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

Tetsu-to-Hagané Vol. 91 (2005), No. 7

  • Characteristics of Hollow Cathode Arc as a Welding Heat Source

    pp. 575-580

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    Hollow Cathode Arc (HCA) was developed as a plasma source under the condition of low pressure in the 1960s, and various researches were performed to make clear the mechanism of the HCA. Since the HCA is a discharge under low pressure environment, it attracts attention as a welding heat source in space. Moreover, the HCA is expected to be useful for the industrial application on the earth, because the melting process by HCA is very active and the penetration is huge in comparison with that by the conventional GTA.
    In the previous paper, it has been shown that the HCA configuration and the melting process by HCA are very sensitive to process parameters, such as gas flowrate and ambient pressure.
    In the present paper, the electron density distribution of HCA has been measured by IR method of plasma diagnostics (IR method). It is concluded that the beam like core of electron density is formed on the arc axis in the case of low gas flowrate, and the huge penetration by HCA is closely related to the beam like core.
  • Outlet Flow Angle Design of Swirling Flow Submerged Entry Nozzle for Wide Slab Casting

    pp. 581-588

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    We have proposed a technology of swirling flow formation in submerged entry nozzle as a fundamental and effective measure for controlling flow pattern in continuous casting mold. A joint study started in 1997 with Nippon Institute of Technology, Osaka University, Kyushu Refractories and Sumitomo Metal Industries to develop a swirling flow submerged entry nozzle with a swirling blade for steel casting. As a result of the collaboration, the swirling flow submerged entry nozzle for wide slab casting has developed in Wakayama Works, which improve productivity and surface quality of slabs and coils.
    Swirling flow formation in the submerged entry nozzle can be effective for controlling flow pattern in the mold in the case with optimum design of outlet port. The outlet port of the swirling flow submerged entry nozzle should be designed adapting a characteristic of swirling downward flow in the nozzle.
    As a result of full-scale water model experiment, we achieved a conclusion of optimum outlet port design that the narrow width of the outlet port is optimum for the swirling flow submerged entry nozzle.
    In addition to that, we got another conclusion of the outlet port design relation to the outlet flow angle that the optimum downward angle of outlet flow is 30-40 degree for stable flow formation in the wide slab mold.
  • Determination of Trace Boron in Iron and Steel by Adsorptive Stripping Voltammetry with Beryllon III

    pp. 589-594

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    Adsorptive stripping voltammetry is proposed for the determination of boron at the low μgg-1 level in iron and steel. Beryllon III was used as a complexing agent for boron(III). Optimum conditions for a complex formation of boron(III)-Beryllon III complex were as follows: 0.06 M nitrate-0.04 M sulfate supporting electrolyte at pH 4.5; 1.0×10-5 M Beryllon III; 24 h complexation time. The complex was accumulated on a hanging mercury drop electrode at-0.35 V for 60 s under stirring, and subsequently was cathodically stripped to -0.8 V at a scan rate of 10mVs-1 by using a differential pulse mode. The interference of iron(III) was eliminated by complexing it with metaphosphoric acid. The cathodic stripping resulted in only a single well-defined peak around -0.5 V. The influence of foreign elements on the determination was evaluated. The calibration graph (peak height vs. boron(III) concentration) in the presence of 1 mg mL-1 iron(III) was linear over the concentration range of 1-25 ng mL-1 (correlation coefficient >0.999), with a relative standard deviation (n=4) of 2.6% at 10 ng mL-1. The minimum limit of determination was 1μgg-1 of boron in iron and steel. The proposed method could be applied to the determination of trace boron in iron and steel with good precision and accuracy.
  • Simultaneous Determination of Trace Tramp Elements (Zn, Pb and Bi) in Steel by Anodic Stripping Voltammetry

