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

ISIJ International Advance Publication

  • The Effect of Manganese on the Thermodynamic Property of Tellurium in Molten Iron

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    DOI:10.2355/isijinternational.ISIJINT-2018-315

    The effect of manganese on the thermodynamic property of tellurium in molten iron was experimentally evaluated as an interaction parameter using a vapor-liquid equilibration technique, where the vapor pressure of tellurium was controlled using the transpiration method. Manganese was found to stabilize tellurium in molten iron and its effect was relatively small compared to other alloying elements.
  • Solidification Structures of Fe–Cr–Ni–Mo–N Super-austenitic Stainless Steel Processed by Twin-roll Strip Casting and Ingot Casting and Their Segregation Evolution Behaviors

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    DOI:10.2355/isijinternational.ISIJINT-2018-193

    Fe–Cr–Ni–Mo–N super-austenitic stainless steels were processed by using twin-roll strip casting and ingot casting, and their solidification structures and segregation behaviors were comparatively studied. The results show that serious center macro-segregation and massive eutectics were detected in ingot, with the amount of eutectics being increased from surface to center. By contrast, macro-segregation and eutectics were inhibited in cast strip (CS) due to its rapid cooling rate during the solidification process. In order to obtain optimum hot workability, homogenization treatments were carried out in the temperature range from 1050 to 1200°C for different time from 30 to 480 min in CS and ingot. The results show that the homogenized temperature of CS should be higher than 1100°C to avoid the formation of precipitates, and the optimum homogenization process was 1150–1200°C for 30 min. For the ingot homogenized at 1200°C, eutectics gradually dissolved into the matrix with increasing the homogenization time, and after 4 hours, they completely dissolved. Ingot could be homogenized after more than 8 hours of homogenization, indicating that CS has intrinsic advantages in homogenization. Finally, mechanical property and pitting corrosion resistance of 1 mm-thick cold-rolled bands, fabricated from CS and ingot, were tested and compared. The results show that the overall performance of cold-rolled bands of CS was superior to that of ingot.
  • Characterization on Microstructure and Carbides in an Austenitic Hot-work Die Steel during ESR Solidification Process

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    DOI:10.2355/isijinternational.ISIJINT-2018-370

    The current work was undertaken to systematically examine the as-cast microstructure and carbides in a developed austenitic hot work die steel produced by conventional electroslag remelting (ESR) and continuous directional solidification of electroslag remelting (ESR-CDS). In addition, the growth pattern of carbides was also discussed. A combination of optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize microstructure and carbides. The segregation was analyzed using an original position analyzer (OPA) and electron probe microanalysis (EPMA). The electrolytically extracted carbides were analyzed by SEM and x-ray diffraction (XRD) to identify their three-dimensional microstructure and compositions. The microstructure of electroslag remelted austenitic die steel was composed of austenite matrix and primary carbides V8C7-type and Mo2C-type. Compared with conventional ESR, ESR-CDS contributed to a finer as-cast microstructure, a smaller amount and smaller size of carbides in remelted steel. Meanwhile, the alloying elements segregation was reduced through ESR-CDS. The enrichment of carbide-forming elements was reduced through directional solidification of ESR, resulting in the change in the morphology of V-rich carbides from rod-like to lamellar-shaped. The hardness and V-notched impact energies of remelted ingot (produced by ESR-CDS) after heat treatment (solution temperature 1180°C for 2 hours, aging temperature 720°C for 2 hours) was increased by 3 to 5HRC and 4 to 6 J/cm2 respectively, in comparison with that produced by conventional ESR.
  • Effect of Rb2O on Inclusion Removal in C96V Saw Wire Steels Using Low-Basicity LF Refining Slag

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    DOI:10.2355/isijinternational.ISIJINT-2018-385

