EFFECT OF CONTROLLED ROLLING PROCESSING ON NANOMETER-SIZED CARBONITRIDE OF Ti-Mo FERRITE MATRIX MICROALLOYED STEEL

Single nanometer-sized particles, which are smaller than 10 nm, can significantly enhance the precipitation strengthening in microalloyed steels, thus causing their strength to be promoted greatly. In order to improve the strength of the steel, it is quite necessary to get a large amount of single nanometer-sized particles through optimizing rolling technology. In this work, the effects of two different kinds of controlled rolling technologies on the size and distribution of precipitated particles in the Ti-Mo ferritie matrix microalloyed steel have been researched using SEM, TEM and small-angle X-ray scattering. The results show that with the same total rolling reduction, the steel rolled only in gamma phase crystallization zone can obtain a higher portion of single nanometer-sized particles than that rolled respectively in gamma phase recrystallization and nonrecrystallization zones, in which those single nanometer-sized particles account for about 75% (mass fraction) of whole precipitated particles. In order to study the effect of deformation potency in gamma phase zone on the amount of precipitates in gamma phase and the micro-crystal size, nucleation rate and incubation time of following precipitates in gamma -> alpha transformation and ferritie matrix after gamma -> alpha transformation, some thermodynamics and kinetics calculations and analysis on precipitation are also conducted.