Qualification of new steel-alloying strategies for LAM powders by combined in-situ additivation, agglomeration and in-/post-process treatments

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Main objective of this joint proposal within SPP 2122 is the development of new starting materials and their qualification for processing martensitic-hardenable tool steels or cast irons by SLM. In a first step of our approach, we will consider our strategies on grey cast iron alloy and adjust the alloying concepts, based on this knowledge, to process white cast iron (2nd step) and ledeburitic cold work tool steel (3rd step), the two classes of materials that are not processible by SLM till now. Thereby, the grey cast iron will not be processed by using a pre-alloyed gas-atomized powder. Here we will admix different volume fraction of SiC-particles to cheap low-alloyed steel powder and the powder mixture will be densified by SLM. The aim is to realize a partial melting of particles, thus a “green body” is shaped without high defect density. The specific adjustment of the microstructure and the associated materials properties will be obtained by a further required post-processing via SLM (in-process) or heat treatment (post-process). Thereby, dissolution of admixed metastable components of the bulk powder during SLM-processing and post-processing (hot isostatic pressing, super-solidus-liquid phase-sintering) will be investigated and how the powders have to be modified to realize a full dissolution and different amounts of Fe3C or graphite. In the second and third step, we are adding further ferro-alloy powders to increase the content of certain elements like Cr, Mn, Ni in order to produce white cast iron and ledeburitic cold work tool steels. Finally, the mixtures of ferro-alloy powders and pure elements, which are conditioned by agglomeration to form flowable powders, will be processed in a similar way. It is assumed that similar alloys or chemical compositions, respectively, with similar properties can be achieved in spite of the difference in the processing routes. If this hypothesis can be confirmed, only a few basic powders with different chemical compositions are necessary to generate multiple alloys. This can significantly accelerate the development of new alloys for laser-based additive manufacturing due to economic and processing advantages as microstructure formation process and the related formation of internal defects are decoupled from SLM densification process. In order to process the complex material-oriented research within SPP 2122, all aspects will be addressed in a holistic approach with regard to powder production and powder conditioning (IWT), alloy design and SLM-processing of the designed powders (LWT) as well as microstructural, micro-magnetic and mechanical characterization of the SLM-components (WPT).