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

Tetsu-to-Hagané Vol. 76 (1990), No. 8

  • Development of High-performance Steel for Steel Buildings

    pp. 1203-1210

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    In the ultimate limit state design and seismic design of steel structures, it is postulated that the structural members have sufficient deformability or rotation capacity. In this context, the relationship of the plastic deformation capacity of steel structural members and the stress-strain curves of their materials are made clear. Namely, to secure the sufficient deformation capacity of structural members, the yield-ratio (the ratio of yield stress to tensile strength) of material should be reasonably low. For flexural members such as beams and beam-columns, the rotation capacity can be evaluated by the complementary energy of materials more exactly. Scattering of yield stress could give an adverse effect on the strength and deformability of steel structures subject to horizontal loading. In this viewpoint, the upper limits of the yield stress and of the yield ratio should be specified in the material standard.
  • Interfacial Stability during Solidification under Microgravity Environment

    pp. 1211-1218

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  • Mechanisms of Sheet Surface Damage in Secondary Metalworking Processes

    pp. 1219-1227

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  • Total Reflection X-ray Fluorescence Spectrometry

    pp. 1228-1236

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  • Transformation Behavior of Steels-Transformation and Properties of Commercial Steels-/Establishment of the Method for Inductively Coupled Plasma Emission Spectrochemical Analysis of Steel(JIS G1258-1989)

    pp. 1237-1253

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  • Kinetic Analysis of Coke Gasification Based on Non-crystal/Crystal Ratio of Carbon

    pp. 1254-1261

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    Gasification of metallurgical coke was studied at 1000, 1200, 1400°C with Ar-CO-CO2 mixtures. Reaction of coke in blast furnace is dominant from about 900°C. And at the same time, growth of graphite crystal (crystallite) in coke begins to occur from that temperature.
    In present paper, two types of carbon crystal were classified by means of X-ray diffraction. One is crystallite that contribute to X-ray diffraction, another is noncrystalline carbon that contribute only to background intensity. In this study, reaction model that the two kinds of carbon have different reactivity and react simultaneously and independently, was developed and kinetic analysis was performed.
    Following results were obtained.
    (1) Lc increases as function of temperature and there is no influence of reaction. (2) La increases as function of temperature in Ar atmosphere. But in existence of reaction, the size of La is so smaller. From this result, it was considered that the gasification reaction proceeds such as mode of decreasing La. And reaction mechanism combining to characteristic of crystallographic structure is proposed.
  • Heating-up and Reaction Characteristics of Burdens in Oxygen Blast Furnace Process

    pp. 1262-1269

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    Heating-up and reaction characteristics of burdens in the oxygen blast furnace process were studied with an one-dimensional mathematical model to obtain the following results ; (1) With increasing oxygen concentration in blast, heat flow ratio augments, temperature goes down and reduction is retarded. Boyond the heat flow ratio of 0.90, the preheating gas injection is required. (2) Appropriate range of preheating gas volume and temperature in which the direct reduction rate is low and low fuel rate is realised is ; gas volume corresponding to heat flow ratio of 0.740.90, temperature 600200°C. (3) The composition of preheating gas has little influence. The level of preheating gas injection is adequate in upper shaft as long as the heat transfer capacity from the top of furnace is sufficient. (4) Solid temperature at tuyere level can be controlled with the theoretical flame temperature, and with preheating gas volume and temperature in the low fuel rate condition. (5) Operational fuel rate range is wide ; 500 kg/t (with preheating gas)1200kg/t (without preheating gas).
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  • Evaluating System for Using the Newly Developed Oil in Actual Cold Mill

