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

Tetsu-to-Hagané Vol. 59 (1973), No. 8

  • 後向きの科学技術

    pp. 1067-1068

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  • On the Pre-reduced Pellets Produced with Addition of Slag Formation Materials

    pp. 1069-1077

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    The effect of Ca (OH)2, SiO2 and pyrite addition on the shrinkage and metallization of pre-reduced pellets Was studied. The results are as follows:
    SiO2 addition was not favorable either from the point of strengthening or of the quality of the pellets. Only 0.2% of pyrite was effective in pellet shrinkage, and pellet strength increased. However, desulphurization was needed because of remains of high percentage of sulphur after reduction.
    Ca (OH)2 addition was very effective both in strengthening and in the quality of pellets. The amount of Ca (OH)2 needed for strengthening and for quality improvement differed according as the kinds of are used and the reduction conditions. In the case of reduction at 1 250°C, it was found that an addition of around 4% of Ca (OH)2 was generally effective owing to the formation of slag containinga large amount of CaO.
    Pre-reduced pellets which are produced with an addition of CaO can be expected to have a quality of of easy fusibility in tne melting process of pellets, because metallic iron is surrounded by slag which has a low melting point as well as being low in FeO.
  • On the Mechanisms of Alumina Cluster Formation in Molten Iron

    pp. 1078-1088

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    Aluminum deoxidation products of molten pure iron were investigated by scanning electron microscopy. The results obtained are summarized as follows.
    (1) Well developed dendritic alumina inclusions were mainly observed on staitic iron bath, and arms of those dendritic alumina tended to be cut off from stems.
    (2) Deoxidation products from stirred bath were mainly consist of spherical alumina particles.
    (3) The neck growth of alumina inclusions on the observation was successfully explained by the introduction of the sintering theory of solid particles.
  • Solidification Structure of High Speed Tool Steel

    pp. 1089-1103

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    Solidification structures of the AISI M2 type high speed tool steel were studied under various solidification conditions by metallographic and thermal analysis. Small laboratory melts were unidirectionally solidified to simplify the freezing process. Also cooling curves were obtained on 300kg ingots to investigate the differences in the solidification structure and freezing process between the unidirectionally frozen ingots and practical ingots.
    The results obtained were as follows:
    1) The secondary dendrite arm spacing, SII (μ), in columnar crystals of unidirectionally frozen ingots, was influenced only by the average cooling rate, R (°C/min), during solidification, exhibiting relationship, SII=100R-0.28, for the M2 steel.
    2) The progression of liquidus isotherm in 300kg ingot varied linearly with square root of time, but that of solidus isotherm did not.
    3) In 300kg ingots, grain diameter of equiaxed crystals, ι(μ), varied with average cooling rate, R, as did the dendrite arm spacing, showing relationship, ι=220 R-0.29. These results indicate that the mechanism of the growth of grobular grain is similar to that of the secondary dendrite arm.
    4) The morphology of the dendrites changed from equiaxed to cellular type with decreasing liquidus isotherm drift rate, V (cm/min), and with increasing temperature gradient, G (°C/cm), across solidified layer.
  • High Temperature Fatigue Properties of 18Cr-12Ni Steels

    pp. 1104-1112

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    Effects of the carbon content and heat treatment on fatigue properties of 18Cr-12Ni steels have been studied by the rotating-bending fatigue test at 600°C and 3000rpm. The results obtained are as follows.
    (1) The fatigue strength of the steel increases roughly twofold as the carbon content of the steel increases from 0.06 to 0.29% in weight.
    (2) As the carbon content of the steel increases, the effect of solution temperature on the fatigue strength becomes conspicuous.
    (3) The optimum solution temperature is the lowest one that gives a complete solution of carbide.
    (4) Slightly aged specimens give a higher fatigue strength than that of completely aged (maximum hardness) or unaged specimens.
    (5) Coaxing behaviors are also influenced by heat treatments, and the treatment to give the highest fatigue strength results in the greatest coaxing effect.
    (6) A coaxing process, which is interrupted before failure, can be utilized as a pre-treatment to improve the fatigue strength.
    (7) Grain sizes, amounts of undissolved or dissolved carbides, and the precipitation during fatigue are influenced by carbon contents of the steel and heat treatments, and from these aspects the fatigue properties described above can be explained qualitatively.
  • The Effect of Heat Treatment on the Creep Rupture Strength of Low Carbon 21/4 Cr-1Mo Steel

