On the Study of Batch Annealing Parameter Optimization for Higher Lankford Value in High Phosphorus Interstitial Free High Strength Steel

Abstract

IFHS grades best known for their superior strength and high formability are conventionally processed through batch annealing. However, high phosphorus contents, which are responsible for rendering the high strength property to IFHS grades, have also been proved to impair the formability of these steels, mainly because of the formation of FeTiP precipitates during batch annealing process. In the present study, two different categories of high phosphorus-containing IFHS steels, viz. (i) Ti and (ii) Ti + Nb stabilized, were subjected to batch annealing simulations targeting r¯ > 2.0. Uniqueness in the present effort lies in the usage of a custom-designed annealing simulator wherein annealing conditions akin to those prevailing in steel industry could be maintained. Processed specimens were characterized for microstructure, texture, tensile properties, and r¯ measurements. Through careful and iterative optimization of annealing parameters and physical simulations, it was possible to achieve r¯ values higher than 2.0 in both the categories of IFHS steels. The optimization of parameters was based upon maximization of γ-fiber texture along with proper recrystallized microstructure. It has been shown that soaking temperature of 710 and 740 °C leads to the achievement of r¯ > 2.0 in case of Ti-stabilized and Ti + Nb-stabilized grades, respectively.