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

Tetsu-to-Hagané Vol. 77 (1991), No. 7

  • Recent Development of Surface Finishing Technology for Steel Products

    pp. 861-870

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  • Oxygen Evolving Anode of Titanium Substrate

    pp. 871-877

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  • The Deposition Behavior of Electrodeposited Zinc-Silica Composite Coating from a Sodium Nitrate-added Bath and the Coating Characteristics

    pp. 878-885

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    The deposition behavior and the coating characteristics of an electrodeposited Zn-SiO2 composite coating have been studied. SiO2 particles were maintained in good suspension in the plating bath without any special agitation. The SiO2 deposition rate was increased when sodium nitrate was added to the plating bath. The amount of sodium nitrate required for SiO2 deposition was mainly determined by the pH of the plating bath. When the pH was low, sodium nitrate was required in relatively large amounts for SiO2 deposition.
    SiO2 particles were distributed uniformly in the coating except for the extreme surface. The extreme surface layer consists of SiO2-rich phase. The grain size is fine and the orientation of the deposit is random for the Zn-SiO2 composite coating. The coating contains small amounts of an oxidized zinc, probably zinc hydroxide.
    The Zn-SiO2 deposition mechanism has been proposed as follows:
    (1) Nitrate is electrochemically reduced at the cathode and raises the pH of the electrolyte at the cathode-solution interface.
    (2) The increase in pH makes the SiO2 particles coagulate and, at the same time, zinc hydroxide precipitates on the surface of the SiO2 particles.
    (3) The cathode is covered with those co-precipitates and the deposition occurs through them. We have speculated that, according to "the Adsorption mechanism" proposed by GUGLIELMI, the SiO2 deposition rate is high for the nitrate-added bath because the cathode is adsorbed by the SiO2-rich precipitate.
  • Morphology and Microstructure of Electrodeposited Zinc-Nickel Binary Alloys

    pp. 886-891

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    Zinc-nickel electrodeposited sheet steels have widely been adopted for automobile bodies for their improvements in the corrosion resistance and formability. In principle, these properties depend on the crystal structure, morphology and microstructure of deposits. The deposits of various zinc contents have been prepared galvanostatically from sulfate baths and examined by scanning and transmission electron microscopies. The 96.8 at% zinc, η-single phase deposit exhibits a collective morphology of hexagonal plates thin in the direction of c-axis. With the decrease of zinc content, the deposit changes to the hexagonal columnar crystals which have triangular pyramidal shape in morphology. These hexagonal columnar crystals are formed by the lateral growth of the hexagonal plate edge i.e. step along (00·1)η side surfaces. The 92.7 at% zinc hexagonal columnar crystals form steps on {10·0}η surfaces, and flatten the steps on {10·0}η surfaces with the decrease of zinc content. Further decrease of zinc content to 88.4 at% zinc, the hexagonal columnar crystals can no more absorb γ-particles. These excess γ-particles form granular crystals, and precipitate between the hexagonal columnar crystals.
  • Epitaxial Growth of Zn and Zn-Ni Electrodeposits on Steel Sheets

    pp. 892-897

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    The crystallographic aspects of zinc and zinc-nickel alloy electrodeposits on steel sheets have been studied by means of transmission electron microscopy (TEM) and O-lattice theory. TEM observation shows that the pure zinc and zinc-nickel hcp η-phase electrodeposits grow epitaxially on α-iron substrate with Burgers' orientation relationship. O-lattice theory predicts this relationship for η-phase while the increase of Ni content changes the dimensions of a-axis and c-axis. TEM observation shows the cube-cube parallel relationship between the zinc-nickel γ-phase and the substrate. This relationship can be also interpreted in terms of O-lattice theory.
  • Characteristics of Ni-Sn-Zn Alloy Coated Steel Sheet by Thermal Diffusion Method

    pp. 898-905

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    The alloy plating method by the thermal diffusion was developed in order to get the Ni-Sn-Zn alloy plated steel. This new method consists of two processes, at first, Ni, Sn and Zn triple layers are electroplated on the steel in this order and then, the electroplated layers are heated for the diffusion. The structure of this Ni-Sn-Zn alloy consists of the multi-component alloy layers, the surface side consists of Sn-Zn eutectic alloy and the steel base side consists of Zn-Ni and Sn-Ni alloys. The diffused multi-alloy layers on the steel have some interesting properties, such as a good corrosion resistance in the salt spray test and the humidity test, an excellent solderability and the suppression for the occurrence of tin whiskers. Therefore, this thermal-diffused Ni-Sn-Zn alloy coated steel sheets (Ni=0.4, Sn=3.0, Zn=0.5 g/m2) are commercially used for the components of electric appliances.
  • Structural Analysis of Black Nickel Deposits on Electrogalvanized Steel Sheet

