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

Tetsu-to-Hagané Vol. 72 (1986), No. 1

  • Present Situation of Study on Vaccum Hot Rolling

    pp. 14-21

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  • Report of Committee, "Metallurgy and Mechanics of Continuous Casting"/Preparation of Certified Reference Materials for Isolation and Determination of Sulphides

    pp. 22-31

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  • Production of Ultra-low Sulfur Hot Metal by Desulfurizing with CaCO3 Base Flux and the Reaction Mechanism

    pp. 32-38

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    Hot metal desulfurization by injecting CaCO3 base flux into a torpedo car has been studied.
    The desulfurization efficiency for CaCO3 base flux has been found to be higher than that for CaO base flux. This is attributed to the increase of the reaction interface area due to the thermal decomposition of the injected CaCO3 particles. The rate determining step of the desulfurization reaction in this process is liquid-phase mass transfer when the sulfur content is less than 0.013%, and mass transfer in solid particles when the sulfur content is more than 0.013%.
    It has also been revealed that the endothermic effect of the thermal decomposition of CaCO3 is compensated by the exothermic effect of the desiliconization reaction by CO2 gas, a product of CaCO3 decomposition, and therefore does not result in larger temperature decrease of the hot metal compared with CaO base flux.
  • Influence of Powder Injection on Dephosphorization and Desulphurization of Pig Iron

    pp. 39-46

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    The effect of CaO-CaF2-CaCl2 powder injection with oxygen gas on dephosphorization and desulphurization reactions of pig iron was investigated experimentally by using 6 ton ladle.
    Both reactions are affected by injection depth, powder size, powder composition and oxygen feeding rate, so that transitory reaction is important for injection process. However, its contribution to dephosphorization reaction is approximately 25% of overall reaction and permanent reaction also plays an important role in such a medium size ladle. From these results we can recognize that effect of injection on improvement of reactions is caused not only by the effective transitory reaction but also by direct feeding of powder into metal, and strong stirring by gas injection accelarating permanent reaction.
  • Influence of Bath Stirring Intensity and Top Blown Oxygen Supply Rate on the Decarburization of High Chromium Molten Iron

    pp. 47-54

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    A basic study was conducted on the decarburization of high chromium molten iron under top-and-bottom combined blowing condition using a small high-frequency induction furnace.
    (1) Decarburization is divided into stage I (high carbon region) and stage II (low carbon region). The critical carbon concentration at transfer from stage I to stage II decreases when the oxygen supply rate is restrained or when the bath stirring intensity is increased.
    (2) At stage I, when the oxygen supply rate is decreased, although the decarburization rate decreases, the Cr loss also decreases. When the bath stirring intensity is increased, the Cr loss decreases, and the decarburization rate increases. The Cr loss is determined by the balance of bath stirring intensity and oxygen supply rate from top lance.
    (3) At stage II, the decarburization rate and the Cr loss are also determined in relation to the oxygen supply rate and the bath stirring intensity, but since the rate of decarburization is controlled by carbon transfer rate in the bath to the reaction zone, the Cr loss increases with the progress of decarburization.
    (4) The total oxygen content in the bath during blowing becomes gradually larger than the dissolved oxygen content as [%C] decreases, and suspended oxides of composition similar to FeO·Cr2O3 appear in the bath correspondingly.
    (5) Coarse oxide particles exist on the bath surface in the low carbon period and fine oxide particles of the FeO·Cr2O3 composition are observed to be dispersed into the bath from the coarse particle as the starting point.
  • Fatigue Crack Growth Curves in Low ΔK Region in 3% NaCl Water for S45C and HT80 Steels

