Gas Injection on Iron Ore Sintering ISIJ International Vol.60(2020), No.4
    2. Influence of Melting Characteristics of Iron Ores on Strength of Sintered Ores ISIJ International Vol.60(2020), No.4
  • Development of a Shape Meter Employing the LED Dot Pattern Projection Method for a Hot Strip Finishing Mill

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    DOI:10.2355/isijinternational.ISIJINT-2019-718

    In recent years, to improve the fuel efficiency of automobiles by reducing their weight while maintaining their strength, smaller-thickness and higher-strength steel sheets tends to be used as automobiles' construction materials. For stable and accurate production of these sheets, it is crucial for them to be flattened through the hot strip rolling process. Therefore, to realize accurate automatic flatness control (AFC), a new shape meter that employed the light-emitting diode (LED) dot pattern projection method was developed. This consists of an LED dot pattern projector that can project the staggered periodic dot pattern, made of 1200 power LED chips, on the rolled strip and area camera that captures the image of the projected pattern. Then, instantaneous strip flatness is measured to analyze the pattern pitch correlative with inclination angle. The shape meter was installed at the hot strip finishing mill's exit, and its measurement accuracy and stability were evaluated. As a result, its inclination angle measurement error was within 0.45 degrees (two sigma) when compared to the set angle of the standard target, and the measured flatness of the rolling strip was consistent with the visually observed one. Its measurement success rate per entire coil was above 98.5%. These results indicated that the developed shape meter could be applied to the AFC. In addition, applying the measured flatness to the AFC of the work roll bender and leveling, it was confirmed that the strip flatness was improved in a short time.
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    1. Effect of Nanofluids on Liquid-solid Heat Transfer on High-temperature Wall ISIJ International Advance Publication
  • Effect of Nanofluids on Liquid-solid Heat Transfer on High-temperature Wall

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    DOI:10.2355/isijinternational.ISIJINT-2019-776

    The industrial application of nanofluids had been explored by many researchers since nanofluids were proposed. However, there were different opinions on the effect in jet cooling. In this paper, 0.4 vol%, 0.8 vol%, 1.2 vol%, 1.8 vol%, 2.4 vol% Al2O3-water, TiO2-water, SiO2-water nanofluids and pure water were used as quenching coolants to complete single jet cooling experiments on the free surface of 50 mm high-temperature steel plate. The results showed that using low concentration (0.4–1.2 vol%) nanofluids could significantly improve the maximum heat fluxes, cooling speed peaks, and moving velocities of peaks along the thickness direction compared with pure water. However, the cooling uniformity in the horizontal direction was reduced, especially with high concentration nanofluids (≥1.8 vol%). Through comprehensive comparison, when 1.2 vol% Al2O3 + water was used as coolant, the optimal cooling efficiency could be achieved, and cooling speed peaks along the thickness were 8.14%–19.70%, 2.16%–3.48% and 0.74%–1.44% higher than that of pure water respectively.
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    1. Development of a Shape Meter Employing the LED Dot Pattern Projection Method for a Hot Strip Finishing Mill ISIJ International Advance Publication
  • Fluid Flow Characteristic of EAF Molten Steel with Different Bottom-Blowing Gas Flow Rate Distributions

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    DOI:10.2355/isijinternational.ISIJINT-2019-794

    As an efficient stirring method, bottom-blowing technology was applied in the present electric arc furnace (EAF) steelmaking process to improve the dynamic conditions of the molten steel. This article describes the development of a numerical model to simulate the 3D multiphase flows (gas, steel, and slag). Comparisons among uniform and non-uniform (linear and triangle distributions) bottom-blowing gas rate arrangements were performed with both metallurgic and dynamic parameters obtained from the numerical simulation process and separated liquid steel analysis. The numerical simulation results indicated that the bottom-blowing scheme with the gas rate in a linear change distribution had the best stirring effects in the molten bath. In addition, the dynamic conditions in the molten bath were worse when the bottom-blowing gas rate change was focused on the nozzle near the eccentric bottom tapping area. Furthermore, water model and industrial experiments were performed. For this purpose, 120 sets of heat industry data were collected in the 100 t EAF steelmaking process. The results showed that the non-uniform bottom-blowing scheme is more able to improve the dynamic conditions of the molten bath compared with the conventional uniform gas rate distribution, which further validated the reliability of the present numerical simulation results.
  • Industrial Ladle Furnace Slag Composition Analysis with Optical Emissions from the Arc

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    DOI:10.2355/isijinternational.ISIJINT-2019-676

    With the strict standards for steel quality and high production rates, the demand for faster and more convenient slag composition analysis for both electric arc and ladle furnaces has become a major issue in industrial steel plants. To overcome the time-delay between slag sampling and results of the slag composition analysis, an on-line slag composition analysis is required. Such a method that can be used in on-line analysis and is also chemically sensitive to the slag composition is optical emission spectroscopy. In this work, the optical emissions from the arc have been measured in an industrial ladle furnace and used for slag composition analysis. This article focuses on CaF2 and MgO, since the CaF2 is a common additive material in the ladle treatment and high MgO content means that the ladle refractory lining is dissolving into the slag. The analysis has been carried out by comparing emission line ratios to the XRF analyzed ratios of CaF2/MgO and MnO/MgO, respectively. The results show that several atomic emissions lines of calcium, magnesium, and manganese can be used to evaluate the CaF2/MgO and MnO/MgO ratios in the slag. It was found out that the plasma temperature derived from Ca I emission lines has a non-linear relation with the CaF2 content of the slag. Additionally, the dissociation pathways of molecular slag components were determined and studied in different plasma temperatures with equilibrium composition computation in order to determine the relations between the slag and plasma compositions.
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    1. Softening–melting Properties and Slag Evolution Behavior of High Titanium Sinter ISIJ International Advance Publication
  • Effect of Direct Powder Additions on the Solidification Structure and Microsegregation of 42CrMo4 Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-787

    Inoculation and its link with the solidification structure is a relatively new field for low alloy steels. In this study, a cold crucible setup is used to realize direct particle inoculation of 50 g steel ingots. Eight different inoculants powders (oxides, nitrides and carbides) were tried with a 0.3 mass% level addition. Solidification structure sizes and morphologies, presence of inoculant particles and microsegregation have been characterized for all the samples. The best grain refinements were obtained for Si3N4, TiN and CeO2 additions whereas the lowest microsegregation intensities are achieved for Si3N4, HfC and W2C additions. The properties of the inoculants – misfits, solubility products and terminal velocities – are used to discuss those changes. The grain refinement could be linked to the misfit in good agreement with the literature. Other morphological changes (secondary arm spacing and dendricity) were attributed to the presence of inert particles staying inside the liquid during the solidification. Last but not the least, the flattest microsegregation profiles were possibly due to inoculant dissolution leading to a change in the MnS precipitation sequence.
  • Softening–melting Properties and Slag Evolution Behavior of High Titanium Sinter

