Mechanism of grain boundary strengthening of steels
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The mechanism of grain boundary strengthening depends on several factors, above all the grain size and the condition of the grain boundaries.
In fine-grained steels the effect of the barrier mechanism of grain boundary strengthening is negligible, while the effect of grain boundaries on resistance to deformation described by the Hall—Petch equation is manifest indirectly through the effect of strain hardening with a more rapid increase of dislocation density.
With decreasing relative length of grain boundaries (large grains) or enrichment of grain boundaries in impurities and precipitates of second phase the number of potential dislocation sources near grain boundaries decreases. In this case the fulfillment of the Hall—Petch relationship indicates the barrier mechanism of grain boundary strengthening.
The barrier effect of cell boundaries is evident in austenitic steels with large deformations, which leads to deviation of σf=f(d−1/2) from linear.
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