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

ISIJ International Vol. 58 (2018), No. 7

  • Nitrogen Solubility in Cast Iron Containing C, Si and Mn

    pp. 1185-1190

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    DOI:10.2355/isijinternational.ISIJINT-2017-689

    The nitrogen solubility in cast iron melt containing carbon, silicon and manganese was measured by the gas-liquid metal equilibration technique in the temperature range from 1573 to 1873 K. The nitrogen solubility in carbon saturated liquid iron decreased with increasing temperature due to the effect of carbon content increasing with temperature. The simultaneous effect of carbon, silicon and manganese on nitrogen was also measured to determine the second-order cross-product parameters of those alloying elements on nitrogen using the Wagner’s interaction parameter formalism. The critical nitrogen content to form nitrogen gas bubbles during the solidification of cast iron for various melt composition can be predicted using thermodynamic parameters determined in the present study.
  • Mechanical Model and Calculation of Dry Masonry Brick Lining of Blast Furnace Hearth

    pp. 1191-1197

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    DOI:10.2355/isijinternational.ISIJINT-2017-692

    According to the principle of thermo elasticity, thermal expansion mechanical characteristics of the dry masonry brick lining of the blast furnace hearth is analyzed, and the thermo elasticity multi-contact state non-linear model of brick lining is established. Based on finite element analysis, thermo-elastic mechanics calculation process and parameterization program are designed, and the feasibility of the algorithm and the program is verified. On the basis of analysis, rather than the brick joint of the hot end which can be closed completely, that of the cold end cannot always be closed when the dry masonry brick lining is heated. The closing length of brick joint near the cold end decreases when the wideness of reservation paving seam increases or linear expansion coefficient of brick decreases. Circumferential stress on the hot end of the brick lining and shell decreases with the increase of reservation brick joint. For ensuring the stability, hermetic sealing, reservation brick joint should be controlled strictly. When the plastic compression of filler exists, the closing length of brick joint is shorter, and the stress on the hot end of brick lining and shell is reduced. For the purpose of its strength and density, the amount of downward reduction of filler in building should increase property to ensure the strength and the density of filler, thus the hermetic sealing can be up to the standard. The internal pressure makes the closing segment of brick joint shorter. The stress of the shell increases when compressive stress on the hot end of brick lining decreases. Considering the hermetic sealing, stress of brick lining, stress of shell and other factors, the model and the parametric calculation program can also be applied to assessment and optimized design of structure parameters and material properties of the hearth.
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    Readers Who Read This Article Also Read

    1. Importance of the Penetration Depth and Mixing in the IRONARC Process ISIJ International Vol.58(2018), No.7
    2. Economical and Efficient Protection for Blast Furnace Hearth ISIJ International Vol.58(2018), No.7
    3. Effect of Lignite Addition on Gasification Properties and Coke Strength after Reaction ISIJ International Vol.58(2018), No.7
  • Economical and Efficient Protection for Blast Furnace Hearth

    pp. 1198-1203

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    DOI:10.2355/isijinternational.ISIJINT-2018-005

    In order to clarify the erosion mechanism of carbon brick and realize the economical and efficient protection for blast furnace hearth at the end of the service. The damaged carbon bricks were sampled from a commercial blast furnace, the microstructure of the damaged carbon bricks was analyzed through SEM and EDS. The carbon undersaturation degrees of molten iron for different volume blast furnace were calculated, the dissolution and the penetration were considered as the reasons for the erosion of carbon brick. A model of economical and efficient protection for hearth was established based on various factors, the economy of protection raw material and the protection effect can be evaluated through the model. The model guides the selection of the economical protection raw material according to the evaluation, the reasonable operation can be obtained according to the calculation of the fettling rate.
  • Analysis of Commercial Activated Carbon Controlling Ultra-fined Particulate Emissions from Iron Ore Sintering Process

    pp. 1204-1209

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    DOI:10.2355/isijinternational.ISIJINT-2018-032

