Hydrogen effect on mechanical and structural properties of an AISI 316L processed by selective laser melting

Full text: Austenitic stainless steels such as AISI 316L have been widely studied by AM-Additive Manufacturing procedures. In many solicitations, especially in the petrochemical sector, components with complex geometry can easily be made by AM processes. The use of this steel in the oil and natural gas industry stands out. However, the environment where these components are applied is often subjected to rich hydrogen surroundings which lead to an effect known as hydrogen embrittlement. Therefore, the behavior of AM obtained metals under such environments are not widely known. In order to study the characterization and mechanical behavior of a 316L austenitic stainless steel produced by Selective Laser Melting (SLM, an AM process), tensile tests with in situ X-ray diffraction measures were conducted in a Gleeble 3S50® thermomechanical system - situated in in the Brazilian Synchrotron Light Laboratory (LNLS) of Brazilian Center for Research in Energy and Materials (CNPEM). Stress-strain curves and diffractograms were obtained for the as printed 316L AM, annealed 316L AM and conventional/rolled 316L samples for comparison. The results at room temperature (without hydrogen influence) showed that both AM conditions presented only austenite, an fcc phase, and the initial phase remain the same during all the mechanical test. For the as-rolled condition, α martensite, a bcc phase, was observed initially. The percentage volume of this phase increased during the tensile test. When the samples were submitted to a hydrogen environment by cathodic charging, the hydrogen was responsible for ε martensite hcp phase formation which led to a TRIP effect during the mechanical tests. Thus, the samples that were hydrogen charged presented higher values of strain in comparison to the non-charged sample without loss of UTS. (author)