Application of Acoustic Emission Techniques to Study of Weld Cracking (2nd Report)

Initiation and Propagation Characteristics of Lamellar Tearing

Abstract

The initiation and propagation characteristics of the lamellar tearing are studied by the AE technique. MIG welding process in a chamber charged with argon is used to eliminate the noises started from the self-crushing of slag.
From the results of the small type through thickness restraint, cracking test, three mechanisms to the occurrence of lamellar tearing are proposed which correspond with the metallurgical factors, such as chemical analysis and non-metallic inclusions, of the rolled plate. As the conventional type of the lamellar, tear, the cracking is originated by the decohesion of the non-metallic inclusions from the matrix and extended to fibrous fractures right after completing the weld deposition prior to the individual element of the crack linking up intermittently. This intermittent behavior reveals to be lasted for several hours, and the propagation of the crack is of the typical hydrogen induced cracking.
For the steel which has sufficiently poor through thickness ductility, the lamellar tear can be initiated and propagated by only shear-mode. For the steel which has high susceptibility to hydrogen embrittlement, the lamellar tear is apt to follow the root or toe cracks in the pattern of parallel to the surface of the plate.