    pp. 1270-1276

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    A system for evaluating the lubricity of newly developed rolling oil is constructed when it is used in an actual cold rolling mill. In the system, the evaluation is carried out as follows ; (1) Coefficients of friction and limitation lines of conventional oil and developed oil are measured by means of the simulation testing machine. (2) The interfacial temperature rises due to friction between roll and workpiece of the two oils are calculated. (3) The pass schedule in the actual mill is examined. (4) The interfacial temperature rise at the stand in which the friction pick up occured is calculated from the data examined. (5) When the developed oil is used in the actual mill, the interfacial temperature rise at the same stand is calculated. (6) From these results, the maximum rolling speed in the actual mill is calculated when the developed oil is used.
    By means of this evaluating system, the maximum rolling speed when the newly developed oil was used in the actual mill increased by 200 m/min compared with that of the conventional oil. It is seen that the evaluating system is effective to develop the new oil.
  • Rib Shape of Steel Pipe with Inner Ribs for Concrete-filled Structural Section and Its Rolling Method

    pp. 1277-1284

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    This report represents the study on the optimum rib shape for the concrete-filled structural steel pipe, and also the study on the rolling method of the hot-rolled strip. The pipe with inner ribs is developed for the composite foundation pipes consisted of steel pipe and filled-concrete in order to get sure bond stress capacity between pipe and filled-concrete. The bond stress capacity tests indicate that the value of rib height divided by rib space is the most essential parameter and the value of 0.1 gives the optimum rib shape. Next, the characteristics of rolling of the rib-strip are studied by experiments with many longitudinal ribs distributed throughout the strip width. The experimental results show that the rib height depends on not only reduction but also the caliber profiles and entry thickness. Based on the experiments, the hot rolling method of the strip with 3.0 mm height ribs on the average is established.
  • The Manufacturing Method of Seamless Clad Steel Pipe and Development of Circumferential Welding for the Pipe

    pp. 1285-1292

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    The manufacture of seamless steel pipe internally cladded with austenitic corrosion resisting alloy has been studied and a new one-side welding method has been presented for non-accessible circumferential seam of clad steel pipe. The results obtained in this investigation are summarized as follows;
    (1) The negative convergence of roll and rolling reduction more than 1.8, can prevent the seamless clad steel pipe from cracks caused by twisting of pipe and disbonding, when hot rolling method is applied to the manufacture of pipe.
    (2) A new one-side welding method with buffer layer of iron containing carbon stabilizer may give double wall structure and higher safety against sulphide stress corrosion cracking to the circumferential seam of clad steel pipe.
    (3) A circumferential carbon steel weld metal of super alloy clad steel pipe deposited by buffer layer method, does not generate cold crack caused by hydrogen, because of larger capacity to absorb hydrogen and shrinkage of preceding austenitic weld metal during cooling.
  • The Characteristics and Evaluation Method of Bonding Strength on Rolled Stainless Clad Steel

    pp. 1293-1300

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    The characteristics of bonding strength of hot rolled stainless clad steel were investigated in conjunction with the microstructures and fracture toughness of bonding interface and the effect of test specimen size on bonding strength. The following results were obtained.
    (1) The bonding ratio is the most important parameter for evaluation of characteristics of bonding interface. The bonding strength and fracture toughness decrease and crack propagation rate increases with decrease of bonding ratio, which results in higher possibility to debond at the interface with T joint welds.
    (2) The shear and ram tensile strengths insufficiently reflect the characteristics of bonding interface and are much affected by the size of test specimen.
    (3) The fracture toughness and crack propagation rate of bonding interface change with the strength of cladding stainless steel and residual stress remained in the interface.
  • Effects of Electrolysis and Bath Conditions on the Surface Roughness, Morphologyand Crystal Orientation of Zinc Electrodeposit

    pp. 1301-1308

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    The study was conducted on the effects of electrolysis and bath conditions on the surface roughness, morphology and crystal orientation of zinc electrodeposit from sulfate bath and chloride bath. (1)The surface roughness of the zinc electrodeposit from sulfate bath was increased by suppressing mass transfer of zinc through variations of electrolysis and bath conditions. (2)Under the conditions which promoted mass transfer in sulfate bath, stacked platelet crystals were formed with the (0001) basal plane of zinc hexagonal lattice parallel to the substrate or slightly oblique to the substrate. Under the conditions which suppresses mass transfer, formation of stacked platelet crystals with <1120> perpendicular to the substrate was observed. (3)From chloride bath, coarse zinc crystals were formed in the low current density range due to a low overvoltage. Roughening of the surface in the high current density range occurred in higher current density range from chloride bath than from sulfate bath. (4) The preferred orientation of the zinc electrodeposit from both of the baths coincided with PANGAROV'S theory.
  • Under-film Corrosion Mechanism of Cold Rolled Steel Sheet for Automobiles

