Effect of Heat Treatment on the Properties of Additively Manufactured Type 316L Stainless Steel

Thin wall test articles were made using Fusion Powder Bed processing of Type 316L stainless steel. This hollow structure was fabricated using a Renishaw AM250. The material was characterized in the as fabricated condition using optical, scanning electron microscopy, and tensile testing. The tensile behavior indicates high initial residual stress due to the higher than annealed material yield strength. A series of thermal treatments were investigated to determine the effect on mechanical properties and microstructural evolution. In order to determine these effects, miniature flat tensile test samples and metallographic samples were wire electrical discharge machined from the structure. These samples were vacuum heat treated at 870, 1040 and 1080°C for 30 to 120 minutes and metallographically examined to determine the microstructural evolution. The samples were tensile tested and the data are evaluated based on the power-law type relationships. AM Type 316L SS exhibits less strain hardening than wrought stainless steel. In addition, the ductility is somewhat lower in the as-fabricated condition compared to the heat-treated condition. The results of the testing and the rationale for these different behaviors will be discussed.