ISIJ International
New Arrival Alert : OFF

You can use this feature after you logged into the site.
Please click the button below.

Log in / Sign up
ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 53 (2013), No. 2

  • Effect of Oxidation State of Iron Ions on the Viscosity of Alkali Silicate Melts

    pp. 185-190

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.185

    Understanding the changes in viscosity due to the different oxidation states of iron ions is important for simulating phenomena related to molten slags and also for understanding the structure of iron-oxide-containing silicate melts. However, these viscosity changes are not well understood. Here, we show the viscosity changes of R2O–SiO2–FexO (R = Li, Na, or K) melts due to changes in the oxidation states of the iron ions by systematically varying the oxygen partial pressure using several Ar-based gases at 1773 K. The initial compositions of the samples were 30R2O–60SiO2–10Fe2O3 (mol%), and the ratio of Fe3+ to Fe2+ in the R2O–SiO2–FexO melts increased with increasing oxygen partial pressure in all samples. Meanwhile, the viscosity of all the R2O–SiO2–FexO melts decreased with increasing Fe2+ to total-Fe ratio. The data indicate that the increase in the amount of Fe2+ ions, which behave as network modifiers, would result in depolymerization of the silicate melts. It should also be noted that the viscosity of the melts increased in the order of alkali cationic radius (K > Na > Li) when the ratios of Fe2+ to Fe3+ in the melts were comparable. This was due to the change in the coordination structure of Fe3+ in the melts. Not only the oxidation state of the iron ions but also the coordination structure of Fe3+ may be important for understanding the viscosity.
  • Determination of Desulphurising Ability for Ca–CaF2 Flux Using Equilibration with Molten Silver at 1673 K in Closed Graphite Crucibles

    pp. 191-198

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.191

    The present study aims to evaluate the desulphurising ability of Ca–CaF2 flux. Desulphurisation equilibrium between molten CaS–CaF2 flux and molten silver has been investigated using a crucible covered with a cap having a capillary. The relationship between calcium and sulphur concentrations in molten silver has been clarified for CaS saturated and unsaturated systems. Two thermodynamic properties have been determined, namely, the equilibrium constant for the dissolution reaction of CaS into molten silver and the activity coefficient product of calcium and sulphur in molten silver from the data for CaS saturated system, as follows:
    CaS(s) = Ca(mass% in Ag) + S(mass% in Ag)
    logK = –6.38
    log(fCafS) = –87.3(±12.3)√C (C < 0.032)
    C = [%Ca]/MCa + [%S]/MS
    The activity coefficient of CaS in CaS–CaF2 flux has been obtained as a function of CaS mole fraction in flux from the data for CaS unsaturated system:
    logγCaS = 2.67(1–XCaS)2–1.26 (XCaS < 0.12)
    Combination of these thermodynamic data leads to the distribution ratio of sulphur between molten Ca–CaF2 flux and molten SUS316L stainless steel, 4.7×106 at 1673 K. This value is extremely higher than that in conventional refining, indicating that metallic calcium based fluxes have extraordinary desulphurising ability.
  • A Kinetic Study on Carburization of Fe by Using 13CO Isotope Gas

    pp. 199-206

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.199

    The current investigations were undertaken to clarify the kinetics of dissociation of CO gas into the molten iron and the effects of impurities in Fe. The interfacial reaction rate of CO on liquid iron at 1823 K was measured by means of 13CO isotope exchange technique. Isotope exchange technique has been widely employed to evaluate the interfacial chemical reaction quantitatively. The experiments were carried out for the compositions of (0.002–3.31 mass%) of carbon, (0.002–0.11 mass%) of oxygen, (0.0026–0.1 mass%) of sulfur and (0.0002–0.08 mass%) of nitrogen employing quadruple mass spectrometry for product gas analysis. In the carburization of molten iron containing oxygen, sulfur, carbon and nitrogen by CO, the interfacial reaction at gas-metal surface can be converted from adsorption limited control to dissociation limited reaction as the impurity concentrations of oxygen and sulfur increase. In particular, it was found that sulfur has greater influence on the conversion of rate limiting step of carburization reaction of molten iron.
  • A Genetic Algorithm Application to Minimize Pig Iron Cost

    pp. 207-212

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.207

    A new mathematical model for sinter ingredients and BF burdens optimization was proposed aiming to reduce hot metal cost, considering the binary basicity (CaO/SiO2) and molar ratio of MgO/Al2O3 of blast furnace slag, sinter composition as the constraints. To solve the optimization model, Genetic algorithm was adopted. The results of the examples indicate that the model is effective to reduce hot metal cost while guaranteeing properties of sinter and BF slag. And the minimum cost of hot metal is attained in optimizing both of sinter ingredients and BF burdens at the same time.
    x

