Molten pool effect on mechanical properties in a selective laser melting 316 L stainless steel at high-velocity deformation

Abstract

Microstructural modification for the molten pool can improve mechanical properties of the selective laser melting 316 L stainless steel (SLM 316 L SS) at high-velocity deformation and can promote application of the SLM 316 L SS in the field of high-velocity deformation. Mechanical properties of the SLM 316 L SS with different volumetric energy densities (VED) were obtained at high-velocity deformation by using a split Hopkinson pressure bar (SHPB). With strain rate increased, compressive strength of the SLM 316 L SS peaked at the strain rates of 1200 s −1 - 1450 s −1 . Analyzed molten pool and mechanical properties of SLM 316 L SS at the strain rate of 1200 s −1 - 1450 s −1 , the SLM 316 L SS with volumetric energy density of 145.83 J/mm 3 had a combination of minimum overlap ratio of molten pool and maximum single pass molten pool width, which brought maximum pool size and exhibited excellent impact energy and compressive strengths, reaching 1185 MPa and 125.4 MJ/m 3 , respectively. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize molten pools of the SLM 316 L SS. Microcracks appear along molten pool boundaries of the failed specimens was found and poor deformation coordination ability due to the misorientation of grains on both sides of molten pool boundaries makes the molten pool boundary as the weak region. Overlap ratio of the molten pool and theoretical width of the single pass molten pool are considered to be main factors in determining the molten pool size, which in turn determines mechanical properties of the SLM 316 L SS at high-velocity deformation. Further, in the process of dynamic compression deformation, microcracks were formed at the molten pool boundary, which lead to failure of the SLM 316 L SS. • Strain rate sensitive index of the SLM 316 L SS changes from positive to negative. • Failure of the molten pool boundary leads to the instability flow. • Molten pool size has a major effect on mechanical properties of the SLM 316 L SS. • Deformation band across cellular structure was found at high-velocity deformation. • Damage of the molten pool boundary is the main failure mechanism.