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    DOI:10.2355/isijinternational.ISIJINT-2019-559

    Vanadium–titanium magnetite (VTM) is an important strategic resource, and now the process of Blast Furnace (BF) is the dominate route for smelting VTM. However, the difficulties of smelting VTM by BF inhibited further increase of VTM proportion in furnace burden due to its complex behavior in cohesive zone. The objective of this study is to reveal the softening–melting behavior of a high titanium sinter. The results indicated that the softening–melting properties of the experimental high titanium sinter were relatively worse than that of ordinary sinter due to its wider melting temperature interval and bad gas permeability in melting stage. The melting temperature interval of 225°C was obtained, and the permeability index (S value) of 1917 kPa·°C was calculated correspondingly. A second increase in pressure drop was observed in the softening–melting process, which may be ascribed to great difference of melting point between pig iron and slag. The mechanism on slag evolution was also clarified by interrupting the softening–melting process at characteristic temperatures. The XRD patterns indicated that initial slag phase mainly consisted of wustite, silicates and perovskite, of which the wustite content decreased gradually during the softening–melting process. The content of wustite was a crucial factor that affected the phase transformation during slag evolution.
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    1. Pressure-drop Modelling in the Softening and Melting Test for Ferrous Burden ISIJ International Advance Publication
    2. Industrial Ladle Furnace Slag Composition Analysis with Optical Emissions from the Arc ISIJ International Advance Publication
  • Pressure-drop Modelling in the Softening and Melting Test for Ferrous Burden

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    DOI:10.2355/isijinternational.ISIJINT-2019-600

    The softening and melting (SM) under load test is routinely conducted to assess the quality of ferrous burden materials and to predict their possible performance in blast furnace. Due to complex phase interactions coupled with chemical reactions at an elevated temperature range (~973 to 1873 K), the flow dynamics in the test system are quite complex. This study systematically investigates the contraction behaviour and associated pressure drop in a SM test bed for sinter, lump (NBLL, Newman Blend Lump) and a mixture of these two types of ore (21 wt% NBLL + 79 wt% sinter). To quantify the structural changes in a sample bed, interrupted tests at various temperatures were conducted and analysed using both synchrotron X-ray computed tomography (CT) at a lower temperature range (1273 to 1473 K) and neutron CT at a higher temperature (1723 K). It was noted that existing packed bed pressure drop models (Ergun model, 1952, fused bed model, Sugiyama et al., 1980, orifice model, Sugiyama et al., 1980) and modified orifice model, Ichikawa et al., 2015) exhibited divergence in their predictions at higher temperature when the porosity parameter was computed directly from the bed contraction data. To avoid this modelling failure, a growth-decay type porosity-temperature relationship based on extensive SM test data was incorporated in the well-known Ergun equation which estimated reasonable bed pressure drops. Furthermore, a simplified ore specific friction factor model was empirically derived which was also shown to produce reasonable pressure drop predictions for all types of ferrous burden samples.
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    1. Softening–melting Properties and Slag Evolution Behavior of High Titanium Sinter ISIJ International Advance Publication
    2. Numerical Simulation on Influence of Coke Oven Gas Injection on Iron Ore Sintering ISIJ International Vol.60(2020), No.4
  • Measurement and Thermodynamics of Carbon Solubilities in Molten Si–Fe, Si–Ni, and Si–Cr–Fe Alloys at 2073 K

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    DOI:10.2355/isijinternational.ISIJINT-2019-511

    The equilibrium phase relations of molten Si–Fe, Si–Ni, and Si–Fe–Cr alloys saturated with either silicon carbide (SiC) or graphite, which are candidates for the solvent for rapid solution growth of SiC, have been investigated. The measured carbon solubilities at 2073 K were 0.19–6.6 mol% for the Si–(24.1–70.1) mol% Fe, 0.061–5.2 mol% for Si–(30.0–85.0) mol% Ni, and 1.1–3.9 mol% for Si–(50-x) mol% Fe–x mol% Cr (x = 10.4–40.1) alloys. A quasi-chemical model that assumes that the carbon atoms are introduced into the interstitial sites of the Si–Fe, Si–Ni, and Si–Fe–Cr solvents and obstruct the bonding between solvent atoms was used to evaluate the activity coefficient of carbon in each alloy. The estimation reproduced the trends of the measured carbon solubilities fairly well. However, the estimation using the sub-regular solution model often overestimated the carbon solubilities. Thus, the carbon behavior in molten silicon–transition metal alloys is well described by the quasi-chemical model.
  • Optimization of the Mixing Time Using Asymmetrical Arrays in Both Gas Flow and Injection Positions in a Dual-plug Ladle

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    DOI:10.2355/isijinternational.ISIJINT-2019-688

    In this work, the multiphase mathematical simulation (steel-argon-slag-air) was used to improve the mixing time in a secondary refining ladle, which is validated with a physical scale model using dye tracer dispertion and measurement of mixing time. An experimental 3k-p design was performed to optimize the number of cases and analyze the effect of injection gas flow arrangement. A mathematical methodology was described to determine the mixing time in a ladle with a multi-sensor system. By means of an analysis of variance, it was found that the angle of separation between plugs is the most relevant variable to reduce mixing time. It was determined that, by using a good asymmetric configuration in both gas flow and location of the porous plugs, it is possible to reduce the mixing time in a secondary steel refining ladle.
  • Partitioning of Solute Elements and Microstructural Changes during Heat-treatment of Cold-rolled High Strength Steel with Composite Microstructure

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    DOI:10.2355/isijinternational.ISIJINT-2019-723

