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

ISIJ International Vol. 51 (2011), No. 5

  • Ultrasonic Velocities of Molten Alkali Silicates

    Miyuki Hayashi, Yousuke Matsuzono, Kazuhiro Nagata

    pp. 689-695

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    DOI:10.2355/isijinternational.51.689

    Abstract

    Temperature and compositional dependencies of ultrasonic velocities on molten alkali silicates have been reviewed. Although compositional correlation equations for the ultrasonic velocities on molten silicates have been previously proposed, the compositional dependency has not been interpreted yet from the viewpoint of the silicate structure. The authors focused on the ultrasonic velocities of molten alkali silicates, closely examined the reported data and have found that there is an identical linear relationship between the adiabatic compressibilities, which are strongly relevant to the ultrasonic velocities, and the molar volumes. This indicates that the molar volume is one of the most significant factors affecting the ultrasonic velocities.

  • China's Iron & Steel Industry and the Global Financial Crisis

    Ji-cheng He

    pp. 696-701

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    DOI:10.2355/isijinternational.51.696

    Abstract

    This article reviews the sustained and fast development of China's iron & steel industry since the reform and opening-up, the serious impact of the global financial crisis in 2008 on China's iron & steel industry and the domestic and foreign market backgrounds which rapidly brought China's iron & steel industry into downturn. It introduces the important measures the Chinese government has taken to expand domestic demand and restrain economic decline. It analyses the profound problems accumulated during the long-term rapid development of China's iron & steel industry and the challenges it faces. It raises important issues which need attention and main measures which should be adopted for China's iron & steel industry to react to the crisis and realize long-term and stable development.

  • Effect of B2O3 on Melting Temperature, Viscosity and Desulfurization Capacity of CaO–based Refining Flux

    Hongming Wang, Tingwang Zhang, Hua Zhu, Guirong Li, Yongqi Yan, Jianhua Wang

    pp. 702-706

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    DOI:10.2355/isijinternational.51.702

    Abstract

    Fluorite is widely employed as fluxing agent in metallurgy flux, which inevitably leads to serious fluorine pollution. In this work, B2O3 is used as fluxing agent of CaO–based refining flux to substitute for CaF2 so as to decrease the melting temperature and to improve the speed of slag forming and the refining efficiency. The effects of B2O3 on the melting temperature, viscosity and desulfurization capacity of CaO–based refining flux were investigated. The results indicate that the fluxing action of B2O3 is better than that of CaF2 and Al2O3. For the high basicity CaO–based refining flux (mass ratio of CaO/SiO2 is 5.0–8.75), when CaF2 is substituted with B2O3, the melting temperature can be decreased remarkably. Especially, when the mass ratios of CaO/Al2O3 and CaO/SiO2 are in range of 1.1–4.0 and 5.25–8.0, respectively, the flux melting temperature is lower than 1300°C. At the same time, the temperature range, in which the flux viscosity is low, is expanded as well as the stability of flux viscosity varying with temperature is improved obviously. These variations of flux properties are favorable for refining process. The results of experiments on sulphur partition equilibrium between metal and flux indicate that the desulfurization capacity of flux can be improved markedly when CaF2 is substituted with equal mass of B2O3. When 4 mass% B2O3 is employed as fluxing agent and the mass ratio of CaO/Al2O3 is in the range of 1.5–7.0, the final sulfur content of metal can be controlled lower than 0.004%.

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  • The Multicell Volume of Fluid (MC-VOF) Method for the Free Surface Simulation of MFD Flows. Part I: Mathematical Model

    Ovidiu Peşteanu, Egbert Baake

    pp. 707-713

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    DOI:10.2355/isijinternational.51.707

    Abstract

    This paper is the first part of a two-part paper which presents a simulation algorithm of unsteady, electromagnetically driven molten metal flows with free surfaces. At the free boundary, the variable space-distribution of the normal Lorentz forces is taken into account by proper computation of the electromagnetic field and pressure. For each calculation time step, a transport equation of the melt's volume is solved for multicell blocks and subsequently, the free surface is reconstructed by an inward gathering of the melt volume. Therefore, the free surface can be more accurately simulated with the following improvements:
    (1) Consideration of the normal electromagnetic force densities exerted on the melt surface.
    (2) Strictly volume conserving displacement of the free surface.
    (3) Absence of numerically created holes in the melt or of separated fluid droplets, respectively.
    Comparisons between computational and experimental results to verify the validity of the mathematical model will be presented in the second part of the paper.

