Relationship between microstructure and acoustic emission in Mn-Mo-Ni A533B steel

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Abstract
The sources of acoustic emission in a steel of the A533B composition with low sulphur content have been investigated using two different recording techniques. First, systematic narrow band (0.1–1.0 MHz) measurements were made of acoustic emission activity during uniaxial tensile tests of specimens with a range of controlled microstructures. Mechanical properties and fracto graphic data were analysed, and the most probable deformation and fracture mechanisms deduced for these microstructures. It appears that only a few processes generate detectable emission in this material. For instance, high-velocity dislocation motion can be detected during the yield of slow-cooled or long-tempered specimens, and cleavage fracture in rapidly quenched specimens. A model is presented to relate the magnitude of the emission to the dynamic operation of dislocation and fracture sources. Second, very wide band (25 MHz) calibrated measurements were made of the most energetic emission sources in rapidly quenched material. These indicate the sources to be consistent with cleavage microcracking. A typical micro crack propagated over a distance of ∼ 50 µm with an average velocity of 450 m s−1.