    The partitioning of solute elements during intercritical annealing and the effects of partitioning on ferrite transformation during slow cooling after intercritical annealing in a 0.17% C–1.5% Si–1.7% Mn (mass%) steel were investigated by a new FE-EPMA (field emission electron probe microanalysis) technique. This new technique enables highly accurate measurement of the C distribution. During the intercritical annealing, C and Mn concentrated into austenite, while Si concentrated into ferrite. The distribution of Mn in austenite was inhomogeneous, and austenite with small Mn content was transformed into ferrite during slow cooling. This ferrite transformation proceeded in the NPLE (negligible partitioning local equilibrium) mode. Two kinds of ferrite were produced due to slow cooling, one being intercritically-annealed ferrite, and the other transformed ferrite. The transformed ferrite had larger Mn content than the intercritically-annealed ferrite. Furthermore, the transformed ferrite was classified into the ferrite grown epitaxially from the intercritically-annealed ferrite and that nucleated in the austenite with relatively small Mn content. Prior microstructure and distribution of solute elements before cooling are determined by the intercritical annealing conditions, and then control the ferrite transformation. Precise control of the ferrite transformation is effective for stable production of cold-rolled high strength steel with composite microstructure.
  • Crystallographic Orientation Control of 316L Austenitic Stainless Steel via Selective Laser Melting

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    DOI:10.2355/isijinternational.ISIJINT-2019-744

    In recent years, additive manufacturing has attracted attention as a technology that enables control of the crystallographic texture of metallic materials. We achieved successful control of the crystallographic texture of 316L austenitic stainless steel using selective laser melting (SLM). Three distinguished textures were achieved by changing the laser scan speed, namely: the single crystalline-like texture with {001} orientation in the build direction, the crystallographic lamellar texture in which two kinds of grains with {011} and {001} orientations in the build direction are alternately stacked, and polycrystalline with relatively random orientation. The melt pool shape and the solidification behavior (thermal gradient and migration velocity of solid/liquid interface) in a melt pool could be important controlling factors for the evolution of the crystallographic texture under the SLM process.
  • Nonlinear Vibration Characteristic Analysis of Roller-Plate System Based on Asymptotic Methods

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    DOI:10.2355/isijinternational.ISIJINT-2019-569

    A roller-plate system is taken as the research object in this paper. The influence of rolled products of metal plates (thick or middle thick plate) as an excitation parameter on the vibration characteristics of the system during warm rolling process is mainly studied. In view of the hysteresis characteristics between rolling force and deformation of rolled products of metal plates in actual process, Duffing equation is innovatively introduced into the dynamic model and used to generate nonlinear force. The analytical solution of the dynamic model of the roller-plate system is obtained by asymptotic methods, and the correctness of the analytical solution is verified by Runge-Kutta method. Finally, the influence of nonlinear stiffness and nonlinear damping on vibration characteristics of rollers is analyzed, which provides an important theoretical basis for the study of nonlinear vibration characteristics and vibration suppression of roller-plate system during warm rolling.
  • Evolution of TiN and Oxide Inclusions in Ti-containing Fe-25Ni-15Cr Alloy during Electroslag Remelting

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    DOI:10.2355/isijinternational.ISIJINT-2019-603

    The present study was undertaken to investigate the evolution of inclusions in a Ti-containing Fe-25mass%Ni-15mass%Cr alloy during electroslag remelting (ESR). The effect of slag composition on the inclusions in alloy was studied. The inclusions in both consumable electrode and remelted ingots are mainly 1 to 3 µm in size. The inclusions in consumable electrode are TiN, Al2O3–Ti2O3, Al2O3–Ti2O3 with a surrounded TiN layer. The inclusions in liquid metal pool and remelted ingots are TiN, MgO–Al2O3–Ti2O3 inclusion surrounded by TiN, MgO·Al2O3 inclusions, MgO·Al2O3 inclusions with an outer Ti2O3-rich layer. Increasing TiO2 content in slag has no influence on the types of inclusions in remelted ingots. The original TiN inclusions in consumable electrode cannot be dissociated at the electrode tip during the ESR process. TiN inclusions in remelted ingots mainly generated in liquid metal pool during ESR, and the TiN inclusions formed during the solidification of liquid alloy takes up a small amount fraction. Part of Al2O3–Ti2O3 inclusions in consumable electrode were removed through absorbing them into molten slag, and the remaining Al2O3–Ti2O3 inclusions in the liquid alloy reacted with Mg dissolved from ESR slag to form MgO–Al2O3–Ti2O3 inclusions which served as the nucleation sites for TiN inclusion formation. MgO·Al2O3 inclusions in the remelted ingots precipitated in the liquid metal pool during ESR process. The generation of MgO·Al2O3 inclusions with an outer Ti2O3-rich layer originated from the reaction between soluble titanium in liquid alloy and MgO·Al2O3 inclusion to form an outer Ti2O3-rich layer on unreacted MgO·Al2O3 inclusion core.
  • Deoxidation of Electroslag Remelting (ESR) – A Review

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    DOI:10.2355/isijinternational.ISIJINT-2019-661

    Deoxidation of liquid steel and alloy during electroslag remelting (ESR) is always an ongoing concern for producing advanced clean steel and alloy. The increasing demands for more excellent performance of steel urge metallurgists to further improve the steel cleanliness. Lowering the oxygen content and non-metallic inclusions amount during the ESR process is of great importance as ESR is the last processing procedure for refining liquid steel in the steel product manufacturing process. Deoxidation of ESR is dependent on one or more aspects including the initial oxygen content and oxide inclusions in the electrode, remelting atmosphere, deoxidation schemes, slag compositions, reoxidation degree, melting rate and filling ratio. This paper reviews the state of the art in the deoxidation of ESR and deoxidation-related oxide inclusions. The oxygen transfer behavior during ESR process is described first. Deoxidation of liquid steel during ESR is discussed based on the thermodynamic and kinetic considerations. The dependence of the oxygen on the processing parameters of ESR is reviewed and discussed. The influence of these parameters on the oxide inclusions associated with the deoxidation of ESR is also assessed. The suggestions for the future work are proposed in this article.
  • Effects of Nitrogen Gas Pressure on the Solidification Parameters and As-cast Microstructure Revolution during Pressurized Electroslag Remelting AISI 304 Stainless Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-203