    pp. 906-912

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    Electroplating in dilute Ni2+ electrolyte over limiting current density has been investigated as the blackening method for the electrogalvanized steel sheet.
    The structure of the black deposits on the electrogalvanized steel sheet was analyzed by the X-ray diffraction method, scanning electron microscope, X-ray photoelectron spectrometer and glow discharge spectrometer and it was found that the surface of the black electrogalvanized steel sheet was partly covered with small Ni granules of about 0.1 μm in diameter.
    The small Ni granules were covered with Ni, Zn, and composite compounds, such as Ni (OH)2, NiO, Ni2O3, Zn(OH)2 or ZnO and further covered with Zn(OH)2, ZnO of around 100 Å thick.
  • Effect of Pulsating Flow on Mass Transfer in Packed Bed under Fe3+-iron Particle System

    pp. 913-920

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    Effect of pulsating flow on mass transfer in packed bed is studied by taking Fe3+-iron particle system as an example of liquid-solid system, because of the industrial importance of iron plating. Spherical and cubic particles are used as packing materials having very different shapes. Pulsation is generated by a rotary cock or a piston.
    Mass transfer coefficient kL for cubes under steady flow is larger than that for spheres. Comparison of kL under steady and pulsating flow without reverse flow (rotary cock) shows no effect of pulsating flow on mass transfer for both spheres and cubes. Comparison of kL under steady and pulsating flow with reverse flow (piston) reveals, however, excellent effect; mass transfer for spheres is accelerated under quasisteady state and that for cubes is promoted much more than in quasi-steady state, where mass transfer is assumed to proceed depending on the absolute value of velocity.
    Velocity fluctuations just after the bed are measured by a hot film probe and the difference between the flow fields for spheres and cubes is discussed in connection with the difference of the mass transfer under steady and pulsating flow.
  • Thin Metal Coating from Non-aqueous Electrolytes

    pp. 921-930

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    [in Japanese]
  • Amorphous Al-Mn Electroplating in Molten Salt Bath

    pp. 931-938

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    Although molten salt electroplating is interesting method to develop new pre-coated steels, there has been little commercial exploitation because of powdery and/or dendritic deposits. In this study, the electroplating of Al, especially Al-Mn alloy on steel sheet in AlCl3-NaCl-KCl molten salt bath is focused. High speed fluid flow of molten salt and deposition of Al-Mn alloy were found to be most effective to smooth-faced deposition at high current density. Consequently, ultra-smooth lustrous deposit with amorphous structure was generated.
  • Crystal Orientation and Element Distribution of Spangle on Hot-dip Galvanizing Steel

    pp. 939-946

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    Spangles formed at hot-dip galvanized steel were classified and the distribution of Pb and Al, which were impurity and additional element respectively in molten zinc bath, on the spangle surface was investigated. The hot-dip galvanized Al-killed steel was produced with gas reduction type hot dipping testing aparatus in which steel sheet was cleaned by heating in reducing atmosphere and dipped into molten zinc bath which contained 0.25 wt%Pb and 0.17 wt%Al. X-ray Laue method was used for determination of crystal orientation and EPMA was used for the measurement of distribution of Pb and Al at the spangles.
    The main results of the study are follows:
    (1) The spangles are classified from the point of view of the crystal orientation and the appearance into the seven types as follows,
    Fern I, Fern II, Mirror, Frost, Half fern, Feather, Triangle.
    (2) The direction of the straight boundary of the spangles coincide with the projected direction of preferred crystal growth orientation (<1010>) on the spangle surface.
    (3) Spangles are classified into α type and β type from the point of view of the inclination of c-axis (<0001>). The c-axis of α type spangle is inclined to the straight boundary of the spangles and the c-axis of β type spangle is inclined to the reverse direction.
    (4) The amounts of Pb and Al at the spangle surface vary with the types of the spangle.
    (5) The spangle with the larger amounts of Pb and Al has less brilliance.
  • Formation Behavior of Alloy Layer in Initial Stages of Galvanizing

    pp. 947-954

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    The formation behavior of the alloy layer in the initial stages of galvanizing at 450°C has been investigated, using ultra low carbon Ti added steel sheet. The formation of Fe-Zn intermetallic compounds on the steel surface was retarded with the increase of Al content in galvanizing bath. For high Al content in the bath, Fe2Al5 intermetallic compound grew with dipping time. At the same time, diffusion of Zn into Fe2Al5 layer occurred. And furthermore, the outburst phenomenon was observed with the increase of immersion. The occurrence site of outburst structure corresponded well to grain boundary of the base steel. Fe2Al5 layer formed in the first step of immersion was fractured by the occurrence of outburst and dispersed in zinc coating. The formation mechanism of the outburst structure which means the initiation of growth of Fe-Zn intermetallic compounds was discussed.
  • Estimation of Isothermal Alloying Behavior in Galvannealing Process of Galvanized Sheet Steel

