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

Abstract

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.

A Systematic Review of Medium‐Mn Steels with an Assessment of Fatigue Behavior

“…Therefore, martensite is tempered, and retained austenite is enriched with carbon, resulting in a microstructure consisting of metastable retained austenite and tempered martensite. [36][37][38] The insights generated from different studies are summarized in Table 1. The table primarily represents the variation in microstructure in terms of morphologies as well as tensile properties in medium-Mn steels depending on their chemical composition, processing, ART annealing temperature, and time.…”

Stress Intensity Range Dependent Slowing Down of Fatigue Crack Growth under Strain‐Induced Martensitic Transformation of Film‐Like Retained Austenite

“…A small amount of finely divided retained austenite (RA) with martensite is known to improve the strengthtoughness combination in steels. [1][2][3][4][5][6] In low-alloy steels, austenite can be retained at room temperature by interrupting the quenching process at a quench-stop temperature between Martensite start (M s ) and Martensite finish (M f ), followed by holding long enough before cooling to facilitate partitioning of carbon from supersaturated martensite to untransformed austenite leading to a "Constraint Carbon Equilibrium". [7][8][9][10][11][12][13][14][15] The quenchstop temperature determines the volume fraction of austenite and martensite in the final microstructure.…”