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

Tetsu-to-Hagané Vol. 67 (1981), No. 10

  • Delayed Cracking Caused by Hydrogen in Steel Welding

    pp. 1657-1669

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  • Recent Trends in Special Steels for Automobiles

    pp. 1670-1676

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  • Resources and Exploitation of Iron Ores

    pp. 1677-1685

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  • Tendency of Vacuum Heat Treatment

    pp. 1686-1695

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  • Metallic Resources Series-Niobium-

    pp. 1696-1707

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  • Recent Progress of Optical Communications

    pp. 1708-1712

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  • Small Experimental Apparatus for High Pressure Fluidized Bed Reduction of Pulverized Iron Ore

    pp. 1713-1719

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    An experimental apparatus with a batch type fluidized bed reactor of 60 mm I.D. for iron ore reduction was developed. The maximum reduction temperature and H2 pressure were 900°C and 40 kg/cm2. Experiments revealed that there were many operational problems to be solved and successive improvements were made. Findings obtained during the development of the apparatus are as follows :
    (1) In order to keep the gas flow and pressure constant at the reduction, the performance of inlet pressure regulators was the most important and it was better to install two independent regulators for high and low pressure ranges.
    (2) In order to decrease the pressure change brought by swiching the gas flow from N2 to H2 at the start of the reduction, it was effective to install two independent outlet pressure regulators for N2 and H2.
    (3) When pressurized Ar was introduced to the space in the electric furnace of external heating type to get the pressure balance with the reactor, heating efficiency of the furnace was found to decrease seriously because of enhanced heat leakage.
    (4) Sufficient gas preheating was very effective for fine control of the reduction temperature in the fluidized bed and also for prevention of the sintering trouble of the reduced iron powder at higher reduction temperature.
  • Temperature-dependency of Interdiffusion in Molten Fe-C Alloys

    pp. 1720-1725

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    In order to measure the precise interdiffusion coefficient of carbon in molten Fe-C alloys (Dc), an experiment was carried out for the carbon content of 1.353.44% at 1 4001 650°C by means of a diffusion couple method. The results are summarized as a following experimental equation ;
    Dc=exp{-(12 100/T+2.568)+(1 320/T-0.554)[%C]}……(±0.12×10-4) cm2/s and can be shown reasonable through the discussions on the temperature- and the concentration-dependencies of the coefficient.
  • Dissolution Rate of Sintered MgO into Molten FetO-CaO-SiO2 Slags

    pp. 1726-1734

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    The sintered MgO (porosity 29.9% and 13.0%) was immersed into molten FetO-CaO-SiO2 slags at temperatures from 1 350 to 1 425°C and the dissolution rate of MgO was determined with the rotating cylinder method by measuring the decrease of the cylinder radius. Also, the section of the MgO cylinder after immersion was examined by EPMA to know the penetration of slag and the dissolution mechanism.
    The results obtained are as follows :
    (1) The dissolution rate of MgO was increased with the rotating speed of cylinder and with temperature, and was found to be controlled by mass transport in the boundary layer of molten slag.
    (2) The change of mass transfer coefficient at 1 400°C with slag composition was correlated well to the change of kinematic viscosity of slag. Utilizing the nondimensional correlation found in literature, the values of diffusion coefficient of MgO into molten slags were estimated to be 1.0×10-53.0×10-5cm2/s at 1 400°C.
    (3) The dissolution of MgO proceeded through the formation of (Fe, Mg)O solid solution layer at the interface and its dissolution. The penetration of slag was retarded by this dense (Fe, Mg)O layer and the depth of penetration after 560 min was only 13 mm in high porosity MgO and <1 mm in low porosity MgO.
  • The Solubility of Magnesia and Ferric-Ferrous Equilibrium in Liquid FetO-SiO2-CaO-MgO Slags