    pp. 55-61

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    It is known that da/dN vs ΔKeff curve is independent on stress ratio and predicts the most conservative fatigue life of structures, where da/dN is crack growth rate and ΔKeff effective stress intensity range. In corrosive environment, however, determining ΔKeff is difficult because corrosion product within crack promotes the crack closure.
    The purpose of this study is to describe an experimental method free from crack closure. Such a method is realized by decreasing ΔK where maximum load is kept constant and minimum load increases with increasing crack length. The experimental results, obtained for S45C and HT80 steels in 3%NaCl water, showed that crack closure did not occur when the test began at an initial condition of ΔK≅7 MPa·m1/2, R≅0.6 and dK/da=-2.3 GPa·m-1/2 and that da/dN continuously decreased down to the region of ΔK≅0.8 MPa·m1/2 and R=0.96. The minimum value of ΔK obtained in 3%NaCl water was one-third than the threshold in air at higher stress ratios such as 0.8. The crack growth curves thus obtained were useful for analyzing crack closure under constant amplitude loading with R=0.1 in 3%NaCl water.
  • Effect of Core Hardness and Notch Shape on the Rotating Bending Fatigue Limit of Induction Surface Hardened S45C Steel

    pp. 62-69

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    This report revealed the effects of preheat treatment, core hardness and notch shape on the rotating bending fatigue limit of induction surface hardened S45C steel. In addition, the effect of fracture mode on it was discussed. The results obtained are as follows;
    1) Fatigue limit of test specimens with gentle notch (stress concentration factor α=1.46) is higher than that of smooth. This reason will be that, the crack initiation of the notch specimen is at specimen surface, but that of the smooth specimen is at fish eye. Therefore, in the case of the fracture starting from fish eye in smooth specimens, the fatigue limit can be increased by the method of making a gentle notch on the smooth specimen.
    2) In the case of the effective depth of about 1.1 mm and 1.5 mm (diameter of the test specimen : 8 mm), the fracture mode starting from surface occurred when the core hardness was more than about HV 260, but the fracture mode starting from fish eye occurred when the core hardness was less than about HV 260. The fatigue limit decreased with the decrease of the core hardness.
  • Effects of Cr and V on the Hydrogen Attack Susceptibility of B Added Cr-Mo Steels

    pp. 70-77

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    In the heavy oil upgrading and coal liquefaction processes, higher service temperature and higher hydrogen pressure of the reactor vessel have required heavily sectional steel used as vessels for high pressure apprications with enhanced design stress intensity values and improved resistance to hydrogen environment. As a result of a previous alloy modification study, a 3Cr-1 Mo-1/4V-Ti-B steel with enhanced design stress intensity values had been developed. In this study, the hydrogen attack susceptibility of the newly developed steel was examined in the view point of the role of Cr and V-Ti-B additions.
    The increasing Cr content and the V-Ti-B additions remarkably improved the resistance to hydrogen attack. The species of precipitating carbide were identified by X-ray diffraction on the extracted deposits of Cr-Mo and Cr-Mo-V-Ti-B steels with various Cr contents. Both intensities of Fe3C and Mo2C, which were unstable under high temperature, were decreased as the Cr content was increased. In the microalloyed steels, Fe3C and Mo2C were futher decreased due to the precipitation of VC carbide. The improved resistance to the hydrogen attack in the developed steel was considered to be achieved through changes in the type of precipitating carbides.
  • Development of Austenitic Stainless Steel PC Wire and Strand

    pp. 78-84

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    The effects of aging and stress-aging (called hot stretching) at the temperatures from 120°C to 700°C on the mechanical properties, relaxation values, Charpy impact values and SCC behavior of hard drawn SUS 304, SUS 316 stainless steel wires have been studied.
    The main results obtained are as follows:
    (1) Yield and tensile strength of the wires increased by aging at 230°C and 530°C as well as by hot stretching. The strengthening after 230°C treatment may be due to the strain aging by C and the increase of strength after 530°C treatment results from precipitation of Cr23C6 on dislocations.
    (2) Stress relaxation values up to 250°C are low due to precipitation of Cr23C6. Almost no difference can be observed between aging and hot stretching.
    (3) Impact value at -96°C of SUS 304 stainless steel wire which was measured with 1 mm V-notched specimen was found to be about the same as that of 9% Ni steel.
    (4) It is considered that in comparison with high carbon PC wire SUS 304 stainless steel showing high tensile strength is insensitive to SCC in NH4SCN and NH4NO3 solutions.
    (5) In practice, tension member of the austenitic stainless steel wire and strand which were produced by aging at 500°C may be useful in special industrial field, for example, (a) SUS 304, in cryogenic field use (b) SUS 316, in intensive magnetic field use as a nonmagnetic material.
  • Influence of Microstructure on Yielding Behavior in Continuous-annealed Multi-phase High-strength Sheet Steels