  • The Multicell Volume of Fluid (MC-VOF) Method for the Free Surface Simulation of MFD Flows. Part II: Experimental Verifications and Results

    Ovidiu Peşteanu, Egbert Baake

    pp. 714-721

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    DOI:10.2355/isijinternational.51.714

    Abstract

    This second part of a two-part paper presents the experimental verifications of the Multicell Volume of Fluid method developed in the first part. The calculated results are compared with measurements performed for a medium frequency of about 0.4 kHz in an induction crucible furnace, at the low industrial frequency 50 Hz in an inductive rotational stirrer and at higher frequencies of about 30 kHz in an electromagnetic levitation device. Thus, the verifications were realized in these three laboratory setups for different values of the penetration depth of the electromagnetic field and also for different turbulent molten metal flows with one or two free surfaces. The computational results show a good agreement with the experimental data.
    The established Multicell Volume of Fluid method, characterized by a strictly volume conserving displacement of the free surface, a precisely defined contour of the calculated free surface without the numerical creation of unphysical holes and separated droplets and by calculation stability, will be further extended to the simulation of the more complex flows and free surface profiles resulted by using a new method of electromagnetic levitation melting in two-frequency magnetic fields.

  • Behavior of Liquid Phase Formation during Iron Ores Sintering

    Xuewei Lv, Chenguang Bai, Qingyu Deng, Xiaobo Huang, Guibao Qiu

    pp. 722-727

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    DOI:10.2355/isijinternational.51.722

    Abstract

    The improvement of industrial parameters like the basicity and sintering temperature and the selection of raw materials to form the acicular calcium ferrites become the hot topic in sintering production. However, the experimental with the sintering pot in the laboratory is still a main method up to now, no effective mathematical model or experience equations were developed. Factsage is a software for thermodynamic calculation in ironmaking and steelmaking. In present study, Factsage was used to calculate the liquid phases formulation during the sintering. The effect of the chemical compositions on the liquidus projection was also discussed. It was found that the content of liquid phase formed is about 25%–70% at 1250°C due to their chemical composition. The more SiO2, the easier to form liquid phase. The experiments were carried out for the validation. It was found that the calculations of the mass of liquid phase generation cannot give a very good and accurate agreement with the measurement of the melting behavior of the sample quantificationally, however, for the ability of the liquid phase formation during the sintering, the calculations can give a good qualitative results, especially in the temperature of melting begin and the temperature of 50% shrinkage. The calculations reported in this study can be used to estimate the sintering behavior of the iron ores under a certain industrial condition to reduce the extra experiments. The experiments also shows that the calculations by Factsage can give some good explanations on the phenomenon of the melting behavior of different samples.

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    2. Rate of Iron Carburization by Carbon in Slags through Carbon/Slag and Slag/Metal Reactions at 1723 K ISIJ International Vol.51(2011), No.8
    3. Indication of the Measurement of Surface Area on Iron Ore Granulation ISIJ International Vol.51(2011), No.9

  • Prevention of Chromium Elution from Stainless Steel Slag into Seawater

    Yusuke Samada, Takahiro Miki, Mitsutaka Hino

    pp. 728-732

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    DOI:10.2355/isijinternational.51.728

    Abstract

    Utilization of steelmaking slag is indispensable for sustainable growth of steelmaking industry. Steelmaking slag contains nutrition such as phosphorus, silicon and iron and may be utilized as a fertilizer if elution of environmentally regulated elements is negligible. Chromium is contained in stainless steel slag as an oxide and stabilization of this chromium oxide in the slag is very important in the view of environmental protection.
    Elution behavior of elements from chromium containing phases into seawater was investigated to observe the stability of phases that may exist in steelmaking slag. It was found that the existence of 2CaO·SiO2 enhanced the dissolution of chromium into seawater. Elution behavior of chromium from especially synthesized stainless steel slag into seawater was investigated. Finally, fixation of chromium was conducted by control of mineralogical phase with SiO2 addition to stainless steel slag. Addition of SiO2 to the slag was very effective for prevention of chromium elution into seawater.

