STRUCTURAL VARIATION ALONG THICKNESS DIRE CTION OF EXTRA-LOW CARBON SHEET STEELS ROLLED IN FERRITE REGION

The application of an EBSD technique in an SEM reveals a new approach to analyze a structural variation along the thickness direction of ext ra-low carbon sheet steels rolled in the ferrite region. The fine recr ystallized grains in the sheet steel relied without lubrication are ob served near the surface due to a strong additional shear strain betwee n a material and a roll, and those grains are considered to recrystall ize dynamically by means of image-quality imaging with EBSD. The nonun iform recrystallization texture through the thickness are formed in th e sheet steel rolled without lubrication by means of orientation imagi ng with EBSD, <110>/ND recrystallized grains being formed near surface , <111>//ND and <100>//ND recrystallized grains being formed at the mi d plane. On the other hand, <110>//ND recrystallized grains are not fo rmed preferentially near surface and <111>/ND and <100>//ND recrystall ized grains are formed uniformly throughout the thickness in the sheet steel rolled with lubrication. The orientation imaging also reveals t he 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 su rface and the <110>//ND grains with larger tolerance being formed at t he thickness location toward the surface and center from 1/10 plane. T he image-quality imaging and orientation imaging allow a more visual a nd intuitive understanding of the nonuniformity of a microstructure an d texture formation in the sheet steel roiled without lubrication than conventional method such as optical microscopy and X-ray diffraction measurements.