Role of grinding induced surface residual stress on probability of stress corrosion cracks initiation in 316L austenitic stainless steel in 3.5% sodium chloride aqueous solution

Abstract

Experimental investigation on the relation of grinding induced surface residual stresses (RS) with stress corrosion cracking (SCC) susceptibility and electrochemical behaviour was conducted on 316L austenitic stainless steel in 3.5% sodium chloride aqueous solution. Grinding was done with the same process parameters to lower the effect of other known parameters on SCC initiation. The corrosion behaviour was characterised by Potentiodynamic and galvanostatic tests. The latest was performed under fixed current density in metastable region. There was a strong relationship between the electrochemical results with RS magnitude. Microscopic investigation showed that the RS induced by grinding could not be the reason for SCC and the dominant defect observed was pitting for all the specimens. The time needed for the breakdown of the passive layer was exponentially related to RS level but the propagation of pits was nearly the same for all the specimens.

Stress Corrosion Cracking Probability of Selective Laser Melted 316L Austenitic Stainless Steel under the Effect of Grinding Induced Residual Stresses

“…Thus, the corrosion behavior detected was almost the same for all specimens. In the previous investigation on rolled and machined sheets of 316L Austenitic stainless steel, the same behavior was detected [35], which shows that after passing the machining-affected layer the corrosion behavior is the same for all specimens irrespective of surface RS magnitude. Figure 8 shows the surface of the specimens after 200 s of Galvanostatic tests.…”

“…Existing pores and melt pool boundaries on the surface also activated as precursors for SCC initiation, as shown in Figures 12 and 13. Since in the author's previous investigation, cracks were not detected in even high RS magnitudes in cold rolled sheets after grinding [35]; to understand the reasons for the detection of SCC cracks in SLM specimens with high RS, it is important to consider the synergistic effect of various factors. First, the intrinsic pores on the surface of SLM specimens act as stress concentration sites in the presence of tensile stresses and this causes higher stress levels within pores [56,57].…”

“…On the other hand, recent investigations reported that tensile RS has no direct effect on SCC of ASS made by manufacturing methods such as hot or cold rolling and it only makes the surface more active compared to annealed specimens. This higher activity results in a more favorable initiation of corrosion pits on the surface that could act as stress concentration sites and precursors for SCC initiation under working loads [33][34][35].…”

Revealing the stress corrosion cracking initiation mechanism of alloy 718 prepared by laser powder bed fusion assessed by microcapillary method

“…6) for both L-PBF and conventional samples, while after tensile loading, conventional specimens exhibit lower E corr compared to L-PBF. Potentiodynamic results suggest a higher sensitivity of E break and breakdown current density (i break ) to tensile stress state than E corr and i corr highlighting a significant correlation between breakdown electrochemical parameters with the stress state of both groups, which is consistent with authors' previous investigations on 316 L austenitic stainless steel [50][51][52] using standard test methods, highlighting the similarity of potentiodynamic polarization behaviour between standard and microcapillary method, confirming the stability and high precision of the measurements in the current study. The potentiodynamic polarization results are summarized in Table 3.…”

“…12) confirms the selective dissolution of the subgrains matrix with unaffected boundaries. The same behaviour was observed in the authors' previous investigations on L-PBF processed 316 L austenitic stainless steel [51,52], revealing the selective dissolution of subgrains and subsequent mechanical rupture of the intact subgrain boundaries as the mechanism responsible for SCC propagation that was different from wrought counterparts [50]. Moreover, a recent investigation on SCC characteristics of L-PBF 316 L by Cruz et al [74] confirms the selective dissolution of subgrain observed in the current investigation, which is confirming the extent of such a phenomenon on austenitic microstructure of stainless steel alloys.…”