Affiliation:
1. Department of Materials Physics Eötvös Loránd University P.O.B. 32 H‐1518 Budapest Hungary
2. Physics Department Faculty of Science Tanta University Tanta 31527 Egypt
3. Department of Design and Engineering Faculty of Science and Technology Bournemouth University Poole Dorset BH12 5BB UK
4. Materials Research Group Department of Mechanical Engineering University of Southampton Southampton SO17 1BJ UK
5. Department of Metallurgical and Materials Engineering Indian Institute of Technology, Madras Chennai 600036 India
6. Institut für Materialphysik Universität Münster 48149 Münster Germany
Abstract
Severe plastic deformation (SPD) is performed on a newly developed medium‐Mn steel with the composition of Fe–7.66Mn–2Ni–1Si–0.23C–0.05Nb (wt%) to achieve a nanocrystalline microstructure. The SPD process utilizes the high‐pressure torsion (HPT) technique, resulting in a nominal shear strain of approximately 36 000% after processing the disk for 10 turns. In X‐Ray diffraction line profile analysis, an increase in dislocation density to around 230 × 1014 m−2 is observed. In addition, under high strains, a face‐centered cubic (fcc) secondary phase emerges within the body‐centered cubic (bcc) matrix. In analytical transmission electron microscopy, using energy‐dispersive X‐Ray spectroscopy, it is indicated that the secondary‐phase particles are enriched in Al, Mn, and Si. As the strain imposed during HPT increases, the simultaneous rise in dislocation density and nanostructuring lead to material hardening. However, the partial phase transformation from bcc to fcc contributes to material softening. As a result of these two opposite effects, the hardness exhibits a non‐monotonic variation with the shear strain, displaying, for 10 turns of HPT, a lower hardness compared to fewer turns, despite the continuous increase in dislocation density and decrease in crystallite size.
Funder
Engineering and Physical Sciences Research Council