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

ISIJ International Vol. 50 (2010), No. 11

  • Problems in the Calculation of Transformation Texture in Steels

    pp. 1517-1522

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    DOI:10.2355/isijinternational.50.1517

    The solid-state decomposition of austenite can lead to a non-random distribution of product crystals. Methods of the quantitative characterisation of this texture are extremely advanced, and there is a deep understanding of the relationship between the texture and macroscopic properties. There remain, however, important barriers to the complete calculation of texture, some of which have not been documented in the published literature. It is the purpose of this review to focus on the difficulties in order to set the scene for further progress. The advent of electron back scatter diffraction has led to an explosion of papers on microscopic aspects of crystal orientations; some of the issues relating to this technique are also described.
  • Thermodynamic Calculation of Liquidus Surface of FeOx–CaO–SiO2 System

    pp. 1523-1531

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    DOI:10.2355/isijinternational.50.1523

    As world's reserve of high grade iron ores declines, the gangue minerals, such as Al2O3, of iron ore have been increasing. To counter the adverse impact of alumina on sinter quality, MgO fluxes are often added to increase sinter MgO. The liquidus surface of Al2O3 and MgO containing FeOx–CaO–SiO2 system is therefore of fundamental importance to understanding of the melting mechanism in the sintering process. In this study, the literature data on the liquidus surface of the FeOx–CaO–SiO2 system containing Al2O3 and MgO under various temperatures and oxygen partial pressures, which are relevant to the iron ore sintering, were carefully reviewed, and the differences between various data sources were analysed. A modified version of the thermodynamic package: Multi-Phase Equilibrium (MPE) software developed by CSIRO was compiled, including refinement of its slag database, to cover the compositional and atmospheric conditions encountered in the sintering process. The effects of oxygen partial pressure and additions of Al2O3 and MgO on the liquidus of the FeOx–CaO–SiO2 system were modelled. The model predictions represent experimental results well, and show that the liquid field at 1573 K shrinks with the oxygen partial pressure decreasing from 10−3 to 10−5 atm and separates into two distinct liquid fields. As the oxygen partial pressure decreases further from 10−5 to 10−8 atm, both liquid fields expands and merges to form a continuum. Addition of Al2O3 and MgO is found to increase the stability of the magnetite (spinel) phase, shift the liquidus away from the FeOx corner, and therefore suppress the formation of the melt during sintering.
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    1. Effects of Oxygen Pressure, Al2O3 and MgO on the Liquidus Surface of FeOx-SiO2-CaO System Tetsu-to-Hagané Vol.86(2000), No.7
  • Thermodynamic Consideration on the Absorption Properties of Carbon Dioxide to Basic Oxide

    pp. 1532-1538

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    DOI:10.2355/isijinternational.50.1532

    Carbon capture and storage (CCS) is a key technology for greatly reducing CO2 emissions in the long term, and therefore a low-energy CCS process needs to be developed. This study focused on the solid absorption process using basic oxide, and thermodynamically examined the carbonation abilities of various basic oxides and compounds containing CaO, BaO or Li2O. The CO2 absorption and desorption behavior of these materials containing alkali earth metal oxides was investigated by measuring the weight change over a wide range of temperatures from room temperature to 1100°C in CO2 atmosphere. It was experimentally confirmed that the partial pressure of CO2 equilibrated with both Ba2TiO4 and BaCO3 was higher than that equilibrated with both BaO and BaCO3. The formation of compound increased the equilibrium partial pressure of CO2 and lowered the starting temperature of CO2 desorption.
  • Influence of Bottom Bubbling Condition on Metal Emulsion Formation in Lead-Salt System

    pp. 1539-1545

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    DOI:10.2355/isijinternational.50.1539

