Quantitative Analysis of Dislocation Density in an Austenitic Steel after Plastic Deformation

Grain size dependence of dislocation density and its character in austenitic stainless steels subjected to plastic strain was evaluated quantitatively by means of X-ray diffraction and Electron Back Scattering Diffraction (EBSD). Various amounts of the plastic strain up to 15% were given by a tensile instrument at 650 degrees C and three kinds of grain size (17, 46 and 87 mu m) were employed. Misorientation in crystal direction in each grain was determined by two parameters, GOS (Grain Orientation Spread) and KAM (Kernel Average Misorientation). GN (Geometrically Necessary) dislocation density was estimated from KAM parameter. GOS parameter increased with a linear relationship to the amount of plastic strain regardless of the grain size, whereas KAM parameter increased with increasing plastic strain but showed the grain size dependence. Change in total dislocation density with plastic strain showed a similar trend in KAM parameter. It is found that the difference in the total dislocation density at a plastic strain was consistent exactly with the difference in GN dislocation density depending on the grain size. These results were confirmed by TEM observations using several kinds of specimens used in X-ray experiments.