    A novel Rb2O-containing synthetic LF refining slag has been developed in order to produce ultraclean C96V saw wire steel. In addition, the thermodynamic and kinetics mechanism of Rb2O on inclusion removal have been discussed fully. The results indicated that (1) Rb2O additions (≤10.00 wt%) seems to significantly enhance inclusion removal in steel melts. ① The average diameter of nonmetallic inclusions decreased significantly with the Rb2O addition in synthetic LF refining slag increasing. In particular, the diameter of most of inclusions was less than 3.0 × 10-6 m (3.0 µm) when Rb2O addition was 10.00 wt% ② The number of nonmetallic inclusions decreased sharply with the content of Rb2O in synthetic LF refining slag raising. ③ Both of the MnO–SiO2–Al2O3, CaO–SiO2–Al2O3 inclusions system mainly concentrated in the low melting point zone. (2) For the 15.00 wt% Rb2O-containing synthetic LF refining slag, not only the average diameter of inclusion increases slightly with reaction times increasing, but also the number. This is due to the fact that, the effect of Rb2O on the ability of refining slag to absorb inclusions is a double-edged sword: On the one hand, Rb2O addition would promote the thermodynamic conditions of inclusion removal, then, inclusions would enter the slag spontaneously easier. On the other hand, Rb2O addition could also exacerbate the kinetic conditions of inclusion removal by increasing the viscosity of slag at the same time.
  • Numerical Simulation of Desulfurization Behavior in Ladle with Bottom Powder Injection

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    DOI:10.2355/isijinternational.ISIJINT-2018-406

    A computation fluid dynamics–population balance model–simultaneous reaction model (CFD–PBM–SRM) coupled model was used to predict the reaction kinetic and desulfurization behavior in 80 ton ladle with bottom powder injection. The reaction rate and evolution of multi-components including Al, S, Si, Mn and Fe at the powder droplet–liquid steel interface, bubble–liquid steel interface, top slag–liquid steel interface and air–liquid steel interface were revealed. Then, the effects of different kinetic conditions on the desulfurization efficiency were investigated, and the importance of various mechanisms was discussed and clarified. The results show that at the lower powder injection rate, the desulfurization is mainly attributed to the joint effort of both powder–liquid steel reaction and top slag–liquid steel reaction which is the prevailing mechanism. At the higher powder injection rate, the powder particle–liquid steel and bubble–liquid steel interface reaction become more important and then predominate the desulfurization behavior. With the increase of gas flow rate, the total desulfurization ratio gradually decreases, and with the increasing of powder injection rate, the total desulfurization ratio increases.
  • Numerical Study of Inclusion Removal in Steel Continuous Casting Mold Considering Interactions Between Bubbles and Inclusions

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    DOI:10.2355/isijinternational.ISIJINT-2018-319

    Bubble coalescence-breakup and bubble-inclusion interaction models were implemented into Eulerian-Lagrangian models of steel liquid flow and discrete particles transport, which was applied to examine the interaction and removal of discrete bubbles and inclusions during continuous casting. Bubble distribution affected by coalescence-breakup and its connection with the inclusion removal rate were analyzed. The inclusion removal rates at different initial bubble diameters and inclusion diameters were predicted. Larger inclusions have a higher removal rate and the predicted removal rates ranging from 14% to 30% agree well with industrial experiment measurements. It is also found that smaller bubbles have a higher capacity to remove inclusions and very small bubbles may cause more production defects when it is attached to inclusions. These results show that the developed model can reasonably predict the behaviors of discrete bubbles and inclusions and their interactions in molten steel. Such a model should be useful for the operation of steel continuous casting.
  • Effect of Introducing Coke into Ore Layer on Softening-melting-dropping Characteristics of Vanadium-titanium Mixed Burden under Simulating BF Conditions

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    DOI:10.2355/isijinternational.ISIJINT-2018-175

