Effects of annealing treatment on microstructure and mechanical property of cold-drawn 316L stainless steel fibers

Abstract 316L stainless steel fibers with diameters of 20 and 8 µm fabricated by bundle-drawing were annealed at the temperatures from 963 to 1003 K with different holding times. Optical microscope observations, electron back-scattered diffraction (EBSD) techniques, transmission electron microscope (TEM) analyses and tensile property tests were performed in order to examine the evolutions of microstructure and mechanical properties of the fibers. Both average recrystallized grain size and volume fraction of recrystallized grains increase with increasing annealing temperature or holding time. The low values of Johnson-Mehl-Avrami-Kolmogorov (JMAK) exponent n can be attributed to the inhomogeneity of original microstructure. Twin boundaries play active roles in the process of deformation and recrystallization nucleation. The earlier initiation of recrystallization for the fiber with a diameter of 8 µm is closely related to larger deformation amount and finer original grains. The textures in the as-annealed fibers are similar with that in the as-drawn fibers, i.e., and orientations. Compared with that of orientation, the regions of orientation in the as-drawn fibers can serve as the preferential sites for recrystallization nucleation. The accelerated nucleation and limited growth of recrystallization for the fiber with a diameter of 8 µm make its recrystallized grain size keeping at a small level. Tensile strengths for the fibers decrease with the occurrence of recrystallization, and its values for the fibers annealed at 983 K for 30 min drop to almost half that of the as-drawn states. Most of the fibers exhibit limited tensile elongations with negligible plastic strain to failure.