    pp. 1735-1744

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    The solubility limit of magnesia and the ferrous-ferric oxide equilibrium have been measured for the FetO-MgO, FetO-SiO2-MgO and FetO-SiO2-CaO-MgO slags in equilibrium of liquid iron at the temperature range from 1 550°to 1 650°C. The results obtained are summarized as follows ;
    1) The solubility limit of magnesia and the ferric oxide content in FetO-MgO slags are represented by the following empirical formulae.
    log(wt%MgO)=-6000/T+4.21 (±0.05) 1 536°-1 660°C ……(1)
    log(wt%Fe2O3)=3553/T-1.00 (±0.05) 1 536°-1 660°C ……(5)
    2) The solubility limit of magnesia in FetO-SiO2-MgO slags has been established at the temperatures of 1 550°, 1 600° and 1 650°C. The value of Λ=Fe3+/Fe2+ in this slags decreases with increasing silica content.
    3) The solubility limit of magnesia in FetO-SiO2-CaO-MgO slags decreases with increasing FetO content and slag basicity, and it becomes almost constant, 6.-8. wt% in the range of basicity higher than 2(=wt%CaO/wt%SiO2). The value of Λ=Fe3+/Fe2+ in these slags increases with increasing the slag basicity and with decreasing FetO content in basic slags.
  • The Distribution of Oxygen between Liquid Iron and FetO-SiO2-CaO-MgO Slags Saturated with MgO

    pp. 1745-1754

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    The equilibria of oxygen distribution between liquid iron and the FetO-MgO, FetO-SiO2-MgO and FetO-SiO2-CaO-MgO slags saturated with MgO havebeen measured in the temperature range from 1 550°C to 1 650°C. The results obtained are as follows :
    1) The oxygen content of metal in equilibrium with FetO-MgO slags saturated with MgO is expressed by the following equation.
    log[wt%O]=-5520/T+ 2.276…… ( 5 )
    2) The iron oxide activity in FetO-SiO2-MgO and FetO-SiO2-CaO-MgO slags was determined at a temperature of 1 600°C, and the maximum value of the iron oxide activity was found along a line joining the orthosilicate composition with FetO apex. The substitution of CaO with MgO in the slag increases the iron oxide activity.
    3) In view of ionic theory, the approximate validity of regular solution model for cations were examined to formulate the thermodynamic properties of complex slag containing MgO. It was confirmed that the regular solution model was applicable to the wide range of slag composition over basic to acidic slag. The values of the interaction energy concerning MgO are as follows :
    α (Fe2+Mg2+)=+3 070 α(Fe3+Mg2+)=-5 620
    α (Si4+Mg2+)=-30 500 α(Ca2+Mg2+)=+4 500 (cal)
  • State of Sulphur and Sulphur-iron Interaction in Na2O-SiO2 Slags

    pp. 1755-1762

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    From the standpoint of external desulphurization, state of sulphur and sulphur-iron interaction in Na2O-SiO2 slags were investigated by optical absorption, electron spin resonance(ESR) and S Kα X-ray emission spectroscopies. An optical absorption was observed near 24 000 cm-1 in the slags produced in the intermediately (Po2=10-5.1 atm.) and strongly(Po2=10-6.7 atm.) reducing atmospheres. The absorption was assigned to polysulphide ions consisting of several sulphurs. Fe3+-S2- interaction was suggested from the increase of the intensity of ESR absorption near g=6.0 in the slags produced in the strongly reducing atmosphere. Chemical shift study of S Kα X-rays in the slags indicated that sulphur atoms are in the form of S6+ ions in oxidizing condition(Po2=0.21 atm.) and in the mixed state of S6+ and S0 in the reducing conditions. It was concluded from these results that, in Na2O-SiO2 slags, polysulphide ions such as S2-> are formed as intermediate stage with reducing partial oxygen pressure of atmosphere. Further, it was indicated that Fe3+-S2- interaction begins to occur in the vicinity of Po2=10-610-7 atm.
  • Formation of Smudges and Iron Oxide Film in the Course of Cold Rolling

