Influence of defects on axial fatigue strength of maraging steel specimens produced by additive manufacturing

In the recent past, structural integrity of additive manufactured (AM) metallic materials and components has become an increasingly important topic because of the possibility to design free-shape geometries. Nowadays many parts in steels, aluminium and titanium alloys can be manufactured using the powder bed solutions consisting in melting subsequently powder layers by means of a laser or an electron beam (Laser Beam Melting – LBM and Electron Beam Melting – EBM). The microstructure obtained from layer-by-layer solidification having high cooling rate cannot be considered isotropic. Therefore, the mechanical properties could be influenced by the building direction. Regarding maraging steel, an high strength steel adopted in aeronautical and tooling application, the study of the influence of the building direction and the heat treatment on the static and axial fatigue strength has been investigated in [1]. A large scatter of the fatigue test results was found because of the presence of detrimental surface and subsurface defects. The aim of this contribution is to synthesise the fatigue test results in terms of initial stress intensity factor range adopting the Murakami’s expression. The effective area of the defect who caused the failure was estimated from SEM analysis of the fracture surfaces.