    This study investigated the characteristics of activated carbon removing ultra-fined particulates PM10 and PM2.5 from sintering flue gas, and discussed the potential mechanism. Experimental results show that activated carbon (AC) exhibited greater removal efficiency to PM10 than PM2.5, and increasing the thickness of AC or reducing AC grain size facilitated the removal of PM10 and PM2.5. The removal ratio of PM10 and PM2.5 achieved 67.3% and 58.7% when AC bed thickness and grain size were 200 mm and 3–5 mm, respectively. Bigger particles in PM10 was susceptible to inertial effect, making their easier removal and higher removal ratio. AC bed thickness and bulk porosity (negatively relatively to AC grain size) presented positive relationship with the removal efficiency of PM10 and PM2.5, which therefore exhibited higher removal ratio with the bed thickness increased and grain size reduced. The research findings benefit the effective control of ultra-fined particulates in practical sintering plants.
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    Readers Who Read This Article Also Read

    1. Effect of Lignite Addition on Gasification Properties and Coke Strength after Reaction ISIJ International Vol.58(2018), No.7
    2. Mechanical Model and Calculation of Dry Masonry Brick Lining of Blast Furnace Hearth ISIJ International Vol.58(2018), No.7
    3. Importance of the Penetration Depth and Mixing in the IRONARC Process ISIJ International Vol.58(2018), No.7
  • Importance of the Penetration Depth and Mixing in the IRONARC Process

    pp. 1210-1217

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    DOI:10.2355/isijinternational.ISIJINT-2018-043

    One of the most important parameters for gas injection into liquid baths is the penetration depth of the gas into the bath. This is due to that it strongly influences the flow structure and hence the stirring and plume behavior in metallurgical processes.The IRONARC process is a new energy efficient process for reduction of iron oxide to produce pig iron. The future goal is to continuously scale up the process to an industrial scale from the current pilot scale. In this process, gas is injected horizontally through a submerged nozzle into a slag bath. Hence, the penetration depth is of great importance since it greatly affect several parameters in this process. Moreover, this information is essential when scaling up the reactor from a pilot scale to an industrial scale.In this work, the penetration depth of gas injection into water in a small scale side blown converter was studied numerically. Two different approaches with different multiphase models were tested, namely the Volume of Fluid (VOF) model and Eulerian multiphase model (EE). The penetration depth could be accurately determined for both numerical models, with a small expected deviation of 13.9% from the physical experiment results. Also, the simulation time was shorter for the Eulerian multiphase model. The penetration depth was then determined for the IRONARC pilot plant process. The results show that the plume is detached from the nozzle wall, which in turn results in a better energy usage of the gas along with a small refractory wear.
  • Effect of Lignite Addition on Gasification Properties and Coke Strength after Reaction

    pp. 1218-1223

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    DOI:10.2355/isijinternational.ISIJINT-2018-039

    In order to clarify the effect of lignite addition on the CO2 gasification properties and strength after reaction of coke, the carbon structure, micro morphology, specific surface area of coke were studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and BET. The results show that the lignite can decrease the coke strength after reaction, especially for the lignite content in coke more than 8%. The results of X-ray diffraction profiles show that the change of the carbon structure has no connection with the addition content of lignite, and is not responsible for the decrease of the coke strength after reaction. However, because of the consume of isotropic and fine mosaic textures enhanced by lignite addition during gasification, the generation, enlargement and coalescence of coke pores were promoted, leading to the increase of specific surface area. With the addition content of lignite increasing, the homogeneous reaction, which is transition from surface reaction to, enhanced the permeation of CO2 gas further into coke. The external reaction of lignite-enriched coke accelerated the rupture of bonds between coke particles, which results in the decrease of coke strength after reaction.
  • Analysis of Power Supply Parameter Control and Its Influence Factors for Electromagnetic Induction-controlled Automated Steel-teeming System

    pp. 1224-1231

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    DOI:10.2355/isijinternational.ISIJINT-2018-023

    The steel-teeming time, which is directly affected by the output parameters of the power supply, is one of the most important technical indicators of an electromagnetic steel-teeming system. Therefore, this work employs numerical simulation to build a power supply output parameter model for the electromagnetic steel-teeming system of a 110 t ladle of a steel mill. The correctness of the model is verified through a high-temperature offline test. The results of the simulation correspond closely to those of the offline test. Furthermore, the best combination of power supply output parameters was found to be: frequency 35.3 kHz, output current 152.9 A, output power 40.1 kW, and steel-teeming time 113 s. The factors influencing these parameters and the teeming time are summarized as follows: the magnitude of each power supply output parameter (i) increases, (ii) decreases initially then increases, (iii) decreases slightly, (iv) decreases initially then increases, and (v) decreases initially, increases rapidly, and then changes gradually with increasing (i) diameter of the liquid steel channel, (ii) length of the liquid steel channel, (iii) static pressure of the ladle, (iv) steel-teeming temperature, and (v) standing time, respectively; larger power supply output parameters are needed for the horn-shaped (as shown in Fig. 3) liquid steel channel than for the cylindrical channel. This article will serve as a theoretical reference for reducing the steel-teeming time of the electromagnetic steel-teeming system.
  • Application of Alkali Oxides in LF Refining Slag for Enhancing Inclusion Removal in C96V Saw Wire Steel

    pp. 1232-1241

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    DOI:10.2355/isijinternational.ISIJINT-2018-048

