ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Volume 35 , Issue 5
Showing 1-15 articles out of 15 articles from the selected issue
  • M. Zamalloa, T. A. Utigard
    1995 Volume 35 Issue 5 Pages 449-457
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The morphological characteristcs of macro and microstructures of commercial cokes were investigated prior to reaction and after reaction with air and CO2 using BET surface area measurements, electron microscopy, and X-ray powder diffraction . The results show that the initial coke morphology is dominated by the type of coking process and by the chemical composition. Upon oxidation, different types of areas accessible for oxidation are developed.
    Download PDF (2128K)
  • M. Zamalloa, D. Ma, T. A. Utigard
    1995 Volume 35 Issue 5 Pages 458-463
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The reaction rates of different sized of commercial cokes with CO2 and air were measured using a combined thermogravimetric and differential thermal analysis technique. The temperature range for air oxidation was varied from 873 to 1073 K, and for the reactions with CO2 it varied from 1173 to 1573 K. The oxidation rates were evaluated on the basis of the percentage weight loss and per unit surface area. Changes in reaction rate were found to depend on changes in the BET surface area.
    Download PDF (981K)
  • C. Diaz, Takashi Iida, Sergey V. Komarov, Masamichi Sano
    1995 Volume 35 Issue 5 Pages 464-471
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The mixing time of a water bath stirred by gas injecton through a rotary lance was measured by an electrical conductivity method. Effects of the gas flow rate, the rotation speed and the bath depth on the mixing time were examined. Measurement of torque produced during the lance rotation was also carried out.
    It is found that the effect of the gas flow rate on the mixing time becomes significant in the deep bath, H, under the low rotation speed, R. In the present experiments, the condition are H/D>0.625 and R<0.33 s-1, where D is the vessel diameter. On the other hand, the effect of the lance rotation is appreciable when the bath is shallow. The torque increases with increasing the rotation speed, whereas the bath depth has no effect on the torque.
    The results are explained in terms of specific powers of the injected gas and the rotary lance. The effects of operating variables on the mixing time are examined quantitatively from the multiple regression analysis.
    Download PDF (1011K)
  • Miao-Yong Zhu, Takeo Inomoto, Ikuo Sawada, Tse-Chiang Hsiao
    1995 Volume 35 Issue 5 Pages 472-479
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Water model experiments and the numerical solution of a mathematical model with three dimensions have been conducted to investigate the flow pattern and mixing phenomena in argon-stirred ladles with six types of tuyere arrangement. It was found that the arrangement of tuyeres has a great effect on the flow patterns and mixing in the ladle, a placement of single tuyere at off-centric position gave the shortest mixing time whereas double tuyeres opposite placed at half radii was found to be the best arrangement considering the aspects of blowing, mixing, inclusion flotation and splashing. An empirical correlation for mixing time in the ladle considering the number of tuyeres was proposed. The predicted and measured results showed quantitatively good agreements.
    Download PDF (1310K)
  • Kwang Ro Lee, Hideaki Suito
    1995 Volume 35 Issue 5 Pages 480-487
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Reoxidation of aluminum in liquid iron containing 00.6 mass%Te with the CaO-Al2O3-FetO (≤3 mass%) slags was studied at 1873 K in an Al2O3 or CaO crucible. After reoxidation for 5 and 60 min, the contents of acid-insoluble aluminum, total oxygen and FetO were obtained as a function of total aluminum content. The relations between FetO and Al contents were observed to be in equilibrium in the experiments except those for the CaO-Al2O3 slags in an Al2O3 crucible at 5 min. The oxygen content in liquid iron for a given Al level was found to be higher than the equilibrium value in the rapid cooling experiments except those for the CaO-Al2O3 crucible at 60 min with Te addition.
    Download PDF (1230K)
  • Makoto Kobashi, Susumu Kuno, Takao Choh, Takao Shimizu
    1995 Volume 35 Issue 5 Pages 488-493
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Measurements of the contact angle of molten aluminum alloys (Al-Mg, Al-Cu and Al-Si alloys) on solid iron substrate have been carried out aiming at developing a filler sheet for a welding between iron and aluminum. The wettability was estimated by a sessile drop method. The contact angle of molten aluminum drop was measured at 773 and 893 K. Magnesium alloying decreases the contact angle of molten aluminum drop because an evaporation of magnesium prevents a formation of a thin oxide layer at the surface of the molten drop. Since the vapor pressures of these elements at an experimental temperature are much lower than that of magnesium, neither silicon nor copper alloying contributes to improving a wettability on a given experimental condition (T=893 K, P=1.33×10-3 Pa). A minute quantity of surface active elements such as bismuth, lead and lithium was added with a view to decreasing the surface tension of molten aluminum alloys. A 0.05 mass% addition of bismuth decreases the contact angle most effectively. An excessive addition, however, results in increasing the contact angle. The effect of bismuth addition is more significant at lower temperatures than at higher temperatures.