    pp. 1113-1123

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    The creep rupture strength of a 21/4Cr-1Mo steel was studied in relation to preheat treatment and microstructure. Results were summarized as follows:
    (1) Creep rupture strength did not always proportional to the strength at room temperature. In the short time range, the creep strength was decreased in the order of the OQ (15mm ∅; bar was quenched into still still oil), the WQ (15 mm ∅; bar was quenched into stirring water), and the FC (furnace cool in 30°C/hr) steel, while in the long time range the order was the FC, the OQ, and the WQ steel.
    (2) The greatest creep strength of the OQ steel, in the short time range, was attributable to the following two points;
    (i) it contained much more finely dispersed carbides than the FC steel, and (ii) the ratio of needle-like carbides to total number of carbides was higher and the ferrite grains were more stable than in the WQ steel.
    (3) The superior creep resistance of the FC steel could be due to the stability of the ferrite grains and the sluggish precipitation of M2C carbides during creep.
    (4) The creep stress influenced on the formation of rod-like carbide, the acceleration of softening in quenched steels and the acceleration of spheroidization of pearlite.
    From these results, it was concluded that carbides, e3pecially the mode of precipitation of carbides during creep test, played an important role in the creep strength, and the shape of ferrite grains was also important to ensure the microstructural stability at high temperatures, though this effect was in a less degree.
  • Effect of Cold Working on Austenite Grain Coarsening Temperature in Low Alloy Steels

    pp. 1124-1130

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    The effect of cold working on the austenite grain coarsening temperature has been investigated by the use of low carbon chromium molybdenum steels and the result has been discussed in terms of the particle size of aluminum nitride and the initial grain size of austenite.
    It is indicated that the austenite grain coarsening temperature decreases with an increase of the reduction of cold rolling and increases by an annealing treatment subsequent to cold rolling in the temperature range of 500 to 700°C.
    There is no significant difference between the particle size of aluminum nitride precipitated in austenite of the cold rolled steel and that of the steel not rolled.
    The initial grain size of austenite decreases with an increase of cold reduction and increases by annealing at 700°C after cold rolling. It can thus be concluded that the depressed austenite grain coarsening temperature for the cold steel results from finer initial grain size of austenite formed from the deformed ferritecarbide aggregates.
  • Effect of Hot Forging, Prior Heat Treatment and Ferrite Grain Size on Austenite Grain Size of Steels

    pp. 1131-1149

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    The effects of hot forging and prior heat treatments on the austenite grain size of high purity specimens have been examined, and the relation between ferrite and austenite grain sizes before and after austenitizing has also been investigated. The results are summarized as follows.
    1) When the austenite grain size of normalized Fe-C alloys is compared with those of as cast specimens and as forged specimens, a fairly good agreement is observed between these two kinds of grain sizes.
    2) The effect of hot forging on the austenite grain size is studied in normalized Fe-C alloys whose forging ratios are 7 and 44. The difference in the forging ratio does not give any influence on the austenite grain size.
    3) The changes in prior heat treatments e.g. normalizing, solution treatment, or precipitation treatment do not give marked differences in the austenite grain size in the case of specimens containing carbon and AlN.
    4) When the specimens are austenitized below their coarsening temperatures, the austenite grain size is nearly same as that of ferrite both before and after the austenitization.
    5) When the specimens are austenitized in the temperature range above their coarsening temperature their austenite grains become coarser than those of ferrite from which the austenite is formed, but their ferrite grains produced from the coarse austenite grains trend to recover their original ferrite grain size. When these coarsened ferrite grains are again austenitized in the temperature range below its coarsening temperature, the austenite grains are again refined and nearly same as the original fine ferrite grains in the size; the ferrite grain size of the specimen thus heat treated comes back to the original fine grain size. This grain refining is more effective of the α-γ transformation than on the γ-α transformation.
  • State Analysis of Chromium in Low Alloy Steel

