The effects of thermomechanical processing on the precipitation in an industrial dual-phase steel microalloyed with titanium

Analytical transmission electron microscopy was employed to characterize th e precipitation at each step of the fabrication process and thermomechanica l treatment of an industrial dual-phase steel microalloyed with titanium. T heoretical thermodynamic calculations as well as experimental analysis show ed that more than half of the titanium carbosulfide (Ti4C2S2) precipitates would dissolve during reheating at 1240 degreesC. Despite this dissolution at 1240 degreesC, the remaining titanium carbonitrides and carbosulfides we re effective in pinning austenitic grain boundaries, keeping the austenitic grain size at around 40 mum (at 1240 degreesC). It is also shown that, dur ing hot rolling, there exist three regions of titanium carbide precipitatio n. The first is defined by an increase of titanium carbide precipitation du e to deformation. The second region is marked by the insignificant change i n precipitation. The third region is indicated by another increase in preci pitation due to the austenite-to-ferrite transformation. The experimental a nd theoretical results on the contribution of TiC precipitation to hardenin g of ferrite (Orowan mechanism) were in excellent agreement, showing that T iC precipitates have the most important effect on increasing the yield stre ngth, overshadowing the austenitic grain-boundary pinning contributions by Ti(C,N) and Ti4C2S2 precipitates.