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    3. Effect of Process Parameters on In-situ Reduction of Chromium Oxide during Electro Slag Crucible Melting of Cu–Cr Alloy ISIJ International Vol.46(2006), No.5

  • Wetting Behavior of Sintered Nanocrystalline Powders by Armco Fe and 22CrNiMoV5-3 Steel Grade Using Sessile Drop Wettability Technique

    Zuriñe Amondarain, Leiv Kolbeinsen, Jose Luis Arana

    pp. 733-742

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    DOI:10.2355/isijinternational.51.733

    Abstract

    The wettability of sintered nanocrystalline oxide powders (CeO2, TiO2, Y3Al5O12, and ZrO2-yttria stabilized) and Al2O3 basis powder (60–70% purity) (product originated in the secondary aluminium production, composed mainly of nano and micrometric aluminium oxide) by liquid Armco Fe and by 22CrNiMoV5-3 steel grade was studied using sessile drop wettability technique. The powders were pressed and sintered under different pressures, heating rates and holding times. The later grinding and polishing surface treatments were characterized by infinite focus microscope. The wetting experiments were carried out under pure Ar atmosphere. A small piece of Armco Fe and steel grade was melted on sintered nano oxides, heating up to 1600°C with a holding time of 10 minutes for each experiment. The contact angles were measured and chemical analyses were conducted on tested samples to characterize the wetting reactions. It was found that sintered nano TiO2 not only suffered considerable wetting by Armco Fe and 22CrNiMoV5-3 steel in both cases, but also reacted with the substrate to form ilmenite and pseudobrookite. The CeO2 substrate and Armco Fe system also showed good wetting behavior. In general terms, it was concluded that wettability was affected by substrate chemical composition, and surface characteristics by sintering conditions. The preliminary results of this investigation may help to determine the suitability of the nanoparticle to be added in a liquid iron based matrix in order to influence the microstructure evolution improving mechanical properties by a fine distribution in the metallic alloy.

  • Numerical Analysis for Film Boiling Heat Transfer of a Moving Hot Steel Plate

    Il Seouk Park

    pp. 743-747

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    DOI:10.2355/isijinternational.51.743

    Abstract

    The cooling of the steel strip in ROT (run out table) of the hot rolling process is very important in that the ROT is the final process to control the mechanical properties of the final products. In general the products are cooled by the circular water jets which makes the comparatively thick residual water layer about 100–200 mm with the supplied flow rate on the plate. The basic phenomenon governing this cooling process is the boiling heat transfer. The boiling phenomenon is one of the most well-understood heat transfer mechanism by the past a few decades research. However, almost all the results have been reached through experimentation. This paper focuses on the boiling heat transfer on the moving hot plate with a fully numerical approach. The simulation was conducted only in a very high temperature region (over the Leidenfrost temperature) where the film boiling can be kept steadily on the plate. The film (the steam layer) was regarded as the heat resistance whose capacity (actually the steam layer thickness) varied with the plate surface temperature and the flow rate and temperature of the water jet. To fix the steam layer thickness showing a very different spatially distribution on the plate, the continuity for the temperature and heat flux at the interface between the cooling water and the steam layer is satisfied by the iterative procedure for the effective thermal conductivity of the 1st cell on the plate wall.

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  • A Six-phases 3-D Model to Study Simultaneous Injection of High Rates of Pulverized Coal and Charcoal into the Blast Furnace with Oxygen Enrichment

    Jose Adilson de Castro, Alexandre Jose da Silva, Yasushi Sasaki, Jun-ichiro Yagi

    pp. 748-758

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    DOI:10.2355/isijinternational.51.748

    Abstract

    Simultaneous injection of charcoal and coal with oxygen enrichment in the blast furnace has recently received remarkable attention due to its possibility of considerable decrease in coke rate, increase in productivity and enhancement of combustion in the raceway. This paper deals with a modeling of simultaneous injection of pulverized coal and charcoal into the blast furnace through tuyeres. This model treats the blast furnace as a multi-phase reactor and six phases are considered simultaneously: gas, lump solids (raw iron ore, sinter, pellets and coke), hot metal, molten slag, pulverized charcoal and coal. Conservation equations for mass, momentum, energy and chemical species are solved simultaneously based on the finite volume method. Firstly two base cases of 200 kg/thm injection of pulverized coal and charcoal respectively are simulated and afterwards mixed injection of coal and charcoal are investigated. Simulation results for the two base cases are compared with measurements on industrial scale trials. Good agreement obtained for major operational parameters and inner temperatures verifies the model developed useful. Afterwards, the simultaneous injection operations are simulated in order to improve blast furnace performance. The simulation results contribute to better understanding of the blast furnace phenomena with combined injection and also to the development of new cleaner technologies to enhance the blast furnace operation.

