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

ISIJ International Vol. 53 (2013), No. 7

  • Carbothermic Reduction of Vanadium Titanomagnetite by Microwave Irradiation and Smelting Behavior

    pp. 1115-1119

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    DOI:10.2355/isijinternational.53.1115

    The recovery rate of the titanium is much low in the current process of the vanadium titanomagnetite resource in Panzhihua, China. The carbothermic reduction process in the microwave filed was proposed because the problem caused by Ti(C,N) should be avoid and the TiO2 content in the slag should increase. The reduction behavior of the ore in microwave and the distribution of the elements during the smelting process were studied. The heating rate of the vanadium titanomagnetite in the microwave field can be divided into three stages: the very fast heating period in initial 25 minutes in which no apparent reduction happens, the slow heating period in which the solid reduction of the magnetite decreases the heating rate, another fast heating period in which the reduction of ilmenite happens. About 60% of iron from 1 kg of the ore and carbonaceous materials was obtained by an energy supply of 10 kW by microwave irradiation in 120 min. The recovery ratios of Fe, V and Si increase with increasing the reduction temperature. The addition of the CaO can increase the recovery ratio of Fe and V, but decrease the recovery ratio of Si.
  • Deoxidation Equilibrium of Zirconium in the Iron-Nickel Melts

    pp. 1120-1124

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    DOI:10.2355/isijinternational.53.1120

    The oxygen solubility in the zirconium-containing iron-nickel melts has been experimentally studied at 1873 K using the Fe–40% Ni alloy as an example. It was shown that zirconium considerably decreases the oxygen solubility in this melt. The equilibrium constant of interaction of zirconium and oxygen dissolved in the Fe–40% Ni melt (logK(1)(Fe–40%Ni) = –6.221), the Gibbs energy of this reaction ([ This part of text is omitted ] = 223078 J/mol), and the interaction parameters characterizing these solutions ([ This part of text is omitted ] = –7.16; [ This part of text is omitted ] = –1.25; [ This part of text is omitted ] = 2.16) were determined. The equilibrium constants of interaction of zirconium and oxygen dissolved in the Fe–20% Ni and Fe–30% Ni melts, the Gibbs energy of this reaction, and the interaction parameters characterizing these solutions were calculated for 1873 K. With an increase in the nickel content in melt the deoxidation ability of zirconium decreases. This is due to the fact that, when the nickel content in melt increases, the bond strengths of zirconium with the melt base ([ This part of text is omitted ] = 4.59·10–4; [ This part of text is omitted ] = 1.40·10–10) rise to a considerably greater degree than the bond strengths of oxygen weaken ([ This part of text is omitted ] = 0.0105; [ This part of text is omitted ] = 0.357).
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    1. Deoxidation Equilibrium of Titanium in the Iron–Nickel Melts ISIJ International Vol.50(2010), No.1
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    3. Effects of Dissolved Oxygen and Size Distribution on Particle Coarsening of Deoxidation Product ISIJ International Vol.46(2006), No.1
  • Carbothermic Reduction of Hematite Powders by Microwave Heating

    pp. 1125-1130

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    DOI:10.2355/isijinternational.53.1125

    To examine the applicability of hematite ore to the ironmaking by microwave heating, the carbothermic reduction of hematite powders by microwave heating were elucidated using the gas analysis of exhausted gas, and were compared with that of magnetite powders. The temperature of the hematite – graphite mixed powders moderately increases at the beginning, and then, starts to increase abruptly at around 400°C owing to the thermal runaway of Fe2O3. Once the reduction reaction starts to take place, the reduction reaction rate of hematite is even faster than that of magnetite, which is the same behavior as that observed by conventional heating. Hematite ore could be a possible raw material for microwave ironmaking: When hematite ore is utilized, the ore should be preheated up to around 400°C prior to the feeding to a microwave furnace.
  • Effect of TiO2 Content on the Structure of CaO–SiO2–TiO2 System by Molecular Dynamics Simulation

    pp. 1131-1137

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    DOI:10.2355/isijinternational.53.1131

