Effect of Lubrication Condition on Recrystallization Texture of Ultra-low C Sheet Steel Hot-rolled in Ferrite Region

The application of the EBSD technique with an SEM provides a new approach to the analysis of variations of the recrystallization texture in the thickness direction of ultra-low carbon sheet steels rolled in the ferrite region. A nonuniform recrystallization texture through the thickness is formed due to the additional shear strain introduced by frictional force between the rolls and the material in sheet steel rolled with a friction coefficient over 0.15, 〈110〉//ND recrystallized grains being formed near the surface, and 〈111〉//ND and 〈100〉//ND recrystallized grains being formed at the mid plane. On the other hand, 〈110〉//ND recrystallized grains are not formed preferentially near the surface, and 〈111〉//ND and 〈100〉//ND recrystallized grains are formed uniformly throughout the thickness in sheet steel rolled with a friction coefficient under 0.15. Orientation imaging also reveals differences related to the tolerance of 〈110〉//ND recrystallized grains around the 〈110〉//ND axis in sheet steel rolled without lubrication, in that 〈110〉//ND grains with a small tolerance form at the 1/10 plane from the surface and 〈110〉//ND grains with larger tolerances form at thickness locations from the 1/10 plane toward the surface and center. The r-value depends on the friction coefficient and increases significantly as the friction coefficient decreases under 0.15, resulting in high r-values over 1.2. This change in the r-value with the friction coefficient corresponds to the distribution of the recrystallization texture through the thickness. Orientation imaging allows a more visual and intuitive understanding of the nonuniformity of the recrystallization texture than conventional methods such as optical microscopy and X-ray diffraction measurement.