    Readers Who Read This Article Also Read

    1. Effects of Metallic Iron Bearing Resources on Iron Ore Sintering ISIJ International Vol.38(1998), No.1
    2. Dissolution Mechanism of Fluorine in Aqueous Solution from Fluorine Containing Synthetic Slag ISIJ International Vol.44(2004), No.3
    3. Elution Mechanism of Fluorine from Steelmaking Slag into Seawater ISIJ International Vol.44(2004), No.5
  • Arc Behaviour and Cathode Melting Process during VAR: an Experimental and Numerical Study

    pp. 213-220

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.213

    The present study aims to understand the melting of the consumable electrode in the VAR process and gain some insight into the influence of an ensemble arc motion on the melting behaviour. In a previous study, a 2D axisymmetric model of the heat transfer in the cathode had been developed. Using the operating parameters as model inputs, it enabled prediction of the melt rate and the evolution of the melting area. Model results were successfully compared to melt rate measurements in an industrial VAR furnace. In recent years, it has been claimed that the electric arc may not be considered as steady and axisymmetric. Our experimental investigation of the luminosity recorded during an actual VAR heat confirms that a transient 3D behaviour may take place. Therefore, a 3D version of the previous model was set up to predict the heat transfer and melting of the electrode, using the unknown ensemble arc motion as an input. The arc is assimilated to a transient distribution of energy flux density. Results evidence that the influence of the arc motion on the shape of the electrode tip can be very important. In industrial practice, the cathode tip usually remains relatively flat during melting. The shapes of the computed electrode tips enable us to propose some arc parameters which remain compatible with both the periodic behaviour of the light emitted and the flatness of the electrode.
  • Effects of Primary Oxide and Oxide-Nitride Particles on the Solidification Structure in a Fe-20 mass%Cr Alloy Deoxidised with Ti and M (M = Zr or Ce)

    pp. 221-229

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.221

    The ratio of equiaxed grains on a cross section and the size of equiaxed grains in a Fe-20 mass% Cr alloy deoxidised with Ti/M (M = Zr or Ce) were studied as function of nitrogen content and particle characteristics such as size distribution, morphology and composition. Fe-20 mass% Cr alloys were melted at 1600°C, deoxidised, and cooled to 1400°C followed by water quenching. Thereafter, the particles were separated from the matrix using electrolytic extraction using a 10%AA electrolyte and collected on a film-filter surface. The inclusion characteristics were determined using SEM. It was found that the number of particles increases with an increased N content. Furthermore, that the solidification structure was clearly affected by the number of primary oxide and oxide-nitride particles in the Ti/Zr deoxidation experiments. However, a similar effect could not be detected in the Ti/Ce deoxidation experiments.
  • Control of Meniscus Stability in Medium Thickness-straight Walls Slab Mould

    pp. 230-239

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.230

    Meniscus stability influenced by fluid flow patterns inside a medium thickness- parallel mould walls was analyzed using water modeling techniques including dye tracer injection, PIV and ultrasonic measurements on real time of meniscus levels. Two different submerged entry nozzles (SEN) were compared, the first is under current operation at the caster which yields a very high level of turbulence and the second is a computer aided design SEN which is aimed to reemplace the first one. The experimental results indicate that the first SEN 1 induces a single-unstable large flow roll which promotes large bath oscillations and generation of vortex flows on the bath surface. Fluid speeds at meniscus level reach magnitudes as large as 0.6 m/min and in the wall mould as high as a 0.95 m/s which are large enough to attain "shell washing conditions". Meanwhile SEN 2, new design, yields a very stable meniscus with speeds as large as 0.45 m/s at the meniscus in a stable-double flow roll. The analysis of entrapment and entrainment mechanisms of slag leads to conclude that the first SEN will induce slag entrapment under almost all operating conditions while the second SEN will induce slag entrapment only under very specific conditions of high casting speed of 3.68 m/min.
    x

