An empirical equation was developed for the prediction of the critical strain for the onset of
dynamic recrystallization (DRX) in microalloyed Nb-containing steels. Single-rolling pass
isothermal compression tests were carried out in a Gleeble 1500TM thermomechanical
processing simulator at 1000, 1050, 1100 and 1150 oC and strain rates of 0.5, 1 and 3s-1. The
strain was 0.85. The Nb content was systematically varied between 0.024 and 0.10 mass
%Nb. No further effect of addition of Nb on the critical strain was observed above 0.068%.
The double-hit isothermal compression tests were carried out to investigate the influence of
retained strain on the critical strain for DRX under the same conditions spelt out above but in
tests in which the pre-strain was kept below the critical strain i.e. 0.142, and the amount of
retained strain was varied by increasing the inter-pass time from 0.5 s to 8 s. As expected, the
introduction of a pre-strain decreased the critical strain for the initiation of DRX. The data obtained
from the experimental tests were used to develop an empirical model for the prediction of the
critical strain for the onset of DRX taking into account the Nb content and the retained strain.
A good correlation was obtained between the predicted and the experimental results.