Effects of solution annealing and ageing treatments on the microstructure and mechanical properties of 17-4PH steel produced by binder jetting

Purpose: Binder jetting of 17-4PH martensitic stainless steel is of great interest to several industries that could exploit the higher degree of geometrical complexity granted by 3D printing, thus this paper aims at providing a comprehensive description of the material development throughout the multiple manufacturing stages and treatments. Design/methodology/approach: In this work, insight into the as-sintered 17-4PH microstructure and the manufacturing process effects on the copper precipitation is provided. Furthermore, conventional ageing treatments were applied to the specimens starting from either the as-sintered or the solution-annealed state and studied with particular attention to the microstructure and the resulting mechanical properties. Findings: The analysis of the as-sintered microstructure revealed a continuous δ ferrite network along martensitic grains, with Cu-rich phases within the ferritic phase. Solution annealing was able to redistribute the alloying elements within the matrix and limit the continuity of the ferritic network leading to an enhancement in ductility. On the contrary, the direct ageing treatments performed on the as-sintered microstructure lead to overageing of the Cu-precipitates and impairing of the tensile properties compared to those starting from solution annealed condition. Nonetheless, hardness remains comparable independently from the ageing temperature and the ferritic network retains its morphology and distribution. Originality/value: A stepwise description of the microstructural development throughout thermal treatments is provided granting the chance to design the most convenient post-processing route to achieve the required mechanical properties with a minimisation of energy and cost consumption.