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    2. Preliminary Evaluation of Fly Ash and Lime for Use as Supplementary Cementing Materials in Cold-Agglomerated Blast Furnace Briquetting ISIJ International Vol.51(2011), No.5
    3. Indication of the Measurement of Surface Area on Iron Ore Granulation ISIJ International Vol.51(2011), No.9

  • Physical and Mathematical Modelling to Study the Effect of Ladle Shroud Mis-alignment on Liquid Metal Quality in a Tundish

    Kinnor Chattopadhyay, Mihaiela Isac, Roderick I. L. Guthrie

    pp. 759-768

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    DOI:10.2355/isijinternational.51.759

    Abstract

    The present work involves the use of physical and mathematical modelling in order to study the effect of slight mis-alignments of the ladle shroud on liquid steel quality output from a delta shaped, four strand, continuous casting tundish. For the physical modelling, a full scale water model was used to observe the effects of ladle shroud alignment on steel quality in terms of “slag” entrainment into the individual moulds. The ladle shroud was purposefully biased by about 4 to 5 degrees off-vertical, and the number of “slag particles” entering individual strands of the 4 strand billet caster were measured during a ladle change, and compared with the “no bias” condition. A one third scale water model was also used to perform tracer dispersion experiments and to help visualize the effects of the biased shroud. Finally, a 3D mathematical model was developed and contours of velocity and/or turbulence were examined under a “biased shroud” condition. In the mathematical model, the shroud was biased in all directions. The mathematical predictions were in good agreement with physical modelling results. Given the great sensitivity of liquid metal quality to this slight misalignment during a ladle change, with the tundish “furniture” used, possible remedial measures are discussed for equivalent steel plant operations.

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  • On the Representativeness of Automated SEM/EDS Analyses for Inclusion Characterisation with Special Regard to the Measured Sample Area

    Susanne K. Michelic, Gerhard Wieser, Christian Bernhard

    pp. 769-775

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    DOI:10.2355/isijinternational.51.769

    Abstract

    The cleanness of steel has emerged to an important quality criterion for a wide field of special applications. In order to ensure the reliable characterisation of non-metallic inclusions, the constant optimisation of current analysing methods is essential. The present study focuses on the automated SEM/EDS analysis, especially determining the influence of the analysed sample area on the obtained particle diameters and size distributions of non-metallic inclusions. Besides the experimental analysis of different area sizes, a model was formulated to estimate the error of area ratio as a function of inclusion content. For the assumed conditions, an area range combining a sufficient and significant area size with a feasible time effort is defined. The model also evaluates the significance of the results for the maximum and medium particle diameter gained out of the measurements. Moreover, the truncation of the data – resulting from an experimental analysing limit – and its consequences are discussed. The results underline the potential of this analysing method for inclusion characterisation but also demonstrate the limitations especially regarding the maximum particle diameter. This work contributes to a better understanding in terms of representativeness of automated SEM/EDS analysis and provides important information for further practical analyses.

  • Preliminary Evaluation of Fly Ash and Lime for Use as Supplementary Cementing Materials in Cold-Agglomerated Blast Furnace Briquetting

    Mikko Mäkelä, Timo Paananen, Tommi Kokkonen, Hannu Makkonen, Jyrki Heino, Olli Dahl

    pp. 776-781

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    DOI:10.2355/isijinternational.51.776

    Abstract

    The utilization of biomass fly ash and lime was investigated as cement replacements in blast furnace briquetting. Sample characterization included chemical (XRF) and mineralogical (XRD) analysis, particle size determination, and thermal behaviour (TGA/DSC-TGA). Additionally, the mechanical performance and fly ash, lime, and fly ash/lime mixtures as cement replacements were determined by incorporation in mortars tested by standardized methods (EN 196-1). Based on the results, detrimental alkali, sulphur, and chlorine contents of the biomass fly ashes do not seem to restrict use in briquetting. However, the utilization of fly ashes as cement replacements resulted in significant decline of 28 day compression strength values. The two different fly ash samples attested to 28 day compression strength of app. 72% and 55% of the respective control. Inferior mechanical performance was related to moisture absorption according to XRD and DSC-TGA and relatively larger particle size. Respectively, lime additions encouraged fly ash strength development only in the case of inferior fly ash performance related to the aforementioned effects. The results provide important information for the forth-coming manufacture of blast furnace test briquettes, which is to commence in the near future.