    The change of structure in the ternary system CaO–SiO2–TiO2 with TiO2 varying from 0 to 25% mole fraction at a fixed basicity of 0.8 was investigated by means of molecular dynamics simulation. The present simulation demonstrates that most Si is coordinated with 4 O within a tetrahedron while the majority of Ti with 6 O in an octahedron. With the addition of TiO2, the coordination number for Si (CNSi–O) changes from 4.12 to 4.03, while the CNTi–O varies from 5.83 to 5.52. The fraction of bridging oxygen (Si–O–Si) decreases resulting in the depolymerization of silicate structure and the Si–O–Ca is gradually replaced by Si–O–Ti with increasing TiO2 fraction. Two [TiO6] octahedrons are connected by two ways with the angles of Ti–O–Ti equaling to 100° and 140°, and the fraction of them are almost the same for sample with 10 mol-% TiO2 addition. The variation of network connectivity Qn of Si also agrees with the above conclusion. Thus, TiO2 is regarded as basic oxide which acts as modifier in this ternary system in terms of its structure within this system.
  • Lab-scale Experiment and Industrial Test for Direct Alloying with the Ferrosilicon-MoO3 Self-reducing Briquette

    pp. 1138-1142

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    DOI:10.2355/isijinternational.53.1138

    Lab-scale experiment and industrial test for direct alloying with ferrosilicon-MoO3 self-reducing briquette have been conducted. In order to avoid volatilization of MoO3 during direct alloying, the high-temperature volatilization characteristics of MoO3 has been studied, and it can inhibit the volatilization of MoO3 when adding ~25% MgO during the heating. Furthermore, lab-scale direct alloying experiments with self-reducing briquette were carried out to determine the optimum composition of briquette to get high yield of Mo in a medium frequency induction furnace. The Mo yield was related to the excess reducing agent (ferrosilicon) and the right flux addition (MgO, CaF2) inside the briquette. The results indicated that the amount of ferrosilicon maintaining the mixing molar ratio Si/O at 2 should be added. The flux addition must be controlled to form molten slag rapidly inside the self-reducing briquette. With the optimum composition of reducing agent and flux addition, the yield of Mo could reach as high as ~96%. When adding the self-reducing briquette into a 60 t ladle of Shijiazhuang Iron and Steel Co. Ltd. for industrial test, the average yield of Mo was 98.25%, and the change in the technology did not have an impact on the quality of products.
  • Relationship between Structure and Thermodynamic Properties in the CaO–SiO2–BO1.5 Slag System

    pp. 1143-1151

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    DOI:10.2355/isijinternational.53.1143

    To understand the relationship between thermodynamic properties and structures in the CaO–SiO2–BO1.5 slag system, the thermodynamic properties of BO1.5 and SiO2 were measured by a chemical equilibrium technique and the local structures of boron(B) and silicon(Si) were investigated by 11B and 29Si magic angle spinning–nuclear magnetic resonance (MAS–NMR) measurements.Activity coefficients of BO1.5 increased with an increase in the BO1.5 content of the slag system. Activity coefficients of SiO2 increased with increasing BO1.5 content and decreased with increasing CaO/SiO2 ratio.By using 11B MAS–NMR, the existence of two types of B sites was confirmed—three- and four-coordinated B sites. The relative fraction of four-coordinated B increased with an increase in the BO1.5 content and decreased with an increase in the CaO/SiO2 ratio. 29Si MAS–NMR results revealed that bridging oxygen bonding to Si atoms increased with an increase in the BO1.5 content and decreased with decreasing CaO/SiO2 ratio. The number of non-bridging oxygen atoms bonded to the tetrahedrally coordinated Si atom (NBO/T) was calculated using 29Si and 11B MAS–NMR under specific assumptions. By comparing NBO/Ts calculated from these two methods, the number of non-bridging oxygen atoms bonded to three-coordinated B in the studied composition region was estimated to be one.Finally, by comparing the thermodynamic properties with the results of MAS–NMR measurements, it was found that the composition dependences on BO1.5 and SiO2 activity coefficients were dependent on changes in the local structure of B and Si with composition.
  • Development of a Bonding Phase within Titanomagnetite-Coal Compacts

    pp. 1152-1160

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    DOI:10.2355/isijinternational.53.1152