    pp. 1309-1316

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    This report attempts to elucidate the under-film corrosion mechanism of cold rolled steel sheet for automobiles in cyclic wet and dry environments.
    It was found that an anodic site was the front of growing rust and a cathodic site was the interface between a substrate and corrosion products.
    The Fe (OH)2was found to be formed at the initial stage of the corrosion and it was transformed into mainly Fe3O4, α, β-FeOOH, Fe2O3by oxidation.
    The porosity of the corrosion products increased by the phase transformation which accompanied the change in density. The void space fraction was about 40%. This void space was a passage of Cl-, H2O and O2 from the cross scribes to the corrosion tip and to the interface between the iron substrate and corrosion products.
  • Under-film Corrosion Behavior of Zinc and Zinc Alloy Coated Steel Sheets for Automobiles

    pp. 1317-1324

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    The behavior of under-film corrosion of zinc and zinc alloy coated steel sheets for automobiles in cyclic wet and dry environments was investigated by EPMA and X-ray diffraction.
    It is recognized that a deteriorated corrosion intermediate of zinc and zinc alloy coatings due to attacking by chlorine ion was formed between a sound coating and corrosion products under paint → regandless of a variety of coatings.
    On the other hand, the final corrosion products of coating observed were ZnCl2·4Zn (OH)2, ZnO, Zn(OH)2.
    Therefore, it was considered that zinc in the coatings is transformed once into chloride and subsequently the chloride is transformed into ZnCl2·4Zn(OH)2, ZnO, Zn(OH)2.
    As a result it was found that corrosion resistance of zinc and zinc alloy coated steel sheet was attributable to resistance to attacking by chlorine ion.
  • Effect of Plated Metals and Cr Contents in Steel on Corrosion Behavior of the Metal Plated Sheets in Methanol Fuel

    pp. 1325-1332

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    In order to develop the metal plated steel sheet for alcohol fuel tank corrosion of metals in methanol solution and effect of chemical composition of steel on corrosion behavior of surface finished steel were investigated.
    Tin and nickel have corrosion resistance in methanol solution. In methanol containing formic acid, tin and nickel have nobler potentials than steel, so they have no ability of cathodic protection for steel. Tin or nickel plated steel corroded at the defect of plating layer in methanol containing formic acid with the yellow corrosion product. To avoid this phenomenon, using of chromium added steel as base metal is effective. Immersion potential of steel shifts to the noble by addition of chromium. The surface of steel was investigated by elipsometry method and X-ray photoelectron spectroscopy method. And it is presumed that chromium added steel has corrosion resistance for methanol containing formic acid by the formation of Cr2O3 film.
  • Effect of Alloying Elements on Perforation Corrosion Resistance of Hot Rolled Steel for Automotive Bodies

    pp. 1333-1340

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    The effect of alloying elements on perforation corrosion of mild steel was studied by cyclic corrosion tests and an outdoor exposure test. Ultra low C-P-Cu hot rolled steel has been alloy-designed for the perforation corrosion resistance application for the automotive bodies.
    The newly designed TS 45 kgf/mm2 steel, produced in the mill, shows the excellent mechanical properties and an equivalent paintability to a low C mild steel. In addition, the perforation life time of the developed steel is about twice longer than that of the mild steel, according to a cyclic corrosion test conducted on automotive underbody parts.
    Its excellent resistance to perforation corrosion was considered to be achieved by the formation of a protective rust layer of amorphous species, judging from the results of rust analysis by EMPA, FT-IR and laser Raman spectrometer.
  • The Growth of γ' and γ'' Precipitates in Nickel-base Superalloys