    Download PDF (865K)
  • C. S. Lin, M. Meshii, C. C. Cheng
    1995 Volume 35 Issue 5 Pages 494-502
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    A technique has been developed so that a number of cross sections of galvanneal coatings can be examined efficiently and reproducibly by transmission electron microscopy, and applied to study the microstructures of a series of simulator-made galvanneal coatings on interstitial-free (IF) interstitial-free rephosphorized (IFP) steel sheets. It is demonstrated in this report that all intermetallic phases observed have been unambiguously identified by electron diffraction and that each intermetallic phase is associated with characteristic microstructure. It is possible to establish a microstructural atlas which enables one to make quick and ready identification of phases only from the appearance in TEM. The present study has clarified several unresolved questions regarding the microstructure and phases of galvanneal coatings, including the existence of the Γ1 phase, clear-cut interface between Γ and Γ1 phases, a layer of single Γ1 phase, and a layer of a mixture of the Γ1 and δ phases. The grain structures of the Fe-Zn intermetallic phases formed by hot-dip galvannealing are compared with those formed by annealing of Fe-Zn diffusion couple and those by electrodeposition.
    Download PDF (1911K)
  • C. S. Lin, M. Meshii, C. C. Cheng
    1995 Volume 35 Issue 5 Pages 503-511
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The evolution of the phases in galvanneal coatings on IF and IFP steel sheets is studied by combining optical microscopy (OM), scanning electron microscopy (SEM) with X-ray microanalysis (EDS) and transmission electron microscopy (TEM). The early stage of galvannealing is dominated by the formation of intermetallic compounds, particularly δ phase by constitutional supercooling except the region near the steel substrate where rapid formation of a thin alloy layer, the nature of which depends strongly on surface segregation of minor elements such as phophorus in a steel substrate. The Γ phase, which shows a well-defined columnar structure, grows at the expense of the Γ1 phase. The thickness of the Γ1 phase decreases, while maintaining the total thickness of (Γ+Γ1) constant, 2 μm, during galvannealing, Three different grain morphologies of δ phase have been observed. The surface segregation of phosphorus in steel was found to promote the nucleation of the Γ1 phase at the solid-liquid interface in the very beginning of galvannealing. The formation of the Γ phase was retarded accordingly. The hot-dip simulator was found to reproduce the microstructures of galvanneal coatings obtained by the in-line production and to facilitate the investigation of the phase evolution during hot-dip galvanizing and galvannealing.
    Download PDF (2321K)
  • Shigeo Matsubara, Tatsuhiro Tsutae, Kazunari Nakamoto, Yusuke Hirose, ...
    1995 Volume 35 Issue 5 Pages 512-518
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Control of the dissolved aluminum concentration in a hot dip galvanizing bath is of great importance for producing galvannealed steel sheets. Since aluminum has much greater affinity for oxygen than zinc, the oxygen potential of Zn-Al-O bath may be determined only by the following equilibrium reaction; Al2O3(s)=2Al(in Zn)+3O(in Zn) when the aluminum concentration in the bath is relatively low. Aluminum sensor based on the emf method using the zirconia solid electrolyte has been devised by utilizing the above equilibrium relation.
    In this paper, emf measurements have been carried out in Zn-Al-O baths having aluminum concentration of 0.02-0.50 mass% under an air atmosphere by using some of the most appropriate combinations of zirconia solid electrolyte and liquid reference electrode for Zn-O baths.
    From the analysis of such emf values at temperatures between 450-500°C, the following relationships between aluminum concentration and cell emf for two reference electrodes were obtained;
    E/mV=57.19 ln[Al]/mass%+506.4, 0.02≤[Al]/mass%≤0.30 (In-In2O3 as ref. electrode)
    E/mV=68.27 ln[Al]/mass%+270.4, 0.05≤[Al]/mass%≤>0.20 (Zn-ZnO as ref. electrode)
    The external AC voltage applied on these sensors immediately after immersion into the bath showed to be effective to their responsibility and stability. The emf measurements were also carried out in Zn-Mn-O and Zn-Cr-O baths, respectively, and it has been ascertained that the sensors work much better in these baths, even though the partial oxygen pressure PO2 of the bath is as low as 10-40 Pa at 450°C. The posssibility of the present aluminum sensor has been ascertained experimentally.
    Download PDF (1087K)
  • Takumi Haruna, Toshio Shibata
    1995 Volume 35 Issue 5 Pages 519-523
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The amount of defects in TiN films coated on SUS304 stainless steel has been evaluated by three electrochemical measuring techniques in a sulfuric acid solution containing potassium thiocyanate. Three different TiN films were prepared by a hollow cathode ion plating technique. A critical passivation current density (icrit) can readily provide the apparent amount of the defects. However, this method was found to overestimate the amount of the defects because active dissolution of the substrate at the measurement caused enlargement of the defects. An activation time, which is a period until free corrosion potential (Ecorr) descends to that of the bare substrate steel, was not useful to evaluate the amount of defects rapidly because about a half the specimens did not activate within a test time of 90 ks. More precise and less destructive evaluation could be achieved by using a reciprocal of polarization resistance (RP-1) which was obtained by an electrochemical impedance spectroscopy immediately after activation. It is concluded that icrit is a suitable parameter for an approximate estimation of the defect area, and RP-1 amount of the original defects.
