Civil Engineering Reference
In-Depth Information
First, nanotechnology has been utilized in endowing the steel bulk mate-
rials with excellent corrosion resistance, mainly by refi ning their crystal
grains to nano-scale. The steel substrate with a nano-phased grain structure
tends to have less defects or inhomogeneities where corrosion attack tra-
ditionally initiates and/or propagates. Miura
et al.
(2010) disclose a steel
with an improved corrosion resistance and ultra-hardness and toughness,
comprising an aggregate of
nano-crystal grains containing a solid-solution
type N (0.1-2.0% by mass). The steel is prepared by MA of fi ne powders
of
α
steel-forming components (e.g., Fe, Cr, Ni, Mn, and C) and an N-con-
taining substance (e.g., N
2
, NH
3
, and nitride of Fe, Cr, and Mn), followed by
forming-by-sintering treatment and subsequent annealing. The crystal
grains are more fi nely divided on a nanometer scale by mixing a particle
dispersant (e.g., AlN, NbN, TaN, Si
3
N
4
, or TiN) or mixing a metal oxide or
a semimetal oxide in the MA process. Furthermore, an oxide, nitride,
carbide, silicide, or boride of a metal or semimetal exists as a crystal grain
growth inhibitor between and/or in the nano-crystal grains. Such SS, having
a high N concentration (in place of expensive Ni or Mn), were reported to
feature much improved resistance to corrosion and particularly to pitting
corrosion as well as signifi cantly reduced sensitivity to SCC.
Buck (2008) discloses the use of TMT to create a fi ne-grained microstruc-
ture imparting the steel good corrosion resistance, high strength, and high
toughness. In one example, a 15 cm thick steel slab was fi rst soaked at
1230°C for 2 h 'such that the structure is mostly face-centered-cubic (fcc)
α
γ
throughout the alloy', before being hot-worked on a reversing rolling mill
at a temperature between 1230°C and 1150°C. During the forming process,
a true strain of 0.22-0.24 per pass was utilized to induce recrystallization.
The resulting plate was then air-cooled to room temperature with or without
further heat treatment, ultimately transformed into a fi ne-grained
SS.
Wright and Jung (2006) disclose the invention of Cr-Ni-Co-Mo-Ti-Al SS
with an excellent combination of strength, toughness, and corrosion resis-
tance across a variety of strength levels. The SS feature 'a predominantly
lath-
α
′
microstructure essentially without topologically close packed inter-
metallic phases and strengthened primarily by a dispersion of intermetallic
particles primarily of the
α
′
-Ni
3
Ti phase'. The Ti and C levels are controlled
'such that C can be dissolved during a homogenization step and subse-
quently precipitated during forging to provide a grain-pinning dispersion'
of carbides of Ti, V, Nb, or Ta.
Second, nanotechnology has been utilized in surface treatments to
improve the performance and service life of steels in oxidizing and corro-
sive environments. A recent invention (Kerber, 2007) is directed to nanopar-
ticle surface treatments and methods of providing such treatments for
forming a thin oxide coating on alloys, thereby providing the substrate with
η
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