| This investigation measured the allotriomorphic ferrite transformation kinetics of a 1541-Nb forging steel. Two thermomechanical processing schedules were designed to vary the niobium solute level prior to the austenite-to-ferrite transformation. Dilatometry and optical metallography were used to measure the rates of ferrite formation and ferrite growth, respectively. Transmission electron microscopy was used to characterize the Nb(C,N) precipitate distributions and hence account for the influence of solute niobium on the transformation kinetics. The experimental data for ferrite formation was fitted to the JMAK phase transformation model, and that for ferrite growth to the Zener model. It was determined that a high niobium solute content retards the ferrite transformation kinetics, primarily by retarding ferrite nucleation. |
