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

Tetsu-to-Hagané Vol. 49 (1963), No. 8

  • Manganese Ore Reduction with CO gas or CO-CO2 gas Mixture.

    pp. 1059-1065

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    Authors studied on manganese ore reduction with CO gas or CO-CO2 gas mixture by the method of thermal balance analysis, and then discussed its reducibility with mineral composition.
    (1) Reducibility decreases in the next order: i. e. MnO2 ore, burnt ore of MnCO3 (manganese low oxide ores such as α-Mn2O3 or Mn3O4 etc.) and manganese silicate ore. It is plain enough that every ore is reduced to MnO with CO gas.
    (2) There is scarcely any difference in reducibility with CO gas among all MnO2 phases i. e. cryptomelane, pyrolusite, γ-MnO2 and birnessite. Only, MnO2 transforms to reduced state (till Mn3O4) through mere thermal decomposition simultaneously with reduction by CO gas.
    Therefore, authors support the general reasoning that easily thermal-decomposable and incomplete crystalline γ-MnO is most reactive.
    (3) Under low temperature reduction, the obtained MnO is unstable in the air after cooling in CO gas flow. Meanwhile it is shown that through reduction at above 700°C, the obtained MnO is rather stable in the air after cooling. X-ray diffraction shows that this phenomenon is due to crystalline structure.
    (4) During manganese are reduction with CO gas, carbon deposition is observed in certain ores; especially in high iron-content ores this tendency is remarkable.
    (5) On the basis of above results, some discussions are made on refining furnace reaction and preliminary reduction.
  • Acceleration of Dephosphorization in Oxygen Converter under Agitation by Blowing of Gas.

    pp. 1065-1071

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    Using a small test L. D. converter, experiments were carried out on preferential dephosphorization in the period of desiliconization blowing of L. D. converter and especially, the relation between the rate of dephosphorization and the intensity of agitation of molten bath was investigated.
    The results obtained are as follows:
    1) The rate of dephosphorization is given by the formula, dp/dt=k [p] n, where n=1 in the period of desiliconization blowing.
    2) Dephosphorization is promoted by hard agitation of molten bath. However, when the agitation of molten bath is intensified by blowing oxygen itself, decarburization is promoted simultaneously.
    3) By injection of inert gas for agitation into the bath in the period of desiliconization blowing, dephosphorization is promoted extremely without any promotion of decarburization; and under the optimum conditions, a very low content of phosphorus can be obtained at high carbon range.
  • On the Correlation between Formability and Nonmetallic Inclusions in Low Carbon Rimmed Steel Sheet.

    pp. 1072-1078

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    A study was carried out to know the correlation between formability and non-metallic inclusion in low-carbon rimmed steel sheets.
    The specimens were made from 6·5 to 15t ingot, basic open hearth furnace steel.
    Formability of the sheet was measured by Erichsen and torsion tests.
    The results obtained are as follows:
    (1) Stretchability of 0·8mm cold rolled annealed steel is reduced by large sulphide (MnS) aad scum (over about 100μ long).
    (2) Plenty of the above mentioned large sulphide (MnS) is precipitated as the content of sulphur reaches 0·035 to 0·040% in sheet. In that case, coarse lamination of hot milled steel is liable to occur.
    (3) The lengths of inclusions measured along the rolling direction of a ore are mostly below about 25μ, in hot milled sheets. Moreover, authors confirm by diffraction of electronbeam that there are MnS, MnS· (Mn, Fe) O, α-Al2O3 (Corundum), α-SiO2 (Cristobalite), Al2O3·SiO2 (Kyanite), FeO·Al2O3-MnO·Al2O3 (Spinel), 3FeO·Al2O3·3SiO2-3MnO·Al2O3·3SiO2 (Garnet), 2FeO·SiO2-2MnO·SiO2 (Olivine) in hot milled sheet.
  • Effect of Heat Treatment on the Creep Rupture Strength of a Cr-Mo-V Steel for Steam Turbine Shafts.

