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HSLA steel (high strength low
alloy steel) is a type of steel alloy that provides many benefits over
regular steel alloys. In general, HSLA alloys are much stronger and
tougher than ordinary plain carbon steels. They are used in cars,
trucks, cranes, bridges and other structures that are designed to
handle a lot of stress, often at very low temperatures.
HSLA steels are so called because they only contain a very small
percentage of carbon. A typical HSLA steel may contain 0.15% carbon,
1.65% manganese and low levels (under 0.035%) of phosphorous and
sulphur[1]. It may also contain small amounts of copper, nickel,
niobium, nitrogen, vandium, chromium, molybdenum, silicon or
zirconium. HSLA's are therefore also referred to as 'micro alloyed',
as they are indeed alloyed in extremely small amounts by comparison to
other main commercial alloy steels. As little as 0.10% niobium and
vanadium can have profound effects on the mechanical properties of a
0.1%C, 1.3% Mn steel. These added elements are intended to utterly
alter the microstructure of plain carbon steels, which is usually a
ferrite-pearlite aggregate, to produce a very fine dispersion of alloy
carbides in an almost pure ferrite. This eliminates the
toughness-reducing effect of a pearlitic volume fraction, yet
maintains and even increases the material's strength by precipitation
strengthening and by refining the grain size, which in the case of
ferrite increases yield strength by 50% for every halving of the mean
grain diameter. Its yeild strength can be anywhere between 250-590 MPa
(35000-85000 psi).
HSLA steels are also more resistant to rust then most carbon steels.
Although the material quickly becomes covered with surface rust, this
is superficial and rust takes a long time to threaten the integrity of
a structure made from the material. The Angel Of The North at
Gateshead, England is a well known example of an unpainted HSLA
structure (the actual alloy used is called COR-TEN and includes a
small amount of copper). HSLA steels usually have densities of around
7800 kg/m^3. |
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