Monitoring of the deformation and fracture process of dual phase steels employing acoustic emission techniques

In this paper, continuing our previous works, a new approach for detection of fracture micro mechanisms of ferrite–martensite dual-phase steels (DPSs) with various microstructures was investigated. For this purpose, dual phase steels with different volume fractions of martensite (VM) were produced by various heat treatment methods on a low carbon steel (0.1% C), and acoustic emission (AE) monitoring was then used during tensile testing of these DPSs. The AE signals from a tensile test using DPS in the range of 12–73% VM and various morphologies, like equiaxed or fibrous martensite phase, were captured. Principally, to understand the AE response and behavior of the martensite or ferrite phase separately, some samples of martensite and heat treated ferrite were tested. After the tests, by utilizing a new function named “sentry function”, we tried to relate the AE signals to various failure mechanisms of these steels. In confirmation of our earlier works, the results show that AE monitoring and sentry function are efficient tools to detect failure micromechanisms, consisting of ferrite–martensite interface decohesion and/or martensite phase fracture, identifying the correlation of failure mechanisms to microstructure in DPS. The results were verified with scanning electron microscopic observations and they indicate that AE monitoring is an efficient tool to detect micromechanisms identifying failure in DPSs.