Fine-grained structures developed along grain boundaries in a cold-rolled austenitic stainless steel

Fine-grained structures developed by cold-rolling in a 31 OS austenitic stainless steel have been investigated by using transmission electron microscopy (TEM). Particular emphasis is laid on the role of initial grain boundaries in the transmutation process of twin-matrix (T-M) lamellae into fine-grained structures. Microstructural evolution in a cold-rolled 31 OS steel is characterized by the development of dense T-M lamellae and their following collapse caused by shear band formation; shear bands destroy the T-M lamellae, and a fine-grained structure develops with increasing the area of shear bands. In the process of this grain refinement, such fine-grained structures have been found not only in shear bands but also in the area along initial grain boundaries. The fine-grained structure preferentially appeared around the intersections of grain boundaries with shear bands, and it expanded along the grain boundaries which were almost parallel to the rolling direction. In selected area diffraction patterns obtained from these fine-grained areas, large scatterings of crystal orientations were observed. On the basis of these results, the role of initial grain boundaries on the grain refinement is discussed.