A novel rolling-annealing cycle for enhanced deep drawing properties in IF steels

Abstract

To give good drawability, a steel needs high volume fractions of the annealing texture component {111}<hkl> and a low fraction of ∼{100}<011>. This is achieved in conventional Interstitial Free (IF) steels by a cold rolling reduction of 85% and an anneal at 750°C-800°C for a few minutes. In this research, a double rolling and annealing process is examined based upon the notion that if {111}<hkl> can be produced, further rolling of the material should provide nuclei of {111}<hkl> by the process of deformation banding. In Canadian prize winning work it was demonstrated that rolling ferrite at 700°C, produced a strong {111}<hkl> texture after annealing at 700°C and so this was also selected for further rolling and annealing. The results were highly encouraging, the intensity of {111}<hkl> increased to levels well above 30X Random. An Orientation Imaging Microscopy (OIM) investigation revealed that the {111}<hkl> oriented grains were subject to orientation splitting around <111>ND, and this process of deformation banding produced the necessary lattice curvature for nucleation of the texture components essential for good deep drawability. A detailed investigation of such two stage deformation processes was undertaken in which the total strain was kept constant, with first and second rolling interrupted by annealing before the final recrystallization anneal was made. The results are complex, but it is certain that <111>{hkl} as a starting orientation before second rolling is essential for the success of the process.