    The development of the bonding phase within reduced ironsand-coal compacts was studied to investigate the reduction of ironsand-coal compacts and to understand how the oxide bonding phase develops during reduction.Ironsand ore and sub-bituminous coal were mixed and pressed into compacts which were reduced by heating in a thermogravimetric furnace (TGA) to 1350°C under argon. The reduced compacts were characterised in terms of their composition, strength and microstructure.The strength in the reduced compacts is brought about by slag bonding between the relict ironsand particles. Formation of a metallic network was limited, and seen only in relatively few samples. As the ironsand particles reduce, oxides surrounding the sponge iron structure form a slag. Slags from different particles then join to form a slag network between the particles. The formation of a slag and the bonding between the particles is aided by inherent silica and added lime.Reducing the spacing between ironsand particles in the green compacts was found to be important in increasing inter-particle bonding. Increasing the coal-iron ratio in the compacts increased the spacing and decreased the bonding. Decreasing the ironsand particle size decreased the spacing between ironsand particles, and increased the bonding in the reduced compacts.
  • Activity Measurement of FeO•Cr2O3 in ‘FeO•(Cr, Al)2O3’ Solid Solution

    pp. 1161-1164

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    DOI:10.2355/isijinternational.53.1161

    Thermodynamic information on the equilibrium between dissolved Cr and O in steel melt is the basic knowledge to control Cr content in the stainless steel production process. In the case of using alumina refractories, molten Fe–Cr alloy equilibrates locally with ‘FeO•(Cr, Al)2O3’ solid solution at the interface between the melt and refractories when Cr content in the alloy is low. Wide composition range of ‘FeO•(Cr, Al)2O3’ solid solution is known, and the activity data of FeO•Cr2O3 in ‘FeO•(Cr, Al)2O3’ solid solution is required to precisely estimate and control the Cr–O equilibrium relation in molten Fe–Cr when the alloy is produced in the furnace lining by Al2O3 refractories. In the present work, crucibles made of ‘FeO•(Cr, Al)2O3’ solid solution were equilibrated with molten Ag under CO–CO2 gas mixture at 1873 K to determine the activity of FeO•Cr2O3 in the solid solution.
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  • Evaluation of Properties of Hyper-coal with Iron Oxide Addition in Thermoplastic Range

    pp. 1165-1171

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    DOI:10.2355/isijinternational.53.1165

    The effect of iron oxide on coals and Hyper-coal (HPC) during caking temperature was investigated. To reveal the effect of the iron oxide reduction reaction on the thermoplastic properties, iron oxide reduction ratios were calculated from titration and gas analysis, and the thermoplastic properties of coal or HPC with and without iron oxide were estimated using thermogravimetric analysis and the Gieseler test. In addition, to investigate the mechanism of the change in the thermoplastic properties of HPC, the reduction ratios calculated from the titration and gas analysis were compared, and the crystal structure of HPC was analyzed using transmission electron microscopy (TEM). As a result, the iron oxide reduction reaction took place in the thermoplastic range, and the weight loss of samples with iron oxide addition increased while the fluidity decreased. On the basis of gas analysis, it was found that the reduction ratio was mainly composed of oxygen derived from H2O vapor. This result suggested that hydrogen atoms generated from the thermoplastic components of the HPC were involved in the reduction reaction. Thus, the polymerization rate of HPC was promoted near iron particles in the thermoplastic range, and the crystal structure of HPC with iron oxide addition was different between near and far from the iron particles. We, therefore, revealed that the reduction reaction by hydrogen atoms from HPC occurred in the thermoplastic range, and that the polymerization rate of HPC with iron oxide addition was increased due to decomposition of the thermoplastic components of the HPC.
  • Flow of Molten Slag through Coke Channels

    pp. 1172-1179

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    DOI:10.2355/isijinternational.53.1172

