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

Tetsu-to-Hagané Vol. 58 (1972), No. 3

  • 革新を担う人々

    pp. 373-374

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  • Experimental Study of the Inactivation of Reduced Pellets at Lower Temperatures

    pp. 375-386

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    Synopsis:
    It is generally recognized that iron oxide pellets reduced by hydrogen at lower temperature are easily re-oxidized by the atmosphere even at room temperature. However, those pellets which were slightly re-oxidized by the inert gas containing the lower oxygen potentials showed inactive behaviors. Very thin oxide layer of less than 9 Å thickness was formed on the pore surface of the pellet during re-oxidation with N2-O2 gas mixture of below 1% O2 content. When O2 content in the gas mixture was below 1%, re-oxidation degree was nearly 0.9% independent of oxygen potential. But if the O2 content exceeded 1%, the re-oxidation degree increased rapidly with the O2 content.
    It was also shown that the rate of the re-oxidation was controlled by the diffusion of oxygen through the boundary layer and the reacted shell layer. Therefore, the exposure time necessary for inactivation could be calculated and it was dependent on the oxygen potential.
    Furthermore, when the resistance of the gas transport could be negligible, the rate of the re-oxidation was represented by the logarithmic rate law.
  • Production of Steels for Sheet and Coil in Continuous Casting

    pp. 387-394

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    Synopsis:
    A number of new casting techniques to produce steels for sheet and coil in continuous casting have been developed and quality of continuously cast slabs with 200×1600 mm2 and products have been investigated. The results are summarized as follows.
    1) It is desirable to decrease oxygen content as low as possible by pre-deoxidation before aluminum addition in converter.
    2) A new method, which is characterized by Al-wire addition with rapid rate into molten steel stirred by inert gas injection in ladle, has been developed. This method results in increase of yield and accurate control of soluble Al content in steel.
    3) The inert gas purging from the bottom of ladle gives a uniform bath temperature and is very beneficial in cleaning the bath.
    4) A new sealing method for perfectly preventing the oxidation of steel stream from open air has been developed. By the application of this method, the content of inclusions in steel has been reduced to 20 to 40 ppm, which have been calculated in terms of oxygen content in steel in tundish.
    5) A new nozzle is designed so that stagnant zone of steel bath is not formed in mold.
  • Effects of Tempering, Prior-austenite Grain Size and Shape of Test Specimen on the Delayed Fracture of Low-alloyed Steels

    pp. 395-410

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    Effects of tempering condition, prior-austenite grain-size, and shape of test specimen on the behavior of hydrogen-induced delayed fracture have been investigated for several low alloysteels for high strength bolt. The main results are as follows;(1) The tempering at temperatures above 500°C improves the resistance to delayed fracture, except for secondary hardenable steels. This resistance depends on the strength level and the strain hardening behavior.(2) Both steels with fine (ASTM 9-10) and coarse (ASTM 0-3) grains of prior-austenite have a tendency to be more susceptible to delayed fracture than these with medium grain size (ASTM 4-5).(3) The thinning of specimen width results in decreasing of the susceptibility to delayed fracture owing to the change of stress condition, from plain strain to plain stress.
  • Properties of Medium Carbon Chromium Steel

    pp. 411-422

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    A study was made of the mechanical properties and hardenability of medium carbon chromium steel which was developed as corrosion resisting steel under weak acid corrosive atmosphere.
    It was proved that retained hydrogen had an extremely bad effect especially on the ductility of this steel. Therefore, the process of production was investigated in order to increase the ductility.
    As the effect of boron on hardenability was different with nitrogen content, the relation between the effect of boron and content of such nitride forming elements as aluminum and titanium was examined.
    The following results were obtained.
    (1) In order to guarantee 8 percent of elongation (JIS No 4 tensile specimen) in steel with 140 Kg/mm2 of tensile strength, hydrogen content had to be kept less than 1 ppm. Hydrogen content was decreased less than 1 ppm by slow cooling of the bloom after blooming.
    (2) The effect of boron on hardenability was remarkable in steels containing nitrogen of less than 40 ppm even if only boron was added to the steels. But in order to make boron more effective for hardenability, aluminum more than 0.01 pet., and aluminum more than 0.04 pet. or titanium more than 0.02 pet. were required for steels containing about 0.006 pet. of nitrogen and for steels containing about 0.01 pet. of nitrogen respectively.
    (3) The effect of boron on hardenability corresponded with content of acid soluble boron which was decided by solubility products of (B)(N), (Al)(N) and (Ti)(N). But in all cases, the relationship between hardenability and the content of acid soluble boron did not always hold good.
    In steels containing aluminum, the content of acid soluble boron which was necessary to secure the same hardenability was much smaller than the content in steels without addition of aluminum.
    (4) It was proved from the investigation on distribution of boron by α-track method that the hardenability was related to the concentration of boron on pre-austenite grain boundaries in steel without addition of aluminum.
  • Effect of Alloying Elements on Carbide Precipitation in Hadfield Steel

