On Optimizing Batch Annealing for the Production of IF Steels

Abstract

Batch annealing characterized by a long heating cycle and low heating temperature is widely used to produce sheet steels including interstitial-free (IF) steels. Optimizing batch-annealing conditions would be helpful in cutting lead time and saving energy while keeping the necessary deep drawability; however, little research has been done on it. The effects of batch-annealing parameters on the deep drawability of a Ti-stabilized IF steel and Nb+Ti–stabilized IF steel have been investigated. In general, a slight improvement in rmvalue was found with the increase of annealing temperature. Because of the higher recrystallization temperatures of Nb+Ti–IF steel, it showed higher sensitivity to annealing temperature than Ti-IF steel. In addition, greater dependency of mechanical properties and deep drawability on soaking time was observed when annealing temperature was lower. Moreover, a heat transfer analysis showed that the annealing time could be reduced by 40% if the temperature decreases from 730°C to 650°C. The industrial production has verified that the analytical results are in good agreement with the recorded annealing temperature curve. Meanwhile, it has been shown that Ti-IF steels annealed at 650°C have very close deep drawability and other tensile properties compared with these annealed at 730°C.