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The effect of oxide particles on the strength and ductility of bulk iron with a bimodal grain size distribution
Casas, C.; Tejedor Busquets, Robert; Rodríguez Baracaldo, R.; Benito Páramo, José Antonio; Cabrera Marrero, José M.
Universitat Politècnica de Catalunya. Departament de Ciència dels Materials i Enginyeria Metal·lúrgica; Universitat Politècnica de Catalunya. PROCOMAME - Processos de Conformació de Materials Metàl·lics
The strength and ductility of bulk nanostructured and ultrafine-grained iron containing 0.39% oxygen by weight was determined by tensile tests. Samples were obtained by consolidation of milled iron powder at 500 degrees C. Heat treatments were designed to cover a wide range of grain sizes spanning from 100 to 2000 nm with different percentages of coarse and nanostructured grain areas, which was defined as a bimodal grain size distribution. Transmission electron microscopy was used to determine the diameter, volume fraction and location of oxides in the microstructure. The strength was analysed following two approaches. The first one was based on the strong effect of oxides and involved the use of a mixed particle-grain boundary strengthening model, and the second one was based on simple grain boundary strengthening. The mixed model underestimated the strength of nanostructured samples, whereas the simple grain boundary model worked better. However, for specimens with a bimodal grain size, the fitting of the mixed model was better. In this case, the more effective particle strengthening was related to the dispersion of oxides inside the large ferrite grains. In addition, the bimodal samples showed an acceptable combination of strength and ductility. Again, the ferrite grains containing oxides promoted strain hardening due to the increase in dislocation activity. (C) 2014 Elsevier B.V. All rights reserved.
Peer Reviewed
Àrees temàtiques de la UPC::Enginyeria dels materials
Mechanical Milling
Nanostructured materials
Oxide particles

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