The relationship between niobium content and austenite grain growth has
been investigated through hot rolling simulation on a Bähr dilatometer.
The effect of delay time between passes during rough rolling in Nbmicroalloyed
steels with nitrogen contents typical for electric arc furnace
(EAF) melting was studied. The results indicate that the grain growth
constants n, Q, and A increase with an increase in Nb content. The
activation energy for austenite grain growth Q was found to be in the
range of 239 to 572 kJ/mol, the exponential constant n ranged from 2.8 to
6.2, and the material and processing condition constant A from 4.24 × 1012
to 4.96 × 1028, for steels with niobium contents ranging from 0.002% Nb to
0.1% Nb. A general constitutive equation for the prediction of austenite
grain growth in these Nb-microalloyed steels under rough rolling
conditions has been developed. Good agreement between the experimental
and the predicted values was achieved with this constitutive equation.