    pp. 423-433

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    Some Hadfield steels with 1%Si, 2%Al, 0.8% Mo, 4% Cr, or 0.5%V were studied mainlyby micrography on isothermal carbide precipitation after solution treatment. Isothermal precipitation diagrams for all steels were determined as C-urve, fundamentally similar to that of standard Hadfield steel. By addition of 1% Si, the carbide precipitation in steel was little affected, but the temperature range in which pearlitic constituent (PC) appeared was slightly extended. By addition of 2%Al, the grain boundary carbide precipitation in high temperature range was accelerated, but the transformation into PC wasretarded and its temper ature range was limited in a slightly narrower range. Moreover, matrix precipitation of carbide in high temperature range was disturbed remarkably by addition of Al. By addition of carbide forming elements such as Mo, Cr, and V, the precipitation of carbide was accelerated especially in high temperature range, and the precipitation temperature range was extended to higher temperature. However, transformation into PC was retarded by addition of these elements, and addition of Cr +V was markedlyeffective. By addition of 4% Cr and 4% Cr+0.5% V, matrix carbide precipitation in steel was remarkably accelerated, and its precipitation area formed a C-urve, which had a nose at 825× in the former steel, and at 800× in the later steel. Addition of V was markedly effective for precipitation hardening of steel. It is considered that the retarding behavior of transformation into PC by addition of carbide forming elements was similar to that by lowering carbon content in steel. In microstructures of V-added steel, peculiar platelet PC which was different from nodular PC in other steels was observed. The formation ofthe platelet PC is considered to be due to a large quantity of platelet carbide precipitation in steel by addition of V.
  • The Microstructure and Toughness of High Tensile Strength Steels

    pp. 434-451

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    The impact properties of some high tensile strength steels were investigated in relation to the austenite grain size and the cooling rate.
    The results showed the existence of optimum cooling rates for the transition temperature. The optimum cooling rate depended on the hardenability of steels, and as the austenitizing temperature was raised it shifted to the lower cooling rate.
    The electron microscopic observation revealed that the structure with superior impact properties was the duplex martensite-bainite structure. The morphology of carbide in this bainite was similar to that in the lower bainite, but the trace analysis for such bainite revealed that it had the same lath-like morphology with a ‹111› α {110} α as that in the upper bainite and the lath martensite.(This bainite in a low-carbon low-alloy steel was named as Bainite-III type in a previous paper.)
    The orientation measurements of facet pit and fracture surface clarified that the cleavage plane was (100). Based on the direct observation of fracture surface by scanning electron microscope, the unit crack path was defined. The unit crack path showed experimentally a better correlation to the transition temperature than the austenite grain size.
    These results suggested that the role of bainite in the duplex structure was the partitioning of austenite grain prior to the martensite transformation.
  • Secondary Recrystallization Behavior during the “Strain-Anneal” of 3% Silicon-Iron Sheet

    pp. 452-463

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    The growth conditions of seed crystals in the sheet material of 3% silicon-iron cold-rolled 70%(1st-stage rolling) and annealed at 800° for 30 min were examined, and the grain growth behavior during the strain-anneal procedure was observed together with the texture change.
    The prestrain of a wide range of 20-60% by cold rolling in the 1st-stage rolling direction or the transverse direction was found to be sufficient to induce the growth of seed crystals. At higher prestrains, seed crystals of (110)[001] orientation aligned to the direction of prestrain appeared. At lower cold reductions, prestrain in any direction gave the seed crystals of (110)[001] orientation aligned to the 1 st-stage rolling direction. The primary recrystallization after the prestrain was accomplished by the nucleation and growth in the former case and by the migration of original grain boundaries in the latter. The transition between them was found to occur around the prestrain of 30% cold reduction, where the seed crystals of both orientations were found. These seed crystals grew selectively during the secondary recrystallization and the difference in the rolling or primary recrystallization texture obtained after various prestrains had no effects on the selective growth of seed crystals.
  • The Influence of Intermittent Friction on Wear Phenomena of Plain Carbon Steel

    pp. 464-471

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    The influence of intermittent friction on wear phenomena of plain carbon steel (S33C) was investigated using high frequency induction hardened steel (S45C) as standard test piece.
    The test was performed by means of rolling friction method having 15% slip without any lubricants, and in addition to the comparison of wear loss, wear particles and sliding surface were analized by X-ray diffraction method.
    Results obtained are as follows.
    1) Wear loss increases as the intermittent frequency and stopping time increase.This is due to that oxide produced on sliding surface is not sufficient.
    2) Hardened steel have a good wear resistibility to intermittent friction and with increasing hardness the proportion of αFe2O3 in wear particles increases.
    3) Under a small load there is little difference of wear loss for intermittent and continuous friction.
    4) Intermittent friction causes a big plastic deformation on sliding surface.
  • State Analysis of Molybdenum in Low Alloy Steel

