Abstract
EN30A, a low-alloy steel, has been tested under tensile load in the quenched condition and after tempering at 650°C for times up to 10080 min in order to investigate systematically the effect of strength and microstructure on acoustic emission. Measurements of the mechanical properties were combined with metallographic studies and extensive fractography in an attempt to determine the mechanisms of deformation and fracture which can generate detectable acoustic emission. The results are consistent with the fracture and/or decohesion of inclusions during both pre- and post-yield loading and fast shear fracture immediately before final fracture, being sources of detectable emission for all heat-treated conditions. In addition, the quenched specimen generated copious emission during plastic deformation, which increased in intensity as final fracture was approached, and this appeared to be linked to the onset of a localized shear mode of deformation and fracture. Material tempered for short times exhibited a zig-zag fracture indicative of appreciable shear, yet generated considerably less emission than the quenched specimen, possibly as a consequence of the lower strength level of this material. Material tempered for long times generated no emission other than that associated with inclusion fracture and final shear lip formation.
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