    Three AISI 304 stainless steel electrodes were remelted using the lab-scale pressurized electroslag remelting furnace under different nitrogen gas pressure conditions. The solidification parameters and microstructure evolution have been investigated with the sulfur print method method, color metallography and EPMA. The results showed that the pool depth, SDAS and mushy zone width firstly increased and then decreased with the increase of gas pressure from 0.1 to 1.2 MPa. With an approximately equal melting rate, the variation of solidification parameters is dependent on the competition between the heat transfer rate at the slag/pool interface and the ingot/mould interface, because increasing the nitrogen gas pressure could simultaneously increase the two heat transfer rates. Under the current pressure range, the solidification mode and microsegregation during solidification are not affected by the variation of gas pressure. In addition, the variation of nitrogen gas pressure could simultaneously change the nitrogen content and cooling rate in ingots. Both the nitrogen content and cooling rate could affect the content and composition of residual ferrite. However, under the current experiment conditions, the variation of nitrogen content plays a more important role in the content of residual ferrite than the cooling rate, because nitrogen is a strong austenite former element and the cooling rate has no wide variation.
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    1. Evolution of TiN and Oxide Inclusions in Ti-containing Fe-25Ni-15Cr Alloy during Electroslag Remelting ISIJ International Advance Publication
    2. Deoxidation of Electroslag Remelting (ESR) – A Review ISIJ International Advance Publication
  • Scheduling Model for the Practical Steelmaking-continuous Casting Production and Heuristic Algorithm Based on the Optimization of “Furnace-caster Matching” Mode

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    DOI:10.2355/isijinternational.ISIJINT-2019-423

    Considering the "furnace-caster matching" modes, this paper focuses on the scheduling problems from practical steelmaking-continuous casting production lacking refining span. Aiming at the improvement on quality and output of steel products, a mathematical model is established with multi-objective optimization including the minimum earliness/tardiness of starting cast times, the shortest waiting times of heats among different processes and the shortest idle times of converters. A heuristic algorithm based on the optimization of "furnace-caster matching" mode is developed to solve this model, which involves two procedures of device assignment and conflict elimination. Through the detailed analysis on workshop layout and production rhythm, four classes of matching modes of "refining furnace-caster" are proposed to perform the assignments of refining furnaces. The assignments of converters rely on three categories of greedy strategies in terms of minimizing conflictions among heats. A rough scheduling solution with some possible conflicts among heats is obtained through combining "furnace-caster matching" modes and greedy strategies. Then applying the linear programming method to eliminate the conflicts and generate the final solution. Based on the proposed algorithm and the improved genetic algorithms, simulation experiments are carried out by introducing actual production plans as instances. The results indicate that heuristic algorithm based on the optimization of "furnace-caster matching" mode is the right candidate owing to its acceptable scheduling solutions with the better process matching relations and the highlighted performances under crane constraint. Currently, the proposed model and algorithm have been successfully used in a large converter steel plant in China.
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    1. Effects of Mn and S on the Grain Growth and Texture in Cold Rolled 0.5% Si Steel ISIJ International Vol.30(1990), No.4
    2. A Formation Mechanism of Transverse Cracks on CC Slab Surface ISIJ International Vol.30(1990), No.4
    3. Tension Leveling Using Finite Element Analysis with Different Constitutive Relations ISIJ International Advance Publication
  • Tension Leveling Using Finite Element Analysis with Different Constitutive Relations

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    DOI:10.2355/isijinternational.ISIJINT-2019-620

    Tension leveling is applied in metal strip production lines to improve the flatness of metal strips by a combination of tension and bending. To develop tension leveling technology, finite element (FE) analysis is increasingly used in tension leveling process design to reduce the number of trial productions and provide a deeper insight into the process. For the FE analysis of tension leveling, since the material properties affect the leveling results, a material constitutive model that can accurately describe the material behaviors during tension leveling should be applied. In our previous investigation, an advanced constitutive model was constructed for the FE analysis of tension leveling with high accuracy. Here, we report the results of an analysis on tension leveling to clarify the effect of constitutive relations on FE analysis results. Leveling mechanisms for high-strength steel strips were also clarified on the basis of FE analysis results.
  • A New Design of Oxygen Sensor for Electromotive Force Measurement and Electrochemical Deoxidation by Using Oxygen Pump

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    DOI:10.2355/isijinternational.ISIJINT-2019-641

    Electromotive force measurement (EMF method) has developed for many decades. It provides a universal approach to measure quantities such as oxygen partial pressure and activity coefficient of metals. Here we present a new design of oxygen sensor, aiming to avoid complications and inaccuracies which are caused by the effect of extra metallic lead wires. Hereafter, we focus on the development of a cleaner electrochemical deoxidation technology by using the newly developed apparatus. The EMF experiments demonstrate a favorable agreement with previous literature, and the electrochemical deoxidation experiments show remarkable results of oxygen contents reducing. All of these results pinpoint the feasibility of the newly developed apparatus. Based on these positive results, we discuss a possible application of this study in the steelmaking process, illustrating a high potential of a further and ultimate deoxidation by a cheaper and cleaner approach.
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    1. Effect of Direct Powder Additions on the Solidification Structure and Microsegregation of 42CrMo4 Steel ISIJ International Advance Publication
  • Iron Powder-based Metal Matrix for Diamond Cutting Tools: A Review

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    DOI:10.2355/isijinternational.ISIJINT-2019-662

    New material technology, advancement in manufacturing technology and development of alternate materials are key enablers for today's process and product development. Although Diamond cutting tools has a long history started back in 1862, this industry has gone through a tremendous change in last 50 years with the development of synthetic diamond and continues exploration of alternate metal matrix materials (alternate to cobalt). For each specific application, powder for metal matrix needs careful selection based on its chemical composition, size, shape and thermal stability. Cobalt powder was the most commonly used metal matrix powder. However, fluctuating price and health concerns associated with cobalt powder has compelled the industry to search for more economical and sustainable alternative. In this context Iron and Iron based alloy powders turned out to be promising metal matrix powder alternatives for use in diamond cutting tools catering cutting, drilling, grinding, etc applications.This paper gives an overview on the diamond cutting tools history, evolution, trends and developments with special focus on the usages of iron powder as an alternate matrix material for diamond cutting tools.
  • Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt

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    DOI:10.2355/isijinternational.ISIJINT-2019-726

    Our strategy is to enhance the fracture property of ultra-high-strength low-alloy steels with a yield strength of 1.4 GPa or over by arresting the propagation of brittle cracks in hierarchical, anisotropic, and ultrafine-grained structures. This provides a fail-safe design in addition to suppressing crack initiation. The present article reviews the strength, ductility, toughness, and delayed fracture resistance of ultra-high-strength low-alloy steels with ultrafine elongated grain structures processed by the deformation of tempered martensitic structures at elevated temperatures (referred to as warm tempforming). The evolution of heterogeneous microstructures during warm tempforming using multi-pass caliber rolling is discussed, as are the microstructural factors controlling the strength and fracture properties of warm tempformed steels. Furthermore, we apply warm tempformed steels with ultrafine elongated grain structures to the fabrication of ultra-high-strength bolts.
  • Sample Temperature Effect on Steel Measurement Using SP-LIBS and Collinear Long-short DP-LIBS

