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

Tetsu-to-Hagané Vol. 58 (1972), No. 8

  • 研究管理雑感

    pp. 1029-1030

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  • On the Composition and Etching Patterns of Minerals in Lime Sinter

    pp. 1031-1038

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    The chemical compositions of minerals of industrial lime sinters were determined by X-ray microanalyzer and their etching behavior were observed.
    Dicalcium silicate containing small amount of FeO and MgO was etched by water. Glassy silicate was dissolved by HC1 (1: 10), and the melilite and iron-gehlenite grains surrounded with the glassy silicate were observed to be brought into relief. The wustite grains containing CaO and MgO were not etched by the ordinary method, but unique etching pattern appeared when HC1 (1: 1) was used. Among the magnetite grains those which showed characteristic straight grooves after etched by HCl (1: 1) at 60°C were found to be the multicomponent system.
    Calcium ferrite grains in the sinter were separated under an optical microscope and analyzed by X-ray diffraction method. All of the examined grains of the types of long columnar, crystallized and high aluminacontaining were identified as hemicalcium ferrite. The etching pattern varied with the existence of inclusion and precipitate, and alumina content in the grains.
  • On the Reduction Swelling of the Pellet Produced from the Ore Treated with Sea Water

    pp. 1039-1043

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    The role of sodium-containing phase in the swelling during reduction of pellet was investigated.
    About 0⋅15% sodium in chloride form was retained in magnetic concentrated are treated with sea water. In firing process, a part of sodium in the pellet produced from such concentrated are was transferred into iron oxide aad slag phases. The amount of sodium in iron oxide phase was evaluated by the extraction with HC1 solution (1: 1) at 90°C. Sodium in slage phase was determined by the ordinary hydrofluoric acid method after the removal of sodium embeded in the iron oxcide. The distribution of sodium in both phases was affected by the firing temperature and the slag volume in the pellet. Moreover, increase of the slag basicity brought about the decrease of the sodium content in the slag.
    The swelling index of the pellet was very small in the case that the amount of sodium in the iron oxcide phase was less than 0⋅005%. However, that of pellet with the sodium content more than 0⋅03% was over 300%. In order to prevent the abnormal swelling, sodium in the pellet should be absorbed by the slag generated in firing process.
  • Behaviours of Recrystallization and Transformation Observed by Hot-Rolling of Nb-containing Steels

    pp. 1044-1053

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    The recrystallization behaviour of austenite of Nb steel at 1-pass or 4-pass rolling was compared with that low carbon steel. The relation between austenite grain size and ferrite grain size was also investigated.
    The recrystallization was greatly influenced by the very fine Nb (C, N) precipitates which precipitated during rolling. When Nb (C, N) remained unresolved, the recrystallization behaviour was the same as that of Si-Mn steel. The recrystallization was more difficult at 1-pass rolling than 4-pass rolling especially in the case of higher reduction. The influence of austenite grain size upon ferrite grain size was found to be small. The main factor controlling ferrite grain size was cooling rate after finishing pass.
  • Effect of Deformation Temperatures on Flow Stress and Dislocation Structures of Low Carbon Steels

    pp. 1054-1066

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    The relation between dislocation structures and tensile properties have been investigated in the temperature range from room temperature to 400°C using four kind of a-irons with different carbon concentration. The grain size dependence of the yield and flow stress have also been studied in the same temperature range.
    The specimens showed serrated flow curves with high flow stress and high work-hardening rate. The higher the solute carbon content was the higher the flow stress and work-hardening rate became, and the temperatures of serrated flow being observable moved to a slightly higher temperature by decreasing the carbon content of the specimens.
    The flow stresses of the specimens were analyzed in term of the Petch parameters k and σi. It was found that kf at the temperatures of blue brittleness region was identical with ky, but σ showed higher value than the value at room temperature. These high values of frictional stress well corresponded to high workhardening rates. The change of flow stress component, therefore, was almost related to the frictional stress (σi). In the temperature range of serrated flow, deformed structures showed high dislocation densities and very small cell structures. Rapid increase in flow stress and high work-hardening rates were closely related with high rate of dislocation-multiplication.
  • Study on Relationship between Impact Fracture Surface and Toughness of Low-carbon Steels

    pp. 1067-1075

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    The brittle fracture surfaces of steels are closely related to the microstructures, and it has been shown that there is a good correlation between the unit crack path (lc) and the impact transition temperature (vTrS) 4-6.
    In this study, it is confirmed that the unit crack path in the ferrite-pearlite structure can be used as the factor controlling the toughness of steel; there is a linear relation between vTrS and log lc-1/2, as previously obtained in the quenched structures. The relationship among the austenite grain size, the ferrite grain size (la), and the unit crack path in the ferrite-pearlite structures is determined. The relation lc=2la is obtained, as expected in the previous paper4.
    The fracture appearance in the brittle-ductile transition range of the ferrite-pearlite and the quenched structures are also invesitgated. In increase of the temperature from the brittle range in Charpy impact test, the ductile networks enclosing the brittle fracture facet are observed. The brittle fracture facet itself becomes ductile with further increase of temperature. However, the unit crack path is found to be unchanged, accordingly, this value is considered as a characteristic of the structure. The areal amounts of the ductile fracture measured by the scanning electron microscope are closely related to the Carpy impact values
  • The Strength and Toughness of Low-carbon Low-alloy Bainite