    Coke-ore mixed charging is a well-known and effective measure to strengthen BF operation and realize low reducing agent BF ironmaking. The objective of this paper is to investigate the effect of coke-ore mixing ratio on softening-melting dropping performance and permeability of vanadium-titanium mixed burden and to clarify the interaction mechanism between mixed nut coke and iron-bearing burden under BF simulating conditions. It was found that the softening-melting-dropping behaviors and permeability of mixed burden get improved obviously with a coke-ore mixing ratio of 20%. However, the generation of carbide of V and Ti would be accelerated with further increasing coke-ore mixing ratio to 50%, which would deteriorate the fluidity of slag and worsen the dropping behavior of mixed burden and lower the yield of V in liquid iron. The interaction between nut coke and vanadium-titanium mixed burden could be summarized as four parts, namely reduction strengthen, carburization promotion, permeability improvement, and the precipitation of the carbide of titanium.
  • Using Red Mud-based Flux in Steelmaking for High Phosphorus Hot Metal

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    DOI:10.2355/isijinternational.ISIJINT-2018-339

    To smelt high phosphorus hot metal effectively, a new flux named Red Mud (RM) was applied in steelmaking to form CaO–FeO–SiO2–Al2O3–Na2O slag. Good slag fluidity and dephosphorization effects can be achieved when using RM-based flux in simulated steelmaking for high phosphorus hot metal. The dephosphorization rates of the RM-based flux were all greater than 82%. Especially, when RM:CaO=1:1.2, high dephosphorization rate (~95%) and low final [P] (=0.02%) was achieved in the situation of high [C] =1.36%. This is of great importance for the production of clean steel. The P2O5 content in the P-rich phase in RM-based slag can reach 29.1 wt%, far higher than the 9.1 wt% in lime-based slag.
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    1. Phosphorus Partition and Phosphate Capacity of Basic Oxygen Steelmaking Slags ISIJ International Advance Publication
  • Image-based Method for Measuring Pellet Size Distribution in the Stable Area of Disc Pelletizer

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    DOI:10.2355/isijinternational.ISIJINT-2018-384

    Disc pelletizer is widely used in the agglomeration process to form powdered iron ore into iron ore green pellets. The pellet size distribution (PSD) is one of the major measures of product quality. An imaging system is developed for measuring PSD in the stable area of the disc pelletizer. Image pre-processing is performed to extract the densely distributed pellets as foreground, followed by identifying surface pellets using pellet markers and K-means clustering method. Then a marker-controlled watershed algorithm is applied to segment overlapping pellets in the image. The pellet sizes and thus PSD are then obtained using circumscribed circle fitting. The proposed image-based measuring method was tested in a steel company. The measured PSD was compared with manual sieving results. It shows good accuracy for different size ranges under different pelletizing conditions. The proposed method also makes it possible to evaluate online the pellet quality.
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    1. In-situ Analysis and Numerical Study of Inclusion Distribution in a Vertical-bending Caster ISIJ International Advance Publication
  • Phosphorus Partition and Phosphate Capacity of Basic Oxygen Steelmaking Slags

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    DOI:10.2355/isijinternational.ISIJINT-2018-129

    The phosphorus partition (LP) and phosphate capacity (CPO43−) were measured for slags in the CaO–SiO2–MgO–FetO–(MnO–Al2O3–TiO2–P2O5) system over temperatures representative of basic oxygen steelmaking. The measured LP values were found to be in good agreement with those predicted from the model of Assis et al. The oxygen potential of the slag-metal systems studied was also evaluated and used in combination with the measured LP to calculate the CPO43− of the slags. Capacity values in the range of 7.77×1016 to 4.27×1019 for temperatures 1550°C to 1700°C were obtained.Correlations of CPO43− with common measures of slag basicity (v-ratio and optical basicity) were sought and reported. Consistent with other researchers it was found that the LP and CPO43− increased with increasing slag basicity and decreasing temperature.
  • Radar Detection-based Modeling in a Blast Furnace: a Prediction Model of Burden Surface Shape after Charging

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    DOI:10.2355/isijinternational.ISIJINT-2018-267