    pp. 1341-1348

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    The nucleation and growth behaviours of spherical ordered γ' (L12)-phase and disc-shaped ordered γ'' (DO22)-phase precipitates in Inconel 718 have been investigated mainly by micro-Vickers hardness test and transmission electron microscopy.
    In this study Inconel 718 type alloy (718) and it's modified Ni-base alloy (718M) were compared.
    The hardness of 718 and 718M aged in various conditions closely related to the size and the quantity of γ', γ'' precipitates and δ-phase.
    Decreasing the (Al+Ti) concentration in alloy while maintaining the Nb content increased the driving force both to coarsen γ'' precipitates and form δ-phase.
    It was considered that γ' and γ'' precipitates in 718 nucleated almost simultaneously at the early stage of aging.
    The growth kinetics of γ' (718) and γ'' precipitates (718, 718M) in the region free of δ-phase followed the predictions of LIFSHITZ-SLYOZOV-WAGNER (LSW) theory of diffusion controlled growth at all aging temperatures. The activation energy for the growth of γ' precipitates in 718 was estimated to be 245 kJ/mol which was nearly similar to those of diffusion of solute atoms; i. e. Al, Ti and so on, in Ni and Ni-base alloys. The activation energies for the growth of γ'' precipitates in 718 and 718M were estimated to be 451 and 464 kJ/mol, respectively.
  • Effect of Graphite, Cementite on Mechanical Properties of Cold Rolled High Carbon Steels

    pp. 1349-1355

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    Either ferrite-cementite or ferrite-graphite mixed microstructure was developed after cold rolling and annealing in 0.65%C steels containing different amounts of Mn and Cr. These steels were again cold rolled and annealed in order to examine the effect of the kind of 2nd phase on the recrystallization process, texture development and the mechanical properties after annealing.
    In the ferrite-cementite steel, recrystallization started at a lower temperature, but the ferrite grain growth was limited. The {111} and {100} textures formed by cold rolling were maintained even after the completion of the primary recrystallization and finally a sharp {111} <112> recrystallization texture was obtained. Whereas, in the ferrite-graphite steel, recrystallized grains grew markedly with large decreases of the {111} and {100} texture components, finally forming rather random texture after recrystallization. The difference in the recrystallization process was thought to be caused by differences in the volume fraction and the distribution of the second phase. The mean γ-value after full annealing was high in both steels, but the planer anisotropy of the γ-value was inverse. The high γ45-value obtained in ferrite-cementite steel could be attributed to the strong {111}<112>plus {100}<011> texture.
  • Morphology of Second Phase and Tensile Properties in a TRIP-Aided Super High Strength Dual-Phase Steel Sheet

    pp. 1356-1363

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    A relationship between retained austenite and second phase morphologies and the influences of these morphologies on the tensile properties have been investigated using a 0.17%C-1.41%Si-2.00%Mn TRIP-aided dual-phase steel containing retained austenite.
    (1) A large amount (above 10 vol%) of retained austenite lay isolated in ferrite matrix and away from hard phase particle if austenite morphology in α+γ region during annealing is a network structure or a fine grained island. In the other case, the retained austenite film (below 5 vol%) remained inside the hard phases and along these lath boundaries. This type of retained austenite was remarkably stabilized.
    (2) The retained austenite increased both the flow stress and the elongation. These relationships between tensile properties and retained austenite content were affected with the morphologies.
    (3) The influences of second phase morphology on flow stress appeared to be small in TRIP-aided dual-phase steel as compared to conventional dual-phase steel because of the retained austenite. While, the elongation considerably depended on the morphology. The network structure of second phase enhanced internal stress and strain hardening rate after most of retained austenite had transformed to martensite. The steel with fine-grained isolated particles exhibited the increased elongation since the void-formation at hard phase/matrix interface was suppressed as compared to the other type of steel.
  • Effect of Short-Time Tempering Treatment on the Resistivity to Sulfide Stress Corrosion Cracking of Steels with 70 kgf/mm2 Yield Strength