    pp. 595-601

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    A sensitive anodic stripping voltammetric method for the simultaneous determination of zinc, lead and bismuth in steel is described. The interference of the iron(III) matrix was eliminated by reducing it to iron(II) with L(+)-ascorbic acid. The optimized experimental conditions were as follows: analyte ions in a steel sample solution containing a nitric-sulfuric acid mixture (pH=2) were electrodeposited as metals on a hanging mercury drop electrode at-1.2 V vs. Ag/AgCl for 5 min with stirring; the deposits were then anodically stripped in the potential range -1.2 to 0 V vs. Ag/AgCl at a scan rate of 50 mV s-1 by a differential pulse mode. Linear relationships held between the peak height and the concentrations of analyte ions in the concentration range 5 to 200 ng mL-1 with relative standard deviations below 5% for 30 ng mL-1. The detection limits (3σ) were less than 1.7 ng mL-1 for the deposition time of 5 min. The influence of foreign elements on the determination was evaluated, and a method for eliminating the interference from other metal ions, in particular copper and nickel, due to the formation of intermetallic compounds with zinc in amalgams was devised. The proposed method was applied to the simultaneous determination of 3.5 to 325 μgg-1 of zinc, lead and bismuth in steels with good precision and accuracy.
  • Dynamic Recrystallization Behavior in Martensite in 18Ni, 17Ni-0.2C and SM490 Steels

    pp. 602-608

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    The 18Ni, 17Ni-0.2C and low carbon (SM490) steels were quenched after austenitization to obtain full martansite structure. Then specimens were heated rapidly up to various temperatures below As followed by compression with various strain rates. During hot deformation, some specimens show dynamic recrystallization, which is well summarized by using Zener-Hollomon (Z) parameter. The Z-values corresponding to the occurrence of dynamic recrystallization depend on chemical compositions of mantensite steels and are much higher than those for IF steel. The dynamic recrystallization observed is so-called continuous recrystallization which is different from discontinous recrystallization in the IF steel; subgrains change to grains with high angle boundaries during deformation. The grain size changes with Z-value and sub-micron sized grains were obtained in the 17Ni-0.2C steel.
  • Three-dimensional Observation of Ferrite Plate in Low Carbon Steel Weld

    pp. 609-615

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    The early stages of the formation of acicular ferrite in a low carbon steel weld were studied by serial sectioning and computer-aided three dimensional (3D) visualization. The specimens were taken from the weld of low carbon steel, containing 0.08% C, 0.9% Si, 1.57% Mn and 0.032% O, and were austenitized and isothermally reacted at 600 and 570°C for less than 10 s. Very thin and long plates were formed initially and thickening occurred probably after lengthening was hampered due to impingement on prior austenite grain boundaries and/or pre-formed ferrite plates. Multi-variant ferrite plates were nucleated at inclusions and grew radially in the directions close to <110>γ with habit planes near {111}γ thus forming a characteristic "Widmanstätten star" noted earlier in a medium carbon steel on polished surfaces.
  • Effect of Microstructure on Elongation in Cold-rolled High Carbon Steel Sheets

    pp. 616-622

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    The effect of void initiation due to microstructural factors, including the size and distribution of spheroidized cementite and ferrite grain size, on elongation in JIS S35C and JIS S65C high carbon cold-rolled steel sheets were investigated.
    Among mechanical properties after 2nd annealing, yield strength (YS) and tensile strength (TS) both increased as cold-rolling reduction increased, and total elongation (T.EI.) also increased simultaneously. This resulted in large improvement in the TS-T.EL. Balance. As mirostructural changes in this case, with the increase in cold-rolling reduction, the ferrite grain diameter decreased and cementite on the ferrite grain boundary increase.
    According to the results of a detailed study of S35C, when the microstructure was composed of fine ferrite and cementite on the ferrite grain boundary, elongation was high. In the tensile deformation process, destruction of the grain boundary cementitie was frequently observed. Voids were initiated from these points of origin, and fracture then occurred rapidly. On the other hand, when the microstructure was composed of coarse ferrite grains and fine cementite existed within the ferrite grain, elongation was low. In particular, uniform elongation was markedly decreased. In this deformation process, voids were initiated from cementite on deformation bands, then joined to form cracks, resulting in fracture.

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