Effect of titanium as a micro‐alloying addition on the apparent activation energy of medium carbon steels

Summary

Five micro‐alloyed steels with medium carbon content and varying percentages of titanium by weight were studied. Different groups of three values were obtained from hot torsion tests for strain rate, temperature and stress, making it possible to calculate the Zener‐Hollomon equations for the five steels, as well as the apparent activation energy value for each steel during the deformation processes. The values corresponding to the parameters of the Zener‐Hollomon equation were obtained from a specially designed algorithm using a mixed, initially iterative system and then optimising the correlation of the Zener parameter for the stresses obtained. The values obtained for the activation energies were experimentally confirmed by other methods: stress plotted against strain rate in the power law range, quantitative metallographic observation of the static recrystallisation, and a study of softening kinetics using the double deformation method. The various methods used give very similar results. They define an increase in the apparent activation energy which reaches a maximum at values of about 0.015–0.019% Ti by weight and which is 45% higher than those usually obtained on micro‐alloyed C‐Mn steels. If this quantity of titanium is exceeded, the activation energy returns to the usual values for low‐alloy steels.