    In the steelmaking process, the reaction rate can be enhanced by increasing the interfacial area and an effective method is to emulsify the metal into the slag phase. This phenomenon is called as metal emulsion. An experimental method for investigating the formation of a metal emulsion was established using the Pb and KCl–LiCl–NaCl system, and the influence of the bottom bubbling condition on the formation of the metal emulsions was clarified. More than 1000 metal droplets were observed in 1 g of molten salt. The total weight and total surface area of the metal droplets increased with bubbling time and reached a steady state. Both values increased with gas flow rate until 300–500 mL/min, and subsequently both values gradually decreased and the local maximums were observed. Two modes of droplet formation were observed by high-speed camera; mode A in which a bubble dome with a metal film formed first and metal droplets formed when the bubble became detached from the interface, and mode B in which a metal column formed after the bubble become detached from the interface. The frequency of droplet formation in mode A showed the local maximum behavior at a gas flow rate of 300–500 mL/min.
  • Fabrication of Ultra High Nitrogen Austenitic Stainless Steel by NH3 Solution Nitriding

    pp. 1546-1551

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    DOI:10.2355/isijinternational.50.1546

    Nitrogen addition to stainless steels is very effective for improving mechanical properties and corrosion resistance. N2 solution nitriding is one of the possible methods to produce high nitrogen stainless steel. However, the nitriding rate by N2 gas is significantly small and also the attainable nitrogen contents in Fe–Cr alloys is less than 1 mass% in general. NH3 nitriding is an attractive alternative since NH3–H2 gas mixtures have high corresponding nitrogen potential than that of pure N2 gas.
    In the present study, aiming for the enhancement of the nitriding rate and the increase of nitrogen contents more than 1 mass%, NH3 and N2 solution nitriding of Fe–Cr alloys under various conditions has been carried out and their behaviors of nitrogen absorption in Fe–Cr alloys are investigated. It is found that the suppression of the pre-decomposition of NH3 before it reaches the sample is critical for the effective NH3 nitriding. Compared with the N contents after 1 h nitriding, NH3 nitriding is found to be about 5 times faster than that of N2 (0.1 MPa) nitriding under the present experimental conditions. In addition the N contents more than 1 mass% were easily achieved by NH3 nitriding. By using devised NH3 gas injection system to minimize the pre-decomposition of NH3 gas, austenitic Fe–23.5Cr alloys with more than 3 mass% of nitrogen (ultra high nitrogen stainless steel) that had never been achieved by solution nitriding was successfully produced.
  • Interfacial Reactions between Oxygen Containing Fe and Al at the Onset of Liquid Fe Deoxidation by Al Addition

    pp. 1552-1559

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    DOI:10.2355/isijinternational.50.1552

    The phenomena taking place at the early stage of Al deoxidation were investigated with specific attention on the formation of Al2O3 inclusions. In a quartz tube, Al was exposed to liquid Fe containing different amounts of dissolved oxygen (O) for 1, 5, 30 and 60 s. In this paper, quenched microstructures of the diffusion couple were examined to identify the interactions and the nature of the phases at the experimental temperature. They revealed that the reaction zone was composed of successive layers of Fe–Al intermetallic compounds, as predicted by the phase diagram of the system, i.e. αFe(Al), FeAl, FeAl2, Fe2Al5 and FeAl3. Based on the microstructure, the concentration profiles, diffusion processes in solid and liquid phases, and the behavior of Al2O3 inclusions in the reaction zone, it was demonstrated that the reaction zone was completely liquid and that the solid Fe shell melted for the samples with holding time of 30 and 60 s.
  • Off-gas Dust in an Experimental Blast Furnace

    pp. 1560-1569

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    DOI:10.2355/isijinternational.50.1560

    In blast furnace (BF) ironmaking, efforts are made to decrease coke consumption, which can be done by increasing the pulverized coal injection rate (PCR). This will cause changes in in-furnace reduction conditions, burden distribution, demands on raw material strength, etc. In order to maintain stable operation, but also to obtain low amounts of material losses through the off-gas, it is important to understand fines generation and behaviour in the BF. Off-gas dust and shaft fines generated in the LKAB Experimental Blast Furnace (EBF) were sampled during operation with olivine pellets and mixtures of acid pellets and sinter as iron-bearing materials. Characterization using XRD, SEM and LOM was focused on fines from iron-bearing materials, coke and slag formers. The results showed that flue dust, mainly <0.5 mm, was mechanically formed and created in the same manner for all investigated samples. Carbon-containing particles dominated in the fractions >0.075 mm and consisted mainly of coke particles from the shaft. Fe-containing particles, as Fe2O3 from the top of the shaft, formed the major part of flue dust fractions <0.063 mm. Particles from slag formers such as quartzite and limestone were observed in flue dust when slag formers were utilized in the feed. Sludge consisted mainly of chemically formed spherical particles <1 μm precipitated from the ascending gas as the temperature decreased.
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    Readers Who Read This Article Also Read