    pp. 1079-1086

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    To investigate the cause for dispersion of the creep rupture strength of the actual largesized steam turbine shaft forgings, creep rupture tests were conducted with specimens heattreated at different austenitizing temperatures, different cooling rates from austenitizing temperature and different tempering temperatures. The types of the specimens used were both plain bar specimens and notched bar specimens, and testing temperatures were 510°C, 538°C, 565°C and 593°C. Creep rupture data were treated with Larson-Millers' parameter and the results were illustrated by master rupture curves.
    It was found that the creep rupture strength of the plain bar specimens was increased remarkably by elevating the austenitizing temperature from 950°C to 1000°C. It is supposed that this difference of the austenitizing temperature will be the most important factor for the dispersion of the creep rupture strength among the actual steam turbine shaft forgings. Such cooling rate from austenitizing temperature as may produce bainitic structures has little effect on the creep rupture strength, while the tempering temperature exercises a relatively large effect when a tempering treatment is carried out at the temperatures between 675°C and 700°C.
    The following was found about the effect of austenitizing temperature on the high temperature notch sensitivity of rotor materials. According to the conditions of the tests, specimens austenitized at 950°C showed notch strengthening, while notch weakening was observed with specimens austenitized at 1000°C and 1050°C. While specimens austenitized at 950°C and tempered at various temperatures showed notch strengthening, oil quenched specimens from austenitizing temperature exhibited notch strengthening at first and then notch weakening as the Larson-Millers' parameter increased. This tendency in notch sensitivity of the materials is approximately corresponding to the tendency of hardness change measured in ruptured specimens, and it was ascertained that high temperature notch sensitivity of a material was influenced by its structural changes.
  • A Study on Structures and Mechanical Properties of Cr-Ni-Mn Stainless Steels

    pp. 1087-1093

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    The effects of Mn additions on structures of Cr-Ni stainless steels are not well known yet. It has been reported that in a certain case Mn acts as a ferrite former and in another it does as an austenite former. In this report, analysis of alloying elements in phases forming Cr-Ni stainless steel was made using Electron Probe X-ray Micro analyzer in order to study the effect of Mn on the structures of Cr-Ni stainless steels and the relations between the structures and mechanical properties such as impact value, deformation resistance and hot work ability were investigated.
    The following results were obtained.
    1) Th amount of δ ferrite decreased with increasing Mn content for martensitic stainless steels but it increased with increasing Mn content for austenitic stainless steels.
    2) Impact property was improved with increasing Mn content in the specimens as solutiontreated but impact values of the specimens aged at 750°C decreased with increasing Mn content because an addition of Mn promoted the formation of σ phase from δ ferrite.
    3) Deformation resistance at high temperature increased with increasing amount of alloying elements but it decreased with increasing amount of δ ferrite.
    4) Hot work ability of the specimens with duplex structure was worse than that of the specimens with single phase.
    It was not the amount of δ ferrite but the duplex structure itself that had a bad influence on hot work ability.
  • Correlation between Age-Hardenability and Precipitation Process of the Austenitic Fe-Co-Cr-Ni Base Heat-Resisting Alloys

    pp. 1094-1101

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    The present investigation aims at establishing the correlation between the age-hardening behaviour and the process of precipitation in austenitic age-hardenable Fe-Co-Cr-Ni base alloys, in order to obtain a useful information on the precipitation strengthening. In several stages of aging, measurements of mechanical properties and X-ray analysis of precipitates were made and microstructures were observed by means of the optical and electron microscopes. The results may be summarized as follows:
    The age-hardenability and the behaviour and dispersion characteristic of precipitates are markedly affected by the minor additional elements such as Mo, W, Cb and N. The precipitates detected by X-ray analysis are CbC or Cb (C, N), M23C6, M6C, π and Laves phases, among which M23C6 and π phase play the main role in the age-hardening.
    There are two types of hardening, that is, one-stepped and two-stepped hardening. The former is observed in alloys with only one phase of either M23C6 or π as precipitate, the degree of hardening being principally affected by the volume fraction of the precipitates rather than the properties of precipitates. On the other hand, the two-stepped hardening is remarkable in alloys containing simultaneously Mo, W and N, and it is related with the transition of precipitates from M23C6 to π. The mechanical properties of these alloys are superior to those of single phase precipitation hardening alloys. Such high precipitation strengthening seems to be induced by favorably combined dispersion of M23C6 and π phases.
  • On the Quenching Effects of Mineral Oil.

    pp. 1102-1109

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    In the present series of study, the quenching effects of mineral oils having different properties were examined, and the following conclusions were obtained:
    (1) Quenching effects on steel of light-and heavy-fraction mineral oils are less remarkable than that of medium-fraction one.
    (2) A medium-fraction distillate, if redistilled, loses the greater part of its hydrocarbon having higher boiling points from itself and shows less remarkable quenching effects than otherwise.
    (3) Among different mineral oils having the same boiling point, the most remarkable quenching effects are to be expected from those consisting mainly of aromatic hydrocarbons, such as the solvent extract.
    (4) In the case of medium-fraction mineral oils having a fixed boiling point, the quenching effects depend upon the concentration of aromatic hydrocarbons in them.
    (5) The duration of formed gas film and the violence of thermal cracking of oil during quenching change with its boiling point as well as with contents of some hy rocarbons having higher boiling points and of aromatic hydrocarbons.
  • On the Roller-Dies Drawing.

    pp. 1110-1117

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  • Highly Basic Slag

    pp. 1118-1123

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  • 抄録

    pp. 1124-1132

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  • 特許記事

    pp. 1135-1138

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  • 鉄鋼ニューズ

    pp. 1139-1141

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