Crystallographic Characterisation of Hydrogen-induced Twin Boundary Separation in Type 304 Stainless Steel Using Micro-tensile Testing

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  • Ueki Shohei
    Graduate student, Kumamoto University, now Shimane University
  • Koga Kaoru
    Graduate student, Kumamoto University, now KYOCERA Industrial Tools Corporation
  • Mine Yoji
    Department of Materials Science and Engineering, Kumamoto University
  • Takashima Kazuki
    Department of Materials Science and Engineering, Kumamoto University, now International Research Organization for Advanced Science and Technology, Kumamoto University

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Other Title
  • マイクロ引張試験を用いた304型ステンレス鋼の水素誘起双晶境界分離の結晶学的評価
  • マイクロ ヒッパリ シケン オ モチイタ 304ガタ ステンレスコウ ノ スイソ ユウキソウショウキョウカイ ブンリ ノ ケッショウガクテキ ヒョウカ

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Abstract

<p>Micro-tensile behaviour and the corresponding microstructural evolution under hydrogen pre-charging conditions were examined on single-crystalline and twinned bi-crystalline specimens with the same [111] loading axis to elucidate the hydrogen-induced twin boundary separation in type 304 stainless steel. A hydrogen pre-charge increased the flow stress during tensile testing but decreased the elongation-to-failure in both single-crystalline and twinned specimens. Although the hydrogen-charged single-crystalline specimen exhibited a quasi-cleavage, the presence of a twin boundary induced a premature failure at the twin boundary interface. Flat-facetted features due to the twin boundary separation had linear steps in the three <110> directions, which corresponded to the intersections between the twin plane and the other {111} close-packed planes of austenite. Matching halves of the fracture surface along the three directions perpendicular to the linear steps, i.e. <112> on the (111) twin plane, revealed two sets of concavity–flat surface and a peak-and-valley correspondence. In addition, electron backscatter diffraction analysis of the substructures below the fracture surfaces revealed that martensite variants developed mainly with their habit planes parallel to the most favourably shear-stressed plane in each crystal, and they grew towards the concavities on the fracture surfaces. These findings suggest that the hydrogen-induced twin boundary separation is triggered by cracks generated by the high hydrogen concentration at the twin boundary due to deformation-induced martensitic transformation, and this is followed by coalescence of cracks through hydrogen-enhanced alternating shear on the slip planes situated symmetrically with respect to the twin boundary.</p>

Journal

  • Tetsu-to-Hagane

    Tetsu-to-Hagane 108 (1), 97-106, 2022

    The Iron and Steel Institute of Japan

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