Austenite Grain Boundary Pinning during Reheating by Mixed AlN and Nb(C,N) Particles

Abstract

The present study investigates the role of aluminium nitride (AlN) on grain boundary pinning during reheating in presence of niobium carbonitrides (Nb(C,N)) and subsequent evolution of grain size distribution. Three as continuously cast slabs of high strength low alloy steels containing different levels of Nb (between 0.045 – 0.019 wt%) and Al (between 0.057 – 0.02 wt%) have been characterized in terms of phase balance, ferrite grain size distribution and particle size distribution. Precipitate distributions have also been determined following simulated reheating schedules. The prior austenite grain size distributions after reheating have been correlated with precipitate distribution. Quantification of precipitate and prior austenite grain size distributions after reheating unveils the governing mechanisms for precipitate dissolution/coarsening. It is observed that grain boundary pinning is controlled by AlN at temperatures below 1125°C, but by Nb(C,N) at higher temperatures.