The Mechanism of Nucleation of Dislocations Around Inclusions in Iron

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  • Kayano Hideo
    The Research Institute for Iron, Steel and Other Metals, Tohoku University

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  • 鉄中の介在物のまわりからの転位の発生機構
  • テツ チュウ ノ カイザイブツ ノ マワリ カラ ノ テンイ ノ ハッセイ キコウ

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The nucleation mechanism of dislocation loops around inclusions in iron was discussed. The stress caused around an inclusion by thermal constriction or mechanical deformation was reduced rapidly as is apart from the inclusion. The line energies of edge and screw elements of the dislocation loop are in the ratio of 1⁄1−ν: 1 where ν is Poisson ratio. Consequently, the shape of the dislocation loop nucleated around the inclusion was considered to be semi-elliptical. The formation energy of the semi-elliptical dislocation loop arised from thermal stress and the temperature dependence of nucleation stress of the dislocation loop were calculated by the rate theory. The nucleation stress of the dislocation loop calculated from the present model is μ⁄22∼μ⁄47 at room temperature, which is consistent with the experimental observation of dislocation nucleation around the Zr2O inclusion. The elastic shear stress distribution around a spherical inclusion in an isotropic elastic medium during tension was considered. In this case, the stress concentration around the inclusion was too small to nucleate a dislocation loop. It is deduced that the residual stress around the inclusion, for example, induced thermally during the cooling plays a major role in the nucleation of dislocations by mechanical deformation.

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