EVALUATION OF CAUSTIC EMBRITTLEMENT SUSCEPTIBILITY OF MILD STEEL BY SLOW STRAIN RATE TESTING

摘要

Caustic embrittlement of processing vessels and pipes in the Bayer processes for alumina processing is of industry-wide concern. This paper investigates applicability of slow strain rate testing (SSRT) to prediction of caustic cracking. SSRT tests were carried out using a caustic solution of 50% sodium hydroxide and paraffin oil at 100℃ and at various strain rates (between 1.2 x 10~(-7) and 5.5 x 10~(-7)s~(-1)). SSRT results of this study have been compared with those in an earlier study that were carried out using a caustic solution of a lower concentration (～20%) at a higher temperature (150℃). The comparison suggests occurrence of caustic cracking at higher strain rates when SSRT tests were carried out using 50% sodium hydroxide at 100℃, whereas caustic cracking occurred at lower strain rates in 20% caustic solution at 120℃. The results also suggest the need for investigating a wide range of strain rates and electrochemical conditions, as well as investigating the role of other test/process variables.