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

Tetsu-to-Hagané Vol. 90 (2004), No. 7

  • Recent Developments in Tube Hydroforming Technology

    pp. 451-461

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    Tube hydroforming is a process for manufacturing highly rigid light-weight parts with complex cross sections by internal high-pressure and axial feeding or axial compressive loading. It offers some advantages when compared with the traditional manufacturing methods such as sheet stamping and welding, or casting. The essential advantages are: integration of parts, reduction in both component weight and manufacturing steps, high accuracy of shape and dimensions, etc.
    Tube hydroforming was developed as an innovative technology in Japan over 40 years ago. Initially, it was available for manufacturing small and simple parts and has been used mainly in both the bicycle industries and the piping industries to manufacture fittings.
    Recently, new computer technology offers advanced control technology in manufacturing large and complex parts, and also offers FE simulations as designing tools for manufacturing sound parts without failure, such as bursting, buckling or wrinkling. Tube hydroforming-refined by computer technology and increased in capacity-is widely regarded as a new technology for manufacturing light-weight parts.
    To meet strong demands for saving fossil fuels and reducing CO2 emissions which cause global warming, automobile industries have recently adopted tube hydroforming technology to reduce the total weight of the cars and cost of production.
    This paper reviews the recent developments of tube hydroforming and discusses the key points of this technology.
  • Recent Applications, Research and Development in Titanium and Its Alloys

    pp. 462-471

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    Titanium and its alloys are still very advantageous for aerospace applications in the world. Non-aerospace applications of titanium and its alloys are much emphasized comparing with aerospace applications in Japan. Recently, titanium and its alloys are getting much attention in medical applications and health care goods. Other new applications of titanium and its alloys are progressively growing. Topics of applications, research and development of titanium and its alloys in aerospace and non-aerospace including medical and health care goods, automobile parts, sport and leisure, consumer goods, architecture, marine and smelting fields are described in this paper.
  • In Situ Observation of Coke Gasification and Behavior of Ash

    pp. 472-479

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    On the basis of the structure of pore distribution, the texture was classified into two regions, one was a dense structure originated from the inerts texture of coal, and the other was a foamed structure originated from the reactives. To clarify the gasification reaction and the high temperature behavior of ash in coke, the direct observation of the structures was carried out by high temperature laser microscope, μ-XRF and μ-XRD. The results were interpreted to explain the high temperature behavior of coke from the viewpoint of the macroscopic and microscopic scale.
    The composition of ash was different according to the structures. The main components in ash of the dense structure were SiO2, CaO and Al2O3. On the other hand in the foamed structure, S and Fe2O3 were main components. From the result of the direct observation of coke reaction in Ar atmosphere, some pore filled with a melted ash in the foamed structure was observed around 1000°C. While in 30%CO2-Ar atmosphere, the melting behavior of ash was not observed in the foamed structure, however, the dense structure was covered by a melted ash. The morphology of the ash observed after gasification reaction was the plate type in one of the dense area, the spherical slags were also observed in the foamed structure and the part of the dense structure. Using μ-XRD, the crystalline size of graphite for the different structure was estimated by Sherrer's equation. The mechanism of growing of graphite crystal in high temperature was proposed.
  • Influence of HAZ Microstructure on Reheat Cracking Susceptibility in Ni Free Type Quenched-tempered High Strength Steel

    pp. 480-486

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    Relation between reheat cracking susceptibility and HAZ microstructure on Ni-free high strength steels were investigated. In this experiment, HAZ microstructure obtained by synthetic-weld heat treatment was researched from relationship between stress relaxation behavior and high temperature properties. Interaction between reheat cracking susceptibility and Post-weld heat treatment (PWHT) was investigated. As a result, from results of stress relaxation test, both specimens (N1 and N2) show the same tendency and reheat cracking of all HAZ microstructure was occurred. Second, results of Constant-load teat on heating, each HAZ microstructure of both specimen was strongly embrittled from 830 to 900K and gained less 5% obtained by reduction of area. Each bainitic structure of both steel (N1 and N2) was different of ratio of bainitic type structure in spite of same cooling rate. Different of an amount of Mo (0.2 mass%) were not influenced by reheat cracking susceptibility.
  • Effects of Si, Mn Contents on the Descalability Behavior of the Scale of Annealed Austenitic Stainless Steels