    Readers Who Read This Article Also Read

    1. Improvement of Life of Immersion Nozzle with Gas-injection ISIJ International Vol.35(1995), No.9
    2. Mechanism of Surface Quality Improvement in Continuous Cast Slab with Rectangular Cold Crucible Mold ISIJ International Vol.38(1998), No.7
    3. Ripple Marks on Cast Steel Surfaces ISIJ International Vol.53(2013), No.7
  • Quality Monitoring Research of Small Scale Resistance Spot Welding Based on Voltage Signal

    pp. 240-244

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.240

    With the rapid development of microelectromechanical systems, small scale resistance spot welding (SSRSW) is ever-increasing used in electronic and medical devices. Whereas there is limited research work dealing with quality control of SSRSW. This paper investigated a real-time and in-situ SSRSW quality monitoring method by means of taking the voltage as the monitoring signature. It was obtained through clipping two leads onto the electrodes during SSRSW. As the linear DC and the high frequency (HF) resistance welding power supplies were the common equipments in SSRSW and constant current mode was used in this study, the variation of voltage with time indicated the conditions of the welding process which issued in the final weld quality. Utilizing four factors extracted from the voltage curve an artificial intelligence algorithm to estimate the weld quality was proposed. The maximum average forecast error of the trained network is about 0.15 mm, showing that the voltage curve is a reliable quality monitoring signature of SSRSW. The most prominent advantage of this method is that weld quality can be perfectly estimated with only two sensor clips compared with other methods reported for normal scale or large scale resistance spot welding (LSRSW).
  • Theoretical Characterizations of Spinels Containing Iron and Vanadium via ab initio Calculations

    pp. 245-249

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.245

    We have employed ab initio approaches to investigate normal and inverse spinels containing iron and vanadium. The valence states of tetrahedral and octahedral Fe and V were firstly calibrated with reference oxides FeO (rocksalt), Fe2O3 (corundum), VO (rocksalt) and Fe2O3 (corundum). The Mulliken charges analyses suggest the valence states of Fe and V are interstices dependent. In Fe rich condition (VFe2O4), bivalent cations Fe2+ and V2+ prefer tetrahedral interstices, while trivalent cations Fe3+ and V3+ prefer octahedral interstices. In V rich condition (FeV2O4), Fe valence states in tetrahedral and octahedral interstices are the same as those in Fe rich cases. However, the V cations have contrary valence states, namely, V3+, in tetrahedral interstices, and mixed valence states in octahedral states.
    The crystalline formation energies of normal and inverse spinels were addressed to determine their stability. The inverse spinels are obviously more favorable than normal spinels. We have quantified probability of two isomeric inverse spinels in Fe rich condition in equilibrium at 300 K and 1700 K. It is in agreement with that entropy plays a more significant role at high temperature. Electronic structures of tetrahedral and octahedral Fe and V cations have also been analyzed using computed x-ray absorption near edge structure (XANES). The chemical shift of white lines, going from Fe2+ to Fe3+ cations in spinels, and 3d orbitals splitting of tetrahedral and octahedral V cations are distinguishable in XANES spectra. Thus, the different electronic structure of Fe and V cations in tetrahedral and octahedral interstices can provide important interpretations of experimental works of spinels containing iron and vanadium elements.
  • Further Assessment of the Kissinger Formula in Simulation of Thermal Desorption Spectrum of Hydrogen

    pp. 250-256

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.250

    The Kissinger-type formula, dX/dt=A(1–X)exp(–Ed/RT), which was thought to be applicable only in detrapping-controlled desorption has proved to be applicable also in the case of diffusion-controlled desorption under certain conditions including existence of effective diffusion coefficient or assumption of Oriani's local equilibrium and pre-exposure of hydrogen before temperature ramp. Analysis indicated that the constant A depends on the specimen geometry and the pre-exponential factor of effective diffusion coefficient. Numerical verification has been carried out by comparing the simulation result of Kissinger-type formula with that using the rigid McNabb-Foster model for typical specimen geometry including plate, cylinder and sphere. The merit of using this formula lies in its simplicity in numerical simulation of the thermal desorption spectrum with an accuracy as high as that based on the M-F model. Two different derivative forms of the Kissinger-type formula, i.e. the Choo-Lee plot d[ln (φ/Tp2)]/d(1/Tp)=–Ed/R and the Lee-Lee plot d[ln(φ/Tp)]/d(1/Tp)=–Ed/R, for determination of desorption activation energy have also been discussed and the analytical result showed that the Choo-Lee plot is a proper method to determine desorption activation energy while the Lee-Lee plot is not correct. The limit of application of the formula and the Choo-Lee plot in thermal desorption analysis is discussed in a semi-quantitative manner.
  • Investigations on Formation of Shape Defects in Square Rolling of Uniform Thin Flat Sheet Product

