Microstructure and corrosion evaluation of as-built and heat-treated 316L stainless steel manufactured by laser powder bed fusion

Abstract

In this study, the effect of as-built and heat-treated additively manufactured 316L stainless steel at different temperatures was examined on the electrochemical corrosion performance. The corrosion was investigated by Tafel polarization and electrochemical impedance spectroscopy methods in a 3.5% NaCl solution. For this purpose, the as-built and heat-treated printed samples were examined via optical and Field Emission Scanning Electron microscopy. Energy Dispersive X-Ray Spectroscopy analysis was used for the elemental mapping for all samples. Vickers microhardness was measured to assess the sample grain structure response and for measurement of phase change, X-ray diffraction was used. Microstructural analysis results confirmed an austenite phase prior to 900 °C. For the heat-treated sample at 900 °C and 1000 °C, the ferrite phase appeared in the austenite field and a fully austenitic structure was obtained at 1100 °C. The microhardness results indicated how the surface hardness decreased at a higher heat treatment temperature. From the corrosion tests, the higher heat-treatment temperatures resulted in better resistance to corrosion due to the larger grain size, uniformity of metallurgical structure, and lattice structure stress relief.