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

Tetsu-to-Hagané Vol. 81 (1995), No. 10

  • Ductilization of Structural Intermetallic Alloys by Microstructural Control

    pp. 943-950

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  • Recent Progress in Corrosion Life Prediction of Steel Structures

    pp. 951-958

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  • Evaporation Rate of Copper in High Carbon Iron Melt under Reduced Pressure

    pp. 959-964

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    For clarifying the evaporation behavior of copper from liquid iron, the evaporation rate of copper has been studied under reduced pressures of several hundred Pa in the temperature range from 1723K to 1823K. Also, the effect of alloying element on the evaporation rate were examined.
    The experimental results obtained are summarized as follows :
    (1) The first order rate equation can be applied to the change of copper content in iron with time, and then the evaporation rate of copper increased with decreasing the pressure. This fact indicates that the mass transport step in the gas phase is a rate determining step under the present experimental conditions, because the mass transfer coefficient in the gas phase is inversely proportional to pressure.
    (2) The apparent activation energy for removal rate of copper was calculated to be about 230 kJ/mol including the enthalpy change for the copper evaporation.
    (3) The evaporation rate of copper was promoted by adding sulfur, but the additions of nickel or chromium lead to the decrease of the evaporation rate of copper.
  • Influence of Reaction between Immersion Nozzle Refractory and Molten Steel on Occurrence of Blisters

    pp. 965-970

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    The effect of the inner porous refractories-molten steel reaction on the incidence of blisters and the mechanism whereby the incidence of blisters is prevented by using an immersion nozzle with a silicaless inner porous refractories that does not react with the molten steel were studied. The following results were obtained :
    (1)Blisters are caused by 0.5 mm and larger argon gas bubbles, and particularly 1.0 mm and larger argon gas bubbles have a direct bearing on the incidence of blisters in the sheet product.
    (2)The mechanism whereby the incidence of blisters depends on the number of sequence cast heats can be explained by the increase in argon gas bubble diameter with the increase in the inner porous refractories-molten steel reaction in the later heats in the sequence cast.
    (3)Fine argon gas bubbles can be stably injected into the molten steel by using an immersion nozzle with a silicaless inner porous refractories that does not react with the molten steel. This stable injection of fine argon gas bubbles helps prevent the occurrence of blisters in the sheet product.
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  • Mathematical Model Analysis on the Growth of Initially Solidified Shell

    pp. 971-976

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    Irregular growth of initially solidified shell in continuous casting is analyzed quantitatively, taking account of the shell deflection. Temperature, thermal stress, and shell deformation are calculated simultaneously in cross section of the initially solidifying shell. Shell irregularity obtained from this calculation is in agreement with the experimental results. This means the model can simulate the phenomena in the mould. Heat resistance at the interface between mould and metal is dominant only for a few seconds from meniscus. After that, heat resistance in the initially solidified shell becomes dominant. This means the careful control of initial solidification for a few seconds from meniscus is important to decrease the irregular shell growth. Calculated results shows that more even thermal resistance between mould and metal, higher speed casting and milder cooling rate will be preferable in decreasing the irregularity.
  • Individual Analysis of Nonmetallic Inclusions in Steel by Using the Gallium Focused Ion Beam Secondary Ion Mass Spectrometry

    pp. 977-982

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    Nonmetallic inclusions frequently exert a lot of unfavorable influences on the quality of steel. The size of nonmetallic inclusions in current steel products is less than a few μm in diameter. It is desirable to make clear the origin and generation process of such small particles of nonmetallic inclusion. In order to measure the shape, size, composition and inner elemental distribution, development of characterization methods for each inclusion particle is required.
    By employing a gallium focused ion beam (FIB) as a primary ion beam of secondary ion mass spectrometry (SIMS), the particle analysis with high spatial resolution is easily achieved. In this paper, we present the novel individual analysis of nonmetallic inclusions in steel by gallium FIB SIMS.
    We analyzed in two ways the nonmetallic inclusion particles segregated by electron beam melting. (1) By crosssectioning of the particle using a gallium FIB, elemental maps of cross-section were obtained. The elements were distributed inhomogeneously on the cross-section. (2) We carried out the compositional analysis for several particles individually. Ten particles were analyzed by the shave-off analysis and the multivariate cluster analysis. Based on the composition of each particle, the inclusions were classified into six types.
  • Effects of Crystallinity on Formability and Corrosion Resistance of the Polypropylene Laminated Steel Sheets by Melt-extrusion Method