    pp. 955-962

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    A mathematical technique has been suggested to estimate more adequate isothermal alloying behaviortime and temperature dependence of Fe enrichment-in galvanized coating in galvannealing process. Galvannealing experiments using salt-bath were conducted with mill products of galvanized steel; and Austin-Ricketts' type equations were applied to data-fitting by means of multiple regression analysis so as to linearize the relation of Fe quantity in coating and heating time.
    The original experimental equations, which involve errors due to unavoidable heating-up periods in heattreatment in salt-bath were adjusted to more adequate ones by applying finite difference approximation and multiple regression analysis repeatedly and alternately.
    It was proved through correlation between estimated values and observed ones that the adjusted equations are more appropriate than the original ones. Corrected log (Fe quantity in coating) vs. log(t) plots indicated the following: 1) Fe enriching behavior at 450°C is subject to the reverselogarithmic time dependence at the outset of the reaction, and to auto-catalytic time dependence after some latent time. 2)The behavior at 500°C and higher temperatures is subject to the parabolic time dependence.
  • Effects of Galvannealing Conditions on Anti-exfoliation Properties of Galvannealed Coating in Bead-drawing

    pp. 963-970

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    Anti-exfoliation properties of galvannealed coatings on extra low carbon Ti-added steel galvannealed under various heating conditions were investigated by using a bead-drawing test, and the result was compared with that of a cylindrical cupping test and an adhesive-bonding tensile test.
    Exfoliation amounts in the bead-drawing test are not necessarily correlated with those in the cupping test: regarding ζ-rich coatings, significant discrepancy between exfoliation amounts in the bead-drawing test and those of the cupping test was observed, and exfoliation amounts in the bead drawing test were larger than expected values deduced from the result in the cupping test. ζ-rich coatings are subject to coating exfoliation at coating/steel boundary in the bead drawing test as well as in the adhesive-bonding tensile test. It was thought that the deterioration of exfoliation resistance of ζ-rich coatings is attributable to high frictional coefficient and relatively poor coating adhesion at coating/steel boundary. Coating adhesion of ζ-rich coatings to steel substrate is improved by eliminating ζ-phase by means of galvannealing at temperatures below 500°C.
    Coating adhesion of δ1-rich ones galvannealed above 550°C was proved very poor in both the bead-drawing test and the cupping test; in both cases, exfoliation of this type coatings seems to be caused by bending-unbending deformation.
  • Effects of Galvanizing and Galvannealing Conditions on Powdering Characteristics of Galvannealed Steel Sheet

    pp. 971-978

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    The effects of various manufacturing conditions on powdering characteristics were investigated. Powdering is suppressed by an increase in Al content of the bath, a decrease in the bath temperature and a decrease in the galvannealing temperature. All of these conditions tend to delay the alloying progress. In the case of low Al content (0.12%), ζ-phase (FeZn13) abruptly, appears and forms homogeneous layer at the initial stage of alloying, and then completely changes into δ1-phase (FeZn7) in a short period. When the Al content is high (0.16%), the alloying progress is slow and ζ-phase appears heterogeneously at localized spots with time lags. The ζ-phase which appeared late remains unchanged up to the δ1-phase. As the hardness of ζ-phase is lower than that of δ1-phase, the ζ-phase deforms preferentially and relaxes a part of stress induced by forming, therefore powdering is suppressed.
  • Effect of Coating Structure on Powdering Resistance of Galvannealed Steel Sheet

    pp. 979-986

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    Effect of coating structure on powdering resistance of galvannealed steel sheet was investigated and the followings are clarified.
    1)Higher galvannealing temperature deteriorates powdering resistance. But slower cooling from higher temperature (500550°C) improves powdering resistance.
    2)In the case of lower galvannealing temperature (=440°C), the powdering resistance is rather good, although the cooling rate doesn't affect powdering resistance.
    3)Exfoliation of galvannealed steel sheet after tensile test correlates with amount of powdering evaluated from draw bead test.
    4)Γ1-phase (Fe5Zn21) is formed along the interface of coating galvannealed at lower temperature (≤500°C) or cooled slowly from high galvannealing temperature.
    5)The decrease of Γ1 ratio [Γ1/(Γ+Γ1)] deteriorates powdering resistance.
  • Effect of Atmosphere in Continuous Annealing on Adhesion of Vapor Zinc Coated Steel Steets

