Grain refinement during the γ-α transformation in a low-carbon steel

Abstract

samples were quenched in water) corresponded to every ferrite grain structure. Austenite and ferrite grain structures were revealed through etching of polished sections in a boiling saturated aqueous solution of picric acid with surfactant additives and in a 4% solution of nitric acid in alcohol, respectively. Images of microstructures were taken at a resolution of 1536 × 1024 on a Neophot 21 microscope with an optical attachment and a Canon EOS 300D digital video camera. Ferrite and austenite grains were measured at magnifications of × 100‐500 by the random intercept method (at least 500‐600 grains per version) using an Epiquant semi-automatic analyzer. The results were processed using the Image Expert Pro program. The average sizes of the initial ( D γ ) and final ( d α ) grains, their ratios (transformation coefficients k ), and their errors were calculated. The change in the transformation coefficient (and the change in the ferrite grain size) as a function of the scale of the initial austenite grain and the cooling rate was estimated for the steel of every grade, k = f ( D γ , w )