    pp. 983-988

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    The effects of crystallinity on the formability and corrosion resistance of the polypropylene (PP) laminated steel sheets by melt-extrusion method were researched.
    The crystallinity of the PP layer varies with the cooling condition. The crystallinity of the rapid cooling sample A (cooling rate was 100°C/s) was about 28%, while the slow cooling sample B (cooling rate was 2°C/s) was about 60%.
    The laminated layer of the sample B became white appearance from impact shock and microcracks were observed. On the other hand, both the whitening and the microcracks were not observed on the sample A. After the corrosion resistance test with a surfactant solution, the high crystallinity sample B showed inferior corrosion resistance to the low crystallinity sample A. In addition, the mechanical properties of the PP layer remarkably changed with the crystallinity.
    It was necessary to cool the PP laminated steel sheet quickly with a cooling rate of not less than 20°C/s at least in the range from 100°C to 50°C in order to restrict the crystallization of the laminated PP resin.
  • Corrosion, Friction and Wear Properties of Various Materials in Molten Zinc

    pp. 989-994

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    Iron and steel have been predominantly adapted for mechanical parts in hot-dip plating pots of continuous galvanizing line. However, corrosion and wear resistance are not enough against molten zinc then mechanical parts such as sink and support rolls must frequently be changed and repaired to maintain good surface finishes of the products.
    In this work, corrosion resistance, friction coefficient and wear resistance against sialon ceramics on various steel, cermet and ceramics in molten zinc using a homemade testing machine were evaluated to search and develope proper materials.
    The results can be sammarized as follows :
    (1) Corrosion resistance of steel and cermet is low especially in moving bath. However, ceramics show excellent corrosion resistance.
    (2) Friction coefficient of steel is low, that of cermet scatters from as same level as steel to 1.5 times higher by sort and amount of metal included. Friction coefficient of ceramics with carbon is low but without carbon is high.
    (3) Amount of wear loss scatters widely based on materials and composition. Wear loss is low in ceramics with carbon and high in without carbon, that of steel and cermet is placed in the middle.
    (4) Ceramics with solid-lubricative property must be used at least one side of bearings at present. However, wettable ceramics against molten metal are of great promise.
  • Growth Behavior of Alloy Layer in Hot-dip Zn-530 mass% Al Coating

    pp. 995-1000

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    The growth of the alloy layer formed in a hot-dip Zn-530 mass%Al coating has been studied by gas-reducing coating and fluxing coating methods. The growth of the alloy layer occured at a bath temperature above 520°C even in a short time immersion (15s), and is accelerated with increasing the Al content in the bath and raising the bath temperature. The grown alloy layer consists of Al-Fe intermetallic compounds (mainly Al5Fe2 phase containing 6.77.8 at%Zn), and Zn phase (94 95 at%Zn) solidified at cavities in Al-Fe intermetallic compounds. In similar to Al5Fe2 phase formed in a hot-dip aluminizing, this Zn-containing Al5Fe2 phase formed in the hot-dip Zn-5-30 mass%Al coating has also a strong orientation of (002) plane and grows even in a vertical direction to the steel surface. However, in the hot-dip Zn-530 mass%Al coating, Al-Fe intermetallic compounds grow preferentially at ferrite grain boundaries of the steel substrate where Zn has diffused.
    It is considered that the grain boundary diffusion of Zn to the steel substrate has a great influence on the growth of the alloy laver.
  • Effects of Ti and La on High Temperature Oxidation Behavior of 20Cr-5Al Steel

    pp. 1001-1006

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    An investigation has been undertaken into the oxidation behavior of foils of 20Cr-5Al steel and similar steels containing titanium and lanthanum additions, in air at 1373 and 1423K.
    Oxides scales on the 20Cr-5Al steel spalled when the specimen was cooled and breakaway took place immediately due to depletion of aluminium in the metal during oxidation. Titanium lowered the depletion rate of aluminium in the metal. The oxide scales on the steel containing titanium maintained relatively good contact with the specimen and breakaway behavior was retarded compared with that of the base steel. The steel with lanthanum and titanium additions showed excellent oxide scales adherence and the protective oxide scales were retained over long periods.
    In addition to depletion of aluminium, the morphology of metal-oxide scales interface influenced the oxidation behavior of the steels. Voids formed at the interface during oxidation. Due to depletion of aluminium, convoluted Cr2O3 scales developed in the voids following breakaway. The 20Cr-5Al steel formed voids in the early stages. However, lanthanum and titanium additions were effective in reducing void formation. These effects can be associated with a cation transport mechanism of oxidation.
  • Improvement of the Descalability of Annealed SUS304 Steel by Using the Vertical Type Direct Fired Heating Furnace

