ACOUSTIC-EMISSION DURING DEFORMATION OF DUAL-PHASE STEELS

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, νd, decreases. The total AE energy, ∑Elp, emitted during Lüders band propagation is related to the Lüders strain, εl and ∑Elp/ εl, decreases as εl increases because of the increase in ε, resulting from the decrease in dislocation velocity, νd. 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. © 1990 The Minerals, Metals & Materials Society - ASM International - The Materials Information Society.