    pp. 987-994

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    As an alternative to the Non Oxidizing Furnace (NOF) method, the subject of a continuous heating process for annealing and surface activation of steel sheets prior to vapor zinc coating was taken up.
    Studies on a laboratory-scale were made up to find out whether production of vapor zinc coated steel sheets with excellent adhesion was possible in a N2 atmospheric gas with limited amount of H2 content using the conventional continuous annealing furnace. As the result, it was found that production of vapor zinc coated steel sheets with superior performance was possible even by the continuous annealing conditions of [700°C×45 s annealing→400°C×240 s overaging] at base steel temperature just before vapor zinc coating of 150°C and above, if O2 concentration was less than 2.5×10-3 vol% in the 2 vol%H2-H2 gas with dew point of -20°C.
  • Structure and Corrosion Resistance of Zinc Alloy Coated Steel Sheets Obtained by Continuous Vapor Deposition Apparatus

    pp. 995-1002

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    New zinc alloy coated steel sheets have been developed by continuous vapor deposition apparatus.
    In a deposition chamber, zinc and alloying metal were evaporated individually by Electron-Beam (EB) irradiation, and were deposited on steel strip continuously.
    Some properties of Zn-Al, Zn-Cr, Zn-Mg, Zn-Ni and Zn-Ti alloy coated steel sheets were investigated. Crystal orientation of these coatings was affected by alloying metals. Depth profiles of alloy composition in Zn-Al and Zn-Mg coatings are almost uniform. The other coatings had double-layered structure, composed of an intermetallic compound layer and a zinc rich layer. The intermetallic compound phases were not the same as those shown in a equilibrium phase diagram for binary alloys.
    Corrosion resistance of Zn-Mg alloy coated steel without painting is excellent in salt spray test. Corrosion product layer of this coating consists of only ZnCl2·4Zn(OH)2 without ZnO and c-axis of hcp structure of ZnCl2·4Zn(OH)2 was parallel to the direction of the film growth.
    Mg ion dissolved from the coating during corrosion seemed to play a role to form this corrosion product layer.
  • Effects of Substrate Pretreatments on Initial Crystal Growth and Film Performance of Ion Plated Chromium Films

    pp. 1003-1010

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    Effects of pretreatments such as argon ion bombardment and preheating of steel substrates on adhesion and formability of ion plated films were studied. The chromium film formed on the steel substrate with preheating at 200°C and argon ion bombardment (proper pretreatment) provided the excellent adhesion and formability compared with that formed without preheating or argon ion bombardment. The compositional depth profiles of chromium films on steels obtained by AES showed that the chromium film formed on the steel pretreated properly had no oxide and carbonaceous contamination at the interface, with much broader mixing zone than that of the chromium film formed without argon ion bombardment or preheating. It was suggested that the good adhesion of the chromium film formed on the steel with proper pretreatment was attributed to both the sputter cleaning effect before deposition and the formation of mixing zone.
    The growth and orientation of the chromium films formed on the steels with various pretreatments were investigated using TEM. Plate-like grains grew epitaxially on the steel with proper pretreatment, whereas very small grains that didn't grow epitaxially were observed in the films formed with improper pretreatment. It was considered that the inferior formability of the chromium film formed without argon ion bombardment or preheating was caused by the high probability of the crack formation in grain boundaries among many small grains.
  • Characteristics of Electrolytically Chromated Steel with Dispersedly Plated Granular Tin as Substrate

    pp. 1011-1018

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    Granular tin was plated on steel prior to chromate treatment.
    The granular tin plating was obtained by extremely low current density electrolysis or by reducing the concentration of additional tin plate.
    The dispersedly plated granular tin improved the weldability for sanitary can production because of its lower electric contact resistance, and gave a good corrosion resistance because of its cathodic protection action to steel in comparison with the conventional Tin Free Steel.
    Suitable covering area of the dispersedly plated granular tin on steel substrate was found to be 1570%.
  • Effects of Kind of Plating and Plating Weight on the Formability of the Film on Prepainted Steel Sheets

    pp. 1019-1025

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    The formability of thermosetting epoxy phenolic lacquer film painted on tin coated steel sheets (TP) and chromium coated steel sheets (TFS) both with chromium oxide layer was evaluated by electric resistance of the painted steel sheets and observation of SEM. The formability of the lacquer film on TFS becomes worse with increasing coating weight of chromium, while in the case of TP, the formability improves with increasing coating weight of tin. It is considered that the formability of plating layer apparently influences the formability of the film on the plating.
    The corrosion resistance of the painted steel sheets in acetic acid aqueous solution was evaluated by measuring the electric resistance of the sheets. The electric resistance of the painted TFS, which is low compared with that of painted TP, decreases rapidly in the solution, while that of painted TP decreases gradually.
  • Effect of Ni Content in Zn-Ni Alloy Electroplated Steel Sheet on Zinc Phosphatability

