Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 95 (2009), No. 1

  • Fabrication of Porous Solidified Materials from Blast Furnace Slag Using Hydrothermal Hot-pressing Method and Measurement of Thermal Conductivity of Solidified Materials

    pp. 1-6

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    DOI:10.2355/tetsutohagane.95.1

    To produce insulating construction materials using hydrothermal reaction from blast furnace slag (BF slag) such as air-cooled, air granulated, and water-cooled slags, we investigated the fabrication of porous solidified materials from BF slag by a hydrothermal hot-pressing method. The thermal conductivity of the solidified materials was also investigated. The experimental conditions were; hydrothermal holding time from 0 to 120 min, hydrothermal temperature from 250 to 350°C, hydrothermal pressure from 20 to 80 MPa, and slag powder sizes less than 15 μm, 39±24 μm, 84±21 μm, 178±72 μm, 375±125 μm and more than 500 μm. It was found that growth of the hydrothermally reacted phase led to a higher density and higher thermal conductivity of the solidified materials. It was noteworthy that the thermal conductivity of the hydrothermal solidified materials became smaller when the size of the slag powder was larger. This was because the more porous structure introduced into the solidified materials resulted in a lower density of the solidified materials. It was also found that glassy slag such as water-cooled and air granulated slags can be solidified even if the size of the slag powder was more than 500 μm.
  • Development of Cellular Automaton Method for Simulating the Coke Gasification in a Pore

    pp. 7-16

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    DOI:10.2355/tetsutohagane.95.7

    The gasification reaction of coke in a pore was simulated using a cellular automaton method, which was mainly used for the simulation of solidification of steel. It was an adequate method for simulating the phenomenon that the reaction interface was changed with time.
    Using the developed cellular automaton simulation program, the gasification in a pore of coke was simulated.
    The simulation conditions were from 1000 to 1400 K for the two kind of pore diameter, 500 μm and 50 μm. Based on the Chapman–Enskog equation and the experimental result of Shigeno, et al., the diffusion coefficient was estimated for two kinds of cokes (m-coke and f-coke). The rate constants for gasification reaction were used on the basis of the results of Kashiwaya, et al.
    The chemical reaction control was dominant in the pore of 500 μm below 1200 K for m-coke and the diffusion control was over 1400 K. For f-coke, it could be considered as the mixed control in the pore of 50 μm from 1000 to 1400 K, which would be changed from the calculation condition such as a depth of pore, while it was obviously decided as the diffusion control over 1400 K.
  • Measurement of Effective Diffusivity for CO–CO2 Gas Mixture in Hot Briquetting Carbon Composite Iron Ore by Wicke–Kallenbach Method

    pp. 17-21

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    DOI:10.2355/tetsutohagane.95.17

    Effective diffusivity for CO–CO2 gas mixture in Hot Briquetting Carbon Composite Iron Ore (CCB) at a temperature range of room temperature to 673 K was measured by Wicke–Kallenbach Method. The results obtained are summarized as follows;
    (1) Effective diffusivity of CO–CO2 gas mixture through CCB increased with increasing temperature and fractional reaction of CCB. The effective diffusivity for CO–CO2 system in CCB was proportional to the 1.50 power of temperature.
    (2) Kundsen diffusion and surface diffusion are negligible in regard to diffusions of CO and CO2 in CO–CO2 gas mixture in CCB. Therefore, diffusions of CO and CO2 in CO–CO2 gas mixture in CCB are described by molecular diffusion.
  • Dendrite Growth of Silicon along the Undercooled Melt Surface of Si–45mass%Ni Alloy

    pp. 22-25

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    DOI:10.2355/tetsutohagane.95.22

    Dendrite growth of silicon from the undercooled melt of Si–45mass%Ni alloy was investigated. The dendrite growing along the melt surface was in-situ observed. By changing the cooling rate of the samples, the undercooling was varied from 6.7 to 18.8 K, and the growth velocity of dendrites was measured for different undercooling conditions. Both rod- and wedge-type dendrites grew in a sample, and the growth velocity of the former was slightly larger than that of the latter. Phase-field simulations were carried out in order to estimate the dendrite growth velocity at small undercooling. As the simulations at the undercooling corresponding to experiments were difficult because of the limitation of computational time, the extrapolated values of simulation results were compared with experiments, and both were in good agreement.
  • Critical Conditions for the Formation of A-segregation in 9Cr1Mo Steels

    pp. 26-32

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    DOI:10.2355/tetsutohagane.95.26