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    DOI:10.2355/isijinternational.ISIJINT-2019-740

    Laser induced breakdown spectroscopy (LIBS) has been investigated as a potential multi-element quantitative analysis tool for the quality control of on-line steel production. This research investigated influence of sample temperature on steel sample measurement using collinear long-short dual-pulse LIBS (long-short DP-LIBS) and single-pulse LIBS (SP-LIBS). The standard steel sample has been uniformly heated in a muffle furnace from 20°C to 700°C. The experimental results show that sample temperature has significantly effect on measurement result using SP-LIBS. However, long-short DP-LIBS can effectively reduce the sample temperature effect on measurement result. The detection characteristics of long-short DP-LIBS and SP-LIBS were compared using the intensity ratio of I Mn 404.136 nm/I Fe 400.524 nm and I Fe 402.187 nm/I Fe 400.524 nm under different delay time and different sample temperature conditions. The signal intensity and plasma temperature can be maintained higher and more stable for a period of time and at different sample temperature by long-short DP-LIBS with smaller error bar compared with that of SP-LIBS, which indicated long-short DP-LIBS has better measurement repeatability than SP-LIBS. The plasma temperature correction method was applied to compare the detection features of long-short DP-LIBS and SP-LIBS. The signal stability of long-short DP-LIBS measurement was improved significantly at different sample temperature with plasma temperature correction. These results demonstrated that the effect of sample temperature can be reduced using long-short DP-LIBS method to improve the on-line detection capability for steel measurement in complex environment.
  • Multiscale Analysis of MnS Inclusion Distributions in High Strength Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-739

    In the present study, manganese sulfide (MnS) inclusions in the high-strength steel were observed by mainly three observation methods (optical microscope, ultrasonic test and serial sectioning) to characterize the size, location and shape distributions across multiple length scales. For the inclusion size, ultrasonic C-scan imaging and three-dimensional internal structure observation with serial sectioning were used to measure the distributions of the square root of the projected area of the inclusion. The obtained size distributions were combined by setting the threshold of ultrasonic amplitude. The validity of the amplitude threshold was verified by observing several inclusions with X-ray CT. The spatial distributions of inclusions were also obtained by the three observation methods, and analyzed on the basis of the coefficient of variation of the mean near-neighbor distance of inclusions (COVd). The results of analyzing COVd in both 2D and 3D spaces revealed that the inclusions in this material were arranged in clusters. For the inclusion shape, the three-dimensional geometries of inclusions were reconstructed from the images obtained by the serial sectioning method, and simplified to ellipsoid by principal component analysis. From the above results, the distributions of inclusion size, aspect ratio and direction (angle between rolling direction and major axis) were successfully obtained. The inclusion distributions were applied to fatigue prediction model, and the fatigue crack initiation life and total fatigue life of the high-strength steel were calculated. The calculation results showed that the multiscale analysis of inclusions would be useful for fatigue life prediction.
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    2. PREFACE MATERIALS TRANSACTIONS Vol.61(2020), No.5
    3. Effect of Silicon, Manganese and Heating Rate on the Ferrite Recrystallization Kinetics ISIJ International Advance Publication
  • Modelling and Crystal Plasticity Analysis for the Mechanical Response of Alloys with Non-uniformly Distributed Secondary Particles

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    DOI:10.2355/isijinternational.ISIJINT-2019-754

    The relationship between yield stress and the distribution of microscopic plastic deformation was numerically investigated by using a crystal plasticity finite element method (CP-FEM) in the model where particles were randomly distributed. It was in order to reveal which particle spacing. i.e., the maximum, minimum or average particle spacing, can be taken as the representative length which controls yielding. The critical resolved shear stress for the onset of the slip deformation in any element was defined under the extended equation in the Bailey-Hirsch type model. The model includes the term of the Orowan stress obtained from the local values of the representative length. Each particle spacing was distributed with a standard deviation of approximately 2 to 3 times larger than the average particle spacing. The macroscopic mechanical properties obtained with CP-FEM were in good agreement with those experimentally obtained. The onset of microscopic slip deformation depended on the particle distribution. Plastic deformations started first in the area where the particle size is larger, then the plastic region grows in the areas where the particle spacing is smaller. Slip deformation had occurred in 90% of the matrix phase by the macroscopic yield point. The length factor in the Orowan equation was the average spacing of the particles in the model, which is in good agreement with Foreman and Makin. The CP-FEM indicated that in dispersed hardened alloys, microscopic load transfer occurred between the areas where the large particles spacing and the small one at the yielding.
  • Effect of B2O3 on Structure of CaO–Al2O3–SiO2–TiO2–B2O3 Glassy Systems

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    DOI:10.2355/isijinternational.ISIJINT-2019-679

    Titanium-bearing blast furnace slag is an important metallurgical waste, but presently, it is difficult for it to be effectively utilized. B2O3 is an important modifier to greatly promote the mass diffusion of crystallization of Ti-enriched phases in molten slags. To furtherly understand the effect of B2O3 on the structure of Ti-bearing slag, CaO–Al2O3–SiO2–TiO2–B2O3 glasses of various B2O3 were investigated by combining Raman, FT-IR, and X-ray photoelectron spectroscopy. The results showed that BO3 was the dominant structure, which decreased slightly as the B2O3 content increased, while BO4 increased. Three coordination forms (TiO4, TiO5, and TiO6) of the Ti-structure were discovered in the prepared Ti-bearing glasses. The percentage of TiO4 gradually increased and became the main structural unit as the increased B2O3. The increase of BO4 and TiO4 leaded to an increased amount of network connection units, such as SiO4, to increase the degree of polymerization of the prepared Ti-bearing glasses.
  • Phase Composition and Properties Distribution of Residual Iron in a Dissected Blast Furnace Hearth

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    DOI:10.2355/isijinternational.ISIJINT-2019-712