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  • Development of Novel Methods for Compensation of Stress-strain Curves

    Yun Ping Li, Emi Onodera, Hiroaki Matsumoto, Yuichiro Koizumi, Shu Yu, Akihiko Chiba

    pp. 782-787

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    DOI:10.2355/isijinternational.51.782

    Abstract

    In this study, we analyze in detail the stress variation due to friction between the top surface of a cylindrical sample and the anvil surface by carrying out FEM analysis. We propose pragmatic and simple approaches to compensate the stress-strain curve for both Rastegaev-geometry samples and arbitrary cylindrical samples. By using these equations, the compensation process becomes easy and convenient, and the compensated flow stresses are reliable for the compression process of 5065B aluminum alloy.

  • Experimental Analysis of Thickness Reduction Limits in Ultra Thin Stainless Steel Foil Rolling

    Junichi Tateno, Toshiki Hiruta, Shigefumi Katsura, Atsutaka Honda, Takeshi Miyata, Akinobu Kamimaru

    pp. 788-792

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    DOI:10.2355/isijinternational.51.788

    Abstract

    In rolling of ultra thin stainless steel foil, there are two rolling limits. One is owing to elastic deformation of work rolls, and the other is owing to edge crack of rolled foil. In this paper, fundamental investigation was conducted about the basic characteristic of the rolling limits of ultra thin stainless steel foil. The influence of several rolling conditions on minimum thickness and behavior of edge crack were investigated experimentally. This paper provides new formula to predict the minimum thickness in ultra thin foil rolling. The relation between the edge crack depth and the rolling conditions is also discussed. The edge crack expands with rolling passes. However, the degree of the edge crack at same foil thickness shows different behavior depending on rolling conditions. The depth of edge crack rolled by small diameter work rolls is shallower than that of same thickness foil rolled by large diameter work rolls. Moreover, when Young's modulus of work rolls is high, it turns out that the edge crack is small. Based on detailed observation of the foil edge phenomenon, good correlation between edge crack depth and foil thickness at extreme edge portion is found. From those experimental results, it is suggested that the rolling conditions advantageous to control edge drop are effective to suppress edge crack expansion.

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  • Three-dimensional Heat Transfer Analysis of Two Wire Tandem Submerged Arc Welding

    Degala Venkat Kiran, Biswajyoti Basu, Arun Kumr Shah, Sourav Mishra, Amitava De

    pp. 793-798

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    DOI:10.2355/isijinternational.51.793

    Abstract

    Two wire tandem submerged arc welding process facilitates high rate of joint filling with little increase in the overall rate of heat input due to the simultaneous deposition from two electrode wires. Since the lead wire is usually connected to a DC welding arc and the trail wire to a pulsed AC arc, the tandem process requires appropriate selection of a large number of process variables. A quantitative understanding of the effect of the welding conditions on weld joint dimensions and weld thermal cycle is difficult through experimental studies only. Here we present a three-dimensional heat transfer analysis based on finite element method using two independent volumetric heat sources to account for heat input from two welding arcs. The shapes of the heat sources are estimated based on the original joint geometry and welding conditions. The results show that the trail wire current pulses significantly influences the reinforcement height and weld width while lead wire current affects the depth of penetration. For a constant trail wire effective current, increase in the negative pulse time results in greater reinforcement height and reduced weld width with very little influence on the cooling rate and weld strength. In contrast, increase in trail wire negative current pulse increases both reinforcement height and weld width while reduces cooling rate and weld strength.

  • Catalysis of Rare Earth Element Nd on Boriding of AISI 1045 Steel

    Xiao Xia Lu, Ce Liang, Xiao Xi Gao, Jian An, Xiao Hong Yang

    pp. 799-804

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    DOI:10.2355/isijinternational.51.799

    Abstract

    The present study evaluate the catalysis of Nd2O3 on the boriding of AISI 1045 steel using a 5% Nd2O3-containing boriding agent in a temperature range of 1213 K to 1350 K for 2 h–5 h. The morphology and types of borides formed on the steel surface were confirmed by optical microstructure, scanning electron microscopy and X-ray diffraction. The results show that the Nd2O3 has contrary effects on boriding process, i.e. promotion at high temperatures or hindrance at low temperatures. Nd2O3 addition can significantly reduce the activation energy of boride growth at high temperatures, decreased it from 198 kJ/mol to 137 kJ/mol, reduced by 31% in the high temperature range of 1133 K–1213 K as compared with that without Nd2O3 addition. The catalysis mechanism of RE element Nd during boriding process was discussed through the analysis of chemical reactions probably occurred in boriding agent, changes in surface morphology and chemical composition.

