Detection of Intergranular Pop-in Cracking during Elastic-Plastic Fracture Toughness Test of Cr-Mo-V Steel by Frequency Analysis of Acoustic Emission

Abstract

The feasibility of using acoustic-emission techniques for elastic-plastic fracture toughness test of a Cr-Mo-V steel at a high temperature has been examined. Fractographic study and frequency analysis characterization of AE behavior have been carried out. AE signals observed during the test can be classified into three groups: Type I, II, III, and three different types of fracture surfaces are observed. Some interruption tests reveal that Type I AE is generated from the micro-cracking due to decohesion of MnS inclusions or coalescence between main crack and voids nucleated by decohesion of MnS inclusions, Type II AE having the largest amplitude from the intergranular pop-in cracking, and Type III AE from the formation of intergranular dimple facet, respectively. J_iAE denoted by an abrupt increase of ∑E_AE-J correlation is proposed as a conservative fracture toughness characterizing the intergranular cleavage cracking.