    1. Effects of Coal Inertinite Size on Coke Strength ISIJ International Vol.48(2008), No.5
    2. Lowering Reduction Temperature of Iron Ore and Carbon Composite by Using Ores with High Combined Water Content ISIJ International Vol.49(2009), No.11
    3. Effect of Carbon Structure Crystallinity on Initial Stage of Iron Carburization ISIJ International Vol.50(2010), No.1
  • Off-gas Dust in an Experimental Blast Furnace

    pp. 1570-1580

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    DOI:10.2355/isijinternational.50.1570

    In the blast furnace process, material losses are caused by particles that are blown out of the furnace by the off-gas. In order to reduce these losses, it is important to understand the correlations between furnace conditions and off-gas dust formation. Off-gas dust, as flue dust and sludge, were collected during shaft probe sampling in LKAB Experimental Blast Furnace (EBF). Process data was used to evaluate the relationship between off-gas dust amounts and furnace conditions. The graphitization degree (Lc value) of shaft coke and coke in flue dust was determined using XRD measurements. Solution loss in the shaft had a negligible effect on coke degradation and the coke particles which ended up in the flue dust were mainly derived from abrasion at low temperatures. The amount of alkali and SiO2 in sludge increased with higher PCR and flame temperature, which confirmed that submicron spherical particles in sludge originated from the high temperature area around the raceway. Theoretical critical particle diameters of materials, which could be blown out with the off-gas, were estimated. Flow conditions in the top of the shaft as well as and the properties of fine particles in terms of size and density are important when outflow of mechanical dust, such as flue dust, is concerned. Low off-gas temperatures, and thus lower off-gas velocities, are favourable for low flue dust amounts expelled from the blast furnace.
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    Readers Who Read This Article Also Read

    1. Effects of Coal Inertinite Size on Coke Strength ISIJ International Vol.48(2008), No.5
    2. Lowering Reduction Temperature of Iron Ore and Carbon Composite by Using Ores with High Combined Water Content ISIJ International Vol.49(2009), No.11
    3. Effect of Carbon Structure Crystallinity on Initial Stage of Iron Carburization ISIJ International Vol.50(2010), No.1
  • Influence of Oxide and Silicate Melt Phases on the RDI of Iron Ore Pellets Suitable for Shaft Furnace of Direct Reduction Process

    pp. 1581-1589

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    DOI:10.2355/isijinternational.50.1581

    The temperature in iron ore pelletizing process is as high as 1300–1320°C, so that a significant amount of liquid slag forms in the pellets. The main components of the slag phases are SiO2, FeO, Al2O3, CaO and MgO in various proportions. The slag or melt phase wets the solid surface and facilitates the diffusion and grain growth. After cooling, melt phase solidifies and acts as important bonding phase in the finished pellets and influence high temperature properties, especially reduction degradation index (RDI) to a great extent. The resistance of pellets against degradation during reduction depends on the type of bonding and increases in the order of hematite, ferrite and silicate. In this study commercial pellets of different RDI rang-ing from 8.5 to 14.3 were characterized. Electron and optical micro structural studies with image analysis revealed that the amount and distribution of silicate melt, alumina content of hematite phase, porosity and pore density are vital in controlling the RDI. Residual magnetite in the core of the pellets was found detrimental to RDI. Distribution of different elements in the oxide and melt phase was identified by using X-ray mapping technique and chemistry of different phases was measured using SEM-EDS analysis.
  • Microwave Penetration Depth in Materials with Non-zero Magnetic Susceptibility

    pp. 1590-1596

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    DOI:10.2355/isijinternational.50.1590

