Online ISSN : 2188-4064
Print ISSN : 0288-0490
ISSN-L : 0288-0490
Volume 59 , Issue 4
Showing 1-2 articles out of 2 articles from the selected issue
Technical Paper
    2019 Volume 59 Issue 4 Pages 215-221
    Published: 2019
    Released: December 11, 2019

    The surface microstructure and growth behavior of an Fe-0.4mass%C alloy formed by lithium-added salt-bath nitrocarburizing were investigated. The Fe-0.4mass%C alloy was prepared by arc melting and nitrocarburized by a salt-bath containing Li+, Na+, K+, CNO-, CN-, and CO32- at 823 K for 0.1 up to 10 h. A compound layer is formed on the surface at the beginning of nitrocarburizing, and then an oxide layer is formed on the compound layer after nitrocarburizing for 1.0 h. After that, the thickness of both layers increases. Internal oxide was formed at interfaces of columnar crystals in the compound layer. On the one hand, the whole oxide consists of LixFe1-xO with an NaCl-type structure, and the growth of the oxide layer is rate-determining by diffusion of iron in the oxide layer. On the other hand, the compound layer consists mainly of an ε-Fe2(N,C)1-y phase and a slight γ’-Fe4(N,C)1+z phase near the substrate.

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Research Paper
  • Takuro MASUMURA, Yuki SETO, Toshihiro TSUCHIYAMA, Ken KIMURA
    2019 Volume 59 Issue 4 Pages 222-229
    Published: 2019
    Released: December 11, 2019

    The remarkably high work hardening rate in high nitrogen austenitic stainless steels is generally believed to be due to the promotion of dislocation accumulation by nitrogen addition. However, analysis of dislocation accumulation behavior by the modified Williamson-Hall/Warren-Averbach method reveals that no difference exists between austenitic steels with and without nitrogen in the increment of dislocation density during deformation. Since cross slipping is markedly suppressed in high nitrogen steels, the moving dislocations are back-stressed by the planar dislocation arrays. This leads to the deformation resistance and high work hardening rate.

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