    Laboratory scale casting experiment in 9Cr1Mo steel of 20 kg in mass was carried out and critical conditions for the formation of A-segregation was investigated. Critical values of cooling and solidification rates of the casing for the formation of A-segregation were evaluated based on the thermal analysis and metallographic examination. The influence of the addition of Mo, V and W on the formation of A-segregation was examined and it was shown that A-segregation was reduced in order of V, Mo and W addition. Phase-field simulations were carried out for the evolution of dendrite in Fe–C–V, Fe–C–Mo and Fe–C–W ternary alloys. It was shown that the effect of the adding elements on the promotion of the branching of dendrite is in order of V, Mo and W. Based on the simulation results, dendrite morphology becomes finer in V addition, then interdendritic fluidity decreased and the formation of A-segregation was suppressed.
  • Development of Swirling Flow Submerged Entry Nozzles for Slab Casting

    pp. 33-42

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    DOI:10.2355/tetsutohagane.95.33

    We have started a development of swirling flow submerged entry nozzles in 1997 as a fundamental and effective measure for controlling flow pattern in continuous casting molds.
    As a first step, we have developed a swirling flow submerged entry nozzle for round billet casting in Wakayama works. Then we started the development of swirling flow submerged entry nozzles for slab casting. A main purpose of our development was to prove the effect of the swirling flow formation in submerged entry nozzles which improve quality of products and productivity of continuous casting processes. We have examined swirling flow submerged entry nozzles with swirl blade in these main bodies, because that was the easiest way to apply swirling flow to submerged entry nozzles in continuous casters without any investment of facilities. We had only to change a submerged entry nozzle for the experiment.
    Swirling flow submerged entry nozzles for slab casting have been developed and examined in Wakayama and Kashima works. As a result of these examinations, the effect of the swirling flow formation in submerged entry nozzles was evaluated to increase casting speed and improve surface quality of slabs and steel sheets.
  • Development of Walking Control Technology in Hot Strip Rolling

    pp. 43-50

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    DOI:10.2355/tetsutohagane.95.43

    This paper describes walking control suppressing the lateral unstable movement of the strip in a hot strip finishing mill. The conventional method for controlling walking is well known as “load difference method”, in which the measured load difference between the drive and operator sides of the rolling stand is fed back to the roll gap slant reference. However, analyzing the relationship between the feedback control gains of load difference and control effects, we found that the conventional method had a defect that the control effect extremely decreased, as the strip width became wide. Therefore, we developed a new control method that the manipulated value of the roll gap slant was determined based on the strip position measured by a newly developed measuring instrument. In this method, because the strip position sensor is equipped at the entry side of the controlled rolling stand with some distance, the measured strip position is not equal to that at the rolling stand, which is the controlled variable. We overcome the difficulty by applying the model predictive control having the function to predict a future value of the controlled variable and optimizing the manipulated value of the roll gap slant. The effectiveness of the new control method has been demonstrated in an actual plant.
  • Development of the Acid Soluble Components and Acid Insoluble Inclusions State Analysis Using Pulse Height Sorting (PSA) Graph in Spark OES Analysis

    pp. 51-58

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    DOI:10.2355/tetsutohagane.95.51

