Microstructural and neutron residual stress characterization of 316L laser-powder bed fusion simplified end-use part: A modelling benchmark

Abstract

In this work, a double hollow cylinder with a joint region, representative of nozzles, pipe systems, valves, or pressure regulators, was chosen to measure and simulate its 3D residual stress (RS) distribution. The part was printed by Laser-Powder Bed Fusion (L-PBF) using commercial 316L steel powders, and a mapping of residual stress along the joint cross-section was measured at three geometrical sample directions. The distribution of RS in the printed part was not homogeneous, showing important gradients of about ±1200 με from the inner to the outer surface of the wall, as well as along the building direction, translated into an equivalent Von Mises stress gradient up to 400 MPa towards the inner surface. After heat treatment only axial strains are significantly affected and relieved 200 με in average, but not necessarily in a homogeneous manner. The comparison of the Von Mises equivalent stress against available simulation tools based on mechanical and thermomechanical models concluded that although these models succeeded in the benchmarking of total macroscopic distortion of components, they do not capture the asymmetric distribution of RS within the bulk in end-use complex geometries and/or joints and those should be implemented from the microstructural level.

Keywords

• Residual stresses
• Thermo-mechanical model
• Neutron diffraction
• Stress relief
• Austenitic stainless steel
• Additive manufacturing