Comparing Stress Corrosion Cracking Behavior of Additively Manufactured and Wrought 17-4PH Stainless Steel

Abstract

As a high-strength corrosion-resistant alloy, stress corrosion cracking (SCC) behavior is a key consideration for the conventional, wrought form of 17-4PH stainless steel. With the increasing popularity of the additively manufactured (AM) form of 17-4PH, understanding the SCC behavior of AM 17-4PH will be similarly critical for its presumed, future applications. The current study quantifies and compares the SCC behavior of both the wrought form, as a baseline, and AM form of 17-4PH at peak-aged (∼1,200 MPa) and overaged (∼1,050 MPa) strength levels. The laser powder bed fusion technique followed by post-process hot isostatic press (HIP), solution annealing, and aging heat treatments is used to produce AM 17-4PH with similar microstructures and strength levels to wrought 17-4PH and facilitate the comparison. SCC behavior is quantified using fracture mechanics-based rising (dK/dt = 2 MPa√m/h) and constant (dK/dt = 0 MPa√m/h) stress intensity tests in neutral 0.6 M NaCl at various applied potentials. Limited SCC susceptibility was observed at open-circuit and anodic potentials for both forms of 17-4PH. At cathodic applied potentials, AM consistently underperforms wrought with up to 5-fold faster crack growth rates and 200 mV to 400 mV wider SCC susceptibility ranges. These results are interrogated through microstructural and fractographic analysis and interpreted through a decohesion-based hydrogen-assisted crack model. Initial analyses show that (1) increased oxygen content, (2) porosity induced by argon processing, and (3) slow cooling (310°C/h) during conventional HIP processing might contribute to degraded SCC performance in AM 17-4PH.