    pp. 1763-1769

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    The effects of the cold rolling conditions on the amount of smudge has been investigated. The smudge formed on the edge of cold rolled steel sheet surface causes the dewetting of tin plate since it can not be removed by the conventional electrolytic cleaning. It is estimated that the smudge consists of iron powders and iron oxide powders, and it deteriorates palm oil. Inhomogeneous distributions of the smudge and the iron oxide film are observed in the strip width. The amount of smudge at the edge of the strip is more than twice as much as that at the center.
    The results suggests that the cold rolling conditions significantly affect the amount of smudge and the iron oxide film thickness on the surface of cold rolled steel sheet.
    The amount of smudge and oxide film thickness increase with the increase of rolling speed and the reduction at the final stand (stand No. 5), but are reduced by supplying the more oil at the final stand. Furthermore, the calculated temperature of the strip at the exit of roll bite suggests that the amount of smudge and oxide film thickness depends on the temperature. It is revealed that the amount of smudge and the iron oxide film thickness are reduced by adding the antioxidant additive to the rolling oil.
  • Development of High Current MIG+2SAW Technique for Heavy Wall UOE Linepipes

    pp. 1770-1776

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    MIG+2SAW technique has been developed for longitudinal welding process to produce the heavy wall UOE linepipes up to 50 mm in thickness.
    (1) An experimented MIG+2SAW equipment is designed so that the leading electrode is DCRP for high current MIG welding and the middle and trailing electrodes are connected in Scott transformer connection for 2SAW. This equipment placing MIG and 2SAW torches on one cart can weld test plates with one-run. The arc interaction between MIG and 2SAW has hardly been observed.
    (2) MIG+2SAW process is devised to disperse the heat input to decrease it per one molten pool as compared with 3SAW because a torch spacing between MIG and 2SAW is long enough and two molten pools are formed. Therefore weld metal and HAZ in the center of plate thickness by MIG+2SAW process give a better toughness than those by 3SAW.
    (3) As the heat input of 2SAW on MIG+2SAW process can be lowered as compared with that of 3SAW, MIG+2SAW process consumes a fewer fluxes than 3SAW. The shielding effect of the molten slag is scarcely deteriorated because it is not overheated even if the fused flux is used. As a result the weld bead in 50 mm thickness plate is sound and slippery.
  • Effect of Calcium Treatment on Stress Relief Cracking in 80kg/mm2 Class High Tensile Strength Steel

    pp. 1777-1786

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    The effects of calcium treatment on stress relief cracking were investigated in Ni-free type HT80 steels. Calcium was added into molten steel in the fountains during bottom pouring. The y-groove restraint cracking test method was primarily used as stress relief cracking test.
    As a result, stress relief cracking was remarkably reduced by calcium treatment and close correlation was observed between the susceptibility to stress relief cracking and the amount of free sulphur which was calculated by (Stotal-32/40Ca). The amount of free sulphur is considered to decrease by calcium treatment. This is explained mainly by the reason that stress relief crack tends to propagate along grain boundary as the surface energy of cavities in the grain boundary is decreased by the segregation of free sulphur.
  • An Evaluation of Threshold Stress-intensity Factor, KISCC Using AE Technique

    pp. 1787-1794

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    In this paper, a new method to evaluate the threshold stress-intensity factor KISCC by the use of acoustic emission (AE) signal analysis is proposed using the material of type 4340 steel, of which hydrogen content was controlled by the cathodic electrolytic method. In the subcritical crack growth due to hydrogen embrittlement, a linear correlation was observed between stress-intensity factor K and emission event counts N. From this relation KISCC was defined as a stress-intensity factor KAE corresponding to the generation of AE events. The effects of K and threshold voltage of AE measurement on the KISCC were discussed in detail, and with the results of fractography it was concluded that the obtained KISCC corresponded to the nucleation of hydrogen induced intergranular microcrack in the maximum triaxial stress field ahead of the crack tip.
  • Grain Refinement of Austenite through Reverse Transformation from Martensite in Fe-15Ni-Co-Mo-Ti Alloys