    Radar detection is an advanced method for monitoring a blast furnace's inner burden surface shape, which is an important factor that largely affects the production efficiency of the iron-making process. In this paper, a radar detection-based model for the prediction of burden surface shape was developed for assisting operators in developing a charging strategy. The data used are composed of both the detection and controlling records of a real, working-state blast furnace obtained by mechanical swing radar and a furnace database system, respectively. By defining and analyzing the stacking density function, the physical meanings of the modeling principles were revealed. Combined with the classical force charging trajectory sub-model and detection-driven burden descent calculation, the proposed model adopts Gaussian radius basis functions to approximate the stacking mechanism of the burden charging process. The parameter identification results show that the model can approximate the burden surface radius profile well. Compared with the results obtained for coke layers, the parameters' ranges for the ore layers are narrower. Performance comparison shows that the proposed model has the advantages of higher prediction accuracy for both local details and global shape over the classical polygonal line model.
  • In-situ Analysis and Numerical Study of Inclusion Distribution in a Vertical-bending Caster

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    DOI:10.2355/isijinternational.ISIJINT-2018-283

    Based on a fast-detection platform (FDP) founded by us, an in-situ measurement of inclusion distribution in slab is successfully performed. The inclusion distribution is obviously asymmetry and non-uniform. Specially, due to the structure differences in the vertical and bending part of a slab caster, the inclusion distribution in these two parts are quite different: In the vertical part, the inclusions entrapped in the outer arc is much more than that in the inner arc, while in the bending part, the inclusions entrapped in the outer arc is a little less than that in the inner arc. Large inclusions are tend to be found near the surface, and sometimes in the center, but they're very few. Then in order to interpret the inclusion distribution in practical measurements, a new LES model is established using Euler-Lagrange approach. A new entrapment criterion is also defined to calculate the entrapped inclusions. Big inclusions are tend to float up to the mold top, and aggregate near the outer arc, which can explain the differences of inclusion distribution in the vertical part; Smaller inclusions are easier to flow deep into the mold, and become clusters when they're getting near, which can explain the big inclusions in the central part. What's more, the drag effect of bending slab is proven to be responsible for the differences of inclusion distribution in the bending part. This mathematical model is helpful for understanding the inclusion movements in slab.
  • A Novel Measurement of Voidage in Coke and Ferrous Layers in Softening and Melting under Load Test Using Synchrotron X-ray and Neutron Computed Tomography

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    DOI:10.2355/isijinternational.ISIJINT-2018-257

    For the first time, the bed voidage of samples from interrupted softening and melting (S&M) under load tests was measured directly using computed tomography (CT). The large size, fused structure and high metallic iron content of the samples required the very high energy synchrotron X-ray source for scanning; samples produced at higher temperatures, e.g., 1450°C, required neutron CT to allow adequate penetration of the samples. This method was able to uniquely and accurately identify the volumes, distributions, and structures of coke, ferrous, and void in the S&M samples, and quantify the tortuosity of the voids. This information is critical for analysis of the pressure drop–contraction relationship in the S&M under load test, and will allow the improvement of the treatment of the cohesive zone in numerical models of the blast furnace.
  • Influence of Agitating Conditions on Agglomeration and Collapse of Iron Ore Mixture

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    DOI:10.2355/isijinternational.ISIJINT-2018-359

    The influence of agitating conditions on agglomeration and collapse of wet iron ore mixture was investigated in the view of kinetics and matrix model analysis. At the initial stage of mixing behavior, it was found that average particle size was dependent on the mixing rate constant defined as the deviation degree of particle size and water distribution from initial state. Mixing rate constants of powder and water were almost consistent with each other and expressed by power function of Froude number of impeller. It was presumed that the water and fine particle moved together as wet granules during mixing at a given water level. According to the analysis of entire mixing behavior based on matrix model, it was found that the collapse indexes defined by matrix parameters increased as particle size and impact force increased. Minimum particle size at initial mixing state decreased as collapse index increased and the size of long term mixing state was expected by intrinsic increasing rates defined by maximum eigenvalue of matrix parameters.
  • Local Buckling of Steel Plates in Composite Structures under Combined Bending and Compression

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    DOI:10.2355/isijinternational.ISIJINT-2018-202

