Pitting corrosion of 17-4PH stainless steel manufactured by laser beam melting

Abstract

The pitting corrosion behaviour of a 17-4PH martensitic stainless steel (MSS) manufactured by power bed laser beam melting (LBM) was compared to that of a wrought MSS. More noble pitting potentials were measured for LBM samples, probably due to a smaller size of NbCs as compared to wrought MSS. The metastable pits were less numerous, but had a higher nucleation rate and longer life time for the LBM samples compared to the wrought MSS. This was explained by assuming a decrease in the repassivation ability of LBM samples due to small gas pores.

Combined XPS / TEM study of the chemical composition and structure of the passive film formed on additive manufactured 17-4PH stainless steel

“…We showed, in a previous study on the corrosion behaviour of 17-4PH MSS manufactured by LBM, significant differences in the pitting susceptibility between LBM and conventional samples in NaCI solution [44]. A more positive pitting potential value was observed for the 17-4PH LBM MSS; this was attributed, at least partially, to smaller NbC precipitates, which acted as preferential pit initiation sites, in agreement with Clark et al [ 45].…”

“…The differences in Cr content for the passive films formed on LBM and conventional MSSs could be explained by referring to the austenite content of the samples. Indeed, we showed in a previous study [ 44] that the austenite content was between 8 and 12 % and only 0.8 % for the LBM and conventional samples, respectively. Langberg et al [53] recently showed, for a super duplex stainless steel, that the passive film formed on ferrite had a higher Cr content than this one formed on austenite due to the higher Cr content in ferrite.…”

“…Results suggested that the Si amount was higher in the passive film formed on the conventional sample as compared to the LBM XY sample, even though the Si content was twice higher in the LBM matrix (Table 1). This could be explained considering that, in the LBM XY sample, a non-negligible Si content was concentrated in the Si-rich oxide inclusions generated by the manufacturing process and present in the alloy [9,44,52]. The interpretation of these results is nevertheless limited by the complexity of EDS detection of small Si amount.…”

“…The microstructures of conventional and LBM MSSs have been described in details in a previous article [ 44]. Only the main results are reminded here in order to help in understanding the analyses of the passive films below.…”

“…3h) and for LBM XZ and YZ samples (Table 2), whereas there is almost no contribution of SiO 2 peak for the conventional one. This SiO 2 is assumed to correspond to Si-rich oxide inclusions formed during the LBM process between two lased layers as described in previous work [9,44,52]. Therefore, the presence of SiO 2 on the Si 2p spectra arises from the underlying alloy only for LBM samples and is not part of the passive film.…”