Fatigue crack growth behavior of wire arc additively manufactured 316L austenitic stainless steel

This study investigated the fatigue crack growth (FCG) performance of 316L austenitic stainless steel produced by wire arc additive manufacturing (WAAM) through fatigue tests and fractographic analyses. A total of 11 compact tension (CT) specimens were designed considering three minimum-to-maximum load ratios (R= 0.1, 0.3, 0.5), various load directions (theta = 0 degrees, 30 degrees, 45 degrees, 60 degrees, 90 degrees) and two surface conditions (milled and as-built). Details of specimen fabrication and design as well as fatigue test setup are presented. The Paris' law material constants of all specimens were derived. The influences of various parameters on the FCG behavior such as crack length development histories and fatigue crack growth rate (FCGR) are discussed. The test results demonstrated that the fatigue crack growth rate increased with the load ratio, and that the specimen with theta = 0 degrees, i.e. load parallel to the welding pass, possessed higher FCGR value than the counterparts characterized by other load directions. The as-built and milled specimens had similar FCG performance. The FCG test results of WAAM 316L austenitic stainless steel obtained in this study were compared against those of 316L steels manufactured by traditional hot-rolling and selective laser melting as well as the predictions by current international standards (BS 7910 and IIW-1823-07). The fractographies of typical CT specimens from macroscopic and microscopic perspectives were analyzed. Transgranular fracture was observed as evidenced by abundant fatigue striations, secondary cracks and dimples.