Dual-phase (DP) steels are one of the most commonly used advanced high strength steels in existing cars due to their composite like nature promoting the combination of low yield strength and high ultimate tensile strength, which in turn provides a wide range of mechanical properties. Today’s technological developments raise the possibility to produce well- established alloys besides the conventional manufacturing methods. As such, additive manufacturing (AM) of metallic components has gained significant importance in the scientific community and industry owing to its disruptive capability to shorten component design and production, while simultaneously enabling the fabrication of geometrically complex parts with minimized waste. Thereby, many competitive industries began to integrate AM for part development and production of the end-use parts.

During AM processes, alloys experience distinct thermal histories associated with the repeating melting-solidification and heating-cooling cycles alongside with steep temperature gradients and significantly high cooling rates leading to various phase transformations. As such, spatially variable thermal profiles facilitate formation of locally dependent microstructures and material properties that can only be achieved by AM. So far, many alloys were utilized in AM. However, low alloy steels (e.g. DP-type steels) have not been intensively investigated in the context of AM, but are of high industrial interest. The unique characteristics of the AM processes can enable the re-design of microstructures, hence, can introduce novel microstructures and tailored mechanical properties in DP steels by offering high degrees of freedom with respect to the manipulation of ferrite-martensite morphology and distribution.

In this presentation, we aim to demonstrate the range of microstructures and material properties obtained by laser powder bed fusion (L-PBF) and post-AM heat treatments by utilizing a dual-phase low alloy steel powder with a composition similar to widely used DP600. Samples were produced by L-PBF and two heat-treatment strategies were applied to obtain ferrite and martensite DP microstructures. The corresponding as-built and heat-treated microstructures were characterized in detail and the underlying physical mechanisms are discussed with respect to the microstructure evolution and mechanical properties alongside with their correlation to chemical and morphological heterogeneities.