The critical strain for dynamic recrystallization in rolling mills

There is considerable controversy regarding the point of initiation of dynamic recrystallization during both constant strain rate and varying strain rate conditions of deformation. A method is demonstrated based on the presence of inflection points in theta/sigma plots, where theta is the rate of work hardening, dsigma/depsilon. Normalization of the stresses and strains by the peak stresses and strains leads to a simple method that applies even under conditions of varying strain rate, as in the roll bite of rolling mills. Analysis of the data obtained on a number of steels indicates that the ratio of critical to peak strain is generally in the range 0.5 to 0.6, depending on the chemistry. The method can be applied to the computer modeling of rolling mills as, on the basis of simple laboratory measurements, it predicts the stage of the process at which metadynamic (post-dynamic) recrystallization can take place. The normalized flow curve can then be used in the reverse sense to predict the softening that is expected to take place during the interpass interval under conditions of strain accumulation.