    A simplified equation for determining the transverse electromagnetic mode (TEM) power penetration depth of microwaves in materials having both magnetic and dielectric response was derived. The penetration depths for a magnetite concentrate were calculated using this “full-response” equation, and a significant difference is shown compared with the penetration depth obtained using only the dielectric response (i.e., assuming no imaginary part of complex relative permeability). The temperature dependence of the power penetration depth, up to 1000°C, was determined using measured values of the real and imaginary parts of complex relative permittivity, εr′, εr″ and permeability, μr′, μr″. The accurate determination of penetration depths can help in optimizing the dimensions of a load in a microwave furnace, producing more uniform heating under microwave irradiation and avoiding thermal runaway.
  • Numerical Simulation for Collision and Growth of Inclusions in Ladles Stirred with Different Porous Plug Configurations

    pp. 1597-1605

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    DOI:10.2355/isijinternational.50.1597

    A mathematical model has been developed to predict the collision and aggregation among inclusions in the ladle with different porous plug configurations. The numerical results showed that the porous plug configuration has a profound effect on the inclusion removal process in ladle. The eccentric bottom blowing is better than the central bottom blowing. The terminal inclusion removal efficiency decreases with the increasing porous plugs. The inclusions captured by the top slag accounts for the majority of the removed inclusions, inclusion adhesion to the sidle wall is the minor manner, and inclusions adhered to the ladle bottom wall can be negligible. In order to avoid newly generated large inclusions to be remained in the liquid steel after about 16 min of treatment, it is necessary to prolong the treating time on the condition of one porous plug configuration.
  • The Composition and Morphology Evolution of Oxide Inclusions in Ti-bearing Ultra Low-carbon Steel Melt Refined in the RH Process

    pp. 1606-1611

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    DOI:10.2355/isijinternational.50.1606

    Before deoxidation, the main inclusions were Fe–Mn–O inclusions in Ti-bearing ultra low-carbon steel melt. After 3 min Al addition, the inclusions changed to be granular and spherical Al2O3. Al2O3 cluster, composed of granular and spherical particles with diameter 1–2 μm, formed in 7 to 10 min after Al addition into the melt. Al2O3·TiOx inclusions with the Ti/(Al+Ti) between 0.15 and 0.30 formed 3 min after ferro-titanium addition and Al2O3·TiOx cluster formed because rich [Ti] and poor [Al] regions existed around the ferro-titanium particles and Al2O3 cluster. The Ti3O5 was hard to be formed when acid-soluble aluminum exceeded 0.035% with titanium blow 0.08%. The activity of Ti3O5 in the complex liquid phase inclusions increased remarkably with the decrease of acid-soluble aluminum and increase of titanium.
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    2. Kinetic Modeling on Nozzle Clogging During Steel Billet Continuous Casting ISIJ International Vol.50(2010), No.5
    3. Production and Technology of Iron and Steel in Japan during 2007 ISIJ International Vol.48(2008), No.6
  • The Effect of Zirconium Disilicide (ZrSi2) Additions on the Carbon Oxidation Behavior of Alumina/Graphite Refractory Materials

    pp. 1612-1621

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    DOI:10.2355/isijinternational.50.1612

    Carbon oxidation is a main industrial problem for Alumina/Graphite Submerged Entry Nozzles (SEN) during pre-heating. Thus, the effect of ZrSi2 antioxidants and the coexistence of antioxidant additive and (4B2O3·BaO) glass powder on carbon oxidation were investigated at simulated non-isothermal heating conditions in a controlled atmosphere. Also, the effect of ZrSi2 antioxidants on carbon oxidation was investigated at isothermal temperatures at 1473 K and 1773 K. The specimens' weight loss and temperature were plotted versus time and compared to each others. The thickness of the oxide areas were measured and examined using XRD, FEG-SEM and EDS. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3·BaO) glass powder of the total alumina/graphite base refractory materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by (4B2O3·BaO) glaze during green body sintering led to an excellent carbon oxidation resistance.
  • Modeling of Slag Eye Area in Argon Stirred Ladles

    pp. 1622-1631

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    DOI:10.2355/isijinternational.50.1622