    In this paper, explicit local buckling analysis of steel plates in composite structures under combine bending and compression and with elastic restraint against rotation is presented. Unique displacement function, which combines sinusoidal and cosine functions along x- and y-directions and satisfies boundary and loading conditions, is proposed to account for the effect of restraint of concrete and the elastic rotational restraint stiffness along both the loaded and unloaded edges of the steel plates. The explicit local buckling solution for the elastically restrained steel plates in composite structures is simplified to several special cases (e.g., the CS, CC, SS and KS steel plates) subjected to combined bending and compression. To verify the accuracy of the explicit solutions, experimental data, available solutions in the literature, and finite element results are compared, and reasonable agreement has been observed, particularly for the simplified cases. Parametric study is further conducted, and the effects of different parameters such as the aspect ratio and the loading stress gradient parameter on the local buckling stress resultants of steel plates with different boundary conditions are discussed.
  • Transient Thermo-fluid and Solidification Behaviors in Continuous Casting Mold: Oscillation Behaviors

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    DOI:10.2355/isijinternational.ISIJINT-2018-169

    A computational model of the continuous casting process has been developed, which includes transient heat transfer, multiphase flow, solidification, and mold oscillation. Succeeding the previous report on the evolution phenomena in the mold, this article describes fluctuations in the pressure, heat flux, and slag films during the oscillation cycle and the coupling effect of these variables on slag flow and shell growth. The results show that the predicted flux pressure is decided by the combined effect of mold velocity and liquid film thickness. The presence of slag rim enhances the nonuniform pressure flow near the meniscus during mold oscillation. Increases in pressure and heat flux occur in the negative strip time while the mold and slag rim move downwards approaching the lowest position, which squeezes the slag flow to be divided into two tributaries, promoting the slag infiltration and the initial shell solidification. Negative consumption rate is identified partly in the cycle based on the velocity distributions of liquid slag. The model provides quantitative analysis regarding the influence of meniscus shape and slag films related to the casting speed on slag consumption and oscillation mark formation.
  • Numerical Investigation of Coke Collapse and Size Segregation in the Bell-less Top Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2018-415

    The coke collapse phenomenon significantly affects the burden and gas distributions, and further gas utilization and CO2 emission. Therefore, it is necessary to investigate the coke collapse in blast furnace. A three dimensional model of bell-less top blast furnace is established based on discrete element method (DEM). The effects of chute angle, rotating speed and sinter amount on the coke collapse charateristics are then investigated based on this model. The results show that coke profile changes a lot after its collapse and the collapse region is more than 40% of the furnace radius. Sinter amount affects the coke collapse amount much, followed by chute angle and chute rotating speed. The coke collapse region is affected most by sinter amount, followed by chute rotating speed and chute angle. Large chute angle, higher rotating speed and small sinter amount are recommended for practical operation since they help to obtain a lighter coke size segregation along radius.
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  • Improving the Desulphurization in COREX-3000 Process by the Optimization of Chemical Compositions of Slag

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    DOI:10.2355/isijinternational.ISIJINT-2018-427

    To improve the desulfurization in the COREX-3000 process, several aspects are studied and practiced. The work documented in the present paper focuses on the effects of chemical compositions of slag, such as CaO/SiO2, MgO, MgO/Al2O3 and MnO, on desulfurization. Theoretical calculations of sulfide capacity and viscosity of slag and diffusion coefficient of S2- in the slag are given to study the effects of slag chemical compositions on the thermodynamics and dynamics of desulfurization. After that, experiments are carried out to verify the theoretical analyses and give the appropriate ranges of these four parameters. The suggested suitable ranges of CaO/SiO2, MgO content, MgO/Al2O3 and MnO content for COREX-3000 are 1.20–1.30, 10 wt%–12 wt%, 0.80–0.90 and 0.4 wt%–0.7 wt%, respectively.
  • Characteristics of Closed Type DC arc Furnace for Molten Slag Reduction (Development of the Molten Slag Reduction Process -1)

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    DOI:10.2355/isijinternational.ISIJINT-2018-188

