Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
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Volume 93, Issue 6
Displaying 1-10 of 10 articles from this issue
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Fundamentals of High Temperature Processes
Regular Article
  • Effects of Alloying Elements on High Temperature Oxidation of 42% Ni Iron-based Alloy
    Tadashi INOUE, Akio KOBAYASHI, Katsuhisa YAMAUCHI, Yoshihiro HOSOYA
    2007 Volume 93 Issue 6 Pages 409-415
    Published: June 01, 2007
    Released on J-STAGE: January 30, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane.93.409
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    The effects of alloying elements on the high temperature oxidation of laboratory melted 42% Ni iron-based alloy were investigated. A mechanism controlling the high temperature oxidation of 42% Ni alloy has been also discussed.
    In the temperature range between 1000°C and 1200°C, scale, intraglanular oxidation layer and intergranular oxidation layer progressed. Addition of Cr was effective on reducing the oxide layers while addition of C and Mn didn't reduce the oxide layers markedly.
    It was suggested by energy dispersive X-ray spectroscopy that oxidation layers were formed mainly by the selective-oxidation of Fe in 42% Ni alloy. The mechanism of reducing the oxide layers of 42% Ni alloy by the addition of Cr was thought to be attributed to the formation of Cr-oxide and Ni-oxide in which diffusion coefficients of metallic ion are very low value.
    Marker test also revealed that the scale forming was controlled by the outer diffusion of metallic ion through the scale.
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  • Thermal Conductivity Measurements and Prediction for R2O-CaO-SiO2 (R=Li, Na, K) Slags
    Sumito OZAWA, Rie ENDO, Masahiro SUSA
    2007 Volume 93 Issue 6 Pages 416-423
    Published: June 01, 2007
    Released on J-STAGE: January 30, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane.93.416
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    Thermal conductivities of Li2O-CaO-SiO2, K2O-CaO-SiO2 and 37CaO-63SiO2 slags have been determined using the non-stationary hot wire method over a wide temperature range between room temperature and 1823K to propose a prediction equation for thermal conductivities of R2O-CaO-SiO2 slag melts, where R represents Li, Na and K. The temperature coefficients of thermal conductivities for all the samples were negative in the liquid state. The thermal conductivities of slags having the same SiO2 concentration, i.e., the same NBO/T (number of non-briging oxygens per tetrahedrally coordinated atom), decreased by replacement of CaO with R2O but took almost the same value at their liquidus temperatures (TL), irrespective of the (%R2O)/(%CaO) ratio. Furthermore, plotting the thermal conductivities against T/TL (temperature normalised by TL) shows that the thermal conductivities for the melts are not dependent upon the (%R2O)/(%CaO) ratio within experimental scatter as long as the SiO2 concentration is kept constant. On the basis of this finding, an empirical prediction equation has been proposed for thermal conductivities of R2O-CaO-SiO2 melts.
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  • Chlorination and Evaporation Behaviors of PbO-PbCl2 System in Ar-Cl2-O2 Atmosphere
    Hiroyuki MATSUURA, Fumitaka TSUKIHASHI
    2007 Volume 93 Issue 6 Pages 424-433
    Published: June 01, 2007
    Released on J-STAGE: January 30, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane.93.424
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    It is quite important to know the reactivity and behavior of Pb contained in steelmaking dust, or bottom ash and fly ash generated from municipal solid waste incineration process with chlorine. In the present study, chlorination and evaporation kinetics of PbO-PbCl2 melt have been investigated in Ar-Cl2-O2 atmosphere from 1023 to 1123K. The weight of PbO specimen increased first and then decreased in Ar-Cl2-O2 stream during experiments, which phenomena mean that produced PbCl2 by PbO chlorination formed liquid oxychloride phase of PbO-PbCl2 system and then PbCl2 evaporated. Increase of partial pressure of chlorine increased the initial chlorination rate, however no effect on the latter evaporation rate was observed. Decrease of maximal weight gain of specimen and the slight increase of evaporation rate were observed with increasing partial pressure of oxygen. Apparent activation energies of chlorination and evaporation of PbO-PbCl2 melt in the steady state were 35 kJ/mol and 156 kJ/mol, respectively. Evaporation rate of PbO-PbCl2 was also investigated at 1073K in Ar-O2 atmosphere, however the change of evaporation rate with changing partial pressure of oxygen was within experimental error. Measured evaporation rate strongly depended on the composition of melt. Composition dependency of evaporation rate estimated from the activity of PbCl2 for the PbO-PbCl2 system generally represented the same trend, however the measured evaporation rate was larger than estimated one in the whole composition range. This result indicates that the formation of oxychloride melt affects the evaporation rate. Chlorination mechanisms and removal efficiency of Pb by chlorination have been discussed based on the present results.