    Slag eye area in an axi-symmetrical water model of an argon stirred ladle has been measured through video photography as a function of gas flow rates, liquid depth, slag layer thickness and different types of upper phase liquid. It is shown that in addition to the principal operating parameters (i.e., gas flow rate, liquid depth and amount of slag), physical properties of the overlying liquid, particularly kinematic viscosity and density exert considerable influence on slag eye formation. Based on our experimental observation, it is shown that existing correlations do not constitute a sufficiently reliable basis for prediction of slag eye area in steelmaking ladles. Accordingly, a new correlation for slag eye area has been formulated through dimensional analysis embodying a large set of experimental data, derived from different combinations of bulk and upper phase liquids. Polynomial regression indicates that dimensionless slag eye area can be expressed in terms of Froude number, (UP2/gH), density ratio, (RL/Δρ), and Reynolds number, (HUPs), via:
    [Equation]

    in which, Aes is the eye area, H is the slag layer thickness, h is the bulk liquid depth and UP is the average plume rise velocity. Experimental data reported by many investigators on aqueous as well as industrial scale ladle gas stirred ladles systems were subsequently applied to demonstrate the adequacy and appropriateness of the proposed correlation. Possible extrapolation of the correlation to eccentric gas injection and melt covered with a thick slag layer, which are more typical of ladle metallurgy steelmaking, is also examined.
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    1. The Physical and Mathematical Modelling of Gas Stirred Ladle Systems ISIJ International Vol.35(1995), No.1
    2. Influence of Solid CaO and Liquid Slag on Hot Metal Desulfurization ISIJ International Vol.52(2012), No.1
    3. A Mathematical Model of Fluid Flow Phenomena for the Liquid Bath in Smelting Reduction Processes ISIJ International Vol.43(2003), No.7
  • The effect of FetO Content on MgO Solubilities in Lime-based Slags

    pp. 1632-1636

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    DOI:10.2355/isijinternational.50.1632

    It was attempted to quantitatively elucidate the effect of FetO content on MgO solubilities in lime-based slags using the measured data of MgO solubility in the slags. The magnesia capacities of the lime-based liquid slags were nicely correlated with the optical basicities in case the ideal solution was assumed for the magnesiowustite saturation phase which is actually in equilibrium with the slags. The substitution of MgO for CaO in lime-based slags increased the activity coefficient of FetO for the constant activity of FetO, resulting in decreasing FetO content in the slags. It is believed that the FetO activities in metallurgical slags containing iron oxide play the decisive role in determining the MgO solubilities into the slags.
  • Development and Application of Dynamic Soft-reduction Control Model to Slab Continuous Casting Process

    pp. 1637-1643

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    DOI:10.2355/isijinternational.50.1637

    Based on the heat transfer and solidification model for simulating two-phase zones by coupling multiple alloys during slab continuous casting process and the soft-reduction theory, the dynamic control model for soft-reduction on slab continuous casting was developed. The control model consists of three major functional modules: real-time tracking simulation, cooling water control and dynamic soft-reduction control. In order to keep stable continuous casting and produce high quality slabs during slab continuous casting process, many significant operating parameters such as the cooling water at the secondary cooling zone and the roll gap at sector section can be dynamically adjusted according to the reasonable metallurgical criterion and on-line feedback information. Industrially, the model has been successfully applied. Industrial practices indicate that the control model with reasonable algorithms and accurate simulation has a certain theoretical value and industrial practicality.
  • A New Model for the Prediction of Roll Force and Tension Profiles in Flat Rolling

    pp. 1644-1652

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    DOI:10.2355/isijinternational.50.1644

    This paper presents a precision on-line model for the prediction of the roll force and tension distributions across the strip in hot strip rolling. The approach is based on an approximate 3-D theory of rolling, and in particular, considers the effect of pre-deformation of the strip, which occurs near the roll entrance before the strip enters the bite zone. The prediction accuracy of the proposed model is examined through comparison with the predictions from the 3-D finite element models.
  • Effect of Simple Shear Deformation Prior to Cold Rolling on Texture and Ridging of 16% Cr Ferritic Stainless Steel Sheets

    pp. 1653-1659

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    DOI:10.2355/isijinternational.50.1653

