A comparative study on microstructure and mechanical properties of 17-4PH processed by a laser powder bed fusion vs rolling process

This study provides a comprehensive benchmark comparison of microstructure, mechanical properties, and their evolution during subsequent heat treatment of 17-4PH Martensitic stainless steel (MSS) processed by laser powder bed fusion (LPBF) and its commercially rolled counterparts. The results reveal that LPBF samples exhibit a finer martensitic microstructure with presence of structural defects, pores, and some non-metallic inclusions randomly distributed at the grain boundaries and within the grains and an almost absence of austenite, compared to rolled samples. Additionally, after identical heat treatment, LPBF samples maintain a relatively unchanged microstructure while aging of rolled samples leads to a reduction in martensite in favor of austenite and Cu- and Si-rich precipitates. The LPBF samples demonstrate slightly elevated hardness (HV 0.5 + 20%), mechanical strength (UTS + 15%) compared to rolled ones. Nevertheless, LPBF samples display a distinct behavior, characterized by abrupt fracture and reduced elongation at failure (El% max. 4% vs. 17.5%). Specifically, failure in LPBF samples is attributed to cleavage and cavities’ coalescence contrasting with the progressive failure mechanism observed in rolling ones driven by plasticity and damage evolution. Furthermore, the impact resistance of LPBF samples is notably weak (K max. 12.5 J/cm 2 vs. 155 J/cm 2 ), which is likely caused by macro- and microstructural defects generated by the LPBF process and the nucleation of harmful precipitates. The study proposes that the ductility of LPBF samples could be improved by implementing appropriate heat treatment and reducing defects through parameter optimization and by specific thermal cycle control during the LPBF process.