Journal of the Southern African Institute of Mining and Metallurgy
On-line version ISSN 2411-9717
Print version ISSN 0038-223X
ANNAN, K.A.; SIYASIYA, C.W. and STUMPF, W.E.. The influence of niobium content on austenite grain growth in microalloyed steels. J. S. Afr. Inst. Min. Metall. [online]. 2015, vol.115, n.10, pp.973-980. ISSN 2411-9717. http://dx.doi.org/10.17159/2411-9717/2015/v115n10a12.
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 Nb-microalloyed 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 χ 1012 to 4.96 χ 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.
Keywords : constitutive equation; austenite grain growth; microalloying; deformation.