Influence of Press‐Hardening in Combination with Quenching and Partitioning Treatment on the Microstructure of Medium Manganese Steel

Abstract

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.