Tensile behaviour of submicrocrystalline ferritic steel processed by large-strain deformation

Abstract

Mechanical tests have been carried out on Fe–15%Cr ferritic stainless steel with various microstructures. Ultrafine-grained microstructures with grain sizes of 0.2–0.3 µm were developed by large-strain cold-working and light annealing. The effects of severe deformation on the mechanical behaviour of as-processed and recovered steel were evaluated with reference to the same material having conventional work-hardened and recrystallised microstructures. Despite the low dislocation density in the fine grain interiors in the as-processed state, the samples with strain-induced submicrocrystalline structure were characterised by high internal stresses that resulted in a higher strength than could be expected from simple grain-size strengthening. These internal stresses were associated with a non-equilibrium state of strain-induced grain boundaries after severe deformation.

Keywords:

• severe deformation
• submicrocrystalline alloys
• grain boundaries
• tensile testing
• strengthening mechanisms
• recovery

Acknowledgements

The authors are grateful to J. Hono, National Institute for Materials Science, for improving the language of this article. A. Belyakov would like to thank the National Institute for Materials Science for providing a scientific fellowship.