Effect of Vanadium and Niobium on Austenite Grain Growth Kinetics in Low Carbon High Strength Steel

Abstract

The coasening of austenite grains has been studied kinetically in low-carbon high-manganese steels containing Al, V, and Nb, respectively.
The austenite grain growth rate is remarkably decreased by a small addition of Nb. In contrast, the effect of V is very small.
The activation energy for the austenite grain growth in the steels containing Al, V, and Nb in solution has been determined to be 65.4, 65.0, and 3.7kcal/mol, respectively; the energy is remarkably increased by a small addition of Nb. This can be attributed to the fact that the activation energy for the diffusion of Nb in austenite and the binding energy between Nb and austenite grain boundary are both great.
The rate constant of the grain growth below 1250°C in the steels containing more than 0.10wt% Nb is smaller than that predicted by “Impurity drag model”. This is considered to be due to the presense of Nb (C, N) which is not dissolved. Such undissolved particles have a great effect of the austenite grain growth.