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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 78 (1992), No. 2

  • Micromachining

    pp. 195-199

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    x

    Readers Who Read This Article Also Read

    1. Deoxidation Equilibrium of Liquid Iron with Barium Tetsu-to-Hagané Vol.78(1992), No.2
  • Slag-Foaming Phenomena and the Suppression

    pp. 200-208

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  • Geometrical Consideration of the Crystallography of Interphase Interfaces

    pp. 209-214

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  • Effect of Flux Compositon on Smelting Reduction of Chromite Ore

    pp. 215-222

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    The smelting reduction behavior of chromite ore in molten slag of (CaO)-(SiO2)-(Al2O3)-(MgO) system by carbon in liquid iron held in graphite crucible has been studied in the temperature range of 1663 K-1953 K. The reduction rate was expressed by the zeroth-order rate equation at an early stage of smelting reduction. During this stage, both (CrO) and the rate were kept constant and unaffected by the dissolution of the ore into slag with the exception that the ore in flux contained 15 mass% (Al2O3) and 15 mass% (MgO) was reduced at 1783 K. Accordingly, the slag was considered to be saturated with (CrO). The rate decreased with an increase in (Al2O3) and (MgO) contents. In particular, it decreased with the former. On the other hand, the rate increased with (CaO)/(SiO2) ratio as it increased up to unity. When the ratio exceeded unity, the rate obtained at 1783 K was unchanged with the ratio, whereas the rate at 1903 K decreased with the ratio. The rate constant was in proportion to -0.80 power of slag viscosity.
  • Rate of Smelting Reduction of Chromite Ore by the Dissolved Carbon in Molten Iron and Slag Foaming during the Reduction

    pp. 223-230

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    The rate of smelting reduction of chromite ore in (CaO)-(SiO2)-(Al2O3)-(MgO) slag by the dissolved carbon in liquid iron held in graphite crucible has been studied in order to investigate the reduction mechanism at the interface between metal and slag. The behavior of slag foaming during the reduction of the ore was also examined.
    The rate constant at the interface between metal and slag was in proportion to -0.82 power of slag viscosity and the apparent activation energies were 167 and 249 kJ/mol. Therefore it was estimated from these that the rate at this interface was controlled by mass transport of (CrO) in slag. The slag foaming height was kept constant during the time when the rate was expressed by the zeroth-order rate equation. The foam life decreased with an increase in both (MgO) content and (CaO)/(SiO2) ratio, whereas a relation between the foam life and the content of (Al2O3) was obscure. The foam life obtained was strongly affected by slag viscosity.
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  • Dephosphorization of Molten High Chromium Iron with CaO-based Flux

    pp. 231-238

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    Dephosphorization of molten high chromium iron with CaO-based flux is investigated in a laboratory scale test and industrial AOD test.
    By using CaO-CaF2-CaCl2-Fe2O3 flux of about 100 kg/t, dephosphorization of 70% is possible in the crucible test, if the molten iron with a chromium content of 16% has a carbon content of 6%. In the AOD test, dephosphorization of 50% is achieved at a carbon content of about 3.5% with CaO-CaF2-Fe2O3 flux.
    The reason why the degree of dephosphorization decreased at low carbon content in the melt is considered to be mainly due to the decrease in phosphorus activity. It is considered that high viscosity slag by the increase in Cr2O3 content also retards the dephosphorization rate.
    To get satisfactory dephosphorization, (T·Fe) content should be controlled to 24% with CaO content of 2030%. Phosphate capacities of the slags (CPO43-=(%PO43-)/(PP21/2·PO25/4)) are 10201021 at 1500°C.
    It is seen that dephosphorization of molten high chromium iron resulted from higher oxygen potential in the slag than that in metal.
  • Phosphorus Equilibrium Partition between MgO-saturated BaO-FetO-SiO2 Slags and Liquid Iron

    pp. 239-244

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    In order to meet the recent demand for low phosphorus steels, highly basic slags must be used to increase the refining efficiency. In this study, the equilibrium partition ratio of phosphorus (LP) between MgO saturated BaO-FetO-SiO2 slags and liquid iron was measured at 1600°C as a function of slag composition. The results are summarized as follows.
    (1)The MgO solubility of BaO-FetO-SiO2 slags is lower than those for the CaO-FetO-SiO2 and Na2O-FetO-SiO2 systems.
    (2)The maximum value of the phosphate capacity of this system is higher than that for the CaO system and not less than that of the Na2O system.
    (3)There is a FeO content to give the maximum LP value at constant BaO/SiO2 ratios. This is in accord with the well known fact applicable for the CaO-FeO-SiO2 system.
    (4)The activity coefficients of FeO and FeO1.5 have been measured and discussed in terms of slag composition.
  • Activities of Sn and Sb in Liquid Fe-S Alloy Saturated with Carbon