    The spark electric discharge optical emission spectrometry has been widely applied to a rapid multielemental analysis of acid soluble elements and insoluble inclusions separately in several minutes in the field of molten steel making processes. In this study, we propose new state analysis method for acid soluble components and acid insoluble inclusions contained in a steel sample during the spark discharge. The developed new method includes the statistical processing of the emission intensity for every pulse during performing spark electric discharge to create a PSA (Pulse Sorting Analysis) graph, in which amounts of emission intensities are sorted on the abscissa according to the pulse height. It was found that multiplying the number of pulses by the 50% intermediate order height gives the representation of Total (acid soluble+insoluble components), subtract total volume from all integral area gives the acid insoluble inclusions volume (Insol.) and subtract acid insoluble inclusions volume from Total volume gives the acid soluble volume (Sol.). These findings led us a more accurate analysis value and expand the application range of insoluble inclusions volume percent at spark discharge analysis.
  • Separation and Preconcentration of Trace Amounts of Lead in Iron-digested Solution by Ion-exchange Adsorption/Ion-pair Elution Followed by Graphite Furnace Atomic Absorption Spectrometric Determination

    pp. 59-64

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    DOI:10.2355/tetsutohagane.95.59

    Trace amounts of lead(II) in an iron-digested solution was derived to anionic iodo complex prior to being preconcentrated and separated from iron matrices by an ion-exchange adsorption/ion-pair elution method. Anionic lead(II)–iodo complex adsorbed on cotton impregnated with capriquat through ion-exchange interaction. The adsorbed lead(II)–iodo complexes could be eluted with methanol so as to be analyzed by graphite furnace atomic absorption spectrometry (GF-AAS). Iron matrices in the digested solution did not adsorb on the anion-exchanging cotton to be separated from lead(II) since iron ions reduced by iodide ion did not form stable anionic iodo complex. Satisfactory separation (more than 99.99%) of iron matrices and quantitative recovery of lead(II) could be achieved with the proposed preconcentration method. GF-AAS exhibited an excellent compatibility with the concentrate in analyzing lead(II) because GF-AAS can remove capriquat and iodide ion in the concentrate at a chirring stage. With 5-fold preconcentration GFAAS measurement allowed to determine trace amounts of lead in a digested solution of iron with a detection limit (3σ) of 5.3×10−9 mol/L, which corresponds to 0.11 μg/g in iron and steel. Lead contents in certified reference materials of iron and steel were successfully determined by GF-AAS combined with the proposed method.
  • Microscopic Observation of Inclusions Related to Microstructure Evolution in Low Carbon Steel Ti–B Weld Metal

    pp. 65-70

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    DOI:10.2355/tetsutohagane.95.65

    Microstructures of low carbon submerged arc weld metals of a Ti–B system with different aluminum contents were analyzed. The inclusions contributing to formation of acicular ferrite were directly sliced into thin foils and crystallographic analyses were performed.
    In the sample with low Al/O ratio (0.48–0.73), acicular ferrite microstructure was observed. Meanwhile, bainite microstructure was observed in the specimen with an Al/O ratio of 1.52. The inclusions contributing to formation of acicular ferrite were surrounded by a narrow Ti-enriched zone which was analyzed as TiO. The Baker–Nutting orientation relationship was satisfied between the TiO and acicular ferrite. It was supposed that the TiO on the inclusion surface contributes to the heterogeneous nucleation of acicular ferrite supplying low interface energy.
  • Ductile-to-brittle Transition in a Bimodal-sized Grain Structure for an Ultrafine-grained Ferrite/Cementite Steel

    pp. 71-78

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    DOI:10.2355/tetsutohagane.95.71

    A bimodal-sized microstructure lied in ultrafine-grained ferrite/cementite steel fabricated through caliber-warm-rolling followed by annealing. The ferrite grain size distribution had a bimodal distribution consisting of two peaks, a large peak and a small peak. A distinct absorbed energy transition or ductile-to-brittle transition occurred in Charpy impact tests. The ductile-to-brittle transition was due to the intrusion of cleavage. The transition shifted to higher temperature region with an increase in average gain size for the larger grain peak, with a simultaneous change in effective grain size on fracture surface. The effective grain size apparently corresponded to the grain size of a larger grain peak of the bimodal grain size distribution. More precisely, the effective grain size was found to better correspond to the larger peak of the bimodal distribution of grains with {100} planes almost parallel to the fracture plane. Fracture stress estimated became higher with a decrease in effective grain size. Namely the ultra-refinement of ferrite grain size could bring about the high fracture stress and contribute to an excellent toughness even for the bimodal-sized structure.
  • Effect of Various Factors on Fatigue Properties of Nitrided Ultrafine Ferrite-Cementite Steels

    pp. 79-85

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    DOI:10.2355/tetsutohagane.95.79