    A novel LF refining slag contains K2O has been developed in order to produce ultraclean saw wire steels. The diameter of ultrafine saw wire is between 50×10−6 m (50 µm) and 80 ×10−6 m (80 µm), any hard inclusion which diameter more than 5×10−6 m (5 µm) should be avoided because it probably will cause wire breaking. In order to enhance inclusion removal in C96V saw wire steel during LF refining process, fundamental work on the effect of alkali oxides (Li2O, K2O) on the absorption ability of inclusions in a typical LF refining slag for C96V saw wire steel has been investigated. The results indicated that K2O additions seems to significantly enhance inclusion removal in steel melts, instead, Li2O additions hindered inclusion removal. In details, K2O improve the cleanliness in the as quenched C96V saw wire steel melts compared to preexisting synthetic LF refining slag compositions: (i) The average diameter of nonmetallic inclusions was decreased sharply with the content of K2O in synthetic LF refining slag increasing. In particular, the diameter of most of inclusions was less than 2.5×10−6 m (2.5 µm) when the content of K2O in synthetic LF refining slag more than 10 wt%; (ii) The number of inclusions descend sharply with the content of K2O in synthetic LF refining slag raising. (iii) Both of the SiO2–MnO–Al2O3, SiO2–CaO–Al2O3 inclusions system mainly concentrated in the low melting zone when the composition of K2O in synthetic refining slag was less than 10 wt%. While the Li2O additions has the opposite effect.
  • Flow Behavior in the Slab Mold under Optimized Swirling Technology in Submerged Entry Nozzle

    pp. 1242-1249

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    DOI:10.2355/isijinternational.ISIJINT-2018-095

    Flow behavior in the slab mold by optimized swirling flow generation in the submerged entry nozzle (SEN) is investigated. Therefore, hydromechanical model experiment was carried out to simulate this metallurgical process, the effect of turning around the nozzle with swirling and different bottom shape of nozzle is especially analyzed. The flow behavior in the mold was recorded by dye tracer and camera; The two dimension average velocity distribution in the slab mold was measured by the Ultrasound Doppler Velocimetry (UDV). The velocity distribution agrees well with flow pattern recorded by camera. The swirling flow in SEN can reduce the impinging to the narrow face and slag entrapment is inhibited by swirling. Furthermore, the flow in the mold was optimized with swirling in SEN as well as turning around the nozzle outlet in reverse, which avoids the impinging to both the wide and narrow faces of the mold at the same time. It is a potential technology for continuous casting.
  • Formation and Evolution of Inclusions in Si-killed Resulfurized Free-cutting Steel

    pp. 1250-1256

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    DOI:10.2355/isijinternational.ISIJINT-2018-105

    In order to control the machinability and mechanical property of resulfurized free-cutting steel, the high temperature experiments at laboratory and thermodynamic analysis were carried out to investigate the formation and evolution of inclusions in the processes of refining and solidification. Furthermore, the migration behavior of sulfur was also assessed between the inclusions and the liquid steel. The results showed that the liquid oxysulfide inclusion (Mn,Si)x(O,S)y with trace amount of sulfur formed after FeS addition at 1600°C. As sulfur segregated in the residual liquid steel during solidification, sulfur rapidly migrated into (Mn,Si)x(O,S)y from the liquid steel at the initial stage of solidification. However, sulfur migrated out from (Mn,Si)x(O,S)y at the middle stage of solidification because MnS precipitated from the supersaturated liquid steel. After the steel solidified completely, sulfur continued to migrate out from the liquid oxysulfide inclusion (Mn,Si)x(O,S)y. When the temperature decreased to 1250°C, the liquid inclusion (Mn,Si)x(O,S)y transformed to two solid phases of (Mn,Si)xOy and MnS. Finally, the complex inclusion composed of (Mn,Si)xOy and MnS formed.
  • Oxidation of Ti Added ULC Steel by CO Gas Simulating Interfacial Reaction between the Steel and SEN during Continuous Casting

    pp. 1257-1266

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    DOI:10.2355/isijinternational.ISIJINT-2018-164

