Examples of microstructure analysis by orientation imaging microscopy

The properties of cold-rolled deep-drawing steels and electrical sheets, as essential products of flat steel production, depend directly on the micros tructural state of the ferrite after primary recrystallization. As the trad itional method of microstructural description, optical microscopy reaches i ts limits in describing the recrystallization or recovery state of the ferr ite, because any definite and direct information on the texture, type of gr ain boundaries, and distortions (dislocation density) in the crystal lattic e cannot be obtained with this technique. The recrystallization state can b e considered by using conventional X-ray diffractometry to determine macrot exture. In the past microstructural inhomogeneities which, requiring a loca l description or grain boundaries, could be investigated only by means of t ransmission electron microscopy (TEM). Nowadays orientation imaging microsc opy (OIM), which is based on electron diffraction and which offers an effic ient metallurgical investigation technique, links the above mentioned inves tigation methods and compensates their disadvantages. The efficiency of ori entation imaging microscopy in interaction with conventional metallurgical methods was demonstrated on two steels with local microstructural anomalies . Both were cold rolled and annealed. It was shown that recrystallization i n the sheet surface of a Ti-IF steel was inhibited by fine oxidic precipita tes. A recovered microstructure with a distinct {001}< 110 >-orientation ap peared after annealing, In the case of silicon steel it was evident that re covery and recrystallization depended on the initial grain orientations in the former states of production.