What if the importance of deformation?
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Answer:
The influence of strain, strain rate, temperature, and grain size on the formation of deformation induced ferrite has been examined. Deformation induced ferrite forms very readily in both fine and coarse grained steels and much more rapidly than the ferrite from strain free austenite. Very small strains are sufficient to induce the production of such ferrite and the temperature range over which it appears spans from just below the Ae3 temperature down to the undeformed Ar3 temperature. Although it forms readily in both coarse and fine grained steels, the volume fraction produced is sensitive to the austenite grain size. In coarse grained steels, deformation at low strain rates is concentrated along the grain faces; extensive dynamic recovery occurs, which is why the ferrite remains soft, so that only thin ferrite films are able to form. At higher strain rates, work hardening takes place so that the strength of the ferrite at high strains approaches that of the austenite.