Abstract
A method has been developed to produce a low cost specimen with controlled residual stress. Specimens were stress-relieved at a temperature of 1080°C and electropolished to remove pre-existing residual stresses. Then a four-point bending jig was used to bend the specimens to generate a residual stress. The residual stress level, as determined by X-ray diffraction, was compared to that calculated from the deflection of the specimens.. However, the X-ray measurements were found to be highly imprecise; this was attributed to the 316L microstructure. The stressed specimens have been used to investigate the initiation of stress corrosion cracking of 316L austenitic stainless steel in boiling magnesium chloride (MgCl2.6H2O). The cracks were observed in the optical microscope and the scanning electron microscope (SEM), and the electrochemical noise technique was also used with the objective of detecting crack initiation and propagation. The sudden changes in the amplitude and frequency of the potential and the current transients, and numerous current and potential transients in the time record were suggested to be the result of the breakdown of the passive film followed by the initiation and propagation of stress corrosion cracking.
