Abstract
Fracture toughness test for AISI 4340 steel is carried out, and the fracture surfaces are analysed, of which patterns consist of ductile dimple patterns and brittle intergranular (IG) cracking induced by hydrogen. The purpose of this paper is to reveal the correlation between IG cracking unit during stable crack growth and acoustic emission (AE) characteristics. It would be concluded that the dominant sorce of AE is attributed to the microscopic IG fracture, from the significant experimental results that the AE event count is propotional to the number of the microscopic IG cracking, and that the AE energy is propotional to the area of the individual IG cracking.
