Understanding the static recrystallization of Ni-Mo alloyed steels for rolling optimization in high strength thick plates

Abstract

The development of high strength/high toughness steel grades for thick plates requires an optimum combination of alloy design and processing conditions. In this contribution, the effect that Molybdenum and Nickel have on the static recrystallization kinetics during roughing passes is analyzed. High alloying additions, especially in the case of Mo, imply intense solute drag delay for static recrystallization. This mechanism, added to the low reductions typically applied during roughing of thick plates, reduces the possibility for a complete recrystallization between passes and limit austenite conditioning and grain size refinement. Under these circumstances, the understanding and modelling of static recrystallization becomes relevant. Hot torsion tests were carried out and the effect of alloying elements on the recrystallization kinetics and recrystallized grain size was quantified in four different steel grades with several Molybdenum (0.25-0.5%) and Nickel combinations (0-0.5%). Finally, the softening behavior and microstructural evolution during multipass roughing rolling simulations was compared with MicroSim® model predictions, showing a reasonable agreement with experimental results.