    In order to elucidate possible mechanism causing nozzle clogging during continuous casting of Ti added Ultra Low C (Ti-ULC) steel, thermodynamic analysis and experimental validation were carried out with an emphasis on the chemical reaction between the liquid steel and nozzle refractory. It was pointed out that the reaction occurs between CO gas from the nozzle refractory and the liquid steel, at the interface between them. A series of thermodynamic calculations were carried out in order to predict related phase equilibria. It was found that Ti in the steel induces the formation of a liquid oxide composed of FetO–Al2O3–TiOx along with solid alumina. This was different to a case of Ti-free ULC where only solid alumina was stable. In order to verify the thermodynamic predictions, a series of experiments were conducted. A number of Fe–Al–Ti alloys were reacted with CO gas at 1560°C in order to simulate the interfacial reaction. Surface and cross section of the alloy samples were analyzed using Scanning Electron Microscopy (SEM) with Energy Dispersive Spectrometry (EDS). The experimental results were in good agreement with the thermodynamic predictions. This finding provides an idea why nozzle clogging is deteriorated by addition of Ti in ULC steel. It is proposed that Ti is oxidized together with Fe and Al by CO gas from a nozzle, and forms a liquid oxide composed of FetO–Al2O3–TiOx, which shows good wettability both to liquid steel and to refractory. This would be a precursor of clog material inside the nozzle.
  • A Novel Method for Improving Cast Structure of M42 High Speed Steel by Pressurized Metallurgy Technology

    pp. 1267-1274

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    DOI:10.2355/isijinternational.ISIJINT-2017-759

    In this paper, a novel method of pressurized metallurgy technology was proposed to improve cast structure of M42 high speed steel (HSS). The effect of solidification pressure (0.1, 1 and 2 MPa) on the cast structure of M42 HSS was investigated by means of experimental analysis and calculation of Thermo-Calc and DICTRA software. Increasing solidification pressure can obviously enhance cooling rate by improving interfacial heat transfer coefficient, which results in some remarkable improvement of the cast structure of M42 HSS. Firstly, the primary/secondary dendrite arm spacing and the average thickness of eutectic ledeburite reduce, which means dendrite structure is refined and eutectic ledeburite more homogeneously distributes with smaller size. Secondly, increasing solidification pressure, the volume fraction of M6C carbides decreases obviously and that of M2C increases correspondingly. And the morphology of M2C carbide changes from larger size lamellar and straight-rod shape into smaller size curved-rod morphology under higher solidification pressure due to larger nucleation number and overgrowth of γ, indicating that carbides are refined and distribute more uniformly. At last, higher solidification pressure is beneficial to reduce the lamellar spacing of M2C carbide and make compositions distribute more homogeneously.
  • Effect of Directional Solidification in Electroslag Remelting on the Microstructure and Cleanliness of an Austenitic Hot-work Die Steel

    pp. 1275-1284

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    DOI:10.2355/isijinternational.ISIJINT-2018-003

    The current study focuses on the effect of directional solidification in electroslag remelting (ESR) on the removal efficiency of inclusion and the shape of molten metal pool during this refining process as well as on solidification structure of remelted ingot. Two ingots were remelted through traditional ESR process and continuous directional solidification in electroslag remelting (ESR-CDS) process for comparison, respectively. Moreover, a two-dimensional (2D) coupled mathematical model was employed to simulate the temperature field, solidification and velocity fields as well as inclusion motion to reveal the refinement mechanism of inclusion removal, microstructure and carbides during remelting process. The results showed that the macro-segregation of carbon was reduced and the microstructure of columnar grains paralleled to axis of ingot was obtained through ESR-CDS process, together with the refinement of carbides distribution. Moreover, the number and size of inclusions in ingot were much more reduced remelting through ESR-CDS process compared to ESR process. The total number and average diameter of MnS particles are obviously reduced from 689 and 2.28 µm in S1 ingot to 78 and 1.78 µm in S2 ingot respectively, remelting through ESR-CDS process. Meanwhile, the number of MnS particles with size >3 µm is reduced from 15.67% in S1 ingot to 1.28% in S2 ingot, and that with size 1–2 µm is increased from 49.93% in S1 ingot to 67.95% in S2 ingot. It was found that ESR-CDS technology was beneficial for refinement of microstructure and carbides as well as removal of inclusions, thus achieving considerable improvement in mechanical properties of austenitic hot-work die steel.
  • Simultaneous Evaluation of Viscous and Crystallization Behaviors of Silicate Melts by Capacitance and Viscosity Measurements

    pp. 1285-1292

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    DOI:10.2355/isijinternational.ISIJINT-2018-009

