Refinement of Ferrite Grain Size through Particle Stimulated Nucleation (PSN) Mechanism in Heavy Steel Sections

摘要

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, PSN, mechanism to refine the ferrite grain size and eliminate the high-carbon low transformation products. In this study, Ti-oxide particles were used to promote the intergranular ferrite, IGF, nucleation mechanism in a typical ASTM A572 grade 50 steel. This work included the study of the decomposition behavior of coarse grained austenite at 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.