    pp. 257-264

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.257

    In rolling of wide strip, longitudinal compressive stresses develop as a result of non-uniform deformation along the plate width, which enhance long-shape wave. Different reduction as a result of uneven geometrical factor along the plate width considered as a main cause of such non-uniform deformation in flat rolling. In order to investigate the non-uniformity of deformation that take place in width direction as a cause of non-geometrical factors, a 3D model of flat rolling process employing ABAQUS software, which includes the buckling features is created. It is realized that in addition to uneven geometrical factor which influence the plate quality, the variation of forming condition along the width as a result of different boundary condition also lead to heterogeneity of the material flow in the roll gap and cause to non-uniform distribution of longitudinal stress. In addition to non-uniform flow of material along the plate width, different transversal flow of material along the plate edge in the roll gap will change the distribution of longitudinal stress after rolling. Despite the fact that variation in residual stresses is calculated to be very low but it is shown that even low values of the residual stresses plays an important role in buckling of thin flat rolled products.
  • Slab Analysis of Asymmetrical Rolling of Bonded Two-layer Sheets

    pp. 265-273

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.265

    In this paper, asymmetrical rolling of bonded two-layer clad sheets is studied using the slab method of analysis. It is assumed that the ingoing sheet is guided to horizontally enter the roll gap and that the work rolls may have different pressure distributions. Unlike the existing slab models, the slabs are not divided into two parts with different materials, and the whole slab is subjected to one stress field containing nonuniform normal and shear stresses acting on the vertical sides. By combining the sticking and coulomb friction models, a mixed friction model is proposed, and the work roll pressure distributions as well as the rolling force and torque are studied at different conditions. The predicted rolling force and torque of the proposed model are shown to be in a very good agreement with the analytical and experimental results of previous investigators.
  • Effect of Accumulative Bending Conditions on Grain Refinement on Hot-rolled Sheet

    pp. 274-278

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.274

    As a technology to manufacture fine-grained steel, accumulative bending process after hot rolling was proposed, and multi-bending equipment of laboratory scale were established. The effects of accumulative bending on microstructure and ferrite grain size by changing the thermo-mechanical conditions were investigated. As the results, a microstructure with the grain size of 2.2 μm was obtained at specimen surface by accumulative bending after hot rolling in the optimized thermal condition. By the results of FE analysis, it was cleared that equivalent strain was accumulated on not only surface but also center of thickness.
  • Influence of Oxygen Content on Microstructure and Inclusion Characteristics of Bainitic Weld Metals

    pp. 279-285

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.279

    The effects of non-metallic inclusions on the as-deposited microstructure of fully bainitic weld metals were investigated in a series of gas-metal arc (GMA) welds produced with four different shielding gases to obtain welds with different oxygen contents. Single run GMA bead-in-groove welds were made using ER100S-G grade wire which contained minimal amounts of aluminum and titanium. It was found that the ‘oxygen effect,’ which is well known in ferritic welds as the maximization of acicular ferrite formation at intermediate oxygen levels of 200–300 ppm and is explained by the shift of CCT curves with oxygen content, took place in the present bainitic welds with the maximum acicular ferrite occurred near 150 ppm oxygen. For a weld containing 150 ppm oxygen, all inclusions were extensively covered with a thin layer of titanium oxide. As the oxygen content decreased to about 100 ppm, a thick sulfide shell surrounded the aluminum oxide core and resulted in a fully bainitic microstructure. On the other hand, for welds containing more than 250 ppm oxygen, less than 50% of inclusions were covered with a titanium-oxide layer, and the coverage rate was substantially lower than for welds of 150 ppm oxygen. This led to a mixed microstructure of acicular ferrite and bainite. Therefore, the oxygen effect in the present welds could be concluded to be not due to the shift of the CCT diagram but to the fact that the inclusion phases vary with oxygen content. A new model based on these facts is suggested.
  • In-situ Measurements of Isothermal Wüstite Transformation of Thermally Grown FeO Scale Formed on 0.048 mass% Fe by Synchrotron Radiation in Air

