Creep Damage Predictions Under Multiaxial Conditions for 316L Stainless Steel Samples Manufactured by Laser Powder Bed Fusion

Abstract

Abstract 316L stainless steel, often used for high-temperature applications, can be manufactured by laser powder bed fusion (LPBF). However, the LFBF manufacturing process can lead to undesirable multiaxial residual stresses (RS), which may require relaxation by heat treatments. The high residual stresses combined with high operating temperatures will induce creep deformation and damage processes. Therefore, the creep behaviour of LPBF 316L under multiaxial stress conditions must be understood, and models are available to predict the creep deformation and damage processes. In this work, a FE modelling methodology has been developed and validated by simulating the creep deformation and damage accumulation in notched bar tests on samples with two different notched acuities, denoted large and medium notches. Notched bar creep tests were simulated for samples built in both the horizontal and vertical orientations (i.e. parallel and perpendicular to the build direction). A new progressive creep damage modelling approach was applied, based on the creep ductility exhaustion approach, enabling the progressive deterioration of material properties as creep damage accumulates. A sensitivity study was performed to account for the significant variabilities in creep deformation rates and creep ductility in LPBF samples. It was generally found that accurate predictions of the creep deformation and failure behaviour could be obtained using a specific combination of creep strain rate and ductility bounds; however, some tests results, particularly for vertically built samples, were not predictable. This has been attributed to the deleterious effects of porosity resulting from the build process.