Microstructure and dynamic-mechanical property of a selective laser melting AISI 316 L stainless steel

Dynamic mechanical properties are the key indicators for the application of the selective laser melting AISI 316 L stainless steel (SLM AISI 316 L SS) in impact-related fields. The σ precipitate can improve the dynamic mechanical properties of the SLM AISI 316 L SS during high-speed deformation, and promote the application of the SLM AISI 316 L SS in field of the high-speed deformation. Dynamic mechanical properties of the as-built and quenched specimens are tested by using a split Hopkinson pressure bar (SHPB). The specimens exhibit excellent impact energy and ultimate compressive strength, reaching 210.33 MJ/m3 and 1411 MPa, respectively. Microstructure of the SLM AISI 316 L SS is observed by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The melt pool boundary and cellular substructure disappear, and the rod-like σ precipitates are mainly distributed at the columnar grain boundary after quenching process. Quantitative analysis of the σ precipitate is obtained by small angle neutron scattering (SANS). Size and volume fraction of the σ precipitates in the quenched specimens can reach 31.5 nm and 2.7%, respectively. Quenched specimens after dynamic deformation mainly produce deformation bands with about 20 µm width. The σ precipitates distributing at the columnar grain boundaries suppress grain growth and dislocation movement by pinning grain boundaries and dislocations, leading to the optimization of the dynamic mechanical properties of the SLM AISI 316 L SS. This work provides theoretical guidance for the strengthening and toughening of dynamic mechanical properties of the SLM AISI 316 L SS.