Acoustic emission during deformation of dual-phase steels

Abstract

The study of acoustic emission (AE) during deformation of dual-phase steels consisting of ferrite (F) and pearlite (P)/martensite (M) indicates that the AE peak in the yielding region always appears at the beginning of the macroplastic deformation. After macroyielding starts, the AE decreases because the dislocation velocity, ν_d, decreases. The total AE energy, ∑E_lp, emitted during Lüders band propagation is related to the Lüders strain, ε_l and ∑E_lp/ ε_l, decreases as ε_l increases because of the increase in ε, resulting from the decrease in dislocation velocity, ν_d. After quenching from the two-phase region at cooling rates larger than a certain critical value, a second AE peak, which is produced by the cracking mainly at the interfaces between M and F and secondly in martensitic particles, appears in a certain plastic strain range in addition to the one in the yielding region. As the cooling rate becomes too fast, the AE peak in the yielding region disappears, and the second AE peak cannot be completed due to the brittle fracture.