Tuning the microstructures and mechanical properties of heterostructured steel fabricated via arc-based directed energy deposition and hot rolling

Abstract

Heterostructured (HS) steels have attracted significant attention because of their excellent comprehensive mechanical properties. However, significant challenges remain, including controlling the distribution of heterogeneous regions, regulating microstructures, and developing efficient manufacturing processes. In this study, an HS steel composed of 18Ni300 maraging steel (MS) and 316 L stainless steel (SS) was fabricated via a combined arc-based directed energy deposition (DED-Arc) and hot rolling process. This approach enabled controlled distribution and adjustable thickness of heterogeneous regions. The HS steel was hot rolled from an initial thickness of 20 mm down to 2 mm and then aged at 500°C for different durations. It retained its heterogeneous structures throughout, demonstrating the feasibility of the proposed processing route. As the aging time increased, both the amount and size of nanoprecipitates within the MS tracks progressively increased. However, the strength of the HS steel initially increased and subsequently decreased, achieving an optimal balance between strength and ductility after aging for 6 h. The enhanced strength is attributed to precipitation strengthening and the heterodeformation-induced (HDI) hardening effects occurring at the heterogeneous interfaces. As the size of the nanoprecipitates increased, the deformation mechanism transitioned from shear mechanism to the Orowan mechanism, which inhibited strain within the martensitic regions near the interface. Strain partitioning at the interface facilitated increased dislocation generation on the austenitic side, leading to a maximum back stress of 954 MPa in the HR-A6 sample. This study contributes to the understanding of strengthening mechanisms in HS steels and proposes an efficient approach for fabricating high-performance HS materials.