    pp. 286-293

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.286

    Isothermal wüstite transformation of thermally-grown FeO scale formed on 0.048 mass% Fe at 948 K for 180 s and annealed at 673, 723 K, and 773 K in air was studied in situ by synchrotron radiation. Wüstite transformation initiated right at the beginning of isothermal heating, either by the formation of a new phase of meta-stable iron-rich wüstite (at 673 and 723 K) or by direct transformation to magnetite (at 773 K). At 673 K, iron-rich wüstite replaced the parent wüstite thoroughly, and then transformed to magnetite and metal iron. At 723 K, formation of the iron-rich wüstite started as well, but the reaction was interrupted and was replaced by a gradual enrichment reaction of iron in both the parent and the iron-rich wüstite phases. Consumption of the parent wüstite and generation of magnetite accompanied. Wüstite transformation to generate magnetite and metal iron at 673 and 723 K was only possible for the iron-rich wüstite. At 673 and 723 K, incubation time was needed to initiate transformation of meta-stable iron-rich wüstite to magnetite and metal iron. Reaction to form the iron-rich wüstite from the parent wüstite was much easier. Tranformation of the iron-rich wüstite to magnetite and metal iron is considered a root cause for the formation of the lamellar structure and the magnetite seam in the scale. The transformation can well be interpreted from the analogy of the formation of the pearlite structure in steels.
    x

    Readers Who Read This Article Also Read

    1. Environmental Influence on the Corrosion Rate of Steel Bars Embedded in Concrete ISIJ International Vol.48(2008), No.2
    2. Effects of Roll Surface Deteriorations on Scale Defect in Hot Rolling Tetsu-to-Hagané Vol.84(1998), No.12
    3. In-situ X-ray Diffraction of Corrosion Products Formed on Iron Surfaces MATERIALS TRANSACTIONS Vol.46(2005), No.3
  • Hot Deformation Behavior of Fe-2%Si

    pp. 294-303

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.294

    The hot deformation behavior of a high purity binary ferritic Fe-2 mass% Si alloy, undergoing no phase transformation or precipitation reactions, was investigated by hot torsion tests. The parameters for the constitutive equation of Fe-2 mass% Si steel were experimentally determined from the stress-strain curves. The activation energy for hot deformation was close to that for lattice self-diffusion in α-Fe, indicating that hot deformation of Fe-2 mass% Si steel occurs by a thermally-activated, diffusion-controlled dislocation climb mechanism. The electron backscattering diffraction technique and transmission electron microscopy were used to analyze the microstructural changes occurring during hot deformation. It was found that the hot deformed microstructure consisted of equiaxed crystallites surrounded by a high proportion of high angle boundaries. These boundaries were homogeneously distributed in the microstructure. A gradual increase in the fraction of boundaries with a misorientation in the range of 10° to 18° was observed in samples obtained from interrupted torsion tests. The formation of high angle boundaries at temperatures above 0.5Tm is attributed to a gradual increase of the misorientation of low angle boundaries by the absorption of dislocations.
  • Identification of Oxide Phases in Oxide Dispersion Strengthened PM2000 Steel

    pp. 304-310

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.304

    The oxide phases in oxide dispersion strengthened PM2000 steel have been investigated by transmission electron microscopes. Two nano-sized yttrium aluminum oxide phases, YAlO3 having a distorted orthorhombic-simple structure with approximate lattice parameters of a/b/c = 5.4197/5.8520/7.6413 Å and Y3Al5O12 having a tetragonal-simple crystal structure, have been identified in the steel. Two aluminum iron oxide phases and one aluminum titanium oxide phase, which are not known to have been identified previously in steels, have been found in the PM2000 steel. They have been determined to be aluminum iron oxide, Al2Fe2O6 having an orthorhombic crystal structure with the lattice parameters a/b/c = 7.235/5.926/7.502 Å, and aluminum iron oxide, Al3FeO6 having a body-centered cubic crystal structure with an average lattice parameter of 3.047 Å, as well as aluminum titanium oxide, Al3Ti5O2 having a face-centered cubic crystal structure with an average lattice parameter of 6.923 Å. The PM2000 steel contains a small amount of Al2Fe2O6, Al3FeO6, Al3Ti5O2 and Al2O3 phases with a large size and block/ or spherical morphology.
  • Effect of η Phase on Mechanical Properties of the Iron-based Superalloy Using Shear Punch Testing

    pp. 311-316

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.311

    In this paper, the shear deformation behavior of A286 Iron-based superalloy was studied with an emphasis on the influence of η phase on shear strength. The η (Ni3Ti) phase precipitates at high temperature heat treatment or during services at the expense of gamma prime phase. According to the microstructural features, no evidences of η phase were found at 650 and 720°C. η phase precipitated at 780 and 840°C and the amount of it increased with an increase the time and temperature. Because of using the alloy as fasteners, investigation of shear properties and the influence of η phase on it are indispensable. The shear strength of the alloy with different volume fractions of η was examined. It was found that, with an increase of η volume fraction, the ultimate shear strength decreases. The shear punch fracture surfaces were also examined by the scanning electron microscopy. The fracture surfaces of sheared samples indicated that low and high volume fraction of η phase result in interior cracks and grain boundary decohesion, respectively. In fact, the fracture of weak grain boundary films (η phase) produces this kind of decohesive cracking.
  • Effects of Distribution and the Formation Process of MA on Deformation and Toughness of High Strength Linepipe Steel

