A New Approach for Interpretation of Strengthening Mechanism of Martensitic Steel through Characterization of Local Deformation Behavior

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Other Title
  • 局所力学特性評価によるマルテンサイト鋼の強化機構解析の新展開
  • キョクショ リキガク トクセイ ヒョウカ ニ ヨル マルテンサイト コウ ノ キョウカ キコウ カイセキ ノ シン テンカイ

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Mechanical characterization in a sub-micron scale by nanoindentation technique is applied to Fe-C base martensitic steels to discuss the strengthening mechanisms. Matrix strengths of block structures were probed to reveal a dependence on a carbon content, tempering temperature and metallurgical process. A grain boundary effect was also evaluated to consider the strengthening factors on the macroscopic strength. It has been found that the grain boundary effect is significantly large on the strength of the Fe-C based martensite due to a fine effective grain of block structure. A locking parameter in the Hall-Petch relation is reduced at tempering temperature above 450°C leading to a "hump" on the temper-softening curve because film-like carbides on grain boundaries are disappeared above 450°C. A microstructure in a conventional quench-tempered process includes high-density carbides on a grain boundary corresponding to a higher locking parameter than that of an ausform-tempered martensite. The lower locking parameter in the ausform-tempered martensite reduces an stress concentration at an interface between the carbide and ferrite phase, which contribute to the improved delayed fracture property of the ausform-tempered martensite.

Journal

  • Tetsu-to-Hagane

    Tetsu-to-Hagane 92 (5), 295-310, 2006

    The Iron and Steel Institute of Japan

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