    The effect of simple shear deformation by equal-channel angular pressing (ECAP) for one pass on the texture and ridging of ferritic stainless steel sheets with 16 mass% chromium has been investigated. Hot rolled and annealed sheets of 4 mm thickness were ECA-pressed for one pass, prior to cold rolling and final annealing. It was found that grains were subdivided by grain-scale heterogeneous plastic deformation, namely, deformation bands, during simple shear by ECAP. Deformation bands appear to contribute to the fragmenting layered structure after cold rolling and facilitate recrystallization of the so-called colonies having {hkl}‹110› texture, which are otherwise difficult to recrystallize in final annealing. In other words, strain energy can be stored more effectively by combining simple shear and cold rolling than by cold rolling alone. Recrystallization occurred at a much lower temperature in the process including ECAP than in a conven-tional cold-rolling only process, replacing colonized {hkl}‹110› grains with more favorable {111}‹hkl› grains, thus enhancing its formability and reducing ridging.
  • Enhancement of Impact Toughness of 0.05% P Doped High Strength Steel through Formation of an Ultrafine Elongated Grain Structure

    pp. 1660-1665

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    DOI:10.2355/isijinternational.50.1660

    An ultrafine elongated grain (UFEG) structure with a strong ‹110›//rolling direction (RD) fibre deformation texture was produced by warm calibre-rolling at 773 K in 1200 MPa-class medium-carbon low-alloy steels with phosphorous (P) contents of 0.001 and 0.053 mass%. Charpy impact tests were performed at room temperature on the UFEG structure along with a conventional quenched and tempered (QT) structure. P segregation embrittlement completely disappeared in the UFEG structure. The UFEG structure exhibited the same high absorbed energy of 150 J regardless of P content, although the absorbed energy of the QT structure was significantly decreased from 93 J for 0.001% P steel to 23 J for 0.053% P steel due to occurrence of intergranular fracture. The high absorbed energy of 150 J for 0.053% P-doped UFEG structure was believed to be due to both delamination fracture and fine/deep ductile dimples. The present results emphasized that the detrimental effects of P grain boundary segregation can be suppressed and the upper shelf energy can be increased through the formation of the UFEG structure.
  • Microstructure and Property of Ni76Cr19AlTi Side in Inertia Friction Weld Joint of the Superalloy Ni76Cr19AlTi and the Martensite Stainless Steel 4Cr10Si2Mo

    pp. 1666-1670

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    DOI:10.2355/isijinternational.50.1666

    The inertia friction welding process was used to weld the nickel base superalloy Ni76Cr19AlTi to martensite steel 4Cr10Si2Mo. Ni76Cr19AlTi is a f.c.c superalloy strenthened by precipitates of γ′. 4Cr10Si2Mo is a martensite stainless steel strenthened by martensite transformation and precipitates of carbides. The microstructure evolution on the nickel base superalloy Ni76Cr19AlTi side of the weld was studied. It was found that the welds formed can be divided into three zones: thermomechanically affected zone, heat affected zone and base metal. The thermomechanically affected zone consisted of two subzones: one is the mixed chemical composition zone of about 100 μm in width formed by mechanical stirring and interdiffusion of alloying elements and the other was pure shear zone located adjacent to the mixedchemical composition zone. In the chemical composition mixture zone, a large number of carbides with sizes of less than 100 nm formed in the austenite matrix. However, no γ′ phase can be observed in this region. The dislocation density decreased gradually as the distance to the weld interface increased. The dislocation density in the pure shear zone was very high. Grain size coarsened markedly in the heat affected zone, in which the γ′ phase was precipitated. The primary mechanism of the grain growth was the bulging of grain boundary between two adjacent grains with high-angle boundary.
  • Simulation of Zinc Solidification and Coating Profile on the Inner Surface of a Tube during Its Galvanisation

    pp. 1671-1675

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    DOI:10.2355/isijinternational.50.1671

    A simulation study was carried out for the first time on zinc solidification and coating profiles in tube galvanising for an industrial line. The entire process was simulated with the help of flow and heat transfer models and surface wave model in this computational heat transfer study. It was observed that the coating on tube inner surface gets solidified for more than one third of its length before the steam blowing to remove the extra zinc. This part of the tube thus becomes insensitive to steam blow for thickness control. The wavy coating profiles developed due to jet blowing of steam were predicted that matched well with the measured profiles from industrially made galvanised tubes.
  • Influence of Al on Kinetics of Discontinuous Precipitation in Ni–38Cr Alloy

    pp. 1676-1682

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    DOI:10.2355/isijinternational.50.1676