    Download PDF (723K)
  • Kiyoshi Kusabiraki, Shin-ichi Araie, Itaru Hayakawa, Takayuki Ooka
    1995 Volume 35 Issue 5 Pages 524-530
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The precipitation and growth behaviors of δ phase in Ni-base superalloy, modified Inconel X-750 type alloy (X-750M), were investigated mainly by optical and transmission electron microscopy. The strengthening phase in the aged X-750M was metastable γ" phase. The γ" phase changed gradually into the stable δ phase during aging. The orientation relationship between γ and δ phase in the cellular and the Widmanstätten precipitates was: {111}γ//(010)δ, <110>γ//[100]δ. The interlamellar spacing of the δ phase in each recipitation type was inversely proportional to the degree of undercooling below the equilibrium transformation temperature of γ phase to δ+γ phases. According to the theory of diffusion controlled eutectoidal growth, the equilibrium transformation temperatures of the cellular and the Widmanstätten precipitation were estimated to be 1279 and 1313K, respectively. These temperatures were consistent with the experimental tendency.
    Download PDF (1844K)
  • M. Pietrzyk, C. Roucoules, P. D. Hodgson
    1995 Volume 35 Issue 5 Pages 531-541
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    A simple approach to calculate rolling loads based on Sims' model was compared to a finite element model (FEM) using the same constitutive law and recrystallization equations. The comparison was done with a Nb microalloyed steel using a laboratory rolling simulation of plate and strip mill rolling schedules. The FEM model accurately predicted the temperature, the change in rolling loads, and the evolution of microstructure before and after transformation. These results clarified the accuracy of carious microstructure models, particularly the model for recrystallization. The FEM model gave an improved prediction of the rolling loads slightly compared with the slab method. For on-line modelling of the rolling loads a simpler approach based on Sims model gave acceptable prediction when using an accurate temperature model to predict the average temperature throughout the rolling process. The combination of the constitutive law and recrystallization kinetics in both cases enabled the prediction of the increase in rolling loads over the entire temperature range. The results also suggest that solute drag, rather than strain induced precipitation, has the primary effect on retarding recrystallization under the conditions examined.
    Download PDF (1728K)
  • Kiyoshi Kusabiraki, Yushin Takasawa, Takayuki Ooka
    1995 Volume 35 Issue 5 Pages 542-547
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The nucleation and growth behavior of γ' and η precipitates in A286 alloy was investigated by micro-Vickers hardness test and transmission electron microscopy. The morphology and the crystallography of them were also discussed. The hardness of A286 aged at 893-1073 K for durations up to 720 ks was closely related to the mean size of γ' precipitates. The growth kinetic of the γ' precipitate in η-phase free region was explained by Lifshitz-Slyozov-Wagner's theory for diffusion controlled growth at 993-1073 K. The activation energy for the growth of the γ' precipitates was estimated to be 283 kJ/mol.
    Download PDF (1488K)
  • Toshiro Tomida, Takashi Tanaka
    1995 Volume 35 Issue 5 Pages 548-556
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    An investigation has been made to develop (100) textures in silicon steel sheets utilizing isothermal austenite (γ)→α-ferrite(α) transformation and related processes. 2% silicon steel sheets containing 1% of manganese and 0.1% of carbon were vacuum-annealed and subsequently decarburized in a wet hydrogen-argon gas mixture. During the vacuum-annealig at the α/γ duplex or γ phase temperatures from 900 to 1050°C, a thin layer just below the sheet surface transforms to α, and strong (100) texture develops in the layer. By the subsequent decarburization, the grains within the layer grow inward as columnar grains retaining the texture. The decarburized material with the columnar grain structure exhibits excellent softmagnetic properties. The γ→α transformation occurring near the surface is due to the removal of manganese during the vacuum-annealing, and the selective driving force for forming the strong (100) texture is thought to reside in the anisotropy of surface energy.
    Download PDF (2051K)
  • E. M. L. E. M. Jackson, R. Paton
    1995 Volume 35 Issue 5 Pages 557-563
    Published: May 15, 1995
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    For the purpose of further increasing toughness, the influence of manganese contents up to 4% was investigated in a 4% vanadium-bearing experimental ferritic stainless steel. The tensile and formability properties were also studied. The corrosion properties were measured using electrochemical techniques in 1 N H2SO4 and 3.5% NaCl solutions.
    No marked effect was found on the tensile and formability properties. In contrast, mangenese has a strong detrimental effect on the general and localized corrosion properties of this 4% vanadium alloy. The passivation characteristics in normal sulphuric acid are much poorer. However, spontaneous passivation occurs in this environment where the manganese content is 0.1%. Similarly, the propensity to pitting corrosion is greatly improved at low manganese Ievels, with pitting potentials superior to both type 304 and 316L stainless steels.
    Download PDF (1361K)
feedback
Top