| The formation of nanocrystalline (NC) structure in steels by shot peening and drilling was investigated. NC layers, several microns thick, with grain size of around 20 nm were successfully produced in steels by both shot peening and drilling. By annealing, the NC structure showed substantially slow grain growth without recrystallization. Comparing shot peening and drilling, it was found that the NC structure formed irrespective of the deformation temperature. As a common deformation condition to produce the NC structure, a large strain gradient is proposed. |
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