Mechanical behavior of selective laser melted 316L stainless steel

Abstract

The tensile, fracture, and fatigue crack growth properties of 316L stainless steel (SS) produced using the selective laser melting (SLM) technique were evaluated and compared with those of conventionally manufactured (CM) austenitic SSs. For SLM, both single melt (SM) and checker board (CB) laser scanning strategies were employed, so as to examine the effect of scanning strategy on the mechanical properties. The experimental results show that the SLM alloys' yield strength is significantly higher than that of CM 316L SS, a result of the substantial refinement in the microstructure. In contrast, only a marginal improvement in the ultimate tensile strength and a marked reduction ductility, which are a result of the loss of work hardening ability, are attributed to the absence of stress induced martensitic transformation common in CM austenitic SSs. In spite of these, the fracture toughness, which ranges between 63 and 87 MPa m0.5, of the SLM alloys is good, which is a result of the mesostructure induced crack tortuousity. The SLM process was found to marginally reduce the threshold stress intensity factor range for fatigue crack growth initiation and enhance the Paris exponent within the steady state crack growth regime. Both tensile and toughness properties were found to be anisotropic in nature. SLM with CB scanning strategy improves both these properties. All these observations on the mechanical properties are rationalized by recourse to micro- and meso-structures seen these alloys.