Evaluation of Resistance to Cracking of Additively Manufactured 120K Alloy 718 in Sour Environments

Abstract Wrought Alloy 718 is widely used in sour service due to its excellent resistance to corrosion and stress corrosion cracking at elevated temperatures. Additively manufactured (AM) Alloy 718 (AM718) is becoming more widely used, partly due to the benefits of more rapid production. Additive manufacturing routes may be proprietary or undisclosed and are often much more detailed/defined than wrought manufacturing routes. The variability of the mechanical properties and microstructure of AM parts resulting from a range of factors made by different manufacturers can be more scattered than their wrought counterparts. Furthermore, there is a lack of awareness of their resistance to cracking in sour environments. In order to generate data on the potential performance of variability of AM Alloy 718 products in sour environments, slow strain rate tensile (SSRT) testing, GHSC (galvanically-induced hydrogen stress cracking) and 4-point bend SCC (stress corrosion cracking) tests were carried out. AM718 specimens were provided by different Suppliers, using the laser-beam powder-bed fusion (PBF-LB) technique, with heat-treatment in accordance with the API Standard 6ACRA in the 120ksi condition (120K). The AM microstructures and mechanical properties were characterized. Results suggest that imposition of conventional wrought 120K heat-treatment might not guarantee consistent response from AM718 reflecting the unique process-property-material relationship of the material from the different Suppliers, and would warrant further specification in order to achieve required mechanical and microstructure properties.