    In the lower zone of the ironmaking blast furnace, liquid iron and slag descend counter-current to reducing gases through a packed bed of coke. The characteristics of the flow of these liquids and their holdup influence product quality and furnace operation. The present study aimed to establish the criteria for the passage of slag through the narrow pore necks that form between coke particles. The flow of slag through coke pore necks has been simulated using an experimental technique that assesses slag flow from a funnel entering a narrow channel of known diameter. Synthetic coke was mainly used to minimise experimental uncertainty associated with the use of variable industrial coke and to allow control of the coke mineralogy. Industrial coke and graphite were also tested. Pellets of slag with compositions in the CaO–SiO2–MgO–Al2O3 system were melted in the coke funnels and heated to 1500°C under argon, then held at temperature for a certain time. After cooling, the passage of slag through the channel was determined and the interactions of the slag and coke were characterized. Variables assessed included slag composition, coke mineralogy and channel diameter.For the slags and cokes studied, the minimum channel diameter that allowed slag to flow was between 4.4 and 5.0 mm. For smaller diameters, slag did not flow through the channel. The flow mechanism was discussed in terms of a simple gravity and capillary/interfacial force analysis of the system.
  • Ripple Marks on Cast Steel Surfaces

    pp. 1180-1186

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    DOI:10.2355/isijinternational.53.1180

    Surface features developing on steel in static ingot casting were investigated using iron melts of 25 kg with 0.09% carbon. The main type of feature was the normal ripple marks which form directly at the meniscus line by the overflow of the melt over the tip of the solid shell. Their spacing and depth (groove depth) was measured, and both were found to decrease with increasing superheat and increasing casting speed (rate of meniscus rise). From the comparison with other spacing data published in the literature, it seems that ripple formation is influenced at least by two main factors. One is heat flow and the other is wave motion. The latter can be understood quantitatively. A different type of surface marks forms at strong cooling of the meniscus when freezing occurs already at the flat surface of the meniscus. This happened in casting in a helium gas phase. Their spacing and depth also decreases with increasing superheat. But they are wider and deeper, respectively, than those of the normal ripple marks developing in an argon gas phase. A third feature are transverse depressions which develop at a later stage, after solidification. Ripple mark formation may play a role also in continuous casting. According to a recent investigation by Tacke1) horizontal surface marks on thick slabs have non-normally wide spacings, compared to regular oscillation marks, at low casting speed. Tacke’s data were discussed with respect to their possible relationship to ripple marks.
  • Effects of Electromagnetic Swirling Flow in Submerged Entry Nozzle on Square Billet Continuous Casting of Steel Process

    pp. 1187-1194

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    DOI:10.2355/isijinternational.53.1187

    In this study, a new method for swirling flow generation in submerged entry nozzle (SEN) in continuous casting of steel process has been proposed. A rotating electromagnetic field is set up around the SEN to induce swirling flow in it by the Lorentz force. And this kind of electromagnetic swirling flow in the SEN is proposed to use in square billet continuous casting of steel process. The effects of coil current intensity and nozzle structure on the flow and temperature fields in the SEN and mold are numerically simulated and verified by an electromagnetic swirling model experiment of low melting point alloy. The overall results of the study show that the magnetic flux density and the swirling flow velocity in the SEN increase with the increase of coil current intensity. The largest swirling flow velocity in the SEN can reach about 3 m/s when coil current intensity 500 A, frequency 50 Hz. The electromagnetic swirling flow in the SEN can reduce the impinging depth of the flow and increase the upward flow. An impinging flow near the mold corner can be observed. The flow field changes mentioned above result in a uniform temperature field in the mold, increase the meniscus temperature, effectively increase the temperature at the mold corner. The divergent nozzle used in this new process also reduces the impinging depth, increases the upward flow and makes the meniscus temperature increase significantly.
  • Characterization of Shear Deformation Based on In-situ Observation of Deformation in Semi-solid Al–Cu Alloys and Water-particle Mixture

    pp. 1195-1201

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    DOI:10.2355/isijinternational.53.1195

