DEFORMATION MICROSTRUCTURE AND NUCLEATION OF RECRYSTALLIZATION IN HOT-DEFORMED SINGLE-CRYSTALS OF 18-PERCENT CR FERRITIC STEEL

Static recrystallization of the hot deformed single crystals with [001 ], [111], [133] and [135] initial orientation of an 18%Cr ferritic sta inless steel was studied. It was clarified that the hot-deformed micro structures and the recrystallization behaviors strongly depend on the initial orientation. The [001] crystal showed coarse and diffuse subgr ains after hot-compression, the [111] and the [135] crystals formed re latively fine and uniform subgrains, and a number of the deformation b ands elongated perpendicular to the compression axis developed in the [133] crystal. The [001] crystal was extremely hard to recrystallize a nd showed no recrystallization after a long time annealing. The [111] and the [135] crystals were relatively hard to recrystallize. The enha nced recrystallization along the deformation bands occurred in the [13 3] crystal, and the recrystallized grains had the orientations between those of the matrix and the deformation bands. The dislocation densit y, i.e., the driving force for static recrystallization, in the hot-de formed subgrain structures were quantitatively evaluated on the basis of the detailed TEM observations. Although the dislocation density in the [001] crystal which showed no recrystallization was lower than tho se of the other orientations, that of the [133] crystal which showed e nhanced nucleation was similar to that of the [111] crystal which was relatively hard to recrystallize. That is, the dislocation density in the deformed matrix does not necessarily correspond with the easiness of nucleation. EBSP measurements clearly showed that the narrow region s (transition bands) between the deformation bands and the matrix in t he [133] crystal bear large misorientations about 50 degrees. It is co ncluded from those results that the large local misorientation in the deformation microstructure does be important for the nucleation of rec rystallization and it is generally treacherous to discuss the nucleati on problem only on the basis of the macroscopic a nd averaged informat ion, such as the mean dislocation density, of the deformed state.