Civil Engineering Reference
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the effective role of plastic deformation in increasing nucleation sites for
subsequent phase transformation.
5.2.4 Modeling of nanocomposite steel
Modeling can be used as a powerful tool to advance the fundamental
knowledge pertinent to nanocomposite steel, especially when integrated
with or validated by experimental investigation. Thermodynamic modeling
can provide insights into phase stability and transformations. For instance,
a Pourbaix diagram (potential-pH diagram) can be used to predict and
guide the synthesis and application of steels under given working conditions
(Kaufman et al. , 2009). Molecular dynamics modeling can shed light on
mechanisms underlying mechanical properties of steels, by simulating the
interactions between dislocations with GBs, twins, precipitates and other
barriers during deformation (Li et al. , 2010; Wu et al. , 2009, 2011). Mecha-
nistic models have also been established for predicting the fatigue life of
SS under various conditions (Lo et al. , 2009). In addition, improved under-
standing of corrosion and inhibition mechanisms has been continually
achieved through characterization and modeling of the steel surface and
corrosion products at various length scales down to the nanometer scale
(Murayama et al. , 2008).
5.3
Properties of nanocomposite steel
5.3.1 Nanotechnology to improve mechanical properties
of steel bulk
Nanotechnology has been employed to enhance the mechanical properties
of the steel bulk itself, by achieving the desirable fi nely crystalline micro-
structure of steel or by modifying its chemical composition or morphology
at the nano- or micro-scale. Table 5.1 summarizes recent research on this
subject, involving various classes of steel: carbon steel (
￿ ￿ ￿ ￿ ￿ ￿
2.1% C, low alloy),
SS (
10.5% Cr), alloy steel, ODS steel, etc. A wide variety of processing
approaches have been investigated for producing nanocomposite steels.
TMT, MA, and SPD have been used individually or synergistically, to induce
nanostructure via phase transformation and deformation processes. There
is also a high level of diversity in the resulting microstructure of nanocom-
posite steel, ranging from single-phase, dual-phase, to multi-phase and
ranging from nano-grains of
α
or
γ
, to
α
laths or bainitic
α
lamellae with
nano-
fi lms in between, to nano-precipitates/clusters in or along nano- or
micro-grains of
γ
. These nano-modifi ed steel bulk feature novel
mechanical properties, characteristic of considerable improvements in
strength (e.g., TS up to 2000 MPa) alone or in strength as well as toughness
α
or
α
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