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Structural Steels
Structural steels are divided into three
groups.
Alloy structural steels have better
mechanical properties than carbon steels . So,
they are widely employed in engineering industry
that require static and dynamic loads in
operation. They have better mechanical
properties than carbon steels especially for
articles of large cross-section.
The alloying elements
- Strengthen the ferrite, which is the chief
constituent of the structure of these steels
- Increase hardenability
- Refine the grain size.
- Increase the resistance to softening on
heating to moderate temperatures.
The main alloying elements in structural
steels are chromium, nickel and manganese.
Tungsten, molybdenum, vanadium and titanium are
not usually employed as independent additions.
Low alloy Structural Steels:
These steels are used for parts manufactured
for application involving dynamic loading where
hardenability, ductility, and fatigue strength
are important. Since most structures are not
heat treated, there is no need for
hardenability. These steels have
- High yield strength.
- Good Weld ability.
- Resistance to atmospheric corrosion.
As rolled, they have about twice the yield
strength of ordinary structural steel. This
property is obtained by adding two or more of
the elements manganese, silicon, chromium,
nickel, molybdenum or phosphorus. About 0.3 -
0.4 % copper is added to provide corrosion
resistance.
Typical strength properties are
- Yield Strength - 52000 psi
- Ultimate strength: 75000 psi
- Elongation on 8": 15 %
Medium alloy Structural Steels:
They contain over 5 % of alloying elements.
High alloy Structural Steels:
They contain more than 10 % of alloying
elements.
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