Tailoring the Ductility Characteristics of Lean-Medium Mn Quenching and Partitioning Steels with Varying C Contents

During recent years, quenching and partitioning (Q&P) steels have gained strong interest due to their promising lightweight potential and crashworthiness. With their microstructure consisting of tempered martensite (α″) and C-enriched retained austenite (RA), they are characterized by balanced ductility, combining the formability properties of conventional dual-phase and complex-phase steels at elevated strength levels. This study thoroughly examines three chemical compositions with 4.0 wt% Mn, 1.5 wt% Si, and varying C contents between 0.10 and 0.20 wt% with regard to their structure–properties relationship. In this context, various parameters are derived from tensile testing to assess the formability behavior of the investigated steels. The results clearly demonstrate a strong effect of the RA fraction and its mechanical stability on the ductility characteristics of lean-medium Mn Q&P steels. Generally, the optimum exploitation of the transformation-induced plasticity effect favors high global ductility, but the resulting heterogeneities in the microstructure remarkably impair the local one. By increasing the C content, larger RA fractions can be stabilized, shifting the ductility characteristics from rather local toward global. For this reason, medium C content of 0.15 wt% allows for the adjustment of the optimum microstructure leading to desired balanced ductility.