Abstract
A broad-band acoustic emission detection system has been used to record the transient surface displacements due to the release of elastic waves during deformation and fracture of EN30A, a low-alloy steel. Acoustic emission signals were recorded from material tested in the quenched, tempered and temper-embrittled conditions: Tests were also performed upon material which had been hydrogen charged prior to testing. The specimens which fractured by ductile mechanisms generated acoustic emission transients with shorter measured risetimes on average than those which fractured by a brittle intergranular mechanism induced by hydrogen. The risetimes of the transient displacements have been tentatively interpreted in terms of source lifetimes, whilst their amplitudes have been related to source areas, and hence their time derivatives to source velocities. The results suggest that the emission from the quenched material is related to the fast shear of interinclusion ligaments, while the source during intergranular fracture is most probably brain-boundary decohesion over areas of one to five grain facets. Source identification in the temper-embrittled material is less certain because of secondary intergranular cracking in an otherwise ductile fracture.
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