    pp. 317-322

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.317

    Based on the strain-based concept of linepipe products, materials with high deformability are desirable and a dual-phase microstructure consisting of harder and softer phases is essential to obtain higher deformability. Martensite-austenite constituents (MA) are very important in the hard phase for achieving good mechanical properties such as deformability and toughness. For understanding the formation process and its effect on mechanical properties, microstructural analysis of the MA formed through two different heat treatments (on-line heat process and off-line heat process) is conducted.
    Based on SEM and TEM observation, it is found that the MA consisted mainly of martensite and its distributions and shapes are different between on-line and off-line heat process samples. Because of the different formation processes, grain boundary character is also different. The interface of MA and matrix in the on-line heat process sample is divided by short length Kurdjumov-Sacks (K-S) orientation grain boundaries. On the other hand, long length random grain boundaries are formed at the interface of the off-line heat process material. This characteristic morphology results in the difference in the toughness of the materials by causing a different strain accumulation and crack propagations mechanism at the vicinity of MA.
  • TWIP Effect and Plastic Instability Condition in an Fe–Mn–C Austenitic Steel

    pp. 323-329

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.323

    We investigated the correlation among deformation twin density, work hardening, and tensile ductility in an Fe–18Mn–1.2C twinning-induced-plasticity (TWIP) steel, and discussed the correlation with the plastic instability condition. The deformation twin density was varied by changing the deformation temperature from 123 to 523 K. An important factor for the uniform elongation is the work hardening rate in a later deformation stage. The increase in the deformation twin density enhanced the work hardening rate significantly but not monotonically just before the fracture, since the deformation twin density is saturated against plastic strain. In addition, dynamic strain aging in a later deformation stage and ε-martensitic transformation were found to accelerate the fracture due to the localized deformation and the premature fracture, respectively. Accordingly, the relationship between uniform elongation and deformation twin density was not simple. The optimum conditions for the TWIP effect were concluded to be (1) considerable amount of deformation twinning in a later deformation stage, (2) suppression of dynamic strain aging in a later deformation stage, and (3) inhibition of ε-martensitic transformation.
    x

    Readers Who Read This Article Also Read

    1. Mechanical Properties of H-charged Fe–18Mn–1.5Al–0.6C TWIP Steel ISIJ International Vol.52(2012), No.9
    2. Hot Deformation Behavior of High Mn TWIP Steel Using the Processing Map ISIJ International Vol.55(2015), No.3
    3. Supra-Ductile and High-Strength Manganese-TRIP/TWIP Steels for High Energy Absorption Purposes ISIJ International Vol.43(2003), No.3
  • Effect of Cold Rolling on Annealing Behavior and Retained Austenite Characteristics of Multiphase CMnSi Steel

    pp. 330-336

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.330

    The newly developed multiphase transformation-induced plasticity (TRIP) steels are of interest for industrial applications because of their excellent combination of high strength and ductility. Retained austenite as a key constituent in final microstructure plays an important role in TRIP steels. The volume fraction, carbon concentration, size and morphology of this phase are the well known parameters which effects on the rate of transformation of retained austenite to martensite and the properties of steel. The performance of steel can be successfully controlled by designing an optimum balance in the volume fractions of ferrite, bainite and retained austenite.
    Against this background, in this research the effect of initial cold-rolling reduction and intercritical annealing temperature on the final microstructure and retained austenite characteristics has been studied on a silicon-containing TRIP steel by electron backscattered diffraction (EBSD) method. The results show that moderate percent of cold rolling followed by intermediate annealing temperature would provide optimum condition for desirable retained austenite characteristics with proper adjacent phase.
  • Effects of Carbon Content and Cooling Path on the Microstructure and Properties of TRIP-aided Ultra-High Strength Steels

