Exploring the Effect of Heat Treatment on the Mechanical Performance of 17-4PH Stainless Steel Specimens Fabricated by Metal Additive Manufacturing

Background: Powder bed fusion (PBF) offers enhanced opportunities to manufacture complex components with a high degree of geometric freedom. However, understanding and designing for mechanical properties remains challenging due to numerous factors, such as processing parameters, building direction, and heat treatments. Objective: In this study, we revealed that the As-built and heat-treated mechanical properties differ from those achieved through traditional manufacturing methods, even when using the same alloy and heat treatments. This phenomenon arises from the intricated microstructures and porosity caused by the repetitive, rapid heating/cooling process involved. Results: To quantitatively investigate the properties, the conventional heat treatments combining a hot isostatic pressing (HIP), solution, and aging treatment, were conducted on 17-4 PH stainless steel printed in both horizontal and vertical directions. Our findings demonstrate that HIP, coupled with aging treatment, was the most effective method for reducing porosity, and enhancing hardness and yield strength by 56% and 118%, respectively, while there was a slight decrease in elongation by 5.6%. The high temperature and pressure during HIP enabled the recrystallization of As-built microstructure into lath martensite, and the aging treatment facilitated the production of precipitates to enhance the strength. The solution treatment, however, resulted in poor elongation to 9.3% while the yield and tensile strength showed similar levels to As-built parts due to insufficient time to recrystallize the As-built microstructure. Conclusions: We believe these results will offer valuable insights into the manufacturing and post processing not only of PBF 17-4PH stainless steel but also of other alloys.