塑性と加工
Online ISSN : 1882-0166
Print ISSN : 0038-1586
ISSN-L : 0038-1586
49 巻 , 566 号
選択された号の論文の11件中1~11を表示しています
説苑
解説
論文
  • 伊藤 樹一, 堂田 邦明, 吉田 広明, 五十川 幸宏
    2008 年 49 巻 566 号 p. 211-215
    発行日: 2008年
    公開日: 2008/03/26
    ジャーナル フリー
    Hard coatings on tools are very effective for wear resistance and the prevention of scuffing in forging; thus, many new coatings are developed yearly. The function of hard coatings in the reduction of friction has markedly improved recently; however, a method for its effective evaluation under practical forging conditions has not yet been developed. In this research work, we discussed the effectivity of the taper cup test, which we developed, as a new evaluation method. The taper cup test estimates the friction coefficient under a high surface expansion ratio, which is almost the same level to as those for mass-produced forging components. In the case of using no lubricant, diamond-like carbon (DLC) has a much lower friction coefficient than TiAlN and TiN. In the case of using one-liquid lubricant, friction coefficient is affected by surface roughness depending on the type of hard coating. In addition, continuous forging smoothened the surface, there by decreasing friction coefficient.
  • 竹士 伊知郎, 鳥塚 史郎, 新冨 達也, 大谷 崇, 津崎 兼彰
    2008 年 49 巻 566 号 p. 216-220
    発行日: 2008年
    公開日: 2008/03/26
    ジャーナル フリー
    We identified the conditions needed to produce ultrafine grained steel in a hot strip mill using a simulation model for microstructure evolution. The following conditions are necessary.
    -high-reduction-level rolling at each latter stand of the finishing mill
    -strong cooling just after rolling
    Low-temperature and continuous high-reduction-level rolling in hot strip mills suppresses static recovery between rolling stands, owing to the low-temperature rolling and the short time interval between rolling stands. Consequently, the effect of the high reduction level of one pass enables the strain in the steel to accumulate, resulting in ferrite-generating nucleation, and ultrafine grained steel is produced by the strong cooling after rolling.
  • 高津 正秀, 廣中 智也, 中塚 章太, 斎藤 尚文, 吉田 総仁, 中 哲夫, 岡原 治男, 東 健司
    2008 年 49 巻 566 号 p. 221-225
    発行日: 2008年
    公開日: 2008/03/26
    ジャーナル フリー
    The mechanical properties and formability of AZ31 magnesium alloy strips having different textures were investigated at a high strain rate based on that occuring in mass production by press forming. Forming at a high strain rate on the order of 100 s-1 requires a high temperature of over 473 K. To obtain accurate stress-strain curves, a high-speed testing machine that can maintain a constant true strain rate was used, and the change in gauge length on a test piece in a furnace was measured during the testing time of about 0.5 s. For the specimens, rolled strips consisting of fine grains (about 10 μm) and an extruded strip consisting of coarse grains (about 40 μm) were used. The {0001} textures of the extruded strip and one of the rolled strips were strongly oriented parallel to the rolled surface, but the texture of another rolling strip had two peaks that were inclined at 5∼15 deg in front of and behind the rolling direction. At the high strain rate of 100 s-1, elongation decreased for every specimen. Nevertheless, a limiting drawing ratio (LDR) of 2.1∼2.2 was obtained under uniform heating above 503 K in all the specimens except for the extruded strip. The high LDR of the rolled strip having a two-peak texture was maintained in forming at temperatures down to 473 K, in contrast to the LDR of the strongly oriented rolled strip, which reduced rapidly when formed at temperatures less than 503 K.
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