Effect of initial grain size on the static recrystallization kinetics of Nb microalloyed steels

The static recrystallization kinetics of a 0.08%C-0.055%Nb steel were investigated at 950 degrees C by means of interrupted hot compression tests; the results obtained in this way were analyzed using three different methods for assessing the fractional softening. In particular, the effect was studied of varying the initial grain size from 12 to 83 mu m The exponent relating initial grain size to the time for 50% recrystallization was found to be about 1.7. This is somewhat less than the exponent of 2.0 conventionally employed for plain C-Mn steels, and which is often quoted in the literature as applicable to Nb grades. In addition, by means of comparison with previous work on grades with tower levels of Nb and Mn, it is shown that higher levels of Mn make significant contributions to the retardation of static recrystallization in Nb steels.