**4. Conclusions**

The susceptibility to selective corrosion behavior of Alloy 625 obtained by means of LPBF was studied. The behavior was compared to commercial hot-worked, heat treated Grade 1 Alloy 625. The morphology of attack after boiling ferric sulfate-sulfuric acid test according to ASTM G28 standard is less penetrating for LPBF 625 alloy compared to hot-worked and heat treated alloy both in as-built condition and after heat treatment at 980 ◦C for 32 min. Furthermore, lower weight loss of LPBF alloy were measured.

The different attack morphology can be ascribed to the oversaturation of the alloying elements in the nickel austenitic matrix obtained due to the very high cooling rate. The precipitates of second phases along and inside the micro-dendrites are too small to promote preferential dissolution paths. On as-built specimens, a shallow selective attack of the border of the melt pools was observed. The Grade 1 heat treatment at 980 ◦C for 32 min followed by water quenching caused the melt pools microstructure to disappear and prevent the in-depth penetration of the selective attack.

**Author Contributions:** Methodology, S.L., C.T., D.M., G.M., F.C.; investigation, S.L., C.T., D.M., G.M.; data curation, S.B., P.F., M.C.; all the authors contributed to writing the original draft of the paper. writing—review & editing T.P., P.F., M.C., S.B.; supervision, T.P., S.B.; project administration, T.P.; funding acquisition, T.P., F.B.

**Funding:** The work was realized with the contribution and reliance on the Collaboration Agreement of INSTM and the Lombardy Region signed on 24th September 2015.

**Conflicts of Interest:** The authors declare no conflict of interest.
