Effect of composition and thermo-mechanical processing schedule on the microstructure, precipitation and strengthening of Nb-microalloyed steel

In order to study the influence of composition and thermo-mechanical processing schedule on the kinetics of austenite recrystallization, strain induced precipitation and final microstructural evolution in Nb-microalloyed steels, thermo-mechanical processing simulations have been carried out inside Gleeble® by varying the number of deformation passes (2-pass vs. 6-pass), deformation temperatures (1000-800 °C) and inter-pass times. Low-C high-Mn steel (LCHMn) has been found to offer finer ferrite grain size and finer Nb-precipitation which contributed to superior hardness to that steel, compared to high-C low-Mn steel (HCLMn). Among the deformation schedules applied, 6-pass schedule has been found to be superior over 2-pass schedule in terms of precipitation strengthening and hardness. This study also proposes a mathematical framework to explain the effect of composition and processing schedule in Nb-microalloyed steels following Dutta and Sellars approach on precipitation-recrystallization interaction.