Structural and textural heredity during phase transformations in IF steel

Ultra-low-carbon interstitial-free (IF) steel sheets are characterized by a deep drawability due to excellent plasticity at room temperature. The ideal texture of sheet material subjected to stamping is characterized by a fiber texture with the <111> axis parallel to the die displacement direction. The issues of texture inheritance become crucial due to various structural and phase transformations that occur during fabrication of IF steel, namely the multi-variant α → γ → α transformation. This study investigates the crystallographic features of the α → γ → α phase transformation in IF steel in order to explain the peculiarities of structural and textural inheritance. For this purpose, the samples from IF steel sheets were heated into the single phase austenitic region and cooled in water and liquid nitrogen. Using the electron backscatter diffraction (EBSD), the structural and textural states of the samples before and after treatment were examined. During the phase transformation, ferrite grains coarsen, while the axial <111> // normal direction (ND) texture is retained with the strengthening of specific crystallographic orientations. Both types of quenching lead to a significant increase in the fraction of CSL boundaries of Σ3‑type. The authors demonstrate that the structural and textural heredity occurs during sequential α → γ → α phase transformations, reproducing the initial crystallographic texture of α-phase. The newly formed α-phase is characterized by the spectra of intergranular and special boundary misorientations typical of a diffusionless phase transformation that proceeds following the orientation relationships close to Kurdjumov–Sachs.

1. Russian Science Foundation (RSF) - 25-19-00683