On the exceptional stress corrosion cracking susceptibility of selective laser melted 316L stainless steel under the individual effect of surface residual stresses

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

“…Therefore, it can be stated that the enhanced localized corrosion resistance of L-PBF 718 specimens under tensile loading, which is the case in almost all industrial applications, could be attributed to submicron structure and higher integrity of passive layer compared to the conventional material. These findings are also in complete agreement with the authors' previous investigations on L-PBF 316 L austenitic stainless steels, identifying the impact of columnar subgrain width on localized corrosion susceptibility [51,52]. Moreover, in a recent study on SCC behaviour of L-PBF 316 L by Cruz et al [74], they indicated higher SCC resistance of L-PBF specimens compared to wrought counterparts as a result of significantly higher resistance of L-PBF specimens to pitting corrosion, leading to less possible active sites for crack initiation.…”

“…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.…”

“…Thus, the presence of compressive RS could potentially improve the corrosion behaviour. For the case of L-PBF 718, RS magnitude, contrary to austenitic stainless steels [51,52,55], was tensile at the centre of the specimens, which could well be responsible for the lower corrosion resistance compared to conventional specimens with a compressive stress state. The difference in RS state between L-PBF stainless steels and alloy 718, could be attributed to the difference in the thermodynamical characteristics of Ni-Fe superalloys [41,53,54].…”

“…However, the shape, size, and type of the pores (gas porosity, lack of fusion, etc.) could significantly affect the local corrosion behaviour, affecting the overall localized corrosion resistance [52,88,89], which must be considered. Moreover, microstructural analysis of the surface after corrosion attack, as shown in Fig.…”