    To develop a slag reduction process (IBX process: Iron Bath for X), three kinds of slag reduction tests were carried out using different pilot scale and commercial scale DC arc furnaces. The goals are to recover the valuable elements such as Fe or P from the steelmaking slag and to modify the slag composition. The main target is to use molten slag directly in the reduction process and to establish a stable operation for improving the energy consumption, productivity, and processing cost. In the present paper, we describe the results obtained in a pilot scale closed-type 2 MW DC arc furnace (Test 1), commercial scale open-type 30-MW DC arc furnace (Test 2), and newly designed closed-type 4-MW DC arc furnace (Test 3). Reduction efficiency and the metallurgical properties in DC arc furnaces, the mechanism of slag foaming, and the influence of the atmosphere in the furnace were discussed based on the experimental results. Finally, model calculations of the flow patterns in the furnace were carried out for further comprehension of the metallurgical phenomena. From these results, it was confirmed that the closed-type DC arc furnace can achieve efficient and stable reduction of steelmaking slag with hot charging.
  • Optimization of Slag Reduction Process with Molten Slag Charging (Development of the Molten Slag Reduction Process -2)

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    DOI:10.2355/isijinternational.ISIJINT-2018-189

    To recover valuable elements such as Fe or P from steelmaking slag and to modify the slag composition, a molten slag reduction process (IBX process: Iron Bath for X) has been developed. So far, pilot and commercial scale test operations have been carried out and it has been clarified that closed-type DC arc furnaces are desirable for the slag reduction process with hot slag charging. In the present work, issues and solutions of the actual operation are discussed. One issue is the optimization of the material feeding method. A hollow electrode, top lance, and injection pipe method were tested in the same furnace and the performance of each was investigated. The second issue is slag boiling and solidification at hot slag charging. To establish stable operation, use of a bottom block to avoid the formation of an emulsion at slag charging and off-gas combustion for heating the slag were proposed and tested. Finally, thermal aspects were discussed and the required energy consumption was estimated to show the effect of hot slag charging. Through these studies, it was confirmed that stable operation of slag reduction with hot slag charging can be attained in closed-type DC arc furnace, representing a great step for realizing of complete utilization process of BOF slag.
  • Effects of Na2O and B2O3 Addition on Viscosity and Electrical Conductivity of CaO–Al2O3–MgO–SiO2 System

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    DOI:10.2355/isijinternational.ISIJINT-2018-212

    The present study was aimed at investigating the effect of Na2O and B2O3 addition on the viscosity and electrical conductivity of slag which was used for mineral wool production. Industrial slag samples of the CaO–Al2O3–MgO–SiO2 system were used to modify its composition with different Na2O and B2O3 addition content and soaked at a certain temperature range (1400–1500°C). Raman spectrum was used to represent the structure of the slag system. Results showed that the Na2O addition modified process had a larger effect on the two parameters (macro aspect) and the relative fraction of the structural units (micro aspect) compared with the results of B2O3 addition.
  • Effect of B on Growth of Recrystallized Grain of Ti-added Ultra-low Carbon Cold-rolled Steel Sheets

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    DOI:10.2355/isijinternational.ISIJINT-2018-301

    The effect of boron (B) on the recrystallization behavior, in particular the growth of the recrystallized grain into the unrecrystallized grain, of titanium (Ti) added interstitial atom free (IF) steel sheets was studied from the viewpoint of the solute-drag effect considering the interaction between B and Ti atoms. The growth rate of the recrystallized grain at 5% fraction recrystallized decreased with increasing the B content. Furthermore, the decrease became more pronounced in the B added steels with the higher Ti content. The interaction energy between B and Ti atoms at the grain boundary was evaluated by the first-principles calculation in the bcc-Fe(111)Σ3[1 10] symmetrical tilt grain boundary. The attractive interaction between B and Ti atoms was obtained in most of the grain boundary atom sites examined. B segregation at the interface between recrystallized and unrecrystallized grains was concluded to induce Ti segregation through the attractive interaction between B and Ti atoms during interface migration. The mechanism for the suppression in the growth of the recrystallized grains was proposed to be caused by the decrease in the interface mobility caused by the enhanced Ti segregation.
  • Evolution of Oxide Inclusions in G20CrNi2Mo Carburized Bearing Steel during Industrial Electroslag Remelting