    This study set out to develop a device capable of simultaneously measuring viscosity and capacitance. The viscosity measurements required prior calibration of the device. However, room-temperature calibration using silicone oil is affected by the immersion depth of the rod, rotational speed of the crucible, and diameter/length of the torsion wire. The calibration results revealed that the potential produced by the torque acting on the torsion wire, generated by the viscous resistance of the silicone oil, was stable when the rod was immersed to a depth of 10 mm. Upon varying the rotational speed of the crucible and viscosity of the silicone oil, the rotational speed of the crucible was found to be proportional to the potential. Furthermore, the measured potential was found to be proportional to the viscosity. Based on the room-temperature calibration results, the immersion depth of the rod was set to 10 mm. By adjusting the diameter and length of the torsion wire, a wide range of viscosities could be measured. High-temperature calibration was performed using the SRM2 standard-viscosity material and involved comparing the measured viscosity with the recommended value for SRM2 or with the results of viscosity measurements obtained by other laboratories. The viscosity measurements obtained in the present study were in good agreement with both the recommended values and the results obtained by other laboratories. Therefore, the device designed in the present study was capable of precisely measuring the viscosity. Finally, the device could also simultaneously measure the viscosity and capacitance of the simple 50CaO-50SiO2 (mol%) and complex 46.4CaO-38.6SiO2-10CaF2-5B2O3 and 43.6CaO-36.4SiO2-10CaF2-10B2O3 (mol%) melts. Furthermore, a drastic increase in the viscosity led to a drastic decrease in the capacitance, corresponding to the crystallization of the melt, which is assumed to affect the viscosity of the melt.
  • Wear Debris Classification of Steel Production Equipment using Feature Fusion and Case-based Reasoning

    pp. 1293-1299

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    DOI:10.2355/isijinternational.ISIJINT-2018-076

    Wear debris classification is of great significance for identifying machine wear states. In this paper, a method of wear debris classification using feature fusion and CBR is proposed. The method integrates local feature LBP, global feature FD and Tamura coarseness, and then the fused features are applied in CBR system with different weights and different similarity, which is adaptable, extendable, modular and fast. The results show that the subdivision of wear debris images into size 32*32 when calculating LBP is helpful for improving the classification, the combination of local features and global features can get better results. The comparative experimental results of different classification methods show that the CBR system has the shortest time-consuming while maintaining high classification accuracy.
  • Electric Arc Coverage Indicator for AC Furnaces Using a Laser Vibrometer and Neural Networks

    pp. 1300-1306

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    DOI:10.2355/isijinternational.ISIJINT-2018-148

    A common operational practice in the electric arc furnace (EAF) consist in keeping the electric arc covered with metallic scrap or foaming slag, this is to prevent that the refractory and water cooled panels absorb part of the radiation that should heat the steel. The radiation not absorbed by the steel is not only a waste of energy and money, it is also a latent danger because it damages the walls of the furnace. Today furnace operators use their experience and common sense to predict the degree of coverage of the arc and decide the electrical power the EAF can safely absorb along the process, without damaging the walls and increase the risk of an internal explosion. However, this method is subjective and might leads to human errors. This research was aimed to find robust indicators of arc coverage that could assist the furnace operator in deciding the amount of electrical power the furnace can safely absorb. During this research, it was found a strong relation between the vibrations of the furnace’s shell and the level of coverage of the electric arc. The vibration measurements were done with a laser and the vibration signal was processed using an Artificial Neural Network (ANN) implemented in LabVIEW™. The ANN was trained to emulate the intelligence and knowledge of a very productive and safe furnace operator. Excellent field results were obtained with this implementation and are reported in this paper.
  • Distribution and Morphology of MnS Inclusions in Resulfurized Non-Quenched and Tempered Steel with Zr Addition

    pp. 1307-1315

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    DOI:10.2355/isijinternational.ISIJINT-2018-081

