Dislocation structures in warm-rolled low-C steels with ultra-fine ferrite grains (~1μm) were analyzed by using transmission electron microscopy and the modified Warren–Averbach procedure for X-ray diffraction profiles. In good accord with the transmission electron microscopic observation results, the dislocation density was derived by the X-ray diffraction profile analysis to be 1.06 x 1014 and 1.98 x 1014/m2, in as-rolled 0.15C and 0.15C–0.1P steel, respectively. In contrast to the straight dislocation segments in the 0.15C steel, tangled and curved dislocations were observed in the P steel in both the as-rolled and annealed conditions. A larger q-value and smaller dislocation arrangement parameter, M = Re√ρ, were observed in the P steel. The P in the low-C steels tended to prompt the ratio of screw dislocation component and the dislocation arrangement with a stronger interaction during plastic deformation. Not only the dislocation density, but also the dislocation interaction behavior controlled the changes in yield strength during annealing of the as-rolled steels at 723K. The modified Warren–Averbach diffraction profile analysis was suggested to be useful for quantitatively characterizing the dislocation interaction behavior.

Phosphorus-Induced Dislocation Structure Variation in the Warm-Rolled Ultrafine-Grained Low-Carbon Steels. F.Yin, T.Hanamura, O.Umezawa, K.Nagai: Materials Science and Engineering A, 2003, 354[1-2], 31-9