    pp. 1364-1371

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    Fundamental analyses with regard to the effect of chemical composition, heat treatment conditions, microstructure and fracture mode on SSC were conducted in order to develop quenched and tempered 70 kgf/mm2 yield strength steel with superior SSC resistance for induction heat treatment. Results obtained were as follows.
    1) In the case of short time tempering, the optimum tempering temperature to give resistivity to SSC is a high temperature range below Ac1.
    2) At the optimum tempering conditions, spheroidized carbides are uniformly dispersed both in grains and at grain boundary.
    3) The steels tempered in the above-mentioned range exhibit the transgranular cracking, where as the steels tempered at lower temperature cracked by intergranular cracking.
    4) Grain boundary segregation of phosphorus which promotes grain boundary embrittlement is suppressed by the addition of molybdenum. It is reduced more by tempering at high temperature for short time than at low temperature for long time.
    From the above results, it was found that in the case of short time tempering the addition of small amount of molybdenum in steel and tempering at high temperature below Ac1 led to the high resistivity to SSC.
  • Effect of Carbide Forming Elements on Hydrogen Attack of 21/4Cr-1Mo Steel

    pp. 1372-1379

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    21/4 Cr-1 Mo steels which were alloyed with V, Nb, Ta or Ti up to 0.23 at% were studied to evaluate the effect of each carbide forming element on the hydrogen attack. Steels were quenched following the austenitization at 950 or 1 250°C and tempered at 690°C for 19.4 h, and exposed to hydrogen at 600°C and 300 kgf/cm2 for 1000 or 3 000 h.
    At the higher austenitizing temperature of 1 250°C, alloying of these elements always decreased the bubble volume density, represented by the bubble volume per unit area of the prior austenite grain boundary. The effect in the reduction of the bubble volume density increased in the order of V, Nb, Ta and Ti, and it correlated well with the standard free energy change for the formation of MC type carbides.
    In the case of austenitization at 950°C, a little effect to decrease bubble formations was unexpectedly found out in steels containing the higher content of Nb, Ta or Ti than that at 1 250°C, and the bubble volume density did not decrease in Nb containing steels. These results are considered to be originated from the undissolved carbides at the lower austenitizing temperature of 950°C. In a longer exposure of 3000 h, addition of Nb, Ta or Ti with the range of 0.05 to 0.24 at%, regardless of the content, always increased the bubble volume density.
  • Effects of N and V on Ferrite Grain Refinement in Normalized Steel

    pp. 1380-1386

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    The effect of grain refinement of steel is well known as a metallurgical method to make both strength and toughness improve. In this study, in order to use VN precipitates for α-grain refinement in normalized steel, the effect of V and N content on γ-grain size at reheating stage and α-grain size after air cooling and the mechanism of grain refinement have been investigated.
    The results obtained are as follows,
    1)The α-grain refinement in high N-V added steel is due to the degree of γ-grain refinement by VN precipitates and high γ/α transformation ratio.
    2) The more the VN precipitates in γ-grain, the finer the α-grain becomes. Its effect becomes distinguished in the range of 3050 ppm N as VN and is saturated with 100 ppm N as VN.
    3) High γ/α transformation ratio is due to the increase of a nucleation site at γ-grain boundary. It is considered that the contribution of VN is not in lowering of transformation temperature and increasing of transformation time, but in playing role as a α-nucleation site or suppressing of α grain growth through precipitation in front of α phase.
  • Determination of C, P and S in Steels by Time-resolved Atomic Emission Spectrometry

    pp. 1387-1394

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    The time-resolving technique was applied to the determination of a trace amount of elements C, P and S in steels.
    The results were as follows:
    (1) A higher precision analysis was performed. The analytical repeatabilities in standard deviations at an elemental concentration of 10 ppm were 2.3 ppm for C, 0.8 ppm for P and 0.5 ppm for S.
    (2) Spectral interferences were almost avoided in this case. The concentration correction factors were 0.16×10-4 for an interference of Ni on the PI 178.29 nm line and 0.2×10-4-5.8×10-4 for that of Mn on the SI 180.73 nm line.

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