Work hardening of low carbon steels

Abstract

A piece of metal can be deformed permanently if it is pulled sufficiently hard in tension, or compressed sufficiently. When the stress is removed, the dimensions of the specimen do not return to their original values, as they would if the deformation was elastic. The permanent distortion suffered by the metal is called plastic deformation. The chief mechanism by which this type of deformation occurs is due to the motion of dislocations. Closely associated with plastic deformation is work hardening. In fact, any crystalline material work hardens. The terms work hardening or strain hardening simply describe the fact that if a crystalline specimen metal already has suffered a plastic deformation, any further deformation will require a stress which exceeds that needed to produce the initial deformation. Work hardening is a temperature dependent phenomenon. In order to occur, the deformation temperature must be low, relative to the melting point of the material. The object of the project was to investigate the effects of work hardening or strain hardening on the yield point of a normalized low carbon steel. The steel chosen for the tests was 0.1%, carbon steel normalized at 900 C. Various aspects of strain hardening were looked into, namely the effect of strain rate, the lapse of time between restraining. Microscopic investigation of the samples was also carried out in order to investigate the effects of the work hardening on the grain boundaries.