Phosphorus-induced dislocation structure variation in the warm-rolled ultrafine-grained low-carbon steels

Dislocation structures in warm-rolled low-carbon steels with ultrafine ferrite grains (∼1 μm) are analyzed by both transmission electron microscopy (TEM) observation and the modified Warren–Averbach procedures for X-ray diffraction profiles. In good accordance with the TEM observation results, the dislocation density is derived by the X-ray diffraction profile analysis to be 1.06×1014 and 1.98×1014 m−2, in the 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 are observed in the phosphorus steel at both the as-rolled and annealed conditions. The larger q value and smaller dislocation arrangement parameter, M=Reρ, are observed in the phosphorus steel. Phosphorus in the low-carbon steels tends 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 behaviors control the changes of yield strength during annealing the as-rolled steels at 723 K. The modified Warren–Averbach X-ray diffraction profile analysis may be useful in characterizing the dislocation interaction behavior quantitatively.