Statistical analysis and recovery behaviors of dislocations in cold‐rolled and annealed reactor pressure vessel steels

Abstract The statistical analysis and recovery behavior of dislocations in cold‐rolled and annealed reactor pressure vessel steels with a thickness reduction of 50 % were investigated by using x‐ray diffraction and electron backscattered diffraction analysis in this study. A new modified Kubin & Mortensen's method was proposed to evaluate the geometrically necessary dislocation density, and this method could effectively improve the accuracy of geometrically necessary dislocation evaluation by eliminating the effect of step size and measurement noises. Comparison analysis between modified Williamson‐Hall and modified Kubin & Mortensen's methods was also performed in this study, which shows different recovery behavior of dislocations. The electron backscattered diffraction results show that geometrically necessary dislocation density remained unchangeable after annealing treatment below and at 550 °C, and it occurred to decrease above 550 °C due to the occurrence of recrystallization. However, dislocations started to migrate and annihilate at 340 °C according to x‐ray diffraction results. A possible explanation is a difference in the effect of pairwise dislocation annihilation on statistically stored dislocations and geometrically necessary dislocations.