Strengthening Mechanisms and Mechanical Behaviours of Nanostructured Steels

納米鋼之強化機制與機械性能

Student thesis: Doctoral Thesis

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Award date28 Aug 2019

Abstract

Precipitation strengthened nanostructured steels have an excellent strength but very poor impact toughness at ambient and low temperatures. In this study, a unique heat treatment is developed to achieve both superior strength and toughness for the nanostructured steels (Fe-0.07C-0.78Ni-1.28Cu-0.53Mn-0.2V-2.41Cr-0.05Ti-0.8Mo, wt.%). Furthermore, our results have demonstrated that our nanostructured steels are insensitive to annealing temperatures. The tensile strengths can reach over 1000 MPa, together with a decent tensile ductility and reduction of area through multiple strengthening mechanisms, including the nanoscale Cu-rich precipitation strengthening, martensite strengthening, grain size strengthening, carbide strengthening, and solid solution strengthening. The state-of-the-art atom probe tomography (APT) was used to characterize the microstructural features down to a nanoscale level for a thorough understanding of the underlying strengthening mechanisms. The contribution of all strengthening components was carefully examined and estimated with various theoretical models. In addition, the dislocation-precipitate interactions were also explored in this study.