    pp. 245-252

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    The activities of tin and antimony in liquid Fe-S alloy saturated with carbon were determined at 1673 K to 1873 K by the distribution method using liquid silver. The concentration range of tin and antimony measured in the iron melt was less than 2 mass% and that of sulfur was up to FeS saturation (about 1.9 mass% at 1673 K).
    The activity coefficients of tin and antimony, γ(Fe-Csat.)Sn and γ(Fe-Csat.) Sb, and the solubility of carbon, [C]sat., in iron melt measured could be empirically expressed as the function of tin, antimony and sulfur contents in liquid iron saturated with carbon and temperature as follows;
    log γ(Fe-Csat.)Sn=485/T+0.777-28.33 XSn-4.20 XS,
    log γ(Fe-Csat.)Sb=-1000/T+0.314-18.34 XSb-2.17XS,
    [C]sat.=2.54×10-3T+0.65-0.33[mass%S]+βM [mass%M] (mass%)
    βSn=-0.11, βSb=-0.12
    (1673K1873 K, Sn≤1.5 mass%, Sb≤1.9mass%, S<1.9 mass% (FeSsat.))
    The activity coefficients of SnS and SbS1.5 in FeS-Na2S flux were estimated to explain the distribution behavior of tin and antimony between the flux and liquid Fe-Csat. by combining the results of the present work with the distribution ratios of tin and antimony between FeS-Na2S flux and Fe-Csat. melt determined in our previous work.
    Equilibrium partial pressure of SnS in Fe-C-S-Sn melt was also estimated by using the activities of tin and sulfur and free energy of formation of SnS, and the possibility of tin removal from iron melt as SnS gas was quantitatively evaluated.
  • Deoxidation Equilibrium of Liquid Iron with Barium

    pp. 253-259

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    Deoxidation of liquid iron with barium was studied in the temperature range from 1600 to 1700°C. Barium and oxygen dissolved in liquid iron were brought into equilibrium in presence of pure barium oxide in the lime crucible under the inert gas atmosphere of argon.
    The equilibrium constant and standard free energy of the deoxidation reaction "BaO(s)=Ba(%)+O(%)" were obtained as follows:
    logK=-9980/T-1.82 (±0.11)
    ΔG°=191000+34.9T(J) (±4 kJ)
    The temperature dependences of the interaction parameters were expressed by the following equations:
    eBaO=27.1-1.48×105/T
    eOBa=233-1.27×106/T
    The standard free energy of solution of barium in liquid iron and the activity coefficient of barium in the infinite dilute liquid iron solution refered to pure barium (γ°Ba) were calculated and discussed.
    x

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  • Nitride Capacities in the CaO-Al2O3 Melts

    pp. 260-266

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    The nitride capacities (CN3-=(%N)P3/4O2/P1/2N2) in CaO-Al2O3 melts were measured by a gas-slag equilibration technique, using CaO, Al2O3, and Mo crucibles in the temperature range from 1723 to 1923 K. The oxygen partial pressures measured by a solid electrolyte cell were controlled by N2-H2-H2O gas mixtures. It was found that the nitride capacities increased with increasing temperature and Al2O3 content in slag. Activity coefficients of AlN increased with decrease of Al2O3 content and temperature.
  • Bubble Dispersion Phenomena in Water, Mercury, Molten Iron and Molten Copper Baths

