Analysis of Mn Effect on Recrystallization Kinetics in High Nb Steels

A physically based model is used to analyze quantitatively, the relative contributions of solute Nb and strain-induced NbC precipitation to the retardation of static recrystallization during the interpass time. The model explicitly takes into account the time evolution of strain-induced precipitation and its interaction with recovery and recrystallization. It is thus possible to quantitatively model the recrystallization kinetics taking into account: i) the effect of solute drag on the boundary mobility, ii) the effect of particle pinning (Zener drag) on the driving force for boundary motion, and iii) the effect of dislocation pinning by strain-induced precipitates, on the recovery kinetics and the nucleation of recrystallization. The analysis shows that there is an optimum partitioning of Nb between matrix solute and strain induced precipitates. This optimum partitioning maximizes particle pinning while ensuring an adequate solute drag effect to prevent the boundary from breaking away from solute atmosphere. The optimum partitioning of Nb between the matrix and the precipitates is shown to depend upon the temperature window of rolling, pass reduction and interpass time. The effect of delaying the kinetics of strain-induced precipitation of NbC through large Mn addition is shown to be an advantage for ensuring adequate solute drag in the low temperature, large pass deformation schedule used in near-net shape processing of thin slab or thick strip castings.