Processing of high-strength C+N austenitic steel by selective laser melting - microstructure and propertiesThursday (27.09.2018) 10:15 - 10:30 S1/01 - A3 Part of:
Biomedical implants often exhibit a high degree of individualization and geometrically complex structures and shapes. In this context, additive manufacturing of these products, e.g. by selective laser melting (SLM), has become an important manufacturing route for the production of medical products . In the field of iron-based alloys, additively manufactured austenitic Cr-Ni steels are widely used for orthopedic implants due to their low prize and good mechanical and chemical properties. Against the background of allergic reactions of the human body to nickel, Ni-free high-nitrogen austenitic Cr-Mn steels represent alternative biomaterials featuring high strength and ductility as well as a superior corrosion resistance . In this study, X40MnCrMoN19-18-1 HNS steel was processed by SLM, in Ar as well as N2 atmospheres. Besides the basic feasibility of processing HNS by SLM, the resulting microstructure and chemical composition were investigated with regard to the used process parameters. The investigations revealed a slight decrease of the N content during SLM in comparison to the N content of the starting powder. In this context, no correlation between the N content and the process parameters as well as the process atmosphere was detected. It was found, that the porosity of the SLM densified samples can be reduced by the use of a smaller point distance and a higher exposure time. Regardless of the used parameters, samples feature a microstructure consisting of the phases austenite and finely dispersed N-rich precipitations. Precipitations were found to be distributed inhomogeneously in single hatches, indicating local differences of the heat flow during SLM process. Moreover, fine dendritic and cellular-dendritic subgrain structures were observed, which can be traced back to the high cooling rates and micro segregation effects during SLM. By solution annealing of the samples, the amount of precipitations could be reduced significantly, leading to quasi single-phase microstructure, promising good mechanical properties. At last, mechanical properties of the SLM densified HNS are compared to those in HIP and casted condition as a reference state.
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