Anisotropic fracture toughness of a selective laser melted martensitic stainless steel

[Display omitted] •Anisotropic fracture toughness of AISI 420 built by selective laser melting is found.•Effects of tempering treatment and microstructure on the anisotropy are studied.•Fracture toughness is greater for loading direction parallel to the build direction.•Elongated cells are mainly responsible for the anisotropic behavior.•Fracture toughness is enhanced by a tempering treatment at 400 °C. Anisotropic fracture toughness of selective laser melted AISI 420 built in two build directions was investigated. Post-process heat treatments were performed at 200 °C and 400 °C to study the tempering effect. The parallel group exhibited better fracture toughness than the perpendicular group in both as-built and tempered states. KIC value of the 400 °C tempered state was superior to that of other states due to a coarser martensite phase. Elongated cellular structure was responsible for the anisotropic behavior because of a build direction effect, while the anisotropy was barely changed by the tempering treatments.