    In-situ observation of deformation at the grain scale in semi-solid Al–Cu alloys has been carried out using synchrotron X-ray radiography. The deformed microstructure was characterized by the quantitative analysis of solid motion from the image sequences during shear in semi-solid Al–Cu alloys. The influence of solid particle shape on shear deformation was also examined by comparing with in-situ observation of deformation in water-polystyrene particle mixtures where the polystyrene particles are spherical with a diameter of 500 μm. In both semi-solid Al–Cu alloys and water-particle mixtures, solid particles located close to the shear plane developed an increasing component perpendicular to the shear plane, and a relatively high shear strain rate and decreased solid fraction was localized in a shear domain. The shear band width in semi-solid Al–Cu alloys (~10 mean particles diameter) was approximately two times wider than that formed in water-particle mixtures due to the difference in the solid particle shape.
  • Application of Pinch Analysis in an Integrated Steel Plant in Northern Sweden

    pp. 1202-1210

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    DOI:10.2355/isijinternational.53.1202

    The energy system in a modern integrated steel plant is a complicated network of units exchanging energy and matter with each other. System studies using process integration tools are important to avoid sub-optimization. At the steel plant in Luleå such studies have been carried out using a MILP-based mathematical programming tool (reMIND), mainly because of its inherent flexibility for handling combined flows and reactions of both matter and chemical, thermal and mechanical energy. There are, however, areas where the energy system is dominated by creation, transport and exchange of thermal energy, and where pinch analysis can be expected to be a valuable tool. For this reason a pinch targeting study was carried out for the plant site of the integrated steel plant in Luleå. The coke plant and the iron making/steelmaking plant were both studied with three ambition levels of possible improvements. The study confirmed that pinch analysis is a powerful tool for targeting energy savings in areas where thermal energy flows dominate the local energy system, e.g., the gas cleaning area at the coke plant. The study also indicated that a connection between the energy systems in the coke plant and the iron making/steelmaking would be valuable. This is not 100% feasible because of distance, but, a common steam net could add a degree of flexibility.
  • Aluminium Nitride Precipitation in Fe-3%Si Steel

    pp. 1211-1214

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    DOI:10.2355/isijinternational.53.1211

    A fine dispersion of precipitates is a key requirement in the manufacturing process of Fe-3%Si grain oriented electrical steel. In the production of high permeability grain oriented steel precipitate particles of copper and manganese sulphides and aluminium nitride delay normal grain growth during primary recrystallization, causing preferential growth of grains with Goss orientation during secondary recrystallization. The sulphides precipitate during the hot rolling process. The aluminium nitride particles are formed during hot rolling and the hot band annealing process. In this work AlN precipitation during hot deformation of a high permeability grain oriented 3%Si steel is examined. In the study, transfer bar samples were submitted to controlled heating, compression and cooling treatments in order to simulate a reversible hot rolling finishing. The samples were analyzed using the transmission electron microscope (TEM) in order to identify the precipitates and characterize size distribution. Precipitate extraction by dissolution method and analyses by inductively coupled plasma optical emission spectrometry (ICP-OES) were used to quantify the precipitation. The results allowed to describe the precipitation kinetics by a precipitation-time-temperature (PTT) diagram for AlN formation during hot rolling.
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  • Distribution of Carbon in Martensite During Quenching and Tempering of Dual Phase Steels and Consequences for Damage Properties

    pp. 1215-1223

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    DOI:10.2355/isijinternational.53.1215