    pp. 1795-1804

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    The effects of 5Mo, 15Co or 2Ti addition to Fe-15Ni-10Co-5Mo base alloy on grain refinement of reversed austenite subjected to single austenitizing were studied at heating rates between 0.083 and 100 °C/s. Grain refinement was promoted by Co or Ti addition and was suppressed by Mo addition. Grain refinement was promoted in the base, (base+15Co) and (base+2Ti) alloys at the lower heating rates, whereas it was suppressed in the (base+5Mo) alloy. Refining processes depended on chemical composition and heating rate, and were classified into the following two groups in terms of the differences in the initial stage of formation of γ grains : (1) after completion of reverse transformation, γ grains were formed due to recrystallization of γ ; and (2) during reverse transformation, γ grains were formed probably by nucleation and growth of diffusionally transformed γ. It was shown that the mechanisms of reverse transformation associated with chemical composition and heating rate played an important role in these refining processes.
  • Effect of Grain Size on High Temperature Creep Properties of Hastelloy X

    pp. 1805-1814

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    The effect of grain size, ranged from 37 to 1220 μm, on creep behavior of Hastelloy X was studied at temperatures of 950, 1 000 and 1 050°C. A steady state creep rate, εs, of the alloy decreased with the increase of the grain size, reached a minimum at the grain size of 100200 μm, LM, and increased with the increase of that. From measurements of friction stress (σf) and observations of microstructures, it is concluded that the increase in εs under a given applied stress with the decrease of the grain size is attributable to the increase of an effective stress, σe(=σaf, whereey σa is the applied stress). On the other hand, recrystallization induced by a high stress concentration at grain boundary triple points in the coarse-grained alloys seems to accelerate the creep. By comparing the results in the Hastelloy X with those in carbon free 17Cr-14Ni steel, it is suggested that the grain size dependence of the εs of the Hastelloy X having finer grains than LM is more remarkable than that of carbon free 17Cr-14Ni steel because of the decrease of fine precipitates within grains in the former alloy, while the dependence of the alloy having coarser grains than LM is minor than that of carbon free 17Cr-14Ni steel because of preventing the stress concentration at the triple points by the grain boundary precipitates.
  • On the Change in the Internal Friction of Stainless Steels in the Fatigue Process

    pp. 1815-1822

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    The internal friction has been measured on the specimens of repeat-bend fatigue test with constant strain amplitude using austenitic SUS316, ferritic 11Cr-0.4Ti and semi-austenitic SUS631 steels. A discussion was then made on plastic deformation, initiation and propagation of cracks, and martensitic transformation of these steels during fatigue test.
    It was considered that in 11Cr-0.4Ti and SUS316 steels the internal friction increased owing for the most part to an increase of dislocation density by the plastic deformation during fatigue test. In SUS631 steel, the internal friction increased markedly due to martensitic transformation rather in the earlier stage of fatigue. The internal friction increased more strongly owing to the initiation and propagation of cracks in these steels. The initiation and propagation of cracks in these steels was also examined by means of both optical and scanning electron microscopy.
  • Determination of Small Amounts of Aluminum in Iron and Steel by X-ray Fluorescence Analysis

    pp. 1823-1828

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    The accuracy of X-ray fluorescence analysis for determining aluminum in steel is generally poor when the aluminum content is below 0.1%. In this study, it is confirmed that the existence of inhomogeneous acid-insoluble aluminum causes the poor accuracy of X-ray fluorescence analysis. The accuracy can be improved by adding granular ferro-zirconium to molten steel when sampling. By using this method, the accuracy of determining aluminum was 0.0024% for low alloy steels and 0.0022% for stainless steels as the standard deviation obtained for a series of differences between an analytical result and a standard value. Corrections for overlapping of the chromium spectrum, and for absorption and enhancement effects of co-existent elements are not necessary for the analysis of low alloy steels, whereas these corrections are necessary for the analysis of stainless steels.
  • Improvement of Higher Productivity Using Bottom Blown Converter

    pp. 1829-1833

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  • Combustion Control by Minute Pressure Pulsation Pattern

    pp. 1834-1841

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  • 自動車における各種材料の競合/Fine Metallurgy/科学知識を新たに応用することによる新技術の開花/ルービック・キューブ雑感/民間企業のみた80年代に開発されると思われる主な技術・製品

    pp. 1841-1841,1851

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  • Development of No-tension Control System for Bar Mill (SNTC) Based on Direct Measurement

    pp. 1842-1847

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  • 抄録

    pp. 1860-1865

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