Strain Localizations in Ultra Low Carbon Steel: Exploring the Role of Dislocations

Ultra low carbon steel samples were near plane strain deformed at different strains, strain rates and temperatures. Density of grain interior strain localizations in gamma(ND//< 111 >) and theta(ND//< 111 >) fibres were evaluated against micro-stress estimates through X-ray line profile measurements. The patterns were remarkably different between the fibres. The increase in strain localizations were associated with increased dislocation density. This effect was more pronounced in gamma-fibre. In theta-fibre, however, the peaks were increasingly more asymmetric and dislocation substructures were stipulated to have lesser recovery. Discrete dislocation dynamics simulations for single crystal pure iron also brought in different behavior for gamma and theta fibres: increase in dislocation density in the former was estimated to be similar to 5 times more. A combination of textural softening and large/positive increase in dislocation density appears to justify the preference for strain localizations in gamma-fibre.