Abstract
Dynamics and susceptibility of austenite/ferrite dual phase stainless steel plate of 1.5mm thickness to delayed fracture were studied by the wave-front simulation of Lamb wave AEs (Acoustic Emissions) and generation frequency, respectively. Ferrite area ratio of the steel increased from 56% at as-received specimen to 81% at heat-treated at 1423K. Attenuation of the first So-mode Lamb wave of as-received specimen was so large that the Lamb wave can not be detected, but decreased with an increase of ferrite phase. Susceptibility to the delayed fracture or AE event counts by micro-fractures increased in the order of as-received specimen, heat-treated specimen at 1073K, 1273K and 1423K. Micro fractures progressed underneath the surface of thin plate through both the ferrite and austenite grains. Source waves for heat-treated specimens, obtained by the waveform simulation of the first arrival So-packet of Lamb wave AEs, revealed fast small fracture in ferrite grains and slow large fracture in austenite grains.
