Particle-stimulated Nucleation of Ferrite in Heavy Steel Sections

Abstract

In heavy steel sections, strength and toughness are improved remarkably by refining and homogenizing the final ferrite microstructure. The production of heavy sections by universal-type rolling mills takes place at elevated temperature followed by slow cooling rates. Therefore, refinement of the ferrite microstructure through modern thermomechanical, TMP, techniques is not feasible. This paper explores and presents the use of particle-stimulated nucleation of ferrite, the PSN (particle-stimulated nucleation) mechanism, to refine the ferrite grain size and eliminate the high-carbon, low transformation products otherwise found in transformed coarse-grained austenite. In this study, MnS and Ti-oxide particles were used to promote intragranular ferrite, or IGF, in a typical ASTM A572 grade 50 Steel. This work included the study of the decomposition behavior of coarse grained austenite as a function of very slow cooling rate. In addition, the nucleation of ferrite grains taking place at γ/γ, γ/α and γ/inclusion interfaces was identified and quantified.