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D. Gatões^a, R. Alves^a, H. Reis Marques^a, A. Mateus^b, M.T. Vieira^a 

^aCEMMPRE, Department of Mechanical Engineering, University of Coimbra, Coimbra, Portugal

^bPolitechnic Institute of Leiria, Leiria, Portugal

Additive Manufacturing of structural materials is considered the illustration of industry 4.0. But the final composition and structure of consolidate powders could be different of the bulk material. Martensitic 420 Stainless Steel (SS), that combines strength and hardness with high corrosion resistance, has only been a recent development in Selective Laser Melting (SLM) due to its high carbon content. Moreover, selective laser melted steel undergo a series of phase transformations and chemical modifications during processing, depending on the processing characteristics. Amongst them, gaseous atmosphere could have an essential role on the properties of the final parts. However, commercial SLM equipments work under two typical atmospheres - nitrogen or argon. On this study it is highlighted the effect of the atmosphere in 420 SS processed under argon and nitrogen on mechanical properties (tensile strength, Young modulus and hardness) and roughness, measured in microspecimens. From X-ray diffraction it is obvious the presence of excessive austenitic phase when the atmosphere is nitrogen.

Figure 1 - Tensile test specimen

Figure  SEQ Figure \* ARABIC 2- X-ray diffraction of the Ar atmosphere(below) and the nitrogen atmosphere (above) (Cobalt).