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  • Crystal Alignment of Sn-Pb Alloy by Controlled Imposition of a Static Magnetic Field and an Alternating Electric Current during Solidification
    Manabu USUI, Kazuhiko IWAI, Shigeo ASAI
    2007 Volume 93 Issue 6 Pages 434-437
    Published: June 01, 2007
    Released on J-STAGE: January 30, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane.93.434
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    In this study, a new process for a crystal alignment of an alloy during solidification has been proposed in which the imposing periods of a static magnetic field and an alternating current are controlled. In the initial stage of the solidification both the magnetic and electric fields are imposed on the alloy to break dendrites into pieces and to spread them to the whole area of the sample. In the next stage, only the static magnetic field was applied for the sample. The function of the static magnetic field in this stage is not only the rotation of the crystals to magnetically stable direction but also the suppression of the disturbance such as liquid motion. The principle of this process was experimentally confirmed by using a Sn-10mass%Pb alloy. In the X-ray diffraction pattern of the sample solidified without the static magnetic field, the first and second highest peaks were (101)-plane and (200)-plane. That is, the crystal direction is random. On the other hand, only the peaks corresponding to a,b-plane were observed in the sample solidified under the imposition of the controlled electromagnetic field. Therefore, this process is useful for the crystal alignment of alloy.
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Note
Ironmaking
Regular Article
  • Influence of Inert Materials on Contractile Behavior and Fissure Formation of Coke
    Kiyoshi FUKADA, Tetsuya YAMAMOTO, Izumi SHIMOYAMA, Takashi ANYASHIKI, ...
    2007 Volume 93 Issue 6 Pages 438-444
    Published: June 01, 2007
    Released on J-STAGE: January 30, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane.93.438
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    Inert materials such as coke breeze have a great influence on the contractile and fissure formation behavior of the coke cake as well as coke quality. Firstly, the contraction coefficient and Young's modulus of semi-cokes, which were produced with the different blending conditions of inert materials, inert brand, grain size and blending ratio, were measured. And then coke shrinkage and fissure formation in coke oven were evaluated by the carbonization test and a mathematical simulation model.
    Due to the inert materials, micro cracks are generated inside the coke and contraction coefficient and Young's modulus decrease. Inert type, grain size and blending ratio affect the contraction coefficient curve and shrinkage ratio declines with the increase of the difference between coal and inert contraction coefficient, grain size and addition ratio. The existence of inert material also has an important effect on the coke cake structure. Clearance enlarges with the increase of inert size to around 0.30-0.50 mm, but further size increase gives negative effect to clearance. It is considered that the decrease in macro fissure becomes smaller than the increase in micro crack with the rise of inert size.
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Surface Treatment and Corrosion
Regular Article
Transformations and Microstructures
Regular Article
  • Effect of Niobium or Vanadium on Mechanical Properties of Hot Rolled High Strength Steel Sheets for Automotive Use
    Daisuke KONDO, Kazutoshi KUNISHIGE, Rintaro UEJI, Shunichi HASHIMOTO
    2007 Volume 93 Issue 6 Pages 451-458
    Published: June 01, 2007
    Released on J-STAGE: January 30, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane.93.451
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    Nb-bearing and V-bearing steels have been well known as typical high-strength low-alloy (HSLA) steels. However, little comparison has been made so far between the formability of Nb-bearing steels and that of V-bearing steels for automotive use. The hot direct rolling (HDR) process has been noticed because it is a very energy saving process. This paper aims to clarify the differences between the formability of Nb-bearing hot-rolled steel sheets and that of V-bearing hot-rolled steel sheets produced by both HDR process and cold charge rolling (CCR) process. A low temperature (450°C) simulated coiling characterized by good formability of steels was applied in a laboratory to 0.025% Nb (25 Nb), 0.049% Nb (50 Nb) and 0.078% V (80 V) steels with the ultimate tensile strengths (TS) ranging from 490 to 590 MPa. Hole expansion test was carried out in addition to the tensile test because stretch flangeability is very important for automobile structural uses. As a result, TS-flangeability balance of Nb-bearing steels was found to be superior to that of V-bearing steel. This is because their microstructures were distinctly different: Nb-bearing steels had a ferrite+bainite microstructure and V-bearing steel had a ferrite+fine pearlite microstructure. For the linearly precipitated carbides, V-bearing steel had a low TS-flangeability balance. It was concluded that Nb-bearing steels is strengthened by ferrite grain refining and bainite transformation hardening rather than precipitation hardening, which is the main strengthening mechanism for V-bearing steels. Change from CCR to HDR increased the strengths of all the steels studied, resulting in nearly the same TS-elongation and TS-uniform elongation balances, but the TS-flangeability balance was still maintained through this change.
