Microstructure and mechanical properties relationship of additively manufactured 316L stainless steel by selective laser melting

Abstract

Additive manufacturing (AM) is rapidly expanding in many industrial applications because of the versatile possibilities of fast and complex fabrication of added value products. This manufacturing process would significantly reduce manufacturing time and development cost for nuclear components. However, the process leads to materials with complex microstructures, and their structural stability for nuclear application is still uncertain. This study focuses on 316L stainless steel fabricated by selective laser melting (SLM) in the context of nuclear application, and compares with a cold-rolled solution annealed 316L sample. The effect of heat treatment (HT) and hot isostatic pressing (HIP) on the microstructure and mechanical properties is discussed. It was found that after HT, the material microstructure remains mostly unchanged, while the HIP treatment removes the materials porosity, and partially re-crystallises the microstructure. Finally, the tensile tests showed excellent results, satisfying RCC-MR code requirements for all AM materials.

Effect of Hot Isostatic Pressing on Porosity and Mechanical Properties of 316 L Stainless Steel Prepared by the Selective Laser Melting Method

“…A prediction is that higher pressure can be significantly more effective for elimination of porosity during HIP. A positive effect of higher pressure is also indicated by the results published by Puichaud [ 17 ], who reports the elimination of nanoscale porosity during HIP at 180 MPa in 316 L steel samples after SLM.…”

“…The comparison of the mechanical properties of samples prepared by SLM under the stated conditions revealed that both yield strength and tensile strength reached higher values than Lavery, Rottger or Chadha [ 2 , 4 , 12 ] and also higher ductility. However, the ductility did not reach as high values (76%) as Puichaud states for samples of 316 L steel prepared by SLM [ 17 ]. However, it must be taken into account that the samples prepared in the context of our study were built in the vertical direction, which, as some publications state [ 2 , 4 , 12 ], is not as suitable in terms of mechanical properties as the horizontal direction.…”

Micromechanisms of Deformation and Fracture in Porous L-PBF 316L Stainless Steel at Different Strain Rates

“…The strengthening effect of the oxide particles in as-built 316 steel was proposed, but an absence of the nanoparticle strengthening effect after annealing makes this hypothesis arguable. Formation of segregation and specific dislocation structures at cell boundaries have also been reported [2,[4][5][6][7]. The dislocation structures observed in as-built L-PBF seem to be quite stable, and they have recovered and annihilated only after annealing at 800-950 • C. Mobility of these dislocations is not high as the as-built 316L steel, which has higher strength and lower ductility characteristics in a comparison with the conventional bulk material [8,9].…”

“…In this work, we studied samples manufactured horizontally in a All structural studies were carried out for the upper plane of the sam perpendicular to the building direction and parallel to the tension seen from Figure 6, the initial as-built state may be rather related to ples. The increase in the strain rate led to a relative attenuation of such as (011) [1][2][3][4][5][6][7][8][9][10][11] and an increase in the components of Goss texture ence of a highly diffuse but pronounced multicomponent axial crys (c) In metals with an FCC lattice, the easy dislocation gliding occurs in {111}<110> system. The close-packed (111) plane is also the plane of FCC twinning: (111) or (11-1) .…”

“…As can be seen from Figure 6, the initial as-built state may be rather related to the textureless samples. The increase in strain rate led to a relative attenuation of texture components such as (011) [1][2][3][4][5][6][7][8][9][10][11] and an increase in the components of Goss texture (011) [100]. The presence of a highly diffuse but pronounced multicomponent axial crystallographic texture (011)[100] + (011) [1][2][3][4][5][6][7][8][9][10][11] was observed only in the deformed with a strain rate of 8 × 10 −3 s −1 .…”