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  • Grain Refinement of α-iron by Repeated Carburizing and Decarburizing Reactions

    In-Hyeon Jeong, Jae-Sang Lee, Sung-Mo Jung, Jang-Gyu Kim, Yasushi Sasaki

    pp. 805-811

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    DOI:10.2355/isijinternational.51.805

    Abstract

    The grain refinement of α-Fe using repeated carburizing and decarburizing at 1073 K are investigated. It is found that the grain sizes are decreased by carburizing reaction but are increased by decarburizing reaction. Repeated α ↔ γ phase transformations make grain size smaller. However, without pinning elements, the reduction of the grain size has limitation. Sulfur does not have enough effects on the grain growth with the grain size of less than 30 μm. To improve the grain refinement process, Fe3C was introduced by annealing at 873 K along with the carburizing and decarburizing processing. Formed Fe3C can supply a lot of nucleation site for austenite nuclei during the reaustenitizing and retards ferrite grain growth during γ → α transformation by the decarburization reaction. The fine uniform grains of less than 10 μm have been produced by the carburizing and decarburizing processing at 1073 K along with adjusting the cementite size and the whole volume during the heat treatment at 873 K.

  • Correlation Between Microstructure and Texture Development in a Cold-rolled TWIP Steel

    Yaping Lü, Dmitri A. Molodov, Günter Gottstein

    pp. 812-817

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    DOI:10.2355/isijinternational.51.812

    Abstract

    X-ray diffraction and optical microscopy were used to characterize the crystallographic texture and the grain microstructure in cold-rolled Fe–23.2Mn–0.57C alloy. The development of texture and microstructure with increasing strain was systematically analyzed. From 10 to 85% rolling reduction the observed microstructure changes can be characterized by four distinctly different features: twin-matrix lamellae, alignment of twins with rolling plane, herring bone structure and macro shear bands. The effect of microstructural heterogeneity on texture was addressed. The observed change of the Cu texture component {112}<111> with increasing strain was attributed to the competition of homogeneous dislocation slip and deformation twinning. The shift of the Brass component towards the Goss orientation at higher reduction levels (> 60%) corresponds to the appearance of a large amount of the shear bands and the formation of the <111> // ND fiber texture – to the alignment of twin-matrix lamellae with rolling plane.

  • Effect of Mn Partitioning during Intercritical Annealing on Following γ→α Transformation and Resultant Mechanical Properties of Cold-rolled Dual Phase Steels

    Yuki Toji, Takako Yamashita, Katsumi Nakajima, Kaneharu Okuda, Hiroshi Matsuda, Kohei Hasegawa, Kazuhiro Seto

    pp. 818-825

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    DOI:10.2355/isijinternational.51.818

    Abstract

    Sequential transformation phenomena of α→γ→α during intercritical annealing and subsequent cooling were investigated to achieve a more advanced control of mechanical properties in a low-carbon cold-rolled DP steel sheet with a chemical composition of 0.13mass%C-1.4mass%Si-2.0mass%Mn. The steel was intercritically annealed at 1073 K for 0–1000 s, then air-cooled to 873–1073 K (quenching start temperature: Tq), followed by water-quenching. The tensile strength increased with an extension of the annealing time, especially at the low Tq, corresponding to the increase in the volume fraction of martensite. This means the γ→α transformation during air-cooling was delayed by extending the annealing time. Microstructural observation and elemental analysis by EPMA indicated that the volume fraction of γ during annealing was almost saturated after annealing for 250 s, whereas the Mn content in γ was still increasing at that time. These results suggest that the retardation of the γ→α transformation during air-cooling by extending the annealing time results from the chemical stabilization of γ by the enrichment of Mn during intercritical annealing. In order to obtain the less scattering of mechanical properties in cold-rolled DP steel sheets, precise microstructural control considering the partitioning of substitutional alloying elements during intercritical annealing is quite important.