    pp. 1076-1085

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    The relationship between the morphology and the mechanical properties in the isothermally transformed low-carbon low-alloy bainite has been investigated in comparison with those of tempered martensite.
    The strength of bainite increased with lowering the transformation temperature because of the reduction of the thickness of the ferrite laths. As the decrease in the transformation temperature also reduced the unit crack path for cleavage fracture, the toughness in the impact test was improved. In the martensitebainite duplex structure formed by isothermally below Ms, higher tensile strength was achieved without losing toughness and this structure exhibited better impact properties than the martensite tempered at lower temperatures to produce the equivalent strength. The toughness of this duplex structure, however, was not so good as that of the bainite-martensite duplex stru
  • Strengthening of Ultra-low Carbon Ni-Cr Steel by Precipitation Hardening

    pp. 1086-1095

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    In order to obtain a new age-hardening steel, a study was carried out to modify the strong and tough matrix of 18Ni maraging steel by reducing Ni content, addition of Cr, etc. It was proved that the Ni-Cr matrix steels with Ni content as low as 6 to 10% and Cr content of over 4% exhibited massive martensite structure similar to the high Ni steel, and promising mechanical properties. Then it was studied to strengthen this matrix by the addition of various elements which are expected to give precipitation hardening. It was shown that the most effective strengthening was obtained by the combined addition of Mo and Co, and a composition of ultra-low carbon 8Ni-6Cr-9Co-6Mo was finally obtained to give 180 kg/mm2 as ultimate tensile strength. This steel exhibited mechanical properties no inferior to those of 18Ni maraging steel and, showed better corrosive properties.
  • Metallurgical Factors Affecting the Work Hardening Exponents of Low Carbon Rimmed Steel Sheets

    pp. 1096-1106

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    Metallurgical factors affecting the work hardening exponents (n-values) of low carbon rimmed steels were studied. The following results have been obtained;
    (1) In the tension test, the amount of work per unit volume which was done on the specimen to the maximum load showed 8.3±0.4 kg/mm2 in the low carbon rimmed steel samples, while those of the sample containing 0.1 wt% of phosphorus showed about 9.2 kg/mm2.
    (2) Theoretical equations concerning n-value, and σ0 and K (which were obtained in a relationship σ=σ0+K.εnear the maximum load) were obtained considering (1), and agreed well with experimental results.
    (3) Effects of grain diameter on n-value shown by the next equation, was obtained by using (1) and (2).n=10/(10+σ1+1.3d-1/2) where d (mm) is average grain diameter and σi (kg/mm2) is intrinsic strength.(4) The true effect of the content of a chemical element on n-value, eliminating the effect of grain size, was determined by using (1) and (2).
    Mn: the effect is related to manganese content in solid solution.
    N: the effect is dependent on manganese content.
    C.: the effect is saturated above about 0.03 wt%.
    S: the effect is far smaller than those of carbon, nitrogen and manganese.
    O: the effect is negligible.
    (5) Singularity of n-values of the samples containing phosphorus above about 0.05 wt% was foundand explained well by using (1).
  • A Study of the Relation between Distribution of Grain Diameters and Flow Stress in Mild Steel

    pp. 1107-1116

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    Effects of grain diameter distribution on the flow stress of mild steel were studied. The flow stress have been usually connected with an apparent average grain diameter which is determined by counting a number of grains appeared in the cross section of mild steel. The difference between a true flow stress calculated considering a distribution of grain diameters and an apparent flow stress connected directly with the apparent average grain diameter was obtained in some distribution of grain diameters.
    The following results were obtained:
    (1) A stress calculated by the strain continuity model and a stress calculated by the stress continuity model coincided well for all the adopted distribution types of grain diameters.
    (2) In Gauss distribution (f (x) = (1/ 2πS)·exp (-(x-μ) 2/2S2), x: grain diameter (mm)), the difference mentioned above increased with S.
    (3) In the uniform distribution (f (x) =1/ 2P), the difference increased with P.
    (4) In Poisson distribution (f (x) =exp (-R)·RX/X!, X=100x), the difference decreased with R and gradually came close to that of Gauss distribution.
    (5) A metallurgical meaning of the equation (σ=g (x, ε)) used in the calculations was discussed using work hardening theory.
    In summary the difference was remarkable in Poisson distribution, but those in Gauss distribution and in the uniform distribution might be neglected except in the case where the flow stress is discussed with an accuracy of the order of 10-1 kg/mm2.
  • The Effect of Creep Test Temperature on Creep Rupture Properties of α-ray Irradiated AISI 316 Stainless Ste