    Rotating bending fatigue tests were conducted for a series of plasma-nitrided ultrafine ferrite-cementite steels 5 types of the ultrafine ferrite–cementite steels, i.e., 15C, 45C, 15C-P, 45C-P and low-Mn, were prepared with a double-melting method to improve their cleanliness. 15C and 45C contained 0.15 and 0.45 mass% of carbon, respectively. 15C-P and 45C-P were 0.1 mass% phosphorus-added versions of them. Low-Mn was a Mn-decreased version of 45C. All of the nitrided specimens had a hardened layer of 1 mm in depth, while the amount of hardening was small in low-Mn. In case of 15C and 15C-P, the hardness beneath the hardened layer largely fell due to grain growth during the nitriding, in contrast to 45C and 45C-P in which the grain growth was successfully suppressed. In the fatigue tests, due to the cleanliness improvement, inclusions never caused fish-eye fracture even in the nitrided specimens. Although the local stress amplitudes beneath the hardened layer exceeded the fatigue limit expected from the local hardness, the nitrided specimens showed surface fracture only. The fatigue strength improvements due to the nitriding were larger in 45C and 45C-P than 15C-P, and those improvements in 15C and low-Mn were negligible. These results meant that C-increase and P-addition improved the surface fracture properties. The results of low-Mn demonstrated that the hardened layers of the nitrided specimens were strengthened by Mn nitrides.
  • Production of Fine Iron Ingot Using Iron Sand and Charcoal Powder by Microwave Heating

    pp. 86-95

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    DOI:10.2355/tetsutohagane.95.86

    The fine iron ingot was developed by the microwave oven heating using the iron sand and the charcoal powder. In the initial stage in which the heating time was 3–6 min, the iron sand changed into the lump consisting of Fe, FeO, Fe2TiO4 and Fe2SiO4. By further increasing the heating time, the iron ingot with a smooth surface and a metallic luster was formed, since the fine Fe particles in the lump aggregated and the Fe particles separated from the other constituent phases. The yield on the iron ingot formed from the iron sand was almost 50 mass%, irrespective of the weight of the iron sand. It is also found that the microstructure in the fine iron ingot changed by the microwave heating time, from the cementite and the pearlite, through the graphite and the pearlite, to the cementite and the pearlite. This suggests that the carbon content in the fine iron ingot increased by the carburization, when the fine iron ingot was just formed. However, the carbon content decreased by the decarburizing reactions with increasing the heating time, since the charcoal powder decreased, and the contact with the charcoal powder was inhibited by the slag.
  • In-use Stock of Steel Estimated by Top-down Approach and Bottom-up Approach

    pp. 96-101

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    DOI:10.2355/tetsutohagane.95.96

    Recently, prices of natural resources have rapidly risen, so recovery of materials from the end-of-life products as secondary resources is of great interest. However, it is generally a challenging task to estimate the in-use stock of materials, especially in developing countries, because of lack of data. In this paper, two approaches, a top-down approach and a bottom-up approach, were adopted for estimating the in-use steel stock in end uses. A top-down approach uses time-series data of consumption and trade of materials and product lifetime data, whereas a bottom-up approach uses the numbers of units of a specified product in a designated area and its material intensities. In this paper, the steel stock in Japan divided into six end uses was estimated by the top-down approach. The steel in-use stock in Japan was estimated as approximately 1,000 Tg in 2005. Steel stock in automobiles in 2005 was estimated as 105 Tg by the bottom-up approach and compared with that estimated as 125 Tg by the top-down approach. In addition, applying the bottom-up approach, steel stock used in automobiles in U.S. was estimated and compared with that obtained by the previous research using a top-down approach. Steel stock used in automobiles in 2000 in U.S. was estimated as 480–870 Tg by the top-down approach and 754–767 Tg by the bottom-up approach. Both approaches have some uncertainties in the parameters used in the estimation. Therefore, complementary use of the two approaches is helpful to estimate in-use stock of materials.

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