Optimizing continuous annealing of interstitial-free steels for improving deep drawability

Abstract

The crystallographic textures and the resulting plastic anisotropy of five interstitial-free (IF) steels with different carbon equivalents and Nb and Ti microalloying content have been investigated. The steels were industrially hot rolled, cold rolled, annealed, and finally hot-dip galvanized. An alternative heat treatment of the cold rolled samples was conducted in laboratory scale using parameters close to those in industry-scale continuous annealing lines. The anisotropy parameters were both measured and predicted on the basis of the measured texture data. The calculated $\bar r$ values were corrected by using functions that were fitted to the experimental data. It was found that for a given hot and cold rolling state even minor changes in the annealing conditions can improve the anisotropy parameter $\bar r$ by up to 13 pct. Increase in recrystallization texture and improvement of the resulting anisotropy parameters are discussed in terms of partial transformation of ferrite to austenite in the intercritical regime.