    pp. 85-92

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    This report describes the influence of microstructure on the yielding behavior of continuous-annealed multi-phase sheet steels. A series of 0.05% carbon steels with various manganese contents were intercritically annealed at 800°C for 2 min and then quenched at various cooling rates ranging from 10 to 1 000°C/s. Some steels were given a pre-heat-treatment at 750°C for 3 h.
    It was observed that the minimum volume fraction of martensite to achieve continuous yielding was dependent on ferrite grain size, solute carbon content in α-iron and the size of martensite. The decrease in solute carbon content was closely related to the decrease in yield ratio for steels in which yield-point elongation, due to the presence of martensite, was below 2%. The solute carbon was thus found to be one of the major structural factors that control yield ratio in the multi-phase steels.
  • Corrosion Behavior of Nickel Base Heat Resisting Alloys for Nuclear Steelmaking System in High-temperature Steam

    pp. 93-100

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    The corrosion behavior of nickel base heat resisting alloys is investigated in steam at 800°C and 40 atm, simulating the superheated steam of the nuclear steelmaking system. The alloys tested are five new alloys developed for the nuclear steelmaking system and one commercial alloy, Inconel 617.
    A protective surface oxide scale, consisting of Cr2O3 mainly and of MnCr2O4, forms on all of the alloys except Inconel 617. Internal oxides, consisting of Al and Ti oxides, also form in the alloys containing Al. For Inconel 617, nodular oxides, consisting of NiO in the outer layer and Cr oxide in the inner layer, form in addition to Cr2O3 and MnCr2O4 after 1 000 h.
  • Factors Controlling the Paint Adhesion of Zinc Alloy Electroplated Steel Sheets

    pp. 101-106

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    Corrosion resistance of Zn alloy electroplated steel sheets was investigated using the salt spray test. Unpainted Zn-Ni electroplated steel sheet showed a higher resistance to red rusting than unpainted Zn and Zn-Fe electroplated steel sheets. The corrosion products of Zn-Ni were more stable than those of Zn and Zn-Fe.
    The corrosion resistance of painted Zn-Fe and Zn-Ni electroplated steel sheets was affected by the composition and the structure of their electrodeposits. The crystal structure of Zn-Fe electrodeposits changed with the composition of electrodeposits and electroplating conditions such as the kind of electroplating solution and current density. The electrodeposit of the small, granular crystals had better corrosion resistance against blistering than the electrodeposit of the big, dendrite crystals. The difference is considered to come from that between the corrosion resistances against OH-ions formed by the cathodic reaction under the paint film.
  • Blistering Phenomena of Painted Zn Alloy Electroplated Steel Sheets

    pp. 107-112

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    Corrosion behavior of painted Zn-Fe and Zn electroplated steel sheets was investegated using the salt spray test (SST).
    Corrosion resistance of electrophoretically coated Zn-Fe electroplated steel sheet was superior to that of Zn electroplated steel sheet. This was considered to be caused by the difference between their corrosion resistances against OH- ions formed by cathodic reaction under the paint film. In the case of painted specimens with cross scribes, the corrosion resistance to the alkaline solution of Zn-Fe electroplated steel sheet was higher than that of Zn electroplated steel sheet. This result agreed with the result of SST. On the other hand, the corrosion resistance to alkaline solution of unpainted Zn-Fe electroplated steel sheet was not higher than that of Zn electroplated steel sheet. When cathodic current was applied in the same solution, Zn-Fe electroplated steel sheet showed a higher resistance. The resistance to blistering of Zn-Fe electroplated steel sheet was due to the corrosion resistance to alkali in the cathodically polarized state.
  • Titanium Alloys, Microstructures and Mechanical Properties

