Metal Additive Manufacturing Conference - MAMC 2022

Many industries desire to replace conventionally manufactured stainless steel (SS) with additively manufactured (AM) SS due to multiple advantages connected to AM. However, questions about the influence of the unique AM microstructures on corrosion resistance and the applicability of standard corrosion tests remain largely unanswered. Furthermore, the influence of post-processing steps on local corrosion resistance and Stress Corrosion Cracking (SCC) of AM SS is only partially explored. In order to safely implement AM SS in corrosive environments, more research is necessary.

This work investigates corrosion properties of two SS alloy systems, austenitic 316L and super-duplex stainless steel (SDSS) 2507, additively manufactured via Powder Bed Fusion – Laser Beam (PBF-LB). The corrosion properties of these alloy systems are correlated to the effect of microstructure, sampling methodology and post-processing operations by either conventional heat treatment or hot isostatic pressing (HIP). Additionally, the effect of post-processing by HIP and shot peening on the SCC properties of PBF-LB 316L SS is explored.

For both materials, microstructure, crystallographic texture, and porosity were characterized by light optical microscopy and scanning electron microscopy with electron backscatter diffraction. Corrosion resistance was assessed by standard tests ASTM G150, ASTM G48 and ASTM G61. Additionally, immersion tests in relevant service media were conducted and microstructure evaluation by Scanning Kelvin Probe force microscopy was performed. For PBF-LB 316L SS, SCC-testing was performed by 4-point bend and slow strain rate tests and correlated with residual stress measurements using X-ray and neutron diffraction.

The results show that the corrosion properties of PBF-LB SS austenitic 316L and SDSS 2507 meet or even exceed that of conventionally manufactured materials. However, a correctly performed heat treatment is crucial to obtain adequate corrosion resistance. Moreover, SCC test results and residual stress data are linked to microstructure and SCC resistance of PBF-LB 316L SS in relation to conventional 316L SS material.