    The influence of Al on the kinetics of discontinuous precipitation in the Ni–Cr system was experimentally examined using ternary Ni–38Cr–Al alloys with Al concentrations of 3.8 mass% and 4.2 mass%. The ternary alloys were homogenized at 1473 K for 16 h, solution treated at 1473–1493 K for 30 min, and then isothermally annealed in the temperature range of 773–1073 K for various times up to 50 h. Due to the solution heat treatment, both ternary alloys show the polycrystalline single-phase microstructure of the Ni-rich solid-solution (γ) phase with the face-centered cubic structure. In the early stages of isothermal annealing, however, fine particles of the Ni3Al (γ′) phase with the L12 structure are formed in the γ matrix by continuous precipitation. On the other hand, the cell of the lamellar microstructure consisting of the γ phase and the Cr-rich solid-solution (α) phase with the body-centered cubic structure is formed along the grain boundary of the γ matrix and then grows into the γ matrix. The fine particles of the γ′ phase are dispersed also in the γ phase of the cell. The migration distance of the moving cell boundary is proportional 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 monotonically increase with increasing annealing temperature. A kinetic model was used to analyze quantitatively the relationship between the growth rate and the interlamellar spacing. Although the discontinuous precipitation in the ternary Ni–38Cr–Al alloys occurs in a complicated manner, the analysis indicates that the growth of the lamellar cell is controlled by the boundary diffusion of Cr along the moving cell boundary.
  • Macro–Micro Combined Texture Evolution Model for Hot Strip with High Reduction Rolling

    pp. 1683-1688

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    DOI:10.2355/isijinternational.50.1683

    Techniques for controlling the texture of polycrystal materials are very important, because texture anisotropy has a strong effect not only on the characteristics of a steel sheet but also on the mechanical and electrical properties. We have produced fine-grained hot steel strips industrially through high-reduction low-temperature rolling and these steels have the same texture as that of thermomechanically rolled steels. In this study, we first obtained the critical resolved shear stress of hot materials from functions of dislocation density and predicted the hot rolling texture in the nonrecrystallized austenite region using Taylor theory. Next, we predicted the transformation texture of fine-grained hot strips from the hot rolling texture of austenite in accordance with the Kurdjumov–Sachs orientation relationship. The accuracy of the new macro–micro combined model for texture evolution is excellent.
  • Modeling of Correlation between Heat Treatment and Mechanical Properties of Ti–6Al–4V Alloy Using Feed Forward Back Propagation Neural Network

    pp. 1689-1694

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    DOI:10.2355/isijinternational.50.1689

    A model for predicting mechanical properties of Ti–6Al–4V alloy has been developed and the Feed Forward Back Propagation (FFBP) as one type of algorithm of the Artificial Neural Network has been applied as the prediction system. Hardness, ultimate tensile strength (UTS), yield strength (YS) and elongation that are basic mechanical properties of Ti–6AL–4V alloy are predicted as a function of heat treatment process. Other tensile testing parameter, i.e. strain rate, is also considered in the model because increase of strain rate will increase UTS and YS, but will decrease elongation. Since the FFBP is a supervised system, it requires a lot of input and output data pairs for training process. The data are acquired from literatures and preprocessed before training. Performance of the model are evaluated by the Normalized Root Mean Square Error (NRMSE) and the Coefficient Correlation (R). The NRMSE and the R values of both training and validation parts show almost excellent values. Therefore, the model using the FFBP is appropriate to predict the mechanical properties of Ti–6Al–4V alloy.
  • Numerical Simulation of Fatigue Crack Initiation in Thin-walled High Strength Steel as Modeled by Voronoi-polygons

    pp. 1695-1701

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    DOI:10.2355/isijinternational.50.1695