    pp. 113-122

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  • Crack Growth Mechanism and Fracture Toughness in Acicular α Structure of Ti-6Al-4V Alloy

    pp. 123-130

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    To understand the microfracture process, Acoustic Emission three dimensional location, Acoustic Emission source characterization and fractography method have been applied for fracture toughness testing of acicular α structure in Ti-6Al-4V alloy. In this fracture process, quas-cleavage microcracks of about 200 μm diameter were nucleated at the pre-fatigue crack tip along crack front, of which distribution in the direction normal to fracture surface was about Δz=1.2 mm. Main crack growth is related to the condition where the coalescence of these microcracks occurs through specimen thickness. From these results, fracture toughness KIC and crack tip opening displacement CTODC were evaluated quantitatively, using ductile fracture criterion, and it could be concluded that these microcrackings enhance the fracture toughness of acicular α-Ti alloy.
  • Decrease of the Strength due to Delayed Quenching in Ti-6%Al-4%V Alloy and Its Mechanism

    pp. 131-137

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    The effect of delayed quenching on the strength of Ti-6%Al-4%V alloy was studied, and the mechanism of strength deterioration with delay time of quenching was investigated based on the quantitative analysis of the microstructural changes. The marked reduction of strength with delay time was a phenomenon peculiar to heat treatment in α+β two phase region, and its susceptibility depended on the chemical composition of the alloy. The microstructural changes taken place with the extension of delay time of quenching were coarsening of primary α phase, formation of acicular α phase in β phase matrix, and lateral coarsening and the increase of the number of acicular α phase, in turn. These microstructural changes were very similar to variations in the quenched microstructure due to the mass effect of quenching in this alloy. The strength after aging in the delayed quenched plates could be analyzed with an excellent accuracy by the mixed law of two phase structures which was taken account of grain size in primary α phase. The susceptibility of delayed quenching was controlled by stability of β phase at the reheating temperature of quenching, that is, by the increase of the content of β-stabilizing elements such as V.
  • Effects of Forging and Heat Treatment Conditions on Mechanical Properties of a High Strength Titanium Alloy, Ti-17

    pp. 138-145

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    This report was to study the dependence of mechanical properties of a Ti-17 forging on processing variables such as final hot working reduction rate and its temperature, and heat treatment.
    The major results obtained are as follows :
    (1) In the case of equiaxed α microstructures, a larger final forging reduction was desirable for raising ductility and also unnotched fatigue strength, and on the other hand a lesser one greatly improved fracture toughness. Putting these results together, it was concluded that the way of raising fracture toughness would be favorably adopted.
    (2) Double solution heat treatment was proved a better way to improve fracture toughness than conventional single solution treatment. Basic data for solution and aging temperature for controlling mechanical properties were acquired.
    (3) β-processed acicular microstructure, which gave the best fracture toughness, showed inferior ductility in the transverse direction of a forged bar, of which problem needs further studies to solve.
  • Anisotropy of Mechanical Properties in Ti-6Al-4V Hot Rolled Plates

    pp. 146-152

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    When the α+β type titanium alloys are not subjected to the proper hot rolling process, the anisotropy in the microstructure appears even after the solution treatment and aging. This study was conducted to examine the anisotropy in mechanical properties of two heats (A and B) of Ti-6Al-4V alloy hot rolled plates which are subjected to the solution treatment and aging, and the mechanical anisotropy was correlated with the microstructural anisotropy. Tensile properties shows isotropic nature for both alloys. KIc and KIscc of alloy A are slightly reduced for transverse direction. On the other hand, KIc of alloy B is not reduced in T direction and KIscc is markedly increased for T direction. The KIscc in T direction is higher than KIc in the same direction. It was found that stress corrosion cracking of alloy B in transverse direction which was formed at the tip of prefatigue crack propagated with some branching along the primary α phase boundaries, leading to the apparent increase in KIscc.
  • In-Situ SEM Observation of Microcutting Process

    pp. 153-158

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  • 鉄冶金学からエレクトロニクス材料の研究まで

    pp. 159-163

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  • 抄録

    pp. 171-172

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  1. blast furnace
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