    pp. 267-274

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    Bubble dispersion phenomena in water, mercury, molten iron and molten copper have been investigated by electro-resistivity probe method. The bath dimension and modified Froude numbers were adjusted in all measurements.
    Bubble dispersion phenomena were qualitatively similar both in cold model and hot metal baths. Namely, the radial distribution of bubble frequency and local gas holdup were well represented by the two dimensional Gaussian distribution function. The radial and vertical distribution of bubble rising velocity were similar in all baths. The radial distribution of mean chord length were flat at every height. The mean chord length decreased with an increase of the height from mozzle, indicating disintegration of bubbles during ascending in the bath. However, they were different quantitatively. The boundary of the bubble dispersion zone, which was quantitatively defined by the locus of twofold standard deviation of the Gaussian distribution function, was wider in high temperature metal baths than that in cold model baths. The bubble rising velocity was higher in the order of molten iron=molten copper>mercury>water bath. The mean chord length was larger in the same order as above. The thermal expansion of bubbles in high temperature metal baths were not completed until the bubbles have ascended upto 150 mm from nozzle.
    In conclusion, the bubble dispersion phenomena in high temperature metal baths cannot be simulated with those in cold model baths, even if the bath dimension and the modified Froude number were adjusted.
  • Effect of Solute Content and Solidification Rate on the Microsegregation of Carbon Steels

    pp. 275-281

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    Casting conditions of continuous casting process especially a solidification rate and a temperature gradient, were reproduced using unidirectional solidification. Contour profiles of solutes in the solidified samples were traced with an electron probe microanalyser (EPMA). A new evaluation method was employed to describe solute distribution in a dendrite. To account for the influences of solid state diffusion and δ/γ transformation on the microsegregation of solutes, numerical analysis was carried out. Results of the analysis were compared with measured one. Considering δ/γ transformation and diffusion of solutes in a solid phase during and after solidification, the influences of carbon concentration and solidification rate on the microsegregation of manganese were discussed quantitatively.
  • Development of Analytical Automation System for Process Control in Steel Making Works

    pp. 282-287

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    An automatic and integrated analysis system for iron and steel making process was developed in Oita Works of Nippon Steel Corporation.
    This automatic analysis system, in principle, needs no human labor except for instrument calibration and treatment in trouble and performed a large quantity of labor-saving.
    Analytical precision after automation showed no difference compared with the former system and has given satisfactory results.
    And also in analysis time improvement can be seen. Thus this automatic system has contributed greatly to the steel production.
  • The Effect of Insoluble Molybdenum Carbide on the Hardenability of Fe-C-Mo Alloys

    pp. 288-295

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    Molybdenum is an important alloying element for obtaining steels with improved strength and toughness, therefore the effect of molybdenum on the hardenability of steel are of great interest. However, data of the past researchers are widely dispersed because the effective molybdenum varies with quenching temperature by being fixed as insoluble carbides due to its strong carbide forming tendency.
    In this study the effect of insoluble carbide on the hardenability has been quantitatively studied by extracting carbides from steels quenched at various austenitizing temperatures and correcting molybdenum and carbon amount which are effective for hardenability. By eliminating the effect of insoluble carbide, re-evaluation of hardenability with effective carbon and molybdenum yields more reliable hardenability data up to about 2% molybdenum in 0.2% to 0.6%C steels.
  • Estimation of Long Time Isothermal Temper Embrittlement in 21/4Cr-1Mo and 3Cr-1Mo Steels

    pp. 296-303

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    Isothermal temper embrittling tests at 425, 450 and 475°C, for 54000, 20000 and 5000 h, respectively, were performed using 2 1/4 Cr-1Mo and 3Cr-1Mo steels with various amounts of Si, Mn, Cu, Ni and impurities. Relationship between long time isothermal embrittlement and step cooling embrittlement is discussed. The results are summarized as follows.
    1) The equations, which can accurately estimate the shift in 50% fracture appearance transition temperature and the 40 ft-lb transition temperature by isothermal embrittling at T°C for th (ΔFATTiT, Δ40 TTiT), are derived from those of step cooling embrittling (ΔFATTSC, Δ40 TTSC) and amounts of impurities defined as Peq.=(10P+5Sb+4Sn+As) ×10-1.
    2) From the equations, the following facts are found. Embrittlement at 425, 450 and 475°C reach 90% saturation by aging for 380652×103, 6497×103 and 1012×103 h, respectively. Saturated isothermal embrittlement at 425, 450 and 475°C are 2.44, 1.98 and 1.51 times the step cooling embrittlement, respectively. Embrittling rate is slower and saturated embrittlement is greater at lower aging temperatures.
    3) Isothermal temper embrittlement at 425°C for 20 years (Δ40 TTi425×20y), which is maximum at this temperature in this study, is calculated to be 2.1Δ40 TTSC. So, 40 TTP+2.5ΔTTSC≤10 or 38°C, where 40 TTP is 40 TT after PWHT, is reasonable evaluation standard to avoid severe temper embrittlement in long time service.
  • Effects of Hot Rolling and Cold Rolling Conditions on Plastic Anisotropy of SUS304 Stainless Steel Sheet