    The fatigue endurance of TS 590 MPa grade low-alloy precipitation strengthened steel was numerically and experimentally examined. The microstructure was modeled using two-dimensional Voronoi polygons. Heterogeneous stress distributions were calculated using the finite element method, taking elastic anisotropy into consideration. The number of cycles before crack initiation was estimated based on the Tanaka–Mura model. By taking into account the effects of the cyclic strain of the preceding cracks, a definable macroscopic crack initiation cycle was obtained. An actual tensile and compression fatigue test was conducted on the same steel. The stress amplitude decreased as the cycle number increased. Distinct dislocation cell structure was not observed by TEM analysis. The experimental strain fatigue limit was, to some extent, lower than that of the simulation. Surface effects, specimen homogeneity, selection of slip system, and dislocation reversibility are mentioned as the probable causes for the difference.
  • Impurities Segregation to Grain Boundary Carbide Interfaces and Grain Boundaries and the Mechanism of Elevated Temperature Intergranular Cracking in Heat-resistant Steel

    pp. 1702-1706

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    DOI:10.2355/isijinternational.50.1702

    It is shown that the time to elevated temperature intergranular failure in a heat-resistant steel is expressed by t=t0σn exp(Q/RT) where n is the stress exponent, Q the activation enthalpy, and t0 the proportional constant. It is also shown that the segregation concentration of impurities is markedly higher in the dimples of grain boundary area than at the smooth grain boundaries and so the dimples observed usually at reheat or stress relief cracked surfaces are not the micro-ductile fracture areas but the carbide/matrix interfaces at the grain boundaries. Finally, it is shown that the elevated temperature intergranular cracking results from the smooth grain boundary cracking following the cracking of the carbide/matrix interfaces at the grain boundaries.
  • Liquid Iron Wetting of Calcium Aluminates

    pp. 1707-1712

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    DOI:10.2355/isijinternational.50.1707

    An investigation has been carried out to assess the wetting behaviour of liquid iron carbon alloys on alumina, CA6 (CaO·6Al2O3), CA2 (CaO·2Al2O3) and CA (CaO·Al2O3). The melt compositions studied were 2 and 5 mass% [C] over a temperature range of 1450 to 1550°C. It was found that the systems studied were in general non-wetting, and that the contact angle dropped from approximately 140° to 110° as the calcium content of the substrates increased. The data for alumina were in good agreement with the literature. These data have been used to assess whether capillary phenomena play a significant role in coke dissolution in liquid iron. In previous studies it was found that as coke dissolved, a mineral layer consisting of alumina and calcium aluminates formed at the coke iron interface and that as time passed the mineralogy of the layer changed from CA6 to CA2 to CA. The rate of coke dissolution slowed considerably with the occurrence of the CA phase. It was not clear whether this was solely a densification effect, or if a capillary wetting issue was contributing to a reduction of the contact area. The contact angle measurements of iron on alumina, CA6, CA2 and CA have been discussed in light of this coke dissolution study, and a simple capillary penetration model used to assess the wetting effects. It was found that the change of wetting associated with the calcium enrichment of the mineral layer did not have a significant effect on the rate of coke dissolution.
  • Formation of an Aluminide Coating on Hot Stamped Steel

    pp. 1713-1718

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    DOI:10.2355/isijinternational.50.1713

    The degradation of type 1 aluminized coating during hot stamping leads to the coating cracking due to the formation of a brittle FeAl2 intermetallic phase. The formation of an aluminide coating prior to hot stamping was investigated as a method to simultaneously improve the coating ductility and achieve a good hot corrosion resistance of the hot stamped parts. A formable aluminide coating was obtained when the coating alloying was achieved during the pre-heating of the steel and an Fe content higher than 70 at% (83 wt%) was reached. The coating was identified as Fe3Al phase at room temperature. The formation of this aluminide coating on 22MnB5 hot stamping steel was investigated in detail. The effect of this alternative hot stamping thermal cycle on the room temperature mechanical properties of the steel was also investigated.
  • Characterisation of ESP Dust Sample from Sinter Plant

    pp. 1719-1721

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    DOI:10.2355/isijinternational.50.1719

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  • Erratum: Thermodynamic Interaction between Chromium and Titanium in Liquid Fe–Cr Alloys Containing 30 mass% Cr
    [ISIJ Int. 50(10): 1373-1379 (2010)]

    pp. 1722-1722

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    DOI:10.2355/isijinternational.50.1722

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