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[ Innovation ]
New lightweight steel
ideal for cars
By manipulating the structure of steel on a nanometre scale,
a South Korean materials scientist has produced a material
which has the strength and the lightness of titanium alloys
but will, when produced at scale, cost a tenth as much. The
key was finding a way to increase the aluminum content while
overcoming the formation of brittle intermetallic compounds.
By Joanne McIntyre
In the February 5 issue of Nature science
journal, materials scientist Sang-Heon
Kim and his colleagues at the Pohang
University of Science and Technology
in South Korea described improving
lightweight steel by altering how metal
compounds are arrayed in an alloy. By
manipulating the structure of steel on a
nanometre scale, Dr. Kim has produced
a material which has the strength and the
lightness of titanium alloys but will, when
produced at scale, cost a tenth as much.
Harnessing the benefits of B2
“We [have] shown that an FeAltype brittle but hard intermetallic
compound (B2) can be effectively
used as a strengthening second phase
in high-aluminum low-density steel,
while alleviating its harmful effect on
ductility by controlling its morphology
www.stainless-steel-world.net
and dispersion. The specific tensile
strength and ductility of the developed
steel improve on those of the lightest
and strongest metallic materials
known, titanium alloys…Alloying of
nickel catalyzes the precipitation of
nanometer-seized B2 particles in the
face-centred cubic matrix of highaluminum low-density steel during heat
treatment of cold-rolled sheet steel. Our
results demonstrate how intermetallic
compounds can b3e harness in the alloy
design of lightweight steels,” Dr. Kim’s
report states.
The steel produced by Dr. Kim and
his colleagues at Pohang University
takes advantage of B2’s hardness and
austenite’s ductility. By adding nickel
and temperature-treating an alloy of
iron, aluminum, manganese and carbon,
they induced smatterings of B2 to
form evenly throughout the steel. The
resulting material, in which the hard B2
lattices reinforce the supple austenite
matrix, has impressive tensile strength.
Great potential
Dr. Kim sees great possibilities for his
alloy to be used in the automotive industry
where weight is critical. His report states
that reducing a car's weight by one-tenth
can boost fuel economy by 6–8%.
While the automotive industry has
always been an important user of steels,
the share of weight of steel and iron in
an average light vehicle has decreased
from 68.1% in 1995 to 60.1% in 2011.
The reduction has largely been driven
by a desire to decrease weight, thereby
improving fuel efficiency.
While the new steel is still in the
development stage the South Korean
company POSCO, the fourth largest
steel producer in the world, is
reportedly interested in Dr. Kim’s
discovery and is planning a trial of the
material later this year to determine
whether it will be commercially viable
on an industrial scale.
The original report from Dr. Kim and his
colleagues can be read and downloaded
as a pdf at www.nature.com
Stainless Steel World March 2015
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