    pp. 1026-1033

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    It is important to study the effect of the Ni content on phosphatability of Zn-Ni alloy electroplated steel sheets which are used in the exposed side of automotive bodies. Phosphate coating weights formed on pure Zn and Zn-Ni alloy containing Ni above 11.5% are independent of zinc phoshate solution flow rates and uniform coatings can be obtained. The alloys containing 3 to 9% Ni, however, show a strong flow rate dependency. A number of zinc phosphate crystal nuclei decreases and the final coating weight increases with a decrease in the flow rate. These alloys may cause trouble in the coating uniformity when they are used in the antomotive phosphating line where the flow rate is not uniform.
  • Application of Scanning Vibrating Electrode Technique for Evaluation of Chemical Surface Treatment on Zinc Coated Steel Sheets

    pp. 1034-1041

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    Using a scanning vibrating electrode technique (SVET), corrosion current distributions in a dilute sodium chloride solution were measured for chemically treated surfaces of two type of the zinc coated steel sheets (hot-dip galvanized and zinc vapor deposited steel sheets).
    The following results were obtained.
    (1)The zinc coated steel sheets with a normal dip-chromating film after painting exhibited excellent paint film adhesion and satisfactory corrosion resistance at cut edges, when anodic current was not detected by SVET over the entire surface of the zinc coated steel sheets after the suitable alkaline surface conditioning treatment and flash chromating.
    (2)The SVET system with a electromagnetic loud speaker unit for vibration proved useful to evaluate the chemically treated film on the zinc coated steel sheet.
  • Influences of Drying Temperature on States and Physical Properties of Dry-in-place Type Chromate Coating Film

    pp. 1042-1049

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    Influence of drying temperature on states and physical properties of a dry-in-place type chromate coating which contains Cr (III), Cr (VI), and PO43- were investigated by thermal analysis method. And also the relationship between thermal states and corrosion resistance was studied.
    The result of the differential thermal analysis method with the chromate coating at wide range of temperature shows characteristics reactions of inorganic materials.
    Endothermic reaction at a range from 85°C till 200°C and exothermic reaction from 200°C till 300°C were found. The chromate coating can be divided into three states from the result of this thermal behavior.
    The result of corrosion test of this chromate coated galvanized steel between visual and electrochemical method exhibits the best performance with drying at the end temperature of the endothermic reaction.
    It was also proved by values of chromium fixed ratio in coating that chromate coating had several thermal states and exhibited different physical properties as adhesion strength etc.
  • The Structure of Phosphate Crystals Influencing the Scab Corrosion Resistance

    pp. 1050-1057

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    The structure of phosphate crystals that exerts a favorable effect on the scab corrosion resistance on the painted steel surface was investigated and characterized by 1) a low Zn/P intensity ratio measured by glow discharge spectrometry, 2) a low preferred orientation of the (100) plane in phosphophyllite, and 3) angular and granular phosphate crystal morphology.
    The aforementioned structure of phosphate crystals depends on the crystal growth process. When the dissolution of iron from the steel sheet during the phosphating treatment is insufficient, the hopeite epitaxial growth plane (020) conforms to the phosphophyllite epitaxial growth plane (100), and the mixed crystals with a high Zn/P ratio grow along the steel surface. When the dissolution of iron from the steel sheet is sufficient, the iron ion concentration in the solution increases, the intrinsically free precipitation of phosphophyllite without the restraint of epitaxy becomes predominant, and phosphate crystals with a lower Zn/P ratio grow.
    The dissolution of iron from the steel sheet is accelerated by the oxides of manganese and silicon in a surface layer of up to 0.1 μm deep that is dissolved during the phosphating treatment.
    x

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  • Phosphotability of Zn-Ni Alloy Electroplated Steel Sheets

    pp. 1058-1065

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    The phosphotability of Zn-Ni alloy electroplated steel sheets was investigated, and the influence of phosphate film appearance was discussed.
    1) When the alkaline degreasing was weak in phosphate treatment, it happened that the phosphate film of Zn-Ni alloy electroplated sheets had "irregular flow pattern" appearance. In this case, electropainting film had same "irregular flow pattern" appearance.
    2) The surface of Zn-Ni alloy which had less than 13 wt% Ni content was easily covered with zinc oxide, and then zinc oxidation controlled the phosphate reaction and caused "irregular flow pattern" phosphate appearance.
    3) In order to prevent this "flow pattern" phosphate appearance, immersion post treatment in electroplating solution had good effect.
    4) As compared with "irregular flow pattern" appearance phosphate film, uniform appearance phosphate film by immersion post treatment had good performance of wet adhesion as well as good electropaintability.
  • Surface Treated Steel Sheet Coated with Silica-organic Composite Coatings

    pp. 1066-1074

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  • Evaluation Method for Distinctness of Image of Coated Surface

