Effect of manganese on recrystallisation kinetics of niobium microalloyed steel

Using hot torsion tests, the influence of Mn on the recrystallisation behaviour of a Nb microalloyed steel was studied. Continuous and interrupted torsion tests were performed in the temperature range 950 - 1050degreesC at strain rates of 0.05-5 s(-1). The kinetics of static and metadynamic recrystallisation (MRX) were characterised and appropriate expressions were formulated for the effect of Mn and of the other deformation parameters on the kinetics. The rate of MRX increases with strain rate and temperature and is observed to be independent of strain, in contrast to the observations for static recrystallisation (SRX). The strain rate dependence of MRX is about twice that of SRX, whereas the activation energy Q(MRX) is about Q(SRX)/2. Thus, results obtained under laboratory conditions must be corrected before application to industrial strain rates. When extrapolated to the much higher mill strain rates (> 100 s(-1)), the present results indicate that SRX is much slower than MRX and is also unlikely to produce much softening in the 1 s interpass times available in such mills.