Civil Engineering Reference
In-Depth Information
wear resistance and anti-fatigue performance of carbon steel (Zhang
et al.
,
2010).
5.3.3 Nanotechnology to improve corrosion resistance
of steel
The corrosion of steel as a result of chemical or electrochemical reaction
with its service environment is a spontaneous process, which can compro-
mise the integrity of the materials and impact assets, environment, and
people if no measures are taken to prevent or control it. The corrosion of
steel is generally electrochemical in nature, and may take many forms such
as uniform corrosion, galvanic corrosion, pitting corrosion, crevice corro-
sion, underdeposit corrosion, dealloying, stress corrosion cracking (SCC),
corrosion fatigue, corrosion wear, and microbially infl uenced corrosion
(MIC).
Nanotechnology has also been employed to enhance the corrosion resis-
tance of the steel bulk or surface layer. Table 5.3 provides a snapshot of
recent research on this subject, involving various classes of steel: weathering
steel, SS, and alloy steel, whereas the following sections review recent inven-
tions on this subject. The improved resistance to pitting corrosion, corro-
sion, wear, or corrosion wear can be derived from nano-phases in the
passive fi lm, high density of GBs as nucleation sites for growing passive
fi lm, hardening by nano-precipitates or nano-grains, etc. As summarized by
Lo
et al.
(2009), laser surface melting (LSM) can reduce the size of carbides
and impurities (e.g., MnS) and alter the microstructure in the surface layer
of SS, often leading to improved resistance to intergranular corrosion and
pitting.
It should be cautioned that some production processes of steels may alter
their microstructure and increase their susceptibility to cavitation erosion
and hydrogen embrittlement (Lo
et al.
, 2009). Amarnath and Namboodhiri
(2003) revealed that for a high strength low alloy steel, heating followed by
normalizing (air cooling) coarsened the grain sizes and lowered the disloca-
tion density, which in turn decreased the number of hydrogen trap sites and
increased the risk of hydrogen embrittlement. Relative to the as-received
steel, its water quenching followed by tempering also led to higher risk of
hydrogen embrittlement. It is hypothesized that a microstructure with high
dislocation density and high concentration of GBs and other interfaces
would be less prone to hydrogen embrittlement in steel. Addition of Mo
and V nanoparticles has been reported to mitigate the delayed fracture of
steel, by reducing the intergranular cementite and associated hydrogen
embrittlement (Mann 2006). Addition of some alloying elements (e.g., Cu,
Cr, Ni, Mo, W) can improve the corrosion resistance of steels.
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