    pp. 1075-1086

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  • Cratering Mechanism of Cationic Electrodeposition Primer over Precoated Steel Sheets

    pp. 1087-1094

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    Cationic electrodeposition primers have been widely adopted by automobile companies due to their advantages with regared to application and corrosion resistance. However, under certain conditions, cationic electrodeposition primers can give craters over precoated steel sheets. Therefore, it is important to establish the exact mechanism of cratering from the viewpoint of cratering control.
    In this study, resistance-time profile which were calculated by means of measured current and voltage at the initial stage of electrodeposition were investigated using digitized measurements to record data over millisecond time scales. Uncured as-deposited paint film in the course of electrodeposition was observed by optical microscope, and defects remained in the deposited film at the end of electrodeposition was also observed during curing process by optical microscope. The results indicate that electrodeposited paint film is ruptured by violent hydrogen gas generated locally during electrocoating, and the defects remaind in the deposited film at the end of electrodeposition cause cratering after curing paint film.
    x

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    1. The Structure of Phosphate Crystals Influencing the Scab Corrosion Resistance Tetsu-to-Hagané Vol.77(1991), No.7
  • Surface Modification of Poly (vinyl chloride) Coated Steel Sheet by Electron Beam Induced Graft-Polymerization

    pp. 1095-1102

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    Surface modification of poly (vinyl chloride) (PVC) coated steel sheet by electron beam induced graftpolymerization with various monomers was investigated. As solubility parameters δ of monomers increased, mutual solubility of monomers and plasticized PVC decreased. As a result, apparent graft decreased with increasing δ of monomers. Degree of stain for grafted PVC coated steel sheet decreased with increasing δ of monomers. It is assumed that graft chains, which consisted of monomers with larger δ, prevented plasticizer from migrating in the interior side of PVC film. As grafting temperature increased, thickness of graft layer and average graft concentration increased, and degree of stain decreased. On the other hand, formability of grafted PVC coated steel sheet decreased with increasing grafting temperature. Layer grafted with methacrylic acid was rigid and made formability of PVC coated steel sheet decreased. In case of grafting with 2-hydroxyethyl methacrylate, graft layer was more flexible and hardly spoiled excellent formability of original PVC coated steel sheet.
  • Effect of Film Thickness on Durability of PVC Coated Steel

    pp. 1103-1108

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    We have studied on the effect of film thickness on durability of PVC mainly unpigmented coated steel. Through experimental works, the following conclusions have been obtained.
    We found that the remarkable degradation of polyvinyl chloride is caused on the thin layer film and there is difference between initial and the later stages of degradation. We recognized the occurrence of carbonyl group at the initial stage of degradation and double bond development of crosslinking in PVC at the later stage. Moreover, we found that deterioration of PVC is remarkably minimised by addition of pigments to the coatings. Although the PVC coated steel is characterized by corrosion resistance, the corrosion resistance is poor when film thickness is thin. In order to maintain its high corrosion resistance, 120 μm or more film thickness should be necessary.
  • The Performance of Urethane Elastmer Coating for Steel Construction Materials

    pp. 1109-1115

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    30 years have passed since steel construction materials were used for base of the marine structures. But their corrosion rate was over the estimation, so development of effective anticorrosive system have been expected.
    We examined the performance of 3 kinds of heavy duty coatings, urethane elastmer coating, tar urethane coating and powderd polyethylene coating which is able to be coated in the mill.
    Urethane elastmer coating is the best of 3 coatings. It had superior performance balance and especially excellent corrosion resistance because of the primer which could keep adhesion strength in wet condition even if without chromate treatment.
    Urethane elastmer coating wasn't damaged for driving test of coated steel sheet pile.
    Now, urethane elastmer coated steel construction materials have been widely used for base of marine structures.
  • Nature of Artificial Passivation Films

    pp. 1116-1121

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  • Electrochemical Study on Under-film Corrosion Mechanism of Zn and Zn-Fe Alloy Coatings

    pp. 1122-1129

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    In order to elucidate the correlation between the durability of coating against chlorine penetration and the composition of Zn-Fe alloy coating, the corrosion mechanism of coating at under-film corrosion tip was investigated.
    The measurement of couple initial current as original method was devised for the purpose of simulating the reaction of coating corrosion. The couple initial current corresponds to the charge transfer controlled corrosion rate of the coating.
    The couple initial current with equivalent two coated steel sheets gradually increases with the increase of Fe content of coating, while the couple initial current with coated and cold rolled steel sheets abruptly decreases with the increase of that.
    Furthermore, the better correlation between couple initial current with equivalent two coated steel sheets and under-film corrosion distance after atmospheric exposure test on Zn-Fe alloy coated steel sheets was recognized.
    On the basis of the knowledge obtained by the laboratory investigation, it was concluded that i) under-film corrosion of Zn and Zn-Fe alloy coatings in atmospheric exposure environment proceeds by charge transfer controlled mechanism and ii) corrosion of Zn-Fe alloy coatings is controlled by corrosion cell on coating iii)corrosion of Zn coating is controlled by corrosion cell between coating and iron substrate.
  • Edge Creep of Prepainted Zn-55%Al Coated Steel Sheet

