2004 Volume 90 Issue 3 Pages 141-145
Dispersion of fine proeutectoid ferrite and/or enhancement of formation of intragranular bainite have been performed to improve mechanical properties at/around welded region in steels. In the present study, effects of Ti-based oxide inclusions on the nucleation and growth processes of proeutectoid ferrite and bainite are examined in terms of the number density and size of the inclusions in steels with different γ-grain sizes. Ti-oxide acts as effective nucleation site of granular proeutectoid ferrite and bainite. Especially, it could be suggested that fine inclusions induce nucleation of high density of intragranular bainite. On the other hand, growth of (Ti, Mn)-oxide on grain boundary enhances both the depletion of Mn at/around grain boundary and formations of elongated proeutectoid ferrite along grain boundary, Widmanstätten ferrite and aggregate of nearly single-variant of bainite at grain boundaries. The Mn depletion could form the three kinds of ferrites mentioned above, remarkably, at grain boundaries, resulting in the suppression of formation of intragranular bainite.