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  • On the Precipitation Sequence in a 10%Cr Steel under Tempering

    Nadezhda Dudova, Rustam Kaibyshev

    pp. 826-831

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    DOI:10.2355/isijinternational.51.826

    Abstract

    Precipitation sequence under tempering in a 10%Cr steel has been considered in details. Two different precipitation processes have been identified, concurrently. First, at 350°C, a dispersion of M2C phase with orthorhombic lattice appears. At 525°C, the M2C phase is displaced by the formation of M23C6 carbide. However, this process remains uncompleted. Dissolution of M2C phase occurs completely due to the formation and growth of more stable M6C phase as a result of tempering in the range of 650 to 770°C. Second, Nb-rich and V-rich M(C,N) carbonitrides precipitate in the temperature interval of 500–770°C. These dispersoids play a role of heterogeneous nucleation sites for precipitations of M23C6 and M6C carbides.

  • Effect of Microstructure and Texture on the Edge Formability of Light Gauge Strip Steel

    Andrew Phillips, Harold Kaul, Josh Burg, Chris Killmore, Jim Williams, Peter Campbell, Wal Blejde

    pp. 832-842

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    DOI:10.2355/isijinternational.51.832

    Abstract

    Twin roll casting (TRC) of low-carbon ultra-thin cast strip (UCS) steel has the potential to deliver significant economic advantages over steels made by conventional processes. Novel microstructures containing intragranularly nucleated acicular ferrite may be produced in UCS products manufactured by the CASTRIP®* process, however, their mechanical property performance has yet to be fully evaluated. This study compared the mechanical properties and edge formability of UCS steel produced by the CASTRIP process to steel produced by conventional hot rolled (HR) and cold rolled and continuously annealed (CR & CA) process routes. The results revealed an apparent paradox, where recent UCS steel produced by the CASTRIP process was shown to have lower total tensile elongation values, yet higher edge formability than products manufactured by the conventional process routes. The discrepancy was largely attributable to the influence of acicular ferrite microstructure on steel plasticity. Acicular ferrite decreased macro-plasticity by reducing the contribution of yield point elongation (lower volume fraction of pro-eutectoid ferrite) and post uniform elongation (strain localisation to softer pro-eutectoid ferrite) components of the total tensile elongation value. Conversely, the high homogeneity of the acicular ferrite microstructure enhanced micro-plasticity of the UCS steel produced by improving resistance to void initiation and propagation during forming. This study also showed that plastic anisotropy can significantly influence the edge formability of low-carbon sheet steel, with failure occurring along the direction where the resistance to through thickness thinning was the least.
    * CASTRIP is a registered trademark of Castrip LLC

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  • Evaluation by Sharp Indentation of Anisotropic Plastic Behaviour in Progressively Drawn Pearlitic Steel

    Jesús Toribio, Beatriz González, Juan-Carlos Matos, Viktor Kharin

    pp. 843-848

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    DOI:10.2355/isijinternational.51.843

    Abstract

    This paper analyzes the evolution of Vickers micro-hardness in progressively drawn eutectoid steels focussing the study on the characteristic sections of the wires. The average value of the Vickers micro-hardness was calculated for each section according to its symmetry, thus studying the variation of these values with cold drawing. The indentation marks after the tests demonstrate the anisotropy caused by the cold drawing process itself on the eutectoid steel, and a finite element modelling allows one to finish material characterization.

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  • Strain Localizations in Ultra Low Carbon Steel: Exploring the Role of Dislocations

    R. Khatirkar, K. V. Mani Krishna, L. A. I. Kestens, R. Petrov, P. Pant, I. Samajdar

    pp. 849-856

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    DOI:10.2355/isijinternational.51.849

    Abstract

    Ultra low carbon steel samples were near plane strain deformed at different strains, strain rates and temperatures. Density of grain interior strain localizations in γ (ND//<111>) and θ (ND//<100>) fibres were evaluated against micro-stress estimates through X-ray line profile measurements. The patterns were remarkably different between the fibres. The increase in strain localizations were associated with increased dislocation density. This effect was more pronounced in γ-fibre. In θ-fibre, however, the peaks were increasingly more asymmetric and dislocation substructures were stipulated to have lesser recovery. Discrete dislocation dynamics simulations for single crystal pure iron also brought in different behavior for γ and θ fibres: increase in dislocation density in the former was estimated to be ~5 times more. A combination of textural softening and large/positive increase in dislocation density appears to justify the preference for strain localizations in γ-fibre.

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  • © 2011 The Iron and Steel Institute of Japan

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