The Effects of Post-processing in Additively Manufactured 316L Stainless Steels

This paper provides a systematic examination of microstructure and corrosion behavior of additively manufactured 316L stainless steel after post-processing by surface finishing, isothermal heat treating, or hot isostatic pressing. The effects of isothermal heat treatments from 500 degrees C to 1300 degrees C and hot isostatic press processing from 1000 degrees C to 1200 degrees C were correlated to the evolution of microstructure, pore morphology and volume fraction, microhardness measurements, and corrosion behavior to reveal the different post-processing temperature regimes and their corresponding characteristics. In particular, this study found that the AM 316L microstructures and properties are stable up to nearly 800 degrees C. Higher temperatures eliminate the fine solidification structure, causing a drop in microhardness and corrosion resistance. Corrosion was primarily driven by the porosity content of the exposed surface and near-surface regions, which is unaffected by isothermal or HIP post-processing, and the corrosion was not significantly affected by recrystallization, which begins around 1050 degrees C and is nearly complete by 1200 degrees C. The amount of porosity was not markedly affected by isothermal post-processing, but could be significantly reduced by HIP processing.