Due to their diverse properties and their low price compared to many other metallic alloys, steels are the material of choice for countless applications in a wide range of areas, such as for numerous automotive body components. Steels are known to exhibit the typical strength-formability discrepancy, i.e. either strong and hard or vice-versa. The manganese-containing steels can be counted as an exception with their combination of high tensile strength and elongation at break. The different manganese-containing steels have in common that manganese is substitutionally dissolved in iron and the manganese content is used specifically to stabilize the austenite phase at room temperature. With medium manganese contents (5-12% by weight), the austenite phase is only partially stabilized, leading to a multiphase structure consisting of austenite, ferrite and/or martensite. While high-manganese steels (HMnS) have an excellent strength/ductility ratio, the high production costs (due to the high Mn content) have severely restricted the industrial use of TWIP steels. Therefore, medium-manganese steels (MMnS) with an ultrafine-grained austenitic-ferritic microstructure were developed. By reducing the manganese content, the alloying costs could be significantly reduced. While HMnS steels achieve impressive elongations, MMnS achieve higher strengths and sufficient plasticity. The mechanical properties of MMnS generally depend strongly on the heat treatment and thus the resulting microstructure and local chemical composition.

Laser-based additive manufacturing (AM) processes have become increasingly important in recent years and today represent an important technology for the production of highly complex components, such as energy-absorbing, density-reduced lattice structures made from a wide variety of metallic alloys. Although it was the focus of many studies before, MMnSs were not investigated for AM route. The cyclic heat input during the layer-by-layer build-up process makes it possible to specifically influence the microstructure, texture, phase distribution and phase stability in the material and thus adjust the mechanical properties. Therefore, a profound understanding of the understanding of the fundamental process-microstructure- property relationships in high-performance metallic materials is imperative for exploring the full potential of additive manufacturing, both the metallurgical as well as the technological aspects the microstructure development.

This presentation aims to demonstrate the characteristics of the phase evolution of MMnS samples that were produced with 3 different scanning speeds via LPBF method. To identify individual austenite stabilization effects (primary and retained austenite content, distribution, grain size and element segregation); a fundamental material-physical knowledge of the solidification and microstructure development through a combination of experimental investigations and computer-aided simulation methods was developed.