    Dissection research is the most meaningful way to understand the internal conditions of blast furnace. Because it can obtain samples from hearth after a blast furnace was shut down. In this paper, a 2200 m3 commercial blast furnace was shut down with residual iron remained inside. And then core drilling method was used to obtain a horizontal sample of residual iron, which was located 1610 mm below the centerline of taphole and had a length of 1840 mm. A variety of techniques, such as scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Optical Microscope, X-ray diffraction (XRD) and Raman spectroscopy were applied to analysis the microscopic morphology, phase composition and properties distribution of residual iron samples at different position. The results show that complex phases appear near the cold side, including Fe, C, Ti3N2, KAlSi2O6 and Al2O3. And distribution of properties along the core sample from inside to cold side like density, degree of graphitization and thermal diffusion also have a big change. These results are considered to be related to the function of cooling system.
  • Casting Defect and Process Optimization of Steel Crossing

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    DOI:10.2355/isijinternational.ISIJINT-2019-612

    The casting quality of crossing in a railway turnout is required to be higher because of the significant impact load on the rail. The simulation results of using different fever risers, the temperature field, solidification process and casting defects, were obtained by the implicit finite element method based on the ProCAST software. To improve the authenticity of the visualization of the casting process, a numerical simulation assumption of the mass flow rate attenuation was proposed for the overflow of molten metal from the risers during tilt pouring. The result shows that the temperature field is more uniform when the risers with exothermic energy of 1200 kJ/kg were chosen and the defects converge to the risers in accordance with the principle of sequential solidification. Compared with insulation riser, shrinkage porosity proportion decreased from 23.10% to 17.01%, and the shrinkage cavity proportion decreased from 1.002% to 0.530%. However, changing the burned time has no obvious effect on the casting. At the same time, the process optimization scheme of risers was put forward in this study and the casting defects such as shrinkage cavity and porosity are predicted according to the ‘V type' feeding area of the fever risers. This improvement has greatly improved the performance of the casting, and the passing gross tonnage could reach 300 million tons.
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    3. Control of Solidified Structure of Cast Metal by Imposing Electromagnetic Field MATERIALS TRANSACTIONS Vol.42(2001), No.2
  • Numerical Simulation of Impinging Gas Jet on a Liquid Bath Using SPH Method

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    DOI:10.2355/isijinternational.ISIJINT-2019-653

    As the basis of injection metallurgy, an impinging gas jet on a liquid bath surface was simulated and experimentally verified. The SPH simulation of the gas-liquid two phase flow was developed by using the XSPH method, and the calculation speed was considerably increased with the use of general-purpose computing on graphics processing units. For N2 gas – water bath system, the simulated shapes and penetration length of the cavity were in good agreement with the experimental results, and the three modes of cavity were reproduced by the calculation. N2 gas–molten iron bath system was also simulated. The cavity mode was "dimpling mode" for all calculations.
  • Data Assimilation in the Welding Process for Analysis of Weld Toe Geometry and Heat Source Model

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    DOI:10.2355/isijinternational.ISIJINT-2019-720

    Finite element simulations are widely conducted to evaluate the heat transfer and deformation during welding. Basically these welding simulations require input variables such as shape parameters and heat source parameters, which are not directly measured by the experimental method. In this study, two methods were proposed to obtain these input parameters more efficiently: a method of automatically identifying toe radius and reinforcement angle from height profile, and a method of estimating a heat source model in welding simulation. In the first method, the toe radius and reinforcement angle were extracted from the height profile by Akaike's information criterion. The extracted results were consistent with the manual fitting results. In the second method, the optimal combination of the heat input parameters was automatically searched by Bayesian optimization. Comparing the accumulated regrets, it was found that the probability of improvement and upper confidence bound provide more efficient optimization than the other acquisition functions in the calibration of the heat input parameters. Both temperature history and shape of fusion zone and heat-affected zone calculated at the optimized condition were in good agreement with the experimental results. These results demonstrated that the two proposed methods are effective to create a numerical model for welding simulation.
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    1. Effect of Magnetite on Mineral Phase Formation in Sintering Process ISIJ International Vol.60(2020), No.2
  • Sulfide Capacities of Solid Oxides in Calcium-Aluminate Systems

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    DOI:10.2355/isijinternational.ISIJINT-2019-793

    To clarify the mechanism of CaS formation on the oxide inclusion of the CaO–Al2O3 system, the sulfide capacities of solid oxides was measured in the present study. The results show that the sulfide capacity of (12CaO·7Al2O3; C12A7) was much larger than of other compounds, and increased with temperature. The value for C12A7 was larger than that measured for the liquid oxide of the same composition. Furthermore, the diffusion behavior of sulfur in solid steel to the inclusion of the CaO–Al2O3 system, was investigated using a diffusion couple. After heating at 1473 K for 72 h, in the case of C12A7, the intensity of sulfur in the oxide was high, but the formation of CaS was not detected. This suggests that the formation of CaS was suppressed around the C12A7 particles by the diffusion of sulfur in the solid oxide.
  • Physico-chemical Properties of Mill Scale Iron Powders

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    DOI:10.2355/isijinternational.ISIJINT-2019-737

    Powdered form of iron typically < 250 microns is phrased as iron powder. Commercial manufacturing of iron powder is majorly restricted to atomization, carbonyl, electrolytic and reduction routes. Powders from the later three techniques generally cater to special iron powders applicable to non-powder metallurgy segments such as food fortification, chemical reagents, water purification, etc. In this work, mill scale iron powders are synthesized by thermo-chemical reduction of mill scale, a steel industry by product, and their properties are analysed and compared with commercial iron powders such as carbonyl, electrolytic and reduced. Chemical and physical characterizations such as Optical Microscopy, Scanning Electron Microscopy and X-ray Diffraction of the powders are performed. Obtained results reveal that, mill scale iron powders MIP and MIP45 possess good product properties. Especially, MIP45 grade exhibited finer particle size of D50< 30 microns and BET surface area of 0.63 m2/g along with Fe (T) > 98%, true density-7.55 g/cc, apparent density 2.67–2.83 g/cc, packed bulk density of 3.44 g/cc and good flowability. This product of mill scale with highest apparent density and good surface area is expected to qualify to new segment of applications along with other commercial iron powders.
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    1. Removal of Impurities from Scrap and Dust ISIJ International Vol.36(1996), No.Suppl
    2. Interfacial Tensions of Liquid Iron-alloys and Commercial Steels in Contact with Liquid Slags ISIJ International Vol.36(1996), No.Suppl
    3. Determination of Free Lime Contents in Slags by Solution Calorimetry ISIJ International Vol.36(1996), No.Suppl
  • Effect of Silicon, Manganese and Heating Rate on the Ferrite Recrystallization Kinetics

