Influence of the Quenching and Partitioning Process on the Transformation Kinetics and Hardness in a Lean Medium Manganese TRIP Steel

Simone Kaar, Reinhold Schneider, Daniel Krizan, Coline Beal, Christoph Sommitsch

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The quenching and partitioning (Q&P) process of lean medium Mn steels is a novel approach for producing ultra-high strength and good formable steels. First, the steel is fully austenitized, followed by quenching to a specific quenching temperature (TQ) in order to adjust an appropriate amount of initial martensite (α’ initial ). Subsequently, the steel is reheated to a partitioning temperature (TP) in order to ensure C-partitioning from α’ initial to remaining austenite (γ remain ) and thus retained austenite (RA) stabilization. After isothermal holding, the steel is quenched to room temperature (RT), in order to achieve a martensitic-austenitic microstructure, where the meta-stable RA undergoes the strain-induced martensitic transformation by the so-called transformation induced plasticity (TRIP) effect. This paper systematically investigates the influence of the (Q&P) process on the isothermal bainitic transformation (IBT) kinetics in a 0.2C-4.5Mn-1.3Al lean medium Mn steel by means of dilatometry. Therefore, the Q&P annealing approach was precisely compared to the TRIP-aided bainitic ferrite (TBF) process, where the samples were directly quenched to the temperature of the IBT after full austenitization. The results indicated an accelerated IBT for the Q&P samples, caused by the formation of α’ initial during quenching below the martensite start (MS) temperature. Furthermore, a significant influence of the annealing parameters, such as TQ and TP, was observed with regard to the transformation behavior. For further characterization, light optical microscopy (LOM) and scanning electron microscopy (SEM) were applied, showing a microstructure consisting of a martensitic-bainitic matrix with finely distributed RA islands. Saturation magnetization method (SMM) was used to determine the amount of RA, which was primarily depending on TQ. Furthermore, the hardness according to Vickers revealed a remarkable impact of the annealing parameters, such as TQ and TP, on the predicted mechanical properties.

LanguageEnglish
Article number353
JournalMetals
Volume9
Issue number3
DOIs
StatusPublished - Mar 2019

Fingerprint

Steel
Manganese
Plasticity
Quenching
Hardness
Austenite
Bainitic transformations
Kinetics
Temperature
Annealing
Martensite
Optical microscopy
Microstructure
Martensitic transformations
Saturation magnetization
Ferrite
Stabilization
Scanning
Mechanical properties
Scanning electron microscopy

Keywords

  • Q&P
  • TRIP
  • lean medium Mn steel
  • transformation kinetics

Fields of Expertise

  • Advanced Materials Science

Cite this

Influence of the Quenching and Partitioning Process on the Transformation Kinetics and Hardness in a Lean Medium Manganese TRIP Steel. / Kaar, Simone; Schneider, Reinhold; Krizan, Daniel; Beal, Coline; Sommitsch, Christoph.

In: Metals, Vol. 9, No. 3, 353, 03.2019.

Research output: Contribution to journalArticleResearchpeer-review

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