    pp. 304-311

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    The effects of hot rolling and cold rolling conditions on plastic anisotropy of SUS304 stainless steel sheet have been investigated with respect to earing behavior. The results obtained are as follows:
    (1) The grain coarsening of the microstructure before cold rolling by the control of hot rolling and annealing temperatures suppressed the formation of main component {112}<111> in the product sheet, and was effective in decreasing the 45° ears.
    (2)The coarsed grain of hot rolled plate was obtained at the following conditions; heating pre-hot rolled plate at the higher temperature (≥1100°C), cooling it to relatively lower temperature (900970°C) and then starting the finish hot rolling.
    (3) When the cold rolling temperature was above 40°C, the 45° ears were formed. On the other hand, the 0° and 90° ears were formed in the case of the cold rolling temperatures below 0°C. It was concluded that, the 45° ears were formed by component {112}<111>, while the 0° and 90° ears were formed by components {210}<001> and {110}<001>.
    (4)The combination of processes of the controlled hot rolling and the cold rolling at lower temperatures, results in the low plastic anisotropy of the product sheet even in the case of the omission of hot rolled plate.
  • Susceptible Potential Region for Stress Corrosion Cracking of SUS316L Stainless Steel in Chloride Solution Containing Thiosulfate Ion

    pp. 312-318

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    Susceptible potential region for stress corrosion cracking, SCC, of SUS316L stainless steel has been investigated in 20 mass% NaCl aqueous solution containing 10-2 kmol·m-3 thiosulfate ion by using a slow strain rate technique, SSRT. Potential from -400 to -340 mVAg/AgCl was controlled either chemically by changing the concentration of dissolved oxygen, DO, in the solution or electrochemically by using a potentiostat. In both cases, cracks always generated at pits. In case of controlling DO, free corrosion potential raised and a shape of pit and crack changed with increase in the concentration of DO. Strain at the maximum stress, eSCC, was, however, independent of the concentration of DO, and depended on the number of cracks in the fracture surface. In case of applying potential, localized corrosion was found to generate beyond a critical potential of -370 mVAg/AgCl; cracks were observed from -370 to -340 mVAg/AgCl and pit size increased with increase in applied potential. eSCC was found not to be sensitive to the applied potential, but to be mainly decided by the strain at which pit generated. The crack growth rate which was estimated by the analysis of the stress-strain curves was found to be almost constant in the potential range between -370 and -340 mVAg/AgCl.
  • Effect of β-region Heat Treatment Conditions on Mechanical Properties of Ti-6Al-4V

    pp. 319-326

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    This paper is concerned with the relation between the mechanical properties and β-grain size on the β-region solution heat treatment and over aging of Ti-6Al-4V alloy.
    When the delayed time was less than 20s on the β-STOA, tensile and yield strength showed constant values regardless of grain size. Elongation and reduction of area decreased gradually until the β-grain size grew up about 0.8 mm. They showed a tendency to be constant when the grain size was more about 0.8 mm.
    When the time was over 20s and the β-grain size was less than about 0.8 mm, tensile strength, yield strength, elongation and reduction of area had a tendency to be constant.
    On the other hand, when the grain size grew up about 0.8 mm over, tensile and yield strength showed a tendency to decrease gradually.
    These elongation and reduction of area showed a tendency to increase gradually.
  • Oxidation Behavior of Pure Titanium at High Temperatures in Air at Reduced Pressures

    pp. 327-334

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    The oxidation behavior of pure titanium at 1 000-1 400 K has been studied in air at 67-2 670 Pa using metallographic and electron probe microanalysis techniques.
    Oxidation scales formed at temperatures less than 1 200 K (67 Pa) and 1 300 K (267 and 2 670 Pa) and more than them consisted of periodic multilayers and a single layer of rutile parallel to the reaction interface, respectively.
    The growth kinetics of periodic multilayers of scale and the permeation depth oxygen in titanium were obayed parabolic rate laws. The apparent activation energies for them were estimated to be 248-263 kJ/mol and 156-183 kJ/mol, respectively. The rate determining diffusion elements for them were discussed.
  • Magnetic Finishing of Titanium Sheet

    pp. 335-337

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