Effects of dislocations on the early stage of TiC precipitation kinetics in ferritic steel: A comparative study with and without a pre-deformation

The influence of a pre-deformation with a true strain of 0.5 on the precipitation behavior during isothermal aging at 580 degrees C in ferritic steel containing 0.03C-0.1Ti-0.20Mn-3Al (mass %) was investigated. Atom probe tomography (APT) analysis revealed that titanium carbide (TiC) precipitates much earlier and more finely in pre-deformed steel than in steel without a pre-deformation. It was found that the precipitation sites of TiC are not only located on the dislocations but are also distributed homogeneously in a matrix in pre-deformed steel. In steel without a pre-deformation, coarse cementite first precipitates during the early stage of aging, and the cementite then dissolves owing to the subsequent precipitation of TiC. Meanwhile, in pre-deformed steel, cementite has difficulty precipitating, and carbon atoms are considered to segregate to high-density dislocations during the early stage of aging prior to the precipitation of TiC. A kinetic model that explains the difference between the precipitation behaviors of steel with and without a pre-deformation is proposed. Moreover, the difference observed between TiC particle strengthening in steel with and without a pre-deformation is discussed. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.