    pp. 487-493

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    In order to improve descalability of annealed austenitic stainless steels, this study investigated the effects of the contents of 0.2-1.0 mass% Si and 0.8-1.6 mass% Mn on the dissolution behavior of the scale of annealed Type304 steels on electrolysis in Na2SO4, solution and pickling in HNO3-HF acid solution in descaling process.
    The results obtained are as follows:
    (1) Descalability of annealed Type304 stainless steels decreased as the Si and Mn contents increased.
    (2) The increase of Mn contents made an outer scale of spinel oxide thick. A dissolution rate of the spinel oxide by the Na2SO4 electrolysis was lower than that of an inner scale of corundum oxide, therefore the time required for electrolysis descaling was longer.
    (3) The increase of Si contents made an inner scale of corundum oxide and amorphous Si oxide under the scale thick. As corundum oxide became thicker, the time required for descaling by the Na2SO4 electrolysis was longer. Besides a thick amorphous Si oxide obstructed permeation of HNO3-HF pickling solution into Cr depletion layer under Si oxide.
  • Effect of Cu and Sn on Phosphatability of Cold-rolled Steel Sheets

    pp. 494-501

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    The promotion of scrap recycling in steel making is effective to reduce the discharge of CO2 and prevent the global warming. But, the scrap recycling has been limited to the production of low grade steel products such as shapes and bars, because of the detrimental effect of tramp elements such as Cu and Sn on the productivity and the quality of steel products.
    In this study, the effect of Cu and Sn on the zinc phosphatability in dip type phosphating of cold-rolled steel sheets annealed in N2-H2 and vacuum atmospheres are investigated to obtain the technical information which is necessary to extend the scrap recycling to sheet products.
    The following results are obtained.
    1) The zinc phosphatability of cold-rolled steel sheets annealed in N2-H2 atmosphere deteriorates slightly with increasing Cu content, however, it deteriorates remarkably with increasing Sn content.
    2) The zinc phosphatability of cold-rolled steel sheets annealed in vacuum atmosphere deteriorates remarkably with increasing both Cu and Sn contents.
    3) The deterioration of zinc phosphatability of cold-rolled steel sheets annealed in both atmospheres with increasing Sn content is considered to be caused the decrease in surface reactionability with the segregation of Sn on surface.
  • Effect of Silicon Content and Prior Structures on Microstructures of Nitrided Hot Working Tool Steels

    pp. 502-509

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    Microstructures of nitrided hot working tool steels SKD61, with various silicon contents and prior structures, were investigated by transmission electron microscopy of extraction replicas, X-ray diffraction, electron probe microanalysis and microhardness measurements. Plasma nitriding was carried out at 773K for 126 ks.
    Any alloying nitride precipitates such as CrN that was previously reported for Cr-alloyed steels were not identified for nitrided specimens. After reheating to 973K, hardness of nitrided layer was decreased accompanying CrN precipitates. Effect of silicon content on hardness was relatively small both of as-nitrided and after reheating. Depth of nitrided case and hardness after 973K reheating decrease with silicon content. Nitrided hardness of quenched specimen was higher than that of annealed one. Grain boundary carbides in diffusion zone and a carbonenriched zone ahead of the nitriding front were also observed for both of quenched and annealed specimens.
  • Recrystallisation of Heavily Cold Rolled RD//<011> Structure in BCC Iron