    The microstructural evolution of martensite in as-quenched and quenched and tempered Fe–0.15C–0.215Si–1.9Mn–0.195Cr wt.% dual phase (DP) steels processed to give four different ferrite/martensite ratios was studied. It was found that partial thermodynamic equilibrium was obtained after intercritical annealing for 130 s. The local carbon distribution in as-quenched martensite was heterogeneous for all quenching temperatures. Significant carbon enrichment was observed at the ferrite/martensite interface at annealing temperatures of 790°C, whereas carbon depletion occurred when the annealing temperature was reduced to 755°C. A possible explanation for the carbon profile in terms of the effect of Mn partitioning on the austenite phase transformation kinetics is given. The kinetics of carbide formation during tempering is strongly influenced by these carbon gradients. A simple analysis shows that the interface carbon depletion observed at lower intercritical annealing temperatures could induce a beneficial increase in the void nucleation strain εn, due to a reduction in the backstress at the ferrite/martensite interface which decreases the local stress triaxiality. We estimate that the upper limit for the improvement in the as-quenched microstructure is ~8%, so the effect could provide a moderate delay in the onset of damage. Further, we propose that the improvement in damage resistance during tempering is mainly due to dispersed void formation at tempered carbides and that this mechanism will be compromised if those carbides are localised at ferrite/martensite interfaces. This argument mitigates for the carbon-depleted interface structure obtained at lower intercritical temperatures.
  • Effect of Grain Size on Thermal and Mechanical Stability of Austenite in Metastable Austenitic Stainless Steel

    pp. 1224-1230

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    DOI:10.2355/isijinternational.53.1224

    In order to clarify the grain size dependence of mechanical stability of austenite, deformation-induced martensitic transformation behavior was investigated on uniaxial tensile deformation in a metastable austenitic stainless steel (Fe–16%Cr–10%Ni) with the grain size controlled from 1 to 80 μm. In addition, crystallographic characteristics of deformation-induced martensite were analyzed by means of the EBSD (electron backscattering diffraction) method to discuss the variant selection rule. It was found that mechanical stability of austenite is independent of its grain size, although thermal stability of austenite is remarkably increased by grain refinement. Some special martensite variants tend to be selected in an austenite grain on the deformation-induced martensitic transformation (near single-variant transformation), and this results in the formation of a texture along tensile direction. This suggests that the most advantageous variants are selected in the deformation-induced martensitic transformation to release tensile strain and leads to the grain size independence of mechanical stability of austenite.
  • Microstructures of Machined Chips in Pure Titanium, Pure Iron and 0.83%C Steel

    pp. 1231-1236

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    DOI:10.2355/isijinternational.53.1231

    Microstructures were examined on the chip specimen of pure titanium with close-packed hexagonal (cph) structure (α-Ti, the shear strain, γ, is ~22), and those of pure iron (α-Fe, γ ≈ 7.5) and 0.83%C steel which had originally pearlite structure (γ ≈ 7.5) with body-centered cubic (bcc) structure by the FE-SEM/EBSP method and optical microscopy. The hardness of the chip specimens was also measured and compared to that of the original materials. UFGed materials could be produced at relatively small shear strain (~7.5) in pure iron and 0.83%C steel. The average grain diameter of the chip specimen was slightly larger in the 0.83%C, because lamellar cementite phase in original pearlite structure hindered the formation of submicron grains. The hardness of the chip specimens increased with increasing shear strain, and the hardness of the chip specimen with γ ≈ 7.5 (391 Hv) was ~4 times as much as that of the original material (93.9 Hv) in pure iron. However, it was impossible to produce the ultra-fine grained materials by machining of α-Ti even at γ ≈ 22. According to the experimental results obtained so far, the number of slip systems (crystal structure) as well as shear strain seems to be one of the important factors controlling the generation of equiaxed submicron grain structure. Higher stacking fault energy is favorable for cross-slip or climb of dislocations in dynamic recovery which probably governs the generation of submicron grains.
  • Dynamic Precipitation Behavior of Secondary M7C3 Carbides in Ti-alloyed High Chromium Cast Iron

    pp. 1237-1244

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    DOI:10.2355/isijinternational.53.1237

