Civil Engineering Reference
In-Depth Information
technology has been playing an increasingly important role. For instance,
Lesuer
et al.
(2010) reported the fabrication of Fe-C alloys with ultrahigh
strength (4600 MPa) through quenching and severe plastic deformation
(SPD). The strengthening was attributed to the nano-size effect of lath and
plate martensite grains and the small interparticle spacing. As reviewed by
Kolpakov
et al.
(2007), metallurgy approaches to the production of high
performance steels with a fi ne-grain structure and/or self-organization of
strengthening nanophases (carbides, nitrides, carbonitrides, intermetallides)
have been burgeoning under the guide of nanotechnological principles,
including nanoprocesses for steel smelting and microalloying, mechanical
pressure treatment (e.g., SPD), and heat treatment (e.g., superfast quench-
ing of melts). One such technology commercialized in the US produces high
performance carbon steels that feature a 'three-phase microstructure con-
sisting of grains of ferrite fused with grains that contain dislocated lath
structures in which laths of martensite alternate with thin fi lms of austenite'
(Kusinski
et al.
, 2004).
Recent years have seen the fabrication of high performance steels desir-
able for light weight construction and other engineering applications. As
detailed later, these steels typically feature an ultrafi ne or nano-grained
microstructure, which leads to excellent properties in both strength and
ductility. In addition, nanotechnology has been employed to enhance the
durability of the steel bulk material or surface layer, in terms of resistance
to wear, fatigue, and/or corrosion. This is made possible by achieving
the desirable fi nely crystalline microstructure of steel (e.g., nano-
crystallization) or by modifying its chemical composition at the nanometer
scale. Formation of Cu nanoparticles at the steel grain boundaries (GBs)
has been used to improve the corrosion resistance of steel. Addition of Cu
nanoparticles has also been reported to mitigate the fatigue cracking of
steel, by reducing the surface roughness of steel and associated stress risers
(Mann, 2006).
This chapter synthesizes the fi ndings of some of the major research
efforts in this area and presents a discussion of utilizing nanotechnology to
greatly enhance the properties of steels, by modifying the chemical compo-
sition and/or microstructure of bulk material or surface layer.
5.2
Research relating to nanocomposite steel
5.2.1 Microstructure and chemical composition of steel
While Fe is the main element in steels, other elements (e.g., C, alloying ele-
ments, and impurities) defi ne the manifold properties of steels, including:
tensile strength, fatigue strength, ductility, hardness, toughness, wear resis-
tance, formability, weldability, fi re resistance, corrosion resistance, etc. The
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