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Strength

  Effect of dislocations     5 of 5
 
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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