Examples of microstructure analysis by orientation imaging microscopy

Abstract

The properties of cold‐rolled deep‐drawing steels and electrical sheets, as essential products of flat steel production, depend directly on the microstructural state of the ferrite after primary recrystallization. As the traditional method of microstructural description, optical microscopy reaches its limits in describing the recrystallization or recovery state of the ferrite, because any definite and direct information on the texture, type of grain boundaries, and distortions (dislocation density) in the crystal lattice cannot be obtained with this technique. The recrystallization state can be considered by using conventional X‐ray diffractometry to determine macrotexture. In the past microstructural inhomogeneities which, requiring a local description or grain boundaries, could be investigated only by means of transmission electron microscopy (TEM). Nowadays orientation imaging microscopy (OIM), which is based on electron diffraction and which offers an efficient metallurgical investigation technique, links the above mentioned investigation methods and compensates their disadvantages. The efficiency of orientation 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 in the sheet surface of a Ti‐IF steel was inhibited by fine oxidic precipitates. A recovered microstructure with a distinct {001}<110>‐orientation appeared after annealing. In the case of silicon steel it was evident that recovery and recrystallization depended on the initial grain orientations in the former states of production.