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The presence of
dislocation networks produced through work hardening can result in
very high levels of strength, however, it reduces toughness and
ductility so is used only for certain steel products. Work hardening
is not used to any extent in plate and section steel products but is
used in some strip and engineering steel products. For example:
- Strip products
- Some strip grades that do not require a high level of
formability but an increased strength level are supplied with a
degree of work hardening. This work hardening is achieved through
controlled cold rolling passes after any annealing process
(annealing removes the dislocation structure by recovery or
recrystallisation). The level of work hardening introduced is
determined by the strain during the cold roll passes (i.e. the
thickness reduction per pass) and controlled to give the strength
levels required. Work hardening, and hence strengthening, can also
occur during fabrication, for example during press forming,
bending, drawing etc.
- High carbon steel products
- For example steel wire is often supplied in a work hardened
condition as the dislocation networks provide much of the
strengthening. High strength steel wire is used in suspension
cables, tyre cords, pre-stressed wire and wires can have a yield
strength up to 5000 MPa (lower strength values are usually seen
for the applications mentioned). The wire is cold drawn from hot
rolled to 90% reduction which produces a heavily worked structure.
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