    pp. 1150-1158

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    This work, a part of a general investigation on the state analysis of steel, was carried out to develope a systematic method for isolation and detemination of chromium compounds in low alloy steel.
    1. Isolation of chromium compounds from steel.
    (a) The steel sample covered with close-texture filter paper as a diaphragm, connected as an anode, is dissolved into 120ml of 1% NaCl-5% EDTA electrolyte (pH 6-7) with a current density of 50mA/cm2 for 1hr. Remove the anode, and the residue is collected into a beaker by making use of methanol.
    (b) To the residue and 50 ml of 2% EDTA solution (pH 5-6), and shake for 1 hr. Filter and wash with 0.01M. EDTA solution. Determine the chromium in cementite from filterate in accordance with section 2.
    (c) Transfer a part of the elestrolyte to a beaker and determine chromium as solid solution in accordance with section 2.
    (d) Transfer the paper and residue (paragraph b) to a beaker, add 50ml of HNO3 (1 to 2) and boil for 10min. Filter and wash with water and determine the chromium as Cr7C3 from the filtrate in accordance with section 2.
    (e) Transfer the paper and residue (paragraph d) to a beaker, add 50 ml of HCl (1 to 1) and boil for 10 min. Filter and wash with water and determine the chromium as CrN from the filterate in accordance with section 2.
    (f) Determine the chromium as oxides from the residue (paragraph e) in accordance with section 2.2. Determination of chromium.
    Add 10 to 30ml of HNO3, 5ml of iron solution (0.01g Fe/ml)(expel electrolyte) and 10ml of acid mixture (H2SO44, H3PO43 and H2O8) to each filterate and residue (section 1. b, c, d, e, and f).
    Evaporate to white fumes and then determine chromium with usual colorimetric method by diphenyl carbazide.
  • X-Ray Fluoresent Determination of Rare Earth Elements in Carbon and Low-Alloy Steel

    pp. 1159-1165

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    In a recent study to improve the properties of steel by the addition of rare earth elements, a need arose for an accurate analytical method of these elements. An investigation was undertaken to determine 4 rare earth elements (La, Ce, Nd, and Pr) in the range of 0.005 to 0.15% by the X-ray fluorescent technique.
    In the absence of reliable standards, the glass-bead technique for odd samples such as drillings was developed. Rare earth elements were precipitated as the fluorides after dissolving 5g of the sample in sulfuric acid, and the filtered fluorides followed by ignition to oxides were mixed with sodium tetra borate and melted to prepare glass-bead.
    The glass-bead method provided for precision less than 2% of the amount present. A good agreement was obtained between the chemical and X-ray results.
    The advantages of the method are the facility of the construction of a calibration curve by using chemical reagents, the absence of interelemental effects because of the separation of rare earth elements, and the versatility to be applicable to other materials with minor modifications.
    The standard samples of low-alloy steel were furthermore prepared for the direct metal disk technique and a conventional procedure was taken with satisfactory results.
  • Observation of Three Dimensional Shape of Inclusions in Low-C Al-killed Steel by Scanning Electromicroscope

    pp. 1166-1173

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    The shapes of inclusions extracted from low-C Al-killed steel from the continuous casting process have been observed by the use of a scanning electromicroscope.
    The results obtained are summarized as follows.
    1) Shapes of inclusions in steel are classified into five groupes, that is, dentritic type, cloud-like type, dumpling-like type, block-like type and others.
    2) The inclusion of dentritic type is a crystal, but ones of cloud-like type and dumpling-like type are coagulation-products of small particles.
    The inclusions of block-like type are considered exogeneous ones.
  • The International System of Units

    pp. 1174-1183

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  • Past and Coming Years with Automotive Industry

    pp. 1184-1194

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  • 抄録

    pp. 1195-1200

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