Effect of log-normal prior austenite grain size distributions on isothermal γ → α transformation in a low carbon low alloy steel

Effect of log-normal prior austenite grain size (PAGS) distributions, with mode PAGS of 35, 65 and125 µm and skewness of 1.57, 1.44 and 1.13 respectively, on isothermal ferrite nucleation site density and initial growth behaviours was investigated. Both mode PAGS and skewness determined the PAG corner nucleation site density for ferrite formation. Faster ferrite transformation kinetics was observed for a higher PAG corner site density. Ferrite grain size refinement was achieved in the final microstructure with the encouragement of PAG corner nucleation, along with an Avrami exponent n of 1.2 for initial ferrite transformation (below 40 vol.%), through modifying mode PAGS / skewness of log-normal PAGS distributions in low carbon low alloy steels.