It has been proven that through targeted quenching and partitioning (Q & P), medium manganese steels can exhibit excellent mechanical properties combining very high strength and ductility. In order to apply the potential of these steels in industrial press hardening and to avoid high scrap rates, it is of utmost importance to determine a robust process window for Q & P. Hence, an intensive study of dilatometry experiments was carried out to identify the influence of quenching temperature (TQ) and partitioning time (tp) on phase transformations, phase stabilities, and the mechanical properties of a lean medium manganese steel. For this purpose, additional scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and energy dispersive X-ray spectroscopy (EDX) examinations as well as tensile testing were performed. Based on the dilatometry data, an adjustment of the Koistinen–Marburger (K-M) equation for medium manganese steel was developed. The results show that a retained austenite content of 12–21% in combination with a low-phase fraction of untempered secondary martensite (max. 20%) leads to excellent mechanical properties with a tensile strength higher than 1500 MPa and a total elongation of 18%, whereas an exceeding secondary martensite phase fraction results in brittle failure. The optimum retained austenite content was adjusted for TQ between 130 °C and 150 °C by means of an adapted partitioning.

Press‐hardening of manganese–boron steels is one of the most efficient production processes for high‐strength automotive components. However, the residual formability of these sheet components is greatly limited by the formation of fully martensitic microstructure. Herein, to extend the application of press‐hardened components also to impact energy‐absorptive parts of the vehicle body, the potential of press‐hardening of a medium manganese steel in combination with a quenching and partitioning (Q&P) treatment is analyzed. Therefore, selected heat treatments from prior dilatometer investigations are reproduced in a laboratory‐scale press‐hardening system equipped with a heated hat‐shaped tool. Instead of a complete martensitic microstructure, the Q&P process leads to a multiphase microstructure consisting of fresh and tempered martensite as well as retained austenite with different carbon content each. Since depending on the phase fractions also strongly different mechanical properties are expected, not only the qualitative distinction but also the quantitative determination of the martensitic phases is of extraordinary importance. Herein, it is shown that using phase maps combined with grain‐average band slope of electron backscatter diffraction measurements is a suitable method to distinguish quantitatively fresh and tempered martensite. Validation of the differentiation method is performed using electron‐probe microanalysis.

Press hardening of manganese-boron steels is one of the most widely used production processes for high-strength automotive components. The low residual formability of these parts is a decisive disadvantage. The low formability originates from a strong, but brittle martensitic microstructure transformed during quenching in the press-hardening tool. In contrast, medium manganese steels (MMnS) contain high fractions of ductile retained austenite improving press-hardened parts toward promising candidates for crash-relevant car body components. Disadvantages include a more complex alloy design, a highly sensitive production process, and more demanding requirements on the tool due to higher strength during press-hardening.A detailed description of the entire production process along the process chain including the material and the press-hardening tool is important for tailoring the properties. Combined information is required to enable a precise control of the production process and its influences on the final properties of the part. Maximum economic use of the material is achieved by digitally describing MMnS as well as the tool along the entire process chain (casting, forging, hot rolling, cold rolling, galvanizing and press hardening including Q&P). To link the process steps and to describe the changes of the material, a new material database structure (idCarl) was developed. All production parameters are recorded and processed as a digital material twin. Ultimately, deviations occurring during production process can be deduced from in-line data analysis and counteracted. These can then be counteracted by adapted process control and the product can be brought back into the required parameter field of properties. Clear identification of the component and the used material allows conclusions about steps responsible for errors in the production process that become apparent during use.