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Comparison of the Hardness-Toughness Relationship of Medium-Mn Steels after Q&T and Q&P Treatments*

Vergleich der Härte-Zähigkeit-Beziehung von Medium-Mn-Stählen nach Vergüte- und Q&P-Behandlungen
R. Schneider, S. Kaar, S. Schneider, D. Krizan and C. Sommitsch

Abstract

In contrast to quenching and tempering (Q&T), with quenching to room temperature, quenching and partitioning (Q&P) usually applies quenching to a temperature between Ms and room temperature. To stabilize a sufficient amount of retained austenite (RA), carbon diffusion from martensite into austenite and a prevention of cementite formation takes place during the successive partitioning step. Larger amount of RA, and its transformation into martensite during plastic deformation, provides Q&P treated steels with an enhanced combination of strength and ductility. In this investigation, the effect of different Q&T and Q&P treatments on the hardness-toughness relationship was determined. These results are compared with the RA contents and mechanical properties provided by tensile testing. The obtained results clearly demonstrate that the optimum parameters for strength and ductility do not match with the best combinations of hardness and toughness. Furthermore, the stability of the RA plays an important role in the understanding of toughness properties of the investigated Q&P steels.

Kurzfassung

Im Gegensatz zum Vergüten (Abschrecken und Anlassen, Q&T), bei dem auf Raumtemperatur abgeschreckt wird, wird beim Abschrecken und Umverteilen (Q&P) normalerweise auf eine Temperatur zwischen Ms und Raumtemperatur abgeschreckt. Um eine ausreichende Menge an Restaustenit (RA) zu stabilisieren, findet während des anschließenden Anlassens eine Kohlenstoffdiffusion von Martensit in Austenit statt und die Bildung von Zementit wird verhindert. Eine größere Menge an RA und seine Umwandlung in Martensit während der plastischen Verformung verleihen den Q&P-behandelten Stählen eine bessere Kombination aus Festigkeit und Duktilität. In dieser Untersuchung wurde die Auswirkung verschiedener Q&T- und Q&P-Behandlungen auf das Verhältnis zwischen Härte und Zähigkeit bestimmt. Diese Ergebnisse werden mit dem RA-Gehalt und den mechanischen Eigenschaften verglichen, die durch Zugversuche ermittelt wurden. Die erzielten Ergebnisse zeigen deutlich, dass die optimalen Parameter für Festigkeit und Duktilität nicht mit den besten Kombinationen von Härte und Zähigkeit übereinstimmen. Darüber hinaus spielt die Stabilität des RA eine wichtige Rolle für das Verständnis der Zähigkeitseigenschaften der untersuchten Q&P-Stähle.


* Reworked version of a lecture held at ECHT – Quenching and Distortion Engineering QDE 2021, 26.-18. April 2021, online


Acknowledgement

The authors sincerely acknowledge the support of the Austrian Research Promotion Agency (FFG) related to the frontrunner project No. 860188 “Upscaling of medium Mn-TRIP steels”

Danksagung

Die Autoren bedanken sich herzlich für die Unterstützung durch die Österreichische Forschungsförderungsgesellschaft (FFG) im Rahmen des Frontrunner-Projekts Nr. 860188 „Upscaling of medium Mn-TRIP steels“.

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Published Online: 2021-12-31

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