    pp. 337-346

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.337

    The effects of carbon content in the range 0.2–0.4 wt% and thermomechanical treatment parameters on the mechanical properties and microstructures of steels containing 0.5Si–2.0Mn–1.0Al–0.6Cr have been studied in order to help develop an efficient processing route for ultra-high-strength TRIP-aided martensitic-bainitic structural steels. The microstructures consist of granular bainite, lath-like bainite, martensite and up to 23 volume % retained austenite as granular islands and lath-like films. Microsegregation of chromium and manganese results in the formation of martensite-rich bands, the volume fraction of which increases with carbon content. Bands of martensite, induced by the segregation of chromium and manganese, become more prominent with increasing carbon content. Good combinations of tensile strength, elongation and impact toughness can be achieved with 0.2 or 0.3 wt% carbon by thermomechanical rolling followed by water quenching to 150–350°C and isothermal holding for 2 h at the quenching stop temperature. The steel with 0.4 wt% carbon shows high strength and good uniform elongation due to high contents of retained austenite, but its impact toughness is clearly inferior to its lower carbon counterparts. Annealing to alleviate microstructural banding produced a marked improvement in impact toughness.
  • Influences of Co, Cu and V on Kinetics of Discontinuous Precipitation in the Ni–Cr System

    pp. 347-355

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.347

    The effects of Co, Cu and V on the kinetics of discontinuous precipitation in the Ni–Cr system were experimentally examined using ternary Ni–39Cr–1.0Co, Ni–39Cr–1.2Cu and Ni–39Cr–0.89V alloys. The alloys were homogenized at 1423 K for 3 h, solution treated at 1423 K for 1 h, and then isothermally annealed in the temperature range of 873–1023 K for various times up to 2300 h. Due to the solution heat treatment, all the alloys show the polycrystalline single-phase microstructure of the Ni-rich solid-solution (γ ) phase with the face-centered cubic structure. During isothermal annealing, however, the cell of the lamellar microstructure composed of the γ phase and the Cr-rich solid-solution (α) phase with the body-centered cubic structure is produced along the grain boundary of the γ matrix and then grows into the γ matrix. At each annealing temperature, the migration distance of the moving cell boundary increases in proportion to the annealing time. Thus, the growth rate of the cell is constant independent of the annealing time. The growth rate and the interlamellar spacing of the cell almost monotonically increase with increasing annealing temperature at 873–1023 K. The cell growth is slightly accelerated by Cu but not by Co and V. However, the acceleration is less remarkable at 1023 K. A kinetic model for the binary discontinuous precipitation controlled by boundary diffusion was used to analyze quantitatively the experimental result. In the moving cell boundary, the thermodynamic interaction is attractive between Cr and V but repulsive between Cr and Cu. Therefore, it is anticipated that the boundary diffusion of Cr along the moving cell boundary may be expedited by V but retarded by Cu. According to the analysis, however, the Cr boundary diffusion is hardly affected by Cu and V as well as Co. On the other hand, the boundary diffusion is lightly faster for Cu than for Co but slower for V than for Co. Consequently, for Cu and V, the thermodynamic and diffusional contributions to the Cr boundary diffusion are compensated each other.
  • Effect of Mode of Rolling on Recrystallization Kinetics and Microstructure Evolution in Interstitial Free High Strength Steel Sheet

    pp. 356-364

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.356

    The recrystallization kinetics and microstructure evolution after unidirectional and multi-step cross rolling of interstitial free high strength steel has been investigated systematically. Microhardness, electron backscattered diffraction and X-ray diffraction was used to characterize the recrystallization kinetics, microstructure and texture evolution during annealing. The obtained experimental data on recrystallization was evaluated in terms of Johnson-Mehl-Avrami-Kolmogorov (JMAK) kinetic model. The Avrami exponents varied between 1.03 at 1073 K to 1.4 at 948 K for unidirectionally rolled sample, while for cross rolling, it varied between 2.6 at 1073 K to 0.83 at 948 K. The recrystallization kinetics was observed to be faster for unidirectionally rolled samples. The deformed textures consisted of strong γ (ND//<111>) and α (RD//<110>) fibres in unidirectionally rolled sample, while a weak γ-fibre and strong rotated cube ({100}<110>) texture component was observed in cross rolled sample. After complete recrystallization, strong γ-fibre was observed in unidirectionally rolled sample, while strong γ and ε (TD//<110>) fibres were observed in cross rolled sample. The formation of recrystallization texture in unidirectionally rolled sample was explained by oriented nucleation. In cross rolled samples, orientation pinning and selective growth have a very strong role to play in developing the recrystallization textures.
  • Influence of Microstructure Difference of Stainless Steels on the Strength and Fracture of Bolted Connections