    pp. 1117-1125

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    Since it is known that helium bubbles deteriorate the mechanical properties of stainless steel used as a fuel cladding in fast-breading-reactors, the effect of helium was studied.
    Thin plate specimens of type 316 stainless steel with helium content of 7.5×10-6 atom fraction which had been injected by α-ray irradiation from a cyclotron were creep-rupture tested at 550, 650 and 750°C.
    The presence of helium caused large reductions in rupture life and elongation as test temperature in creased. The loss of ductility showed to be constant at one test temperature.
    By observing fracture surfaces with optical and scanning electron microscope, the difference between the specimen with or without containing helium was clear, and it was shown that the embrittling effect of helium resulted from its tendency to concentrate at grain boundaries, leading to intergranular cracking.
  • Electrochemical Properties of the Buffed Surface of Pure Iron in Chromate Aqueous Solutions

    pp. 1126-1133

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    The relations between electrode potentials of buffed surface of iron in chromate solutions and pH values of the solutions were studied in relation to the corrosion region (pH<4) in the Pourbaix diagram for the Fe-Cr03-H20 system at 25°C. The results obtained were as follows:
    The buffed surface is covered with thin Fe304 films. The electrode potentials vary with the pH values and the presence of anions, Cl- and SO2-4. The surface reactions are estimated from the observed pH- potential relations as follows:
    (1) 0<pH<2;
    3Fe+6Fe3O4+4CrO2-4aq+26H+=3Fe2++9γ-Fe2O3+4Cr3+aq+13H2O
    (2) 2<pH<4;
    3Fe+6Fe3O4+4CrO2-4aq+10H+=3Fe2++9γ-Fe2O3+4CrO-2aq+5H2O
    The electrode potentials of the Fe304 film depend on the presence of anions, Cl- and SO2-4, and on the structure of chromic ion species, and concerned with the solid state electrolyte reaction, i. e. the dissolution of Fe2+ ion from iron crystal surface into the thin Fe3O4 film.
    The Fe3O4 film is rapidly dissolved in the solution by the presence of Cl- or SO2-4, and the surface reactions of pure iron without oxide film are estimated from the observed potentials as follows:
    (1) 0<pH<2;
    Fe+CrO2-4aq+8H+aq=Fe3+aq+Cr3+aq+4H2O
    (2) 2<pH<4;
    Fe+CrO2-4aq+3H+aq=FeOH2+aq+CrO-2aq+H2O
    The dissolution reactions and their electrode potentials of pure iron in chromate solutions depend on the structures of both chromic ion and ferric ion species.
  • A Study on the Possibility of Determination of Nitride and Dissolved Nitrogen in Steels Containing Al and N by Hydrogen Hot Extraction

    pp. 1134-1144

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    Hydrogen hot extraction for the determination of metallurgically dissolved nitrogen was investigated. Alminium-killed steel with nitride-nitrogen and dissolved nitrogen was heated in hydrogen stream at 500-1000°C, and after the extraction, total nitrogen retained in steel, nitride-nitrogen and nitrogen as NH3 in hydrogen collected in diluted sulfuric acid were determined.
    A kinetic consideration shows that the technique is only successful when the rate of dissociation of nitride, k1 and that of precipitation, k2 are negligibly smaller than that of formation of NH3, k3. In this case (k1+k2<<k3), nitride-nitrogen remains unchanged in steel after hot extraction, while dissolved nitrogen is removed from steel as NH3
    Experimental results of aluminium-killed steel showed that the relation (k1+k2<<k3) was not valid and this technique was unsuccessful. In steel having dissolved nitrogen only, aluminium-nitride precipitated during hot extraction, while dissolving of the nitride and removal of nitrogen were observed in steel with nitridenitrogen during hot extraction; this technique did not give the original contents of nitrogen of various states.
  • A Study of Flow Rate Control of Molten Metals by Electromagnetic Pump

    pp. 1145-1151

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    The flow rate control of molten metal was investigated by means of a pair of 3 phase 200 V flat type linear induction electromagnetic pumps.
    Two pumps of each capacity 11.5 KVA were placed at both sides of the vertical nozzle and were operated to induce the force in the direction opposite to the free falling of the metal.
    The molten metals used were Al alloy and cast iron.
    For Al alloy, the flow rate decreased from 1.20 Kg/sec to 0.83 Kg/sec by increasing the input voltage from 0 to 200 V, resulting in the maximum control of the molten metal flow rate of 30%.
    For cast iron, the power output of the pumps was not sufficient to control the flow rate, because of the lower electrical-conductivity of cast iron as compared with Al alloy.
    These results were confirmed theoretically, and the data necessary for design of electromagnetic pump were obtained.
  • Recent Progress in Ferroalloy Production

    pp. 1152-1167

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  • Impressions of the International Symposium on Metallurgical Chemistry

    pp. 1168-1175

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  • Error in Measurement of Upper Yield Stress in Impact Test

    pp. 1176-1177

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  • 抄録

    pp. 1178-1186

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