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    DOI:10.2355/isijinternational.ISIJINT-2019-475

    This study presents the effects of silicon (Si) and manganese (Mn) concentration and of heating rate on the ferrite recrystallization kinetics in seven model alloys with different Si and Mn concentrations, which are of relevance for the development of Advanced High Strength Steels (AHSS). The recrystallization kinetics were studied with in-situ 2D X-ray Diffraction (2D-XRD) and ex-situ microstructure observations using Scanning Electron Microscopy (SEM). The experimentally observed differences in the recrystallization start temperature (Ts), dependent on the Si and Mn concentrations and the heating rate, can be described by combining the non-isothermal JMAK-model with a modified version of Cahn's solute drag model. The modified Cahn model takes into account – in an approximate manner – that the interaction energy of the solute atoms with the grain boundary depends on the Si and Mn concentrations in the boundary and the Wagner interaction parameters. The collective contribution of the Si and Mn atoms to the increase in the Ts with respect to the reference alloy (without Si and with very little Mn) is higher than would be expected from the simple addition of the effects of the Si and Mn concentrations alone. This means that the interaction between Si and Mn atoms leads to an additional increase in Ts, i.e. a coupled solute drag effect. For the later stages of recrystallization, we have studied the change in the number density and the growth rates of the recrystallizing grains using SEM. The observations show non-random nucleation, early impingement of the grains in the normal-direction and non-constant growth rates of recrystallizing grains.
  • In-situ Phase Identification of Crystallized Compound from 2CaO·SiO2–3CaO·P2O5 Liquid

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    DOI:10.2355/isijinternational.ISIJINT-2019-449

    In dephosphorization process in steelmaking, phosphorus in molten iron is distributed into molten slag after oxidized, and it forms 3CaO·P2O5. It has been known that dicalcium silicate (2CaO·SiO2) formed in molten slag and 3CaO·P2O5 make a solid solution, which could promote dephosphorization efficiency from molten iron. It has been reported that 2CaO·SiO2–3CaO·P2O5 solid solution (α phase) is formed for entire composition range at higher temperatures than 1673 K, and many previous studies on dephosphorization behavior assumed that the α phase would be precipitated from molten slag. However, we found that the α phase cannot be obtained at low phosphorus concentrations when the pellet of 2CaO·SiO2 and 3CaO·P2O5 powders mixture is annealed and quenched to room temperature. In this study, we conduct high temperature in-situ X-ray diffraction analysis to the aerodynamically levitated sphere of the 2CaO·SiO2–3CaO·P2O5 liquid to identify primary crystallized phase. It has been verified that the α phase is precipitated from the liquid for wide phosphorus concentrations. In addition, a rapid phase transition of the 2CaO·SiO2–3CaO·P2O5 solid solution has been detected by the time-division X-ray diffraction with high resolutions when the levitated sample containing the α phase is quenched from the precipitated temperature.
  • A Data-Driven Multiobjective Dynamic Robust Modeling and Operation Optimization for Continuous Annealing Production Process

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    DOI:10.2355/isijinternational.ISIJINT-2019-570

    There are many dynamic disturbances during the continuous annealing production line (CAPL) in iron and steel enterprise. Traditional robust operation optimization considers only the maximum disturbance range in previous production and overrides the dynamic changes of these disturbances, which often results in high production cost and low product quality. Therefore, this paper proposes a novel multiobjective dynamic robust optimization (MODRO) modeling method by further taking into account the dynamic changes of these disturbances and adopting a time series prediction model based on a least square support vector regression (LSSVR) to predict the range of disturbances in next time slot. The main feature of the model is that the robustness can be dynamically adjusted according to the disturbance range predicted by the LSSVR. To solve this model, an improved NSGA-II algorithm is developed based on a new crowding metric. Numerical results based on actual production process data illustrate that the proposed MODRO modeling method is obviously superior to traditional static robust operation optimization, and that it can significantly improve the strip quality and the capacity utilization of the CAPL, and reduce the total energy consumption.
  • Segregation Mechanism of Al-based Oxides on Surface of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets

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    DOI:10.2355/isijinternational.ISIJINT-2019-749

    It is known that the Al added to the Zn coating layer of hot-dip galvanized steel sheets (HDG) segregates on the surface of temper-rolled HDG as Al-based oxides with increasing aging time in air at room temperature. In this study, the surfaces of Zn-0.2mass%Al HDG with and without temper rolling were investigated to clarify the segregation mechanism. Specimens with a Zn coating weight of 55–57 g/m2 including 0.19–0.20 mass% of Al were used. The specimens were aged in air at 20°C or held in liquid nitrogen, and the surface and cross sections of the specimens were then observed and analyzed by XRF, SEM-EDX and EBSD. As a result, it was found that the velocity of Al-based oxide segregation on the surface of the temper-rolled HDG was much higher than that of the HDG without temper rolling. This was attributed to the difference in the area where formation of Al-based oxides was possible. It was also found that the Zn crystal grains in the coating layer were refined by recrystallization due to contact with the temper roll, resulting in an increased number of grain boundaries that can serve as Al diffusion paths. Some unrecrystallized grains also remained after temper rolling and could increase the number of formation sites for Al-based oxides, as they contain numerous dislocations that can serve as Al diffusion paths. These two different formation sites could lead to difference in the segregation rates observed in this study.
  • Selection of Atomic Emission Lines on the Mutual Identification of Austenitic Stainless Steels with a Combination of Laser-induced Breakdown Spectroscopy (LIBS) and Partial-least-square Regression (PLSR)

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    DOI:10.2355/isijinternational.ISIJINT-2019-549

    Laser-induced breakdown spectroscopy (LIBS) is a promising method for the rapid determination of compositions of stainless steels in steel scrap. LIBS is widely known as a method for very rapid elemental analysis in open-air without any pretreatment. We applied a laboratory-build LIBS system for mutual identification of 5 types of austenitic stainless steels, SUS304, SUS310, SUS316, SUS321, and SUS347. The certified reference materials of JSM M 200 were employed for establishing supervised models, conducting partial-least-square regression (PLSR) for the determination of Cr, Ni, Mo, Ti, and Nb. Since it needed more than 10 minutes of calculation time when all the wavelength range were utilized for PLS2 regression, suitable emission lines in the determination were picked up for the reduction of calculation amount and time. When we select single emission lines having higher excitation levels to avoid an affection by self-absorption, the good determination results for Cr, Ni, Mo, and Nb could be obtained with reasonable accuracy and precision by the calculation with PLS1 regression.
  • Microstructure and Mechanical Properties of a Hot-rolled High Manganese TWIP Steel Containing 0.3%V

