EFFECT OF RESIDUAL STRESS AND STRAIN GENERATED DURING MANUFACTURING PROCESS ON THE STRESS CORROSION CRACKING SUSCEPTIBILITY OF AUSTENITIC STAINLESS STEEL

As received tubes of AISI 304L having different levels of residual stresses and solution annealed 304L stressed as per ASTM G30 to produce constant strain samples having a known amount of residual strain were used in this study. To study the effect of stress/strain generated on the surface, due to machining involved in fabrication, AISI 304L sample was surface ground to a depth of 0.5mm. Quantification of the magnitude of stress levels was obtained by XRD analysis and EBSD measurements. The SCC susceptibility has been measured by exposing the samples to boiling 42% MgCl₂ as per ASTM G36 and similar exposures were done in 5N H₂SO₄ + 0.5 N NaCl solution at 26⁰C. The MgCl₂ tests were done for 10, 16, 22h respectively followed by detailed characterization of the sample to determine the nature of cracking when present and to locate the preferentially sites of crack initiation. The samples exposed to sulfuric acid solution were examined after exposures upto 7 days at 26⁰C. The morphology of SCC from both these solutions was compared for various conditions of the samples. The nature and extent of cracking was correlated with the material condition and levels of residual stress/strain in the samples.