DETERMINATION OF STRESS CORROSION CRACKING (SCC) SUSCEPTIBILITY (KISCC) AT IMPOSED POTENTIALS USING A NOVEL CIRCUMFERENTIAL NOTCH TENSILE (CNT) TECHNIQUE

摘要

A fracture mechanics based technique has been employed for determination of susceptibility of engineering materials to stress corrosion cracking (SCC) and threshold stress intensity factor for (K_(Iscc)) using small circumferential notch tensile (CNT) specimens. This relatively new technique was tested successfully on mild steel at free corrosion potential (E_(corr)) in 12.5 M NaOH at 150℃. The K_(Iscc) has been determined to be 27.7 MPa.m~(1/2). In order to establish the application of the CNT technique in understanding the mechanistic aspects of caustic cracking, tests have also been performed under the imposed electrochemical potentials. When the test was performed at a controlled potential in the active-passive transition region (E_(a-p)) the specimen failed extremely quickly than the specimens tested at E_(corr) employing similar K_I. The other test was conducted under an imposed potential in the passive region (E_p) and the specimen did not fail even after relatively very long exposure time. The fractography of the specimens tested at E_(corr) and E_(a-p) presented evidence of SCC, i.e., intergranular crack propagatation. The experimental CNT testing is a simple, relatively fast and cost-advantageous approach for generating the K_(Iscc) data.