    Distribution and morphology of MnS inclusions in as-cast ingots and as-forged bars of two Zr-bearing resulfurized non-quenched and tempered (NQT) steels have been performed. In the low Zr-bearing steel (0.001 wt%), MnS inclusions, which are teardrop-shaped or rod-like in two-dimensional (2D) morphology and dendritic or skeletal in three-dimensional (3D) morphology, are mainly distributed and segregated at the grain boundaries. While in the high Zr-bearing steel (0.0066 wt%), MnS inclusions are spherical or angular in both 2D and 3D observation and the distribution is more uniform than those in low zirconium steel. The calculated results by Thermo-Calc software show that the content of oxygen is not the direct factor that influences the morphology and distribution of MnS inclusions in medium-sulfur low-oxygen NQT steels. ZrO2 particles are ideal partcles for generation of spherical type I MnS inclusions owing to their strong nucleation capability and large amounts. However, the Zr and Al contents should be controlled cautiously to avoid generating large-sized agminated complex oxides, which are not easy to float and be removed owing to their high density. Otherwise, the ideal particles ZrO2 would decrease sharply in number and fail in offering sufficient heterogeneous nuclei for type I MnS inclusions. Besides, high proportion of complex MnS inclusions would decrease the supersaturation when pure MnS inclusions begin to precipitate, suppressing the generation of dendritic type II MnS inclusions.
  • Electrochemical Evaluation of Corrosion Resistance of Trivalent Chromate Conversion Coatings with Different Organic Additives

    pp. 1316-1323

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    DOI:10.2355/isijinternational.ISIJINT-2018-044

    The corrosion resistance of electrogalvanized steels with trivalent chromate conversion coatings is investigated electrochemically to analyze the effect of organic additives on the corrosion resistance under wet-dry cyclic conditions. Three sets of polyamine additives, namely (i) imidazole and epihalohydrin, (ii) polyquaternary amine salt, and (iii) polyethyleneimine, are examined and compared. Electrochemical impedance spectroscopy and anodic stripping were employed to evaluate the corrosion resistance. Crystal-structure and compositional analyses were also applied to demonstrate the role of organic additives in controlling the structure of the zinc layer and the formation of the trivalent chromate conversion film.
  • Grain Boundary Engineering of Medium Mn TWIP Steels: A Novel Method to Enhance the Mechanical Properties

    pp. 1324-1331

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    DOI:10.2355/isijinternational.ISIJINT-2017-710

    The grain boundary engineering (GBE) approach was employed on a medium manganese (Mn) based twinning induced plasticity (TWIP) steel to improve its mechanical properties. Two specially designed thermo-mechanical processing (TMP) routes, one involving unidirectional rolling (UDR) and the other one employing multi-step cross rolling (MSCR), with intermediate short term annealing treatment have been used. The annealing temperatures are chosen considering recrystallization and grain growth. Of the two routes, the one involving MSCR, has shown a higher fraction of special or coincident lattice site (CSL) grain boundaries. A detailed grain boundary microstructural analysis has been carried out by electron backscatter diffraction (EBSD) for differently processed samples. A significant improvement in ductility is observed in MSCR processed samples due to increase of CSL boundary fraction.
  • Fractographical Analyses of Crack Initiation Site in High-cycle Fatigue for Ti–Fe–O Alloy at Low Temperature

    pp. 1332-1340

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    DOI:10.2355/isijinternational.ISIJINT-2017-673

    High-cycle fatigue properties of a Ti–Fe–O alloy with different processed products such as rolled plate (L and T), cross-rolled plate (CR) and groove-rolled bar (CS) were evaluated at 77 K and 293 K. Fine equiaxed α grains randomly oriented with [0001] perpendicular to tensile axis were produced in the CS. No significant difference of 107 cycles fatigue strength was recognized among the test materials at each temperature, although the CS exhibited an improved fatigue strength in long-life regime at 293 K. The subsurface crack initiation was dominant in lower stress level and at 77 K. The subsurface crack initiation sites consisted of facet or facets. The facets were identified as (0001) in the L, T and CR. In the CS, the (0001) facet provided an origin of subsurface crack initiation site, but the {1010} facets mainly covered the sites at 77 K. The combination of shear stress and opening stress on {1010} may be responsible for forming a facet and its growth in the neighboring grain. The dependence of subsurface crack initiation site size on the maximum stress range was evaluated, where the maximum stress intensity factor range, ΔKImax, revealed the temperature and stress dependences.
  • On the Effect of Q&P Processing on the Stretch-flange-formability of 0.2C Ultra-high Strength Steel Sheets

    pp. 1341-1350

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    DOI:10.2355/isijinternational.ISIJINT-2018-121

