High cycle fatigue strength of additively manufactured AISI 316L Stainless Steel parts joined by laser welding

The present paper deals with the high cycle fatigue behavior of 316L stainless steel parts, obtained either by rolling or by LPBF additive manufacturing process, and their assemblies by autogenous laser welding. The aim is to study the effects of this assembly process on the fatigue strength, assessed at a 106 cycles, of additively produced parts, compared to that of raw rolled products. An original campaign of high cycle fatigue tests based on seven batches of specimens, manufactured additively or cold rolled, one-pieced or assembled, raw or polished, is carried out with a positive load ratio (R= 0.1). A stress relieving heat treatment is applied to all specimens to reduce residual stress levels. Particular attention is paid to identifying the damage mechanisms associated with each batch. Preliminary results allowed an original conclusion that laser welding does not degrade the fatigue strength of additively produced parts. In addition, the fatigue behavior of the studied system depends essentially on the stress concentration generated on the surface or a few micrometers in the underlayer, mainly by the roughness of the LPBF produced parts combined with the lack of fusion (LoF) defects, and in a second order by the geometry of the laser welding channel. Furthermore, additively produced parts showed higher sensitivity to the presence of defects than rolled parts. •An original HCF test campaign is conducted on specimens with different conditions•Studied materials are LPBF or rolled, whole or laser welded, polished or raw•Welding LPBF parts is found possible without degrading the assembly’s HCF strength•LPBF parts are more sensitive to defects and to the scale effect than rolled parts•LPBF welded polished show fracture competition between LoF and welding undercuts. [Display omitted]