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  • Yielding Behavior and Change in Dislocation Substructure in an UltraLow Carbon Martensitic Steel
    Koichi NAKASHIMA, Yoshitomo FUJIMURA, Hiroyasu MATSUBAYASHI, Toshihiro ...
    2007 Volume 93 Issue 6 Pages 459-465
    Published: June 01, 2007
    Released on J-STAGE: January 30, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane.93.459
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    As-quenched martensitic steels exhibit a unique yielding behavior characterized by very low elastic limit. This phenomenon deeply relates to the behavior of mobile dislocations which have been introduced by martensitic transformation. In order to clarify the effect of mobile dislocations on the yielding behavior of martensitic steels, tensile testing, measurement of dislocation density by X-ray diffractometry and TEM observation were carried out in an ultralow carbon martensite (Fe-18% Ni alloy). And then the effect of dislocation strengthening on the yield stress was also discussed in terms of Bailey-Hirsch relationship. Elastic limit and 0.2% proof stress are very low in the as-quenched martensite, however slight pre-straining to the martensite has caused a marked increase in the both properties despite of a significant decrease in dislocation density. It is also confirmed that slight pre-straining to the martensite causes a clear microstructural change from randomly distributed dislocations to cellar tangled dislocations. These results suggest that mobile dislocations in martensite can easily disappear through the dislocation reaction and remained dislocations form cellar tangled structure in the early stage of tensile deformation. The Bailey-Hirsch plot for 0.2% proof stress indicated that the data of pre-strained martensite are just on the line extended from the data of cold-worked ferritic iron, while that of as-quenched martensite is obviously lower than the value expected from the Bailey-Hirsch relationship. This means that mobile dislocations in martensite do not contribute to dislocation strengthening but only make the yield stress lower through the generation of plastic strain.
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Mechanical Properties
Regular Article
  • Characterization of Creep Deformation Behavior of 2.25Cr-1Mo Steel by Stress Change Test
    Hiroyuki HAYAKAWA, Daisuke TERADA, Fuyuki YOSHIDA, Hideharu NAKASHIMA, ...
    2007 Volume 93 Issue 6 Pages 466-471
    Published: June 01, 2007
    Released on J-STAGE: January 30, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane.93.466
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    To characterize the creep deformation mechanism of 2.25Cr-1Mo Steel, stress change tests were conducted during creep tests. In this study it was confirmed that the dislocation behavior during the creep tests were in viscous manner, because no instantaneous plastic strain was observed at stress increments and transient backward creep behavior was observed after stress reduction same as Modified 9Cr-1Mo Steel. Mo-bilities of dislocation were evaluated by observed backward creep behavior after stress reductions. Internal stresses were evaluated by the changes of creep strain rate in stress increments. These values were almost stable during creep deformation. Mobile dislocation densities were evaluated with the estimated mobilities of dislocation and the changes of creep strain rate in stress increments. Variation of evaluated mobile dislocation densities with creep strain showed the same tendency as variation of creep strain rate. Therefore mobile dislocation density is the dominant factor that influences the creep strain rate in creep deformation of this steel. The difference of estimated mobility of dislocation between 2.25Cr-1Mo Steel and Modified 9Cr-1Mo Steel was considered to be caused by the different amount of solute Mo between these steels.
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