| The acoustic emission (AE) characteristics of ASTM A533B steel during tensile and fracture testing are highly anisotropic, originating from the decohesion of flattened MnS inclusions. The present study explores this source of AE and effects of various heat treatment practices on the MnS/matrix interfaces. The AE characteristics associated with different fracture mechanisms are identified, and the effects of test temperature and notch geometry examined.;During fracture testing, slow-bend tests were performed on Charpy V-notch samples at temperatures from -75(DEGREES) to 150(DEGREES)C. Tests were also interrupted so as to isolate the fracture processes. Tear and shear fracture and dimple formation by microvoid coalescence generated low-amplitude AE events. Quasi-cleavage and cleavage fracture processes emitted events with a broad range of amplitude. Decohesion of MnS showed the characteristic Weibull distribution. When decohesion occurs, AE events from this process would mask those from other processes except cleavage or quasi-cleavage. (Abstract shortened with permission of author.);As-received samples exhibited significant preyield burst emissions (PYBE), but few PYBE was observed when S-samples were quenched from the austenitizing temperature. PYBE gradually recovered as the quenched samples were tempered. The observed AE behavior was correlated to fractographic observations and to Auger electron spectroscopy (AES) analysis. The absence of PYBE in quenched S-samples was attributed to the debonding of the MnS/matrix interfaces due to thermal stresses set up during quenching. In addition, after an initial tensile loading of as-received S-samples, PYBE was also suppressed during subsequent loading. Recovery of PYBE associated with tempering was found to originate from mechanical and chemical recohesion processes. |
