Abstract
The effects of cementite particles and subgrain boundaries on the work-hardening behaviour of spheroidized carbon steels were investigated by making direct measurements of residual internal stresses. These internal stresses developed due to plastic incompatibilities between elastic particles and the surrounding elastic–plastic matrix. A continuum analysis of these internal stress fields, based upon a multiple slip model, was found to be in good accord with the experiments regarding its predictions of the Bauschinger effect. The internal stresses appear to saturate in the plastic strain range of ∼ 3–5% where a transition in strain-hardening behaviour was observed (double-n behaviour), and to contribute approximately 20% to the total work-hardening. The cementite-particle-pinned subgrain boundaries, formed during a post-quench annealing treatment, were found to lower the internal stress levels, thus indicating that they assisted the relaxation processes of entrapped Orowan loops by acting as sources of dislocations. The flow stress curves of these spheroidized carbon steels were found to be approximately described by a modified mean-square-root addition of several identifiable contributions to work-hardening.
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