Anisotropic fracture toughness of a selective laser melted martensitic stainless steel

•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.