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Nitrogen is used as an alloying element, substituting the expensive and allergenic element nickel, in austenitic stainless steels to improve their mechanical properties and corrosion resistance. The development of austenitic stainless steel powders with increased nitrogen content for laser additive manufacturing has recently received great interest. To increase nitrogen content in the austenitic steel powders (for example AISI 316L), two measures are taken in this study: (1) melting the steel under a nitrogen atmosphere, and (2) adding manganese to increase the solubility of nitrogen in the steel. The steel melt is then atomized by means of gas atomization (with either nitrogen or argon). The resulting powders are examined and characterized with regard to nitrogen content, particle size distribution, particle shape, microstructure, and flowability. It shows that about 0.2-0.3 mass % nitrogen can be added to the austenitic stainless steel 316L by adding manganese and melting the steel under nitrogen atmosphere. The particles are spherical in shape and very few satellite particles are observed. The steel powders show good flowability and packing density, therefore they can be successfully processed by means of laser powder bed fusion (L-PBF).

A co-spray forming process was developed to produce gradient deposits from two sprays of different tool steels using scanning gas atomizers. The tool steel melts were atomized and co-sprayed simultaneously onto a horizontally moving flat substrate, resulting in a flat deposit with a gradient zone between two layers of the different steels when the two sprays were overlapped. The gradient deposits were investigated with respect to the porosity, element distributions, microstructure, and hardness. It showed that a sound deposit with a desired gradient zone could be achieved under proper processing conditions.

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