Impact of hot isostatic pressing on the microstructure of AISI 316L austenitic steel processed by laser direct energy deposition

Abstract

This article deals with the microstructural analysis of austenitic steel AISI 316L processed by the direct energy deposition (L-DED) process and further processed by hot isostatic pressing (HIP). The samples for the experiment were made from atomized powder with an average spherical particle size of 55±30 μm. The powder was processed into blocks with dimensions of 33x33x18 mm, using a deposition layer thickness of 0.6 mm and a Zig-Zag deposition strategy. HIP processing was performed at a temperature of 1150 °C and a pressure of 100 MPa. The analysis of the samples consisted of X-ray phase diffraction analysis and scanning lectron microscopy analysis. X-ray phase analysis revealed that the HIP process causes coarsening of the crystallite structure and a change in the residual stresses acting in the (111) plane, where both tensile and compressive stresses were detected after additive manufacturing process, while only compressive stress was measured after HIP processing. From the point of view of microstructural analysis, recrystallization of the structure was observed, including the formation of a twin structure with an increased fraction of special Σ3 grain boundaries. This was accompanied by the coarsening of oxide inclusions.