Acoustic emission behavior during tensile deformation of welded steel joints

An investigation has been carried out to study the acoustic emission (AE) behavior during tensile deformation of welded steel joints of low-carbon low alloy steel. The results indicate that the AE characteristics of the base metal is distinctly different from those of the heat affected zone (HAZ) and the weld metal. For the base metal consisting of ferrite-pearlite microstructure, most of the AE events are produced near the yield point, mainly due to the dislocation movements during the deformation. However, 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. This second AE peak is attributed to the existence of martensite and, its amplitude is proportional to the volume fraction of the martensite. The sources of the second AE peak were the debonding of ferrite-martensite interfaces and the micro-cracking of brittle martensite plates, as rationalized by the microstructural and the frequency spectrum analysis.