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

Abstract

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 H 2 SO 4 + 0.006 M KSCN solution with a scan rate of 0.1 V min −1 at 25°C The severe IGC occurs in the temperature range of 500-650°C and the nose temperature locates at approximately 600°C. The I r /I a value rises up to 16.99% when heat treated at 600°C for 30 min. After aging treatment, M 23 C 6 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.

Investigation on intergranular corrosion susceptibility of a nitrogen-containing austenitic stainless steel QN2109 by optimized DL-EPR tests

“…3.1 Temperature-time-sensitization and temperaturetime-precipitation curve for QN2109 The results of DL-EPR tests cannot be compared for different kinds of alloys. Besides, the optimized conditions vary for various stainless steels to characterize IGC sensitization (Sun et al, 2018). Therefore, it is essential to explore the appropriate test conditions for QN2109 before conducting the DL-EPR tests.…”

“…Besides, the TTS curve was inside the TTP curve. It was because the TTP curve reflected the precipitation of carbides, whereas the TTS curve revealed the degree of Cr depletion (Deng et al , 2010; Hong et al , 2013; Sun et al , 2018).…”

“…There are plenty of experiment methods for investigating IGC. Compared to traditional immersion tests (Strauss, Huey and Streicher tests), double-loop electrochemical potentiodynamic reactivation (DL-EPR) tests are widely used on account of simple operation, little damage to specimens and good reproducibility (de Assis et al, 2013;Cheng et al, 2021Cheng et al, , 2019Deng et al, 2010;Hong et al, 2013;Lopez et al, 1997;Qiang et al, 2015;Sun et al, 2018). The degree of sensitization (DOS) obtained by DL-EPR tests can clearly reveal the degree of Cr depletion (Hong et al, 2013;Sun et al, 2018Sun et al, , 2021.…”

The Intergranular Corrosion Susceptibility of Metastable Austenitic Cr–Mn–Ni–N–Cu High-Strength Stainless Steel under Various Heat Treatments

“…For all the aging temperatures, the anodic polarization curves present similar shapes. First, the current density increased gradually with the scanning potential, and a peak current density (i a ) of around 15 mA/cm 2 was present near −0.2 V SCE during the anodic scan, indicating the active dissolution of the whole alloy surface [39]. The current density decreased sharply to around 0 A/cm 2 with the further increased potential, representing the growth of passive film on the sample surface.…”

“…The R a values were summarized in Table 2 as average values ± standard deviations derived from repeated tests. Although a higher R a value suggests higher IGC sensibility, it is known that the inner-grain dissolution can also contribute to the current density peak in the reverse scan, leading to higher R a values in the DL-EPR test [35,39]. It is necessary to evaluate the surface morphology of samples after the DL-EPR test to verify the reliability of R a values and clarify the R a value range that can represent different degrees of intergranular corrosion.…”