Effect of hot isostatic pressing on the microstructure and mechanical properties of 17-4PH stainless steel parts fabricated by selective laser melting

17-4PH stainless steel parts, fabricated by selective laser melting, were subjected to the solution and aging treatments conducted under vacuum and hot isostatic pressing (HIP) conditions. The microstructure of as-built and heat-treated specimens were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Mechanical properties were evaluated using microhardness and tensile testing. The relative density of the as-built samples was improved after the conduction of HIP treatment. Microstructural characterization showed that precipitates with the co-occurrences of Cu-, Mn-, Si- and Nb-enrichments were formed in the HIP-processed specimen. Results of mechanical testing indicated that a simultaneous improvement of tensile strength and ductility could be obtained through solutionizing and aging treatments done in the HIP followed by a high-pressure gas quenching. In addition, a significant enhancement of tensile strength without sacrificing ductility could be attained by combining solutionizing treatment done under high pressure and consequent aging followed with water cooling.