    pp. 1130-1137

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    The effects of pretreatments and paint coatings on the edge creep performance of prepainted Galvalume were studied by means of salt spray test and outdoor exposure test. Edge creep progress behavior in salt spray test was different from that in outdoor exposure test. According to the results of outdoor exposure test for up to 10 years, the edge creep of prepainted Galvalume is more appreciable than that of the prepainted galvanized steel sheet in the early stages of exposure. However, the edge creep rate of prepainted Galvalume decreases with the lapse of time while that of prepainted galvanized steel sheet is kept almost constant. As the results, edge creep width becomes larger in galvanized steel sheet than in Galvalume in 7 to 9 years of exposure. Meanwhile in salt spray test, edge creep width of prepainted galvanized steel sheet does not exceed that of prepainted Galvalume up to 1000 h of exposure. Effects of pretreatments and coatings were not clearly noticed except that special primer for Galvalume decreased edge creep width of prepainted Galvalume in salt spray test.
  • The Influence of Drying Process in Cyclic Corrosion Test on the Underfilm Corrosion of Galvanized Steel Sheets

    pp. 1138-1145

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    The influence of the drying time ratio on the underfilm corrosion growth of zinc coated steel sheets at the leading edge of corrosion was investigated using salt spray/drying cyclic corrosion test.
    The temperature and relative humidity were fixed at 35°C and 60%.
    The dependence of the growth of underfilm corrosion on the zinc coating weight changes with drying time ratio. At high drying time ratio (93.8%) the underfilm corrosion rate decreases with an increase of zinc coating weight.
    At the leading edge of underfilm corrosion of galvanized steel, anodic dissolution of zinc coating layer occurs from its upper side. This area increases with a decrease of drying time ratio. For salt spray test, the largest zinc dissolution zone was observed.
    From these results, an underfilm corrosion mechanism of galvanized steel is thought to be as follows;
    There are two kinds of corrosion electric cell. At the leading edge of corrosion, there is an anode followed by a cathode. There is an electric corrosion cell between the scribe and the zinc coating surface under the paint by the scribe. The proportion of these cells changes with drying time ratio, which change the underfilm corrosion ratio and morphological feature of galvanized steel sheets.
  • Photo Acoustic Method to Evaluate Degradation of Coated Steels during Cyclic Corrosion Tests

    pp. 1146-1153

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    Photo acoustic images of coated steels degraded under cyclic corrosion tests were obtained by scanning a chopped and focused Laser beam and detecting the heat wave, which was produced by the beam, at the opposite side of the incidence. Amplitude of the signals was decreased and phase shift (time lag) of the wave measured with the incident beam was increased at the points where the delamination or under film corrosion occurred. The width of the delamination or the under film corrosion from the scribes of the coating was quantitatively evaluated, and it increased with the duration of the tests. The size and the area ratio of blisters formed around the scribes were also determined by this method. The spatial resolution of the images was achieved to 20 μm and discussed related to the measurement conditions, such as chopping frequency.
  • Evaluation Method of the Corrosion Resistance of Zinc-alloy-plated Steel Sheet Applied to Automobile Body

    pp. 1154-1161

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    There are two typical of corrosion occuring in the areas of the world where automobilies are most susceptable to corrosion. One is charactarized as inside-out perforation corrosion caused by salty or muddy water entering places that do not dry readily, such as panel joints and the inner surfaces of closed structures. Another is characterized as cosmetic corrosion caused by paint chipping damage to outer panel surfaces or damage resulting from interference between parts.
    Since the anti-corrosion warranty period for automobilies is expected to be further extended in the years ahead, there is a need to estabilish a life prediction method, based on the use of accelerated corrosion tests, which will allow performance evaluations to be completed in a shorter period.
    This paper describes an optimized accelerated test procedure for evaluating the anti-corrosion life of body panels. It also discusses the inside-out perforation and cosmetic corrosion resistance of a Zn-Ni electro-plated steel sheet with a thin organic film, which has been developed on the basis of the results obtained with the optimized test procedure.
  • An Analysis of Corrosion Cracking Phenomena of Electrodeposited Zn-Ni Alloy Layers

