Quantitative Evaluation of Aged AISI 316L Stainless Steel Sensitization to Intergranular Corrosion: Comparison Between Microstructural Electrochemical and Analytical Methods

Abstract

The evaluation of the degree of sensitization (DOS) to intergranular corrosion (IGC) of a commercial AISI 316L austenitic stainless steel aged at temperatures ranging from 550°C to 800°C during 100 to 80,000 hours was carried out using three different assessment methods.(1) The microstructural method coupled with the Strauss standard test (ASTM A262). This method establishes the kinetics of the precipitation phenomenon under different aging conditions, by transmission electronic microscope (TEM) examination of thin foils and electron diffraction. The subsequent chromium-depleted zones are characterized by X-ray microanalysis using scanning transmission electronic microscope (STEM). The superimposition of microstructural time-temperature-precipitation (TTP) and ASTM A262 time-temperature-sensitization (TTS) diagrams provides the relationship between aged microstructure and IGC. Moreover, by considering the chromium-depleted zone characteristics, sensitization and desensitization criteria could be established. (2) The electrochemical method involving the double loop-electrochemical potentiokinetic reactivation (DL-EPR) test. The operating conditions of this test were initially optimized using the experimental design method on the bases of the reliability, the selectivity, and the reproducibility of test responses for both annealed and sensitized steels. The TTS diagram of the AISI 316L stainless steel was established using this method. This diagram offers a quantitative assessment of the DOS and a possibility to appreciate the time-temperature equivalence of the IGC sensitization and desensitization. (3) The analytical method based on the chromium diffusion models. Using the IGC sensitization and desensitization criteria established by the microstructural method, numerical solving of the chromium diffusion equations leads to a calculated AISI 316L TTS diagram. Comparison of these three methods gives a clear advantage to the nondestructive DL-EPR test when it is used with its optimized operating conditions. This quantitative method is simple to perform; it is fast, reliable, economical, and presents the best ability to detect the lowest DOS to IGC. For these reasons, this method can be considered as a serious candidate for IGC checking of stainless steel components of industrial plants.

Effect of electro discharge machining (EDM) on the AISI316L SS white layer microstructure and corrosion resistance

“…The chromium depletion is the consequence of the chromium carbide precipitation in the melting structure of the white layer. The chromium level below 13 at.% is likely reached at the interdendritic space to enhance IGC sensitisation according to Sidhom et al [29] works on the same austenitic stainless steel. Moreover, the high values of the I r /I a ratio reveal the existence of relatively large areas that are heavily depleted from chromium and molybdenum [29].…”

“…The chromium level below 13 at.% is likely reached at the interdendritic space to enhance IGC sensitisation according to Sidhom et al [29] works on the same austenitic stainless steel. Moreover, the high values of the I r /I a ratio reveal the existence of relatively large areas that are heavily depleted from chromium and molybdenum [29]. The fact that these values I r /I a going from 30 % for finishing conditions to 60 % for roughening conditions, indicates that this phenomenon is mainly related to the existence of the white layer microstructure and chemical heterogeneities at the submicron scale.…”

“…1). The operating conditions of the tests are reported in Table 5 as recommended in previous work [29]. & RSCC susceptibility was evaluated by SEM observation of the sample surface before and after immersion during 48 h in a 40 % magnesium chloride solution (MgCl 2 ) heated at 140°C.…”

“…14). Moreover, the appearance of I r during the double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests, performed under appropriate operating conditions [29], is indicative of an IGC sensitivity induced by EDM (Fig. 15).…”

Characteristic of Acoustic Emission Signal from Stress Corrosion Cracking in Low-Carbon Nitrogen-Enhanced Stainless Steel

“…(5)(6)(7)(8)(9) Numerous investigations show that austenitic stainless steel is more sensitive to SCC in a high-temperature, high-pressure water environment. (10) SCC is a cracking phenomenon of metal or alloy under the integrated effect of the media environment and tensile stress.…”