Slip
Steel is malleable, meaning it can be drawn or
pressed into many different shapes without breaking. It is also
ductile, which means that it can be drawn into bars or even thin
wires without breaking. The concept of slip partially accounts for
this behavior.
Picture 1
When steel bends, what actually happens is that layers of ions in the
steel are slipping over other layers and then forming attractions
with the ions now around them. This is why the steel bends without
breaking. See Picture 1.
Dislocations
The lattice structure naturally contains many
defects, that is, missing ions in layers. When a force is placed on
the steel, dislocations move through the lattice structure. Unlike
slip, only a relatively few number of ions need to move, not an
entire layer. See Picture 2.
Together, dislocation and slip account for malleability and
ductility of steel.
Picture 2
Grains
and dislocations Grain boundaries hinder the movement of dislocations. The more
grain boundaries that exist, the more difficult it is for
dislocations to move, and as a result, the steel is harder,
stronger, and stiffer.
Coarse grained steel contains fewer grains and grain
boundaries than fine grained steel with many more grains and
boundaries. Because of this, fine-grained steel has
the potential to be stronger and more ductile than coarse grained
steel.
Often times, elements like vanadium are added to the
mixture of steel to provide nuclei around which grains can grow.
The objective of this process is to produce finer grained steel, and
vanadium is well known for its ability to assist in the control of
grain size.
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