Investigation on ultra-pure ferritic stainless steel 436L susceptibility to intergranular corrosion using optimised double loop electrochemical potentiokinetic reactivation method

The susceptibility of 17Cr ferrite stainless steel to intergranular corrosion (IGC) was investigated using the double loop electrochemical potentiokinetic reactivation (DL-EPR) test and the microstructural characterisation. The results show that the optimised DL-EPR test condition for 17Cr ferrite stainless steel is l M H2SO4+0.006M KSCN solution with a scan rate of 0.1 V min(-1) at 25 degrees C The severe IGC occurs in the temperature range of 500-650 degrees C and the nose temperature locates at approximately 600 degrees C. The I-r/I-a value rises up to 16.99% when heat treated at 600 degrees C for 30 min. After aging treatment, M23C6 precipitates are detected using transmission electron microscopy, resulting in the presence of the Cr depletion zone. However, the degree of IGC for 436L is extremely limited due to the Cr element diffusion form the matrix despite prolonging the aging time to 5 h.