    Quenching and Partitioning (Q&P) has been proposed as a novel heat treatment to produce cold rolled sheets with excellent strength and sufficient formability for cold stamping. The impact of Q&P processing on microstructure and tensile properties has been extensively studied in contrast to the lower attention devoted to its effect on stretch-flange-formability. In this study, the stretch-flange-formability of Q&P microstructures is investigated by means of hole expansion tests carried out on punched holes. The balance between tensile properties and hole expansion ratios (HER) is discussed and compared to three model microstructures: biphasic dual-phase (DP), single phase quenched & tempered (Q&T) and quenched & austempered (QAT). It is shown that Q&P microstructures exhibit a better combination of tensile ductility and stretch-flange-formability than fully martensitic (excellent HER but poor tensile ductility) and austempered microstructures (good ductility but poor HER). The study of the impact of the Q&P parameters demonstrates that stretch-flange-formability is further promoted by choosing low quench temperatures and long partitioning times. The hole expansion properties are linked to the hardness gradients in the microstructure, evaluated by nanohardness mapping. The narrower nanohardness distribution in the Q&P microstructure leads to better hole expansion ratios compared to bainitic microstructures obtained by austempering, where the presence of hard M/A blocks is unavoidable.
  • Extraction of Phosphorus from Steelmaking Slag by Selective Leaching Using Citric Acid

    pp. 1351-1360

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    DOI:10.2355/isijinternational.ISIJINT-2017-658

    An approach to leach phosphorus from slag was applied to commercial fertilizers made from steelmaking slag, which has relatively coarse grains. After leaching at pH 3 with citric acid, about 60% of the P2O5 had been dissolved, but the dissolution ratio of MnO was less than 30%. The separation index, calculated from the dissolution ratio of P2O5 divided by that of MnO, was 2.1. In addition, the dissolution ratio of the solid solution was 90% or greater. However, 25% or more of the matrix was also dissolved. To improve the selectivity of leaching, the mineralogical phases comprising the matrix were synthesized, and their leaching behaviors were investigated. The results indicate that it is important to eliminate the glassy phases and to change the valence state of iron in its oxides to 3+ to suppress the dissolution of the matrix. Finally, a synthesized slag, containing only Fe2O3 as the only iron oxide, was prepared by slow cooling, and leaching tests were conducted. About 99% of the P was dissolved, but the dissolution ratio of Mn was less than 10%. In addition, the separation index increased to 14.1. In this case, the dissolution of the matrix was suppressed, and almost all the solid solution phase was dissolved.
  • Iron Removal from Copper-based Alloy Scraps through Oxidation Slagging Process

    pp. 1361-1367

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    DOI:10.2355/isijinternational.ISIJINT-2017-751

    A process of removing iron from copper-based alloy scraps using oxidation slagging method is researched, in which the iron is oxidized to FeO and then reacted with SiO2 forming Fe2SiO4 and enter into the slag phase. The addition of SiO2 could restrict the Fe3O4 generation through the transformation of FeO to 2FeO·SiO2 in a certain O2 pressure, which is favorable to decreasing the melt viscosity and increasing the separation efficiency of Cu and Fe. Under optimized conditions of O2 flow rate of 40 ml/min, temperature of 1673 K, oxygenation time of 8 min, and SiO2 amount of 2.17 mass%, Fe content in the metal phase is decreased to 0.0030 mass% with Cu loss rate being of 1.14%.
  • A Semi-Empirical Model of Particle Velocity in Foam

    pp. 1368-1370

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    DOI:10.2355/isijinternational.ISIJINT-2018-245

    A semi-empirical model was developed to predict the apparent velocity of particles falling through foams. Different foams were generated from liquids with different viscosities and surface tensions. Particles with different sizes and densities were dropped into the foam and average velocities were calculated. Based on the experimental work, the semi-empirical model was derived from an energy balance between buoyancy, drag and the energy needed for the particles to deform the bubbles in their path.

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