    pp. 1162-1168

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    The corrosion cracking phenomena of electro-deposited Zn-Ni alloy layers were investigated in relation to the coating structures. Zn-Ni alloy layers with nickel content over 10%, corresponding to γ single phase are subject to the corrosion cracking at potential more noble than their corrosion potential in an aqueous solution. The corrosion cracking of these layers can be prevented by thermal treatment at temperatures above 450°C. The corrosion cracking seems to occur by internal tensile stress generated by preferential dissolution of a small amount of zinc in Zn-Ni alloy layers.
  • Recent Adhesive Bonding Technology in Automotive Industry

    pp. 1169-1176

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  • Behavior of Paint Loss at the Punched Edge of Pre-painted Galvannealed Steel Sheet

    pp. 1177-1183

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    Paint loss at the sheared and punched edge of pre-painted galvannealed steel sheet, so called enamel-hair, deteriorates corrosion resistance at the edge and mars appearance of paint film.
    Effect of paint film and punching condition on the paint loss was investigated and this behavior was discussed by applying strain-induced grain growth. The results are summarized as follows;
    (1) Polyester powder paint produced more paint loss than acryl solvent paint.
    (2) Paint loss increased with an increase in punching clearance, an increase in punching speed and a decrease in punching temperature.
    (3) Putting protect film on paint film increased paint loss in case of polyester powder paint and decreased paint loss in case of acryl paint.
    (4) Microstructure of deformed base steel at the punched edge was studied by the strain-induced grain growth method. Behavior of paint loss can be explained by strain distribution at the edge and properties of paint film.
  • Influence of Fe-P Flash Coating on Anti-powdering Property and Friction Behavior of Galvannealed Steel Sheets

    pp. 1184-1191

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    Both anti-powdering property and press-formability are the most important performances for the galvannealed steel sheet to be processed into automobile body panels successfully. The press-formability is to be strongly influenced by friction between the coating surface and the press-forming die. Because these properties depend on the coating compositions, it is meaningful to discuss the mutual relationship between these performances either in production of the material or in press-forming. The increase in Fe content of the coating deteriorated the anti-powdering property and decreased the friction resistance. The formation of Γ phase at the interface of the coating and the substrate metal fatally affected the antipowdering property and the existence of ζ phase on the coating surface increased the friction resistance. In a view point of the Fe content, therefore, the friction property is contrary to the anti-powdering property. When the galvannealed steel sheet was electroplated with Fe-P alloy, the friction property was remakably improved. The friction property did not influence the delamination of the coating by bending but the amount of the coating peeling off at the shrinking flange in the cylindrical cup forming increased with the decrease of the friction resistance. It is supposed that the decrease in friction resistance increases the compression of material at the shrinking flange and that the compression enhances the delamination of the coating.
  • Formation Process of Colored Films on SUS304 Stainless Steel with the Square Wave Potential Pulse Method

    pp. 1192-1197

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    A thick film with interference color could be obtained on the surface of SUS3O4 stainless steel with the square wave potential pulse method in 5 kmol·m-3 H2SO4 solution of 323 K with no addition of chromium ions. The higher potential, EH, and the lower potential, EL, of the square wave potential pulse were controlled in the range between the active peak potential and the transpassive potential of chromium. A thick colored film was obtained at the condition that EL is kept in the transient region from the active peak to the passive range of chromium and EH in the passive range of iron and chromium. The deposited hydroxide film including Fe2+ and Cr3+ formed at EL losses protons and grows under the high field provided by EH. The colored film thus formed has many diffusion paths, which permit the further growth of the film without any decrease in the growth rate. Therefore, the thickness of the film, i. e. the color, could be easily controlled by the polarization time and/or potential.
  • Effect of Surface Condition on the Anodizing Behavior of Titanium

    pp. 1198-1205

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    The influence of surface condition on the anodization coloring behavior of titanium has been studied. It was found that uniform coloring was observed on polished surfaces while multiple coloring was observed on pickled surfaces. From the relationship obtained between crystal orientation of base metal and anodized film thickness, it was concluded that the film growth was faster on prism surfaces and was slower on basal surfaces. It was also confirmed by in-depth analysis of anodized surface on Ti alloy that the film was of inward growth type.
  • Sputter Deposition of Pure Titanium onto Complete Denture Base of Ti-6A1-4V Deformed by Superplastic Forming

    pp. 1206-1212

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    In order to improve the biocompatibility of function-shared titanium-base alloy, coatings of pure titanium on the TiNi shape memory alloy and Ti-6A1-4V alloy were investigated. DC source was superior to RF source in characteristics of sputtered film and the rate of deposition. After cleaning method was examined, the sputtering conditions dependence of the thickness of sputtered film was investigated on DC sputter deposition. The sputtered titanium accumulated on substrate proportionally to electric power and showed orientation highly depended on the heating temperature of substrate. Complete denture bases of Ti-6A1-4V deformed by superplastic forming were well coated with pure titanium by DC sputtering in Ar gas atmosphere.

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