Acoustic emission behavior during tensile tests of low carbon steel welds

Abstract

The tensile behavior of a low-carbon low alloy steel has been studied by means of acoustic emission (AE) technique for the welded joint consisting of three regions (the base metal, the heat affected zone (HAZ) and the weld metal). The AE characteristics of the base metal are distinctly different from those of the HAZ and the weld metal. For the base metal with a ferrite-pearlite microstructure, most of the AE events occur around the yield point, mainly due to the dislocation movements associated with the tensile deformation. For the HAZ and the weld metal, a second AE peak with higher energy is evident after yielding, in addition to the AE peak occurring around the yield point. The second AE peak is attributed to the presence of martensite, as examined by the AE results obtained from the base metal heat-treated to have different martensite volume fractions. The ferrite-martensite interfacial debonding and/or the martensitic plate cracking act as the principal sources of the second AE peak, as confirmed by the microstructural observations and the frequency spectrum analyses.