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    DOI:10.2355/isijinternational.ISIJINT-2019-578

    In this paper, the microstructure, precipitates and mechanical properties of a 0.3%V-alloying high Mn austenitic TWIP steel after hot rolling and aging treatment were investigated, aimed to improve the yield strength of high Mn austenitic steel. Experimental results showed that an elongated and unrecrystallized grain structure could be obtained at a finish rolling temperature of 850°C or below in 0.3V steel. The amount of VC precipitates was very small and most vanadium remained in solution after hot rolling. Therefore, the solute drag effect of dissolved vanadium rather than the Zener pinning effect of VC precipitates was mainly responsible for the inhibition of recrystallization. The yield strength increase of 0.3V steel with deceasing finish rolling temperature was much more remarkable than that of V-free steel. Quantifying possible strengthening mechanisms revealed that most of the YS increase was due to the dislocation strengthening in 0.3V steel. The aging treatment for 30 min promoted the precipitation of VC, but the precipitation amount was still much less than the equilibrium precipitation amount. The comparative analysis on precipitation kinetics of VC in high Mn and low Mn steels indicated that the former had a more sluggish precipitation rate than the latter. This result was further analyzed in terms of the effect of Mn on the solubility product of VC in austenite.
  • Simultaneous Broadening Analysis of Multiple Bragg Edges Observed by Wavelength-resolved Neutron Transmission Imaging of Deformed Low-carbon Ferritic Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-656

    With the goal of real-space mapping of dislocation information using a wavelength-resolved (spectroscopic) neutron transmission imaging method, broadenings of multiple Bragg-edges in neutron transmission spectrum were investigated in detail for the first time. Data of time-of-flight (TOF) neutron transmission imaging and diffraction experiments on a polycrystalline low-carbon ferritic steel sample while undergoing tensile testing were analysed. The Bragg-edge neutron transmission spectroscopy was combined with the classical Williamson-Hall method corrected by the crystal elastic anisotropy using the ratio of diffraction Young's modulus, namely, the corrected classical Williamson-Hall (ccWH) method. As a result, the broadening values evaluated from the ccWH analysis of Bragg-edge data were consistent with results of both our TOF neutron diffraction experiments and previous reports. In addition, it was deduced that the line-broadenings appearing in the plastic deformation condition during tensile testing in our experiment were mainly caused by micro-strain (dislocation density) effect and not by crystallite size effect. Finally, a Bragg-edge broadening mapping method, using a simultaneous multiple Bragg-edges profile analysis based on the ccWH method, could identify plastically deformed zones in the sample more clearly than a traditional single Bragg-edge broadening analysis method.
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  • Scheduling in Continuous Steelmaking Casting: A Systematic Review

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    DOI:10.2355/isijinternational.ISIJINT-2019-574

    The converter furnace and the continuous casting are the most important stages in steel production. Modern integrated processes directly connect the converter furnaces and the continuous casting machines with a flow of molten metal, and the steel is manufactured synchronously between the various machines. Starting from the traditional handmade programs for the management of these processes, during the last two decades there has been a notable increase in studies and publications in this field, trying to formulate scheduling in a rational and automatic way. The process has been approached for years through the development of both physical and operational research models, many of them theoretically. The main purpose of this study is to present a critical and in-depth evaluation of the previous studies, so that the state of the art of scheduling in steelworks can be evaluated. An approach based on a Systematic Literature Review (SLR) has been used, trying to search, evaluate, synthesize and analyze all the relevant studies for this specific field. As a result, the conclusions of the various analyses are presented and a study route is proposed for the design of the optimal planning methodology in the steelworks.
  • Review on the High-Temperature Thermophysical Properties of Continuous Casting Mold Fluxes for Highly Alloyed Steels

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    DOI:10.2355/isijinternational.ISIJINT-2019-522

    Several recently developed highly alloyed steel grades have shown unsurpassed performance in terms of physical, chemical, and electromagnetic properties. However, broader commercialization of these steels has been hampered by limitations in mold flux performance. Newly developed steels containing considerable amounts of dissolved Al, Mn, and Ti actively react with typical CaO-SiO2-based mold fluxes, which severely changes the composition and subsequently the thermophysical properties of the mold flux that determine the external and internal quality of the as-cast steels. These dynamic changes result in nonuniform heat transfer, lubrication issues, surface defects, and caster breakouts. This work critically assesses the current status of the high-temperature thermophysical properties of CaO-SiO2-based and CaO-Al2O3-based mold fluxes intended for use in casting highly alloyed steel grades. Thermophysical properties, including viscosity, crystallization, thermal conductivity, and heat flux, have been evaluated. The effect of compositional variables including CaO/SiO2, CaO/Al2O3, and Al2O3/SiO2 mass ratios and the additions of CaF2, B2O3, Li2O, K2O, Na2O, TiO2, and BaO on these high-temperature thermophysical properties are discussed.
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    2. Scheduling in Continuous Steelmaking Casting: A Systematic Review ISIJ International Advance Publication
    3. Vortex Dynamics and Fluctuations of Impinging Planar Jet ISIJ International Vol.60(2020), No.5

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  5. Microstructure and Mechanical Properties of Simulated Heat Affected Zone of Laser Welded Medium-Mn Steel ISIJ International Advance Publication
  6. Analysis of Microstructures and Voids on Ductile Fracture of Ferrite/Martensite Dual-Phase Steels through Three-dimensional Observation Tetsu-to-Hagané Vol.106(2020), No.5
  7. Perspective on Progressive Development of Oxygen Blast Furnace for Energy Saving ISIJ International Vol.55(2015), No.9
  8. A Review of the Twin-roll Casting Process for Complex Section Products ISIJ International Advance Publication
  9. Hydrogen-assisted Crack Propagation in Pre-strained Twinning-induced Plasticity Steel: from Initiation at a Small Defect to Failure ISIJ International Advance Publication
  10. Effect of Cooling Rate on the Controlled Solidification of “Fe2O3”–CaO–SiO2 Liquids in Air in Synthetic Iron Ore Sinter ISIJ International Vol.60(2020), No.5

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