Structural Variation along Thickness Direction of Extra-low Carbon Sheet Steels Rolled in Ferrite Region

Abstract

The application of an EBSD technique in an SEM reveals a new approach to analyze a structural variation along the thickness direction of extra-low carbon sheet steels rolled in the ferrite region. The fine recrystallized grains in the sheet steel rolled without lubrication are observed near the surface due to a strong additional shear strain between a material and a roll, and those grains are considered to recrystallize dynamically by means of image-quality imaging with EBSD. The nonuniform recrystallization texture through the thickness are formed in the sheet steel rolled without lubrication by means of orientation imaging with EBSD, <110>//ND recrystallized grains being formed near surface, <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 surface and <111>//ND and <100> //ND recrystallized grains are formed uniformly throughout the thickness in the sheet steel rolled with lubrication. The orientation imaging also reveals the tolerance of <110>//ND recrystallized grains around <110> //ND axis in the sheet steel rolled without lubrication, resulting in the <110>//ND grains with small tolerance being formed at the 1/10 plane from surface and the <110> // ND grains with larger tolerance being formed at the thickness location toward the surface and center from 1/10 plane. The image-quality imaging and orientation imaging allow a more visual and intuitive understanding of the nonuniformity of a microstructure and texture formation in the sheet steel rolled without lubrication than conventional method such as optical microscopy and X-ray diffraction measurements.