    In-situ observations on the dynamic precipitation behavior of secondary carbides in Ti-alloyed High Chromium Cast Iron (HCCI) were performed by using a Confocal Laser Scanning Microscope (CLSM). Moreover, the detailed characterization of the microstructure before and after heat treatment was performed by using scanning electron microscopy (SEM). The secondary carbides, which precipitate from the matrix during heat treatment, were identified as M7C3 type carbides by using transmission electron microscopy (TEM). The number, size and volume of secondary carbides during heating, holding and cooling process were quantitatively evaluated based on the in-situ observation and SEM results. It was found that ferrite (α) and secondary carbides start to precipitate from the matrix at around 575°C and 840°C, respectively, during the heating process. In addition, the in-situ results showed that the number of secondary carbides increase with an increased heating temperature and time. Moreover, it was found that the size of these secondary carbides increase at higher temperatures and longer holding times. However, the number of secondary carbides increased with a decreased temperature. Finally, it was found that the volume fraction (~5%) of secondary carbides was not changed to a large extent for the different heat treatment conditions being investigated.
  • Influence of Carbide Particles on the Grain Growth of Ferrite in an Fe–0.1C–0.09V Alloy

    pp. 1245-1252

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    DOI:10.2355/isijinternational.53.1245

    The pinning effects of carbide particles on the grain growth of ferrite were studied in an Fe–0.1C–0.09V alloy. The distribution of real particle sizes in touch with grain boundary was determined coupling the measurement of diameters of the largest section of each particle on multiple sections with computer simulation. This procedure can improve remarkably the accuracy in evaluating the number of particles in the system composed of particles of widely varying sizes. The particle numbers in contact with grain boundary faces, edges and corners were considerably greater than those calculated assuming random distribution. The theory that all particles pin grain boundaries, Nishizawa et al.’s correlation model and a modified Hunderi-Ryum’s model are able to predict the grain size in fair agreement with experiment. A better account for final grain size was given by the mean size of particles in contact with grain boundaries rather than that of all particles probably because the particle size was highly non-uniform due to the formation of cementite and vanadium carbide.
  • Exploring Carbide-Free Bainitic Structures for Hot Dip Galvanizing Products

    pp. 1253-1259

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    DOI:10.2355/isijinternational.53.1253

    Recently, advanced high strength steels for automotive applications were designed to achieve a carbide-free bainitic microstructure after conventional thermo-mechanical processing and a continuous annealing treatment. The microstructure obtained consists of ferrite laths interwoven with thin films of untransformed retained austenite. The sufficiently tough matrix and the control of the heterogeneity in the microstructure allowed an optimum combination of strength, ductility, and formability to be achieved. However, this work probed that even using a devoted theoretical alloying, carbide-free bainitic steels are hardly compatible with a conventional hot dip galvanizing annealing process, without any consideration about Zn coatability and adherence. The hardenability of the designed alloys was insufficient in some cases and the amount of austenite retained in the microstructure was too low or/and mechanically too unstable for high ductility. As a consequence, the obtained mechanical properties were comparable to those in high-Si dual phase steels without a beneficial transformation induced plasticity effect.
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  • Static Tensile Deformation Behavior of a Lean Duplex Stainless Steel Studied by In Situ Neutron Diffraction and Synchrotron Radiation White X-rays

    pp. 1260-1267

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    DOI:10.2355/isijinternational.53.1260

