Precise Characterization of Dislocations and Cementite in Pearlitic Steels at Different Drawing Strains Using X-ray Diffraction

The dislocation characteristics and subgrain size of cold-drawn pearlitic steels with different carbon compositions were analyzed using X-ray diffraction line profile analysis to determine the work-hardening mechanism, with particular focus on microstructural deformation resulting from the rotation of pearlitic colonies. Modified Williamson-Hall and modified Warren-Averbach methods, which use multiple diffraction profiles, were applied to evaluate the microstructural parameters of the ferrite phase. Although the dislocation density increased with an increase in the drawing strain, the subgrain size was almost constant up to a strain of about 0.7. It was also shown that the higher carbon composition in the pearlitic steels contributes to the refinement of subgrains of the ferrite phase and the accumulation of dislocations. Moreover, the single-line profile analysis was performed for the cementite powder, which was prepared by electrolytic extraction from the steel specimens. The thickness of the cementite lamellae decreased with increasing drawing strain, indicating that the decomposition of the cementite phase occurred at the low strain level of 0.7. On the basis of these microstructural parameters, the strengthening mechanism as a function of the strain level is discussed.