    pp. 510-517

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    The present paper prompts to demonstrate the recrystallisation procedure of {h, 1, 1}(1/h, 1, 2)fibre from heavily cold rolled α-fibre structure, or RD //<011> texture. Firstly the partially recrystallised cold rolled steel was analysed with OIM measurement. At the stage of 50% recrystallisation, {100}<011>-{211}<011> α-fibre was remained as deformed structure, and only ND//<111> texture was appeared for the recrystallised area. The slight recrystallisation was observed at the grain boundary of α-fibre grains, therefore, a by-crystal of {100}<011> was employed to simulate the irregular deformation at the grain boundary. After the cold rolling, a warp toward the grain boundary was observed. Although the interior of the {100}<011> single crystal was hardly recrystallised, sharp {411}<148> texture was created along the grain boundary. In order to recreate the phenomenon at the grain boundary, a cold rolled {100}<011> single crystal was bent along the rolling direction and annealed. Very sharp {411}<148> recrystallisation texture was formed again at the bent perimeter. These results suggest that the irregular strain was sufficiently piled at the grain boundary after the heavy deformation and generates {h, 1, 1}(1/h, 1, 2) texture. The orientation relationship in recrystallisation was confirmed by another recrystallisation that a {211}<011> single crystal generated another {h, 1, 1}(1/h, 1, 2), equivalently rotated around RD with the rotation from {100}<011> to {211}<011>. These recrystallisation textures were equivalently scattered around three <100> poles on (100) pole figures, therefore the rotation relationship around <111> axes with the original orientation was discussed.
  • Development of Ni-based Single Crystal Superalloys for Power-generation Gas-turbine Blades

    pp. 518-525

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    In advanced industrial gas-turbine systems, there has been a great demand for new single crystal (SC) superalloys with an excellent combination of high-temperature creep strength, hot-corrosion resistance and oxidation resistance. In this study, ten nickel-based SC superalloys were designed with the aid of the d-electrons concept. Their chemical compositions were in the range of 1.2-1.5% Ti, 3.8-6.5% Cr, 11% Co, 0-1.4% Mo, 6.5-7.4% Ta, 5.0-6.0% W, 3.6-5.4% Re, 5.1-5.5% Al, 0.12-0.14% Hf and balanced Ni in mass% units. A series of experiments such as creep rupture tests, burner rig tests and cyclic oxidation tests was conducted with the heat-treated SC specimens of these alloys. All the designed alloys were found to be superior in the creep rupture life to a second generation superalloy, CMSX-4. In the hot-corrosion resistance estimated from the barner rig tests, any designed alloys were comparable or even superior to CMSX-4. The oxidation resistance was very different amount the designed alloys, but some of them showed higher resistance than CMSX-4. Thus the SC alloys containing about 4-5 mass% Re had about 20 K higher temperature capability than CMSX-4, while exhibiting excellent hot-corrosion resistance and oxidation resistance.
  • Toughness Evaluation by Means of Side-notched Charpy Test

    pp. 526-532

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    Fracture path deviation (FPD) is often observed in the standard Charpy V-notch (STD-Cv) test on laser welded joint due to the steep gradient of hardness distribution. The side notched Charpy V-notch (SN-Cv) test is often used to avoid FPD. Fundamental study on the comparison between STD- and SN-Cv tests on laser welded joint for high strength ultra-fine grained steel and on base metal for conventional steels indicates that the results obtained from SN-Cv test gives higher transition temperature and lower absorbed energy compared with those of STD-Cv test.
    A big difference between these two tests is observed on the fracture surface. The fracture surface is divided into three types; that is, flat ductile fracture observed at the notch tip and the specimen end (Df), slant fracture at both sides (Ds) and brittle fracture (B). SN-Cv specimen has smaller area of Df and no Ds. The areas of each fracture surface were measured and the unit fracture energies for these fracture surfaces are determined by using regression analysis method. Unique relationships of EB/EDf=0.1 and EDN/EDf=2.3 are obtained irrespective of steels tested. The difference of fracture surface areas between SN-Cv and STD-Cv are formulated and finally, STD-Cv absorbed energy is well estimated from SN-Cv test results.

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