    To investigate the tensile deformation behavior of a lean duplex stainless steel (S32101) from the viewpoints of plastic deformability among phases or grains, we performed static tensile tests, in situ neutron diffraction, and white x-ray diffraction experiments at room temperature. In the static tensile tests, the S32101 steel displayed a larger uniform elongation and a better tensile strength–uniform elongation balance than a commercial SUS329J4L duplex stainless steel. A larger uniform elongation of S32101 is associated with the macroscopic work hardening behavior that a work hardening rate higher than the flow stress can maintain up until high true strains. From the experimental results of synchrotron radiation white x-ray diffraction experiments, the hard phase of S32101 was changed from the ferrite (α) phase to austenite (γ) one during tensile deformation. This led to a larger stress partitioning between the phases at the latter stage of deformation. From the experimental results of in situ neutron diffraction, it was found that the stress partitioning of the γ phase in the S32101 was the largest among the present results. Therefore, the larger work hardening rate of S32101 can be explained by the large stress partitioning of the γ phase, that between γ and α phases and γ volume fraction.
  • Effects of Static and Dynamic Strain Aging on Hydrogen Embrittlement in TWIP Steels Containing Al

    pp. 1268-1274

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    DOI:10.2355/isijinternational.53.1268

    Al effects on strain aging and resistance against hydrogen embrittlement were examined in Fe–18Mn–0.6C-based twinning-induced plasticity steels deformed at different strain rates. These steels showed a hydrogen-induced fracture when they were pre-deformed at a strain rate of 1.7×10–6 s–1. This fracture was suppressed by increasing the strain rate and Al content. The two important factors for improving the resistance to hydrogen embrittlement from the viewpoint of material strengthening by strain aging were found to be (1) the suppression of dynamic strain aging by increasing the strain rate and Al content, and (2) the suppression of static strain aging under loading by the Al addition.
  • Innovative Method on Simulating the Damage Mechanism of the Refractory

    pp. 1275-1279

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    DOI:10.2355/isijinternational.53.1275

    The presentation of the simulating method of the refractory damage is the subject of this paper. Based on the assumption of uniform temperature, the two kinds of load of compression and tension are endowed with two different kinds of damage models. In the tension state, the matrix is gradually amalgamated with stomata, at the same time, the aggregate is “swallowed” by the amalgamated matrix; On the other hand, in the compression state, only the matrix is amalgamated with stomata and the aggregate remains unchanged. According to the hypothesis proposed, the damage is simulated by the improved Generalized Self-Consistent Scheme (GSCS). Contrast to the experimental data, the numerical results indicate that the introduction of the damage hypothesis is feasible.
  • Damage Pattern Recognition and Feature Extraction of MgO–C Refractory

    pp. 1280-1285

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    DOI:10.2355/isijinternational.53.1280

    The determination of the damage mode and the quantitative description of the damage of the refractory are the subjects of this paper. Through the three-point bending tests, a magnesia-carbon refractory has been investigated using an Acoustic Emission (AE) unsupervised pattern recognition procedure and a frequency-energy coupled analysis. By means of coefficient analysis of the wavelet energy spectrum, the damage is divided into three periods. Based on the periods, time-frequency analysis is used to extract the damage characteristics and the centroid energy carried by the centroid frequency is put forward in the explanation of the extent of the damage. Finally, the time history plot of the centroid frequency is produced. It shows the similarity of that of the energy which indicates that the extent of the damage could be explained by the centroid energy carried by the centroid frequency brought forward.
  • Inheritance of Dislocations and Crystallographic Texture during Martensitic Reversion into Austenite

    pp. 1286-1288

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    DOI:10.2355/isijinternational.53.1286

  • Mechanism of Grain Boundary Embrittlement in Fe–Ni–S Alloys

    pp. 1289-1291

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    DOI:10.2355/isijinternational.53.1289

  • In Situ Neutron Diffraction during Tension-Compression Deformation for Nodular Graphite Cast Irons

    pp. 1292-1294

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    DOI:10.2355/isijinternational.53.1292

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