Development of crystallographic texture under plane and shear strain in ultrahigh-strength strip steels

The effect of centerline and subsurface microstructures on the crystallographic texture of three 8 mm thick low-alloyed hot-rolled and direct-quenched ultrahigh-strength strip steels with yield strengths in the range 800 – 1100 MPa has been investigated. Detailed microstructural features were studied using LCSM, FESEM, FESEM-EBSD. In addition textures and crystallographic features were analyzed using Matlab combined with MTEX software. Rolling to lower finish rolling temperatures increased austenite pancaking leading to the formation of ferritic/granular bainitic and the upper bainitic microstructures at the subsurface. In addition, increased austenite pancaking was found to increase the intensities of ∼{554}<225>_α, ∼{112}<110>_α and ∼{112}<131>_α texture components at the centerline and ∼{112}<111>_α and ∼{110}<112>_α/<111>_α texture components in the surface layers, especially in upper bainitic microstructures. Parent austenite reconstruction shows that crystallographic texture at the centerline derived from {112}<111>_γ and {110}<112>_γ and the subsurface the shear texture components derived from the {112}<110>_γ and {111}<112>_γ components, as expected. The Matlab reconstruction code was found to work well for martensitic and upper bainitic morphologies even with the highly pancaked prior austenite structure. However, it was less precise for granular bainite and ferrite. (paper)