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    DOI:10.2355/isijinternational.ISIJINT-2018-072

    Industrial experimental and thermodynamic analyses were carried out to investigate the evolution of oxide inclusions from consumable electrode to droplet and refined ingot during electroslag remelting (ESR) of G20CrNi2Mo carburized bearing steel. All the oxide inclusions in electrode were CaO–MgO–Al2O3, most of which compositions were located in the liquid region. During droplet formation, most electrode inclusions were absorbed by molten slag, and it was inferred that the Ca content in metal film obviously decreased. A few inclusions were still remained in the liquid steel mainly owing to low interfacial energy. In addition, pure Al2O3 inclusions smaller than 2 µm were generated in droplet, indicating that significant Al-oxidation occurred. The ingot inclusions were low-MgO-containing MgO–Al2O3, Al2O3-based irregular CaO–(MgO)–Al2O3 and spherical CaO–Al2O3, all of which compositions were outside of the liquid region, indicating that no ingot inclusions could be identified as the relics of that in electrode. Thermodynamic calculations showed that the dissolved Ca and Mg reduced by Al at slag/metal interface could not transfer into the metal pool. FactSageTM 7.0 was used to elucidate the formation of inclusions in metal pool, and the results were basically in accordance with the experimentally observed inclusions, showing that a quasi-thermodynamic equilibrium could be established.
  • Phase Transformation of Cohesive Zone in a Water-quenched Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2018-227

    The paper investigates the transformation of iron and slag phase in cohesive zone from a water-quenched blast furnace through SEM images, EDS spectra and thermodynamic calculation. The results show that the wustite structure exists as an independent interphase insoluble in slag and iron. The content of carbon keeps about 2% in iron, and the carburization function of coke is inhibited in cohesive zone. The compositions of slag phase fluctuate in cohesive zone, while the basicity maintains about 1.8, higher than that in final slag. The liquids temperature of iron in cohesive zone is about 1673 K, while that of slag phase gradually decreases from top to bottom. The separation between slag and iron is basically completed at lower part of cohesive zone. The blocked voids caused by softening and melting burden restrains the indirect reduction at lower cohesive zone, hence an apparent titanium attachment exists around iron due to the development of direction reduction.
  • Texture Evolution during Recrystallization and Grain Growth in Heavily Cold-rolled Fe-3%Si Alloy

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    DOI:10.2355/isijinternational.ISIJINT-2018-268

    Recrystallization and grain growth are important phenomena for controlling the mechanical and magnetic properties of steels through texture. Only a limited number of studies have been carried out on texture evolution during recrystallization and grain growth in heavily cold-rolled Si steel. The present study first focuses on clarifying the texture evolution during normal grain growth, followed by an investigation into the development of the {411}<148> component during recrystallization. The {411}<148> component is remarkably developed during normal grain growth after the completion of recrystallization. At just fully recrystallized stage, the diameters of the {411}<148> grains were larger than that of the grains with other orientations. Therefore, the {411}<148> grains significantly grew owing to the size advantage.Just at the commencement of recrystallization, differences in grain diameter of recrystallized grains in terms of crystal orientation were not detected. However, it is worthwhile to mention that the nucleation of {411}<148> recrystallized grains is unexpectedly fast in heavily cold-rolled Si steel. Recrystallized {411}<148> grains were observed to nucleate in the deformed α-fiber grains, especially near the grain boundaries. Nuclei with {411}<148> orientation grow easily due to the high mobility of the interface between the recrystallized/non-recrystallized grains and the high driving force. Consequently, the diameter of a {411}<148> recrystallized grain becomes relatively large upon the completion of recrystallization. This contributes to the selective grain growth during the normal grain growth stage because of the size effect.

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