    pp. 365-374

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.365

    Recently, since stainless steel has a variety of significant characteristics such as corrosion resistance, durability, aesthetic appeal and fire resistance, the use of stainless steel in construction has been steadily increasing. Also, stainless steels can be classified into five main groups; austenitic, ferritic, martensitic, duplex and precipitation hardening according to metallurgical microstructure. Austenitic stainless steels are the most widely utilized in buildings. This paper focused on comparing material properties and ultimate behaviors such as strength, fracture mode and curling effect of single shear bolted connections fabricated with two different stainless steels; austenitic and ferritic types. Bolt arrangement and end distance in the parallel direction of applied load are considered as main variables. Specimens have same edge distance perpendicular to the direction of load, plate thickness, bolt diameter, pitch and gauge. A monotonic tensile test has been carried out for specimens under shear and some bolted connections with long end distance were accompanied by curling; out of plane deformation, which caused strength reduction. Furthermore, it is found that the fracture shape and curling effect patterns of two kinds of bolted connections differ from two stainless steel materials.
  • Effect of Microstructure on Fatigue Strength of Intercritically Austenitized and Austempered Ductile Irons with Dual Matrix Structures

    pp. 375-381

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.375

    In the present study the fatigue strength of austempered ductile irons with dual matrix structures (ADI with DMS) has been studied for an unalloyed ductile cast iron. For this purpose, specimens were intercritically austenitized (partially austenitized) in two phase region (α + γ) at various temperatures (810°C, 820°C and 830°C) for 20 minutes and then quenched into salt bath held at austempering temperature of 315°C and 375°C for 120 minutes and then air cooled to room temperature to obtain various ausferrite volume fractions and their morphologies. Conventionally austempered specimens (austempered from 900°C) with fully ausferritic matrix and unalloyed as cast specimens having ferrit + pearlite structures were also tested for a comparison. Rotating bending fatigue test were carried out an the experimental results showed that, in ADI with DMS, volume fraction of ausferrite and continuity of ausferritic structure along intercellular boundaries play important role in determining fatigue strength. The fatigue strength of these specimens increases with increasing ausferrite volume fraction. The fatigue strength was correlated with the ausferrite volume fraction and high carbon austenite and its carbon content. Conventionally austempered specimens exhibited much greater fatigue strength than ADI with DMS specimens.
  • Physical Interpretation of Grain Refinement-induced Variation in Fracture Mode in Ferritic Steel

    pp. 382-384

    Bookmark

    You can use this feature after you logged into the site.
    Please click the button below.

    Log in / Sign Up

    DOI:10.2355/isijinternational.53.382

Article Access Ranking

21 Jan. (Last 30 Days)

  1. Heat Transfer Characteristic of Slit Nozzle Impingement on High-temperature Plate Surface ISIJ International Advance Publication
  2. Hydrogen Embrittlement Susceptibility Evaluation of Tempered Martensitic Steels Showing Different Fracture Surface Morphologies Tetsu-to-Hagané Vol.105(2019), No.1
  3. Effects of Impurities and Processing Conditions in Al–1%Mn Alloys on the Formation of Thermally Stabilized Substructures MATERIALS TRANSACTIONS Vol.59(2018), No.11
  4. Fusion Zone Microstructural Evolution of Al-10% Si Coated Hot Stamping Steel during Laser Welding ISIJ International Vol.59(2019), No.1
  5. A Review of the Chemistry, Structure and Formation Conditions of Silico-Ferrite of Calcium and Aluminum (‘SFCA’) Phases ISIJ International Vol.58(2018), No.12
  6. Effects of Sulfur and Titanium Interaction in Molten Pig Iron on Erosion of Carbon Brick ISIJ International Vol.59(2019), No.1
  7. Recent Progress on Advanced Blast Furnace Mathematical Models Based on Discrete Method ISIJ International Vol.54(2014), No.7
  8. Preface to the Special Topics Entitled “To Solve Problems of Hot Rolling Rolls” Tetsu-to-Hagané Vol.104(2018), No.12
  9. Effect of Annealing Time on Oxides Phases and Morphology along Oxidized Depth of Fe-3%Si Steel during Decarburization ISIJ International Vol.59(2019), No.1
  10. Preparation of High-Carbon Metallic Briquette for Blast Furnace Application ISIJ International Vol.59(2019), No.1

Search Phrase Ranking

21 Jan. (Last 30 Days)

  1. blast furnace
  2. blast furnace productivity
  3. blast furnace permeability
  4. 鉄と鋼
  5. laser welder
  6. titanium
  7. activity feo
  8. argon steel
  9. eaf operation
  10. electric arc furnace