    pp. 472-481

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    This work, a part of a general program of research on the state analysis of steel, was carried out to develop a simple method for extraction and determination of molybdenum carbides [(Fe, Mo) 3C and Mo2C] in low alloy steel. The procedure is as follows:
    1. Extraction of molybdenum carbides from steel.
    (a) Cover the steel sample with close-texture filter paper as a diaphragm, connected as an anode, is dissolved into 100 to 130ml of 1% NaCl-5% EDTA electrolyte (H 6 to 7) at a current density of 50mA/ cm2 for 1 to 2 hr. Remove the anode and the residue is collected into an Erlenmeyer flask. To the residue add 20ml of 6N HCl and pass in a stream of argon gas for 10 min at room temperature.
    (b) Filter and wash with water. Add 5 ml of HNO3 and 10ml of HC1O4 to the filtrate and evaporate to dense white fumes. Cool dilute to 100 ml and determine Mo as (Fe, Mo) 3C in accordance with section 2.
    (c) Transfer a quarter of the electrolyte to a beaker. Add 20ml of HNO3 and 10ml of HC1O4 and evaporate to dense white fumes. Cool, dilute to 100 ml and determine Mo as solid solution in accordance with section 2.
    (d) Transfer the paper and residue (paragraph (b)) to a beaker, and 30 ml of HNO3 and 10 ml of HC1-O4 and evaporate to dense white fumes. Cool, dilute to 100 ml and determine Mo as Mo2C in accordance with section 2.
    2) Photometric determination of molybdenum.
    Transfer 10 to 20 ml of each of solutions (section 1 (b), (c) and (d)) to 50ml volumetric flasks. If the iron contents is less than 40 mg, add iron solution (0.02g Fe/m/) until a total of40 to 50 mg of iron. To each flask add 5 ml of thiourea solution (10%), 8 ml of HC1O4, 2 ml of NaCNS solution (30%) and 10 ml of ascorbic acid solution (5%), dilute to 50 ml and let stand for 10 min. Measure the absorbance of solution against water at 460 mu.
    A complete analysis can be carried out in 3 to 4 hr.
  • A Fundamental Study of Isolation and Determination of Titanium Compounds in Steels

    pp. 482-494

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    A fundamental study of isolation and determination of titanium compounds in steels was carried out by means of hydrochloric acid, sulphuric acid, phosphoric acid, bromine-ester, iodine-alcohol, and potentiostatic electrolysis methods.
    The results are as follows:
    1. According to the experimental results on chemical behaviors of various synthesized titanium compounds,
    (1) Titanium carbide, TiC is very stable in mineral acids, but easily decomposed in oxidizing reagents.
    (2) Titanium nitride, TiN is decomposed in nitric acid, while in other mineral acids it is slightly decomposed at elevated temperatures.
    (3) Titanium oxides, the higher the valency of titanium, the more stable the oxide is. And ferrous titanium oxides are attacked in mineral acids.
    (4) Above-mentioned titanium compounds, TiC, TiN and titanium oxides, are very stable in iodinealcohol and bromine-ester.
    (5) Titanium sulphides, TiS and Ti3S4 are unstable in mineral acids and easily decomposed in iodinealcohol, bromine-ester and other oxidizing reagents.
    2. Carbide, TiC in steels can be extracted by any methods quantitatively.
    3. Nitride, TiN in steels is also extracted by any methods but the isolated TiN is gradually decomposed in mineral acids.
    4. For isolation of titanium compounds in steel, the electrolytic method is desirable, because in acid and halogen-organic solvent the unstable compounds such as TiO, 2FeO·TiO2, TiS and the precipitates of very fine particles are attacked slowly.
    5. Chemical separation of synthesized titanium carbide, nitride, oxide and sulphide is possible, but chemical behavior of inclusions and precipitates in steels are affected by their size, disorder of their lattice and coexisting elements so that accurate separation is very difficult.
  • Potentiometric Acid-base Titration of Slags in Molten Potassium Nitrate

    pp. 495-500

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    Several slags were potentiometrically titrated in molten potassium nitrate. The sample was allowed to react with a definite amount of potassium dichromate in the melt at 400°C, and then the excess dichromate was titrated back with the weighed portions of potassium carbonate. An antimony rod was used as the indicator electrode, and a Pt/Pt (II) couple in a eutectic mixture of LiCl-KCl asthe reference electrode. The potential break through the end-point was 0.2-0.3V, and reproducible results could be obtained for each slag sample. The amounts of the acid consumed by the slags were compared with the basicities of the samples, which were calculated from various methods. Almost linear relationship could be obtained between the amounts of the acid required and the following basicities based on the chemical analyses of the samples; they are lime-silica ratio, V-ratio, basicity ratio, the basicity by KERLIE and the basicity by MORI.
  • Relation between Formability and Mechanical Properties of Metal Sheet

    pp. 501-518

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  • The Present and Problem of Powder Metallurgy and New Development

    pp. 519-532

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  • Estimation of the Japanese Standard Sample of Iron and Steel for Instrumental Analysis by Photoelectric Emission Spectrochemical Analysis

    pp. 533-548

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  • 抄録

    pp. 549-555

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