    pp. 1007-1012

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    Effects of heating conditions on the thickness and composition of the scale, and on the descalability (ease of descaling) of annealed stainless steel were investigated. Cold rolled SUS304 steel strips were continuously heated, soaked and cooled using an experimental annealing line which was equipped with direct fired heating furnaces. Then, specimens from the strips were analyzed by secondary ion mass spectrometry and thin film X-ray diffractometry, and were examined in descaling test. The results obtained are as follows :
    Rapid heating of SUS304 steel with impinging flame burners at 6731173K decreases accumulation of Fe and Si oxides into scale, meanwhile soaking at the temperature above 1273K for 1020s accumulates Cr and Mn oxides into the scale. We presume that two annealing conditions above mentioned improve the descalability of SUS304, because oxides of Cr and Mn dissolve rapidly by electrolysis in Na2SO4 solution in descaling process, while oxides of Fe or Si does not dissolve so rapidly or at all. But, too long soaking forms a thicker and Si concentrated scale which makes the time required for descaling longer.
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  • Influences of Ni and Ru on Corrosion Resistance of Ti-0.5%Ni-0.05%Ru(Grade13)

    pp. 1013-1018

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    Influences of Ni and Ru on corrosion resistance of Ti-0.5%Ni-0.05%Ru (Grade13) were investigated. Study on its microstructure indicates that Ni precipitates in α-Ti matrix as an intermetallic Ti2Ni and Ru is detected intensively in the Ti2Ni. When Ti2Ni or Ti2Ni-Ru electrodes were connected to commercially pure titanium (C.P.Ti) which was corroded in 5%HCl solutions, they raised the potential of C.P.Ti up to a passivation potential and thus prevented the corrosion by means of promoting an cathodic reaction on their surfaces. Ru in Ti2Ni was confirmed to increase its corrosion resistance and to promote an cathodic reaction to larger extent than Ti2Ni itself does, by which Grade13 indicated passivation in concentrated HCl solutions.
  • Inclusion Rating by Statistics of Extreme for Electron Beam Remelted Super Clean Bearing Steel and Its Application to Fatigue Strength Prediction

    pp. 1019-1024

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    The inclusion content of recent high strength clean steels has been remarkably reduced by the progress of steel making process. Nevertheless, it is known that inclusions still cause fatigue fracture and decrease in fatigue strength. Thus, the quantitative correlation between fatigue strength and inclusion content or size must be made clear.
    In order to investigate the critical lower bound of inclusion size which influences the fatigue limit, a special steel with extremely low inclusion content, the electron beam remelted super clean bearing steel (EB-CHR), was prepared.
    The inclusion rating based on the statistics of extreme was applied for the quantitative evaluation of inclusion size in EB-CHR with decreasing size of inclusion, detrimental effect of inhomogeneities which have larger size than nonmetallic inclusions was revealed in place of inclusions.
    The obtained results are summarized as follows ;
    (1) The size of inclusions in EB-CHR measured by the inclusion rating based on statistics of extreme is extremely small in comparison with commercial clean bearing steels.
    (2) The fatigue limit of EB-CHR is extremely high in comparison with commercial bearing steels.
    This is due to the reduction of inclusion size by electron beam remelted process.
    (3) The fatigue fracture origins of EB-CHR are seldom at inclusions but mostly at a small inhomogeneity which is presumed to be a local imperfectly heat-treated structure, bainite with lower hardness in the martensite matrix. This is because, based on the rating by statistics of extreme, the size of inhomogeneity (bainite) has relatively larger size than nonmetallic inclusion.
  • Hydrogen Occlusion Behavior during Delayed Fracture in Cold Drawn Steel Wire and Heat Treated Steel Bar for Prestressed Concrete

    pp. 1025-1030

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    Stress-relieved steel wire for prestressed concrete (PC Wire), which is produced with cold drawing, has a higher resistance to delayed fracture than steel bar for prestressed concrete (PC Bar), which is produced with heat treatment. However, the hydrogen occlusion behavior of PC Wire has not been investigated yet. To clarify this behavior, fracture surfaces were examined, the hydrogen occlusion content was measured by using hydrogen thermal analysis, and hydrogen trapping sites were observed by using secondary ion mass spectrometry. It is found that PC Wire occludes hydrogen released at 470 K which affects delayed fracture and at 620 K which does not affect delayed fracture. This shows that PC Wire decreases the ratio of hydrogen content at 470 K which affects delayed fracture. PC Wire has a higher critical hydrogen content at which delayed fracture occurs than PC Bar. Since PC Wire traps hydrogen along the direction of cold drawing, it does not create linear crack at delayed fracture. The hydrogen behavior of PC Wire thus increases the resistance of PC Wire to delayed fracture.
  • Fabrications and Thermoelectric Properties of Semiconducting Iron Disilicides

    pp. N454-N460

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