Improving the strength-ductility balance of medium-Mn Q&P steel by controlling cold-worked ferrite microstructure

Jiayu Li, Yunbo Xu*, Yi Jing, Yijing Gao, Hongliang Liu, Yongmei Yu, Alexandros Banis, Leo A.I. Kestens, Roumen H. Petrov

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

The phase transformations, microstructure and properties of two Medium-Mn processed via quenching and partitioning steels were compared in this contribution and a new strategy for controlling mechanical properties by introducing and controlling cold-worked ferrite prior to heat treatment is proposed. It was found that during heating, the recovery and recrystallization of cold-worked ferrite compete with austenitization, thereby inhibiting the coarsening of austenite. The cold-worked ferrite interface will significantly delay the austenitization kinetics during the partitioning local equilibrium stage compared to martensite. These results lead to a diverse parent austenite, as well as a refined martensite substructure. As a result, the randomly distributed variants increase the number of effective grain boundaries, thus enhancing yield strength. The intercritical annealing process at a temperature of 860 °C resulted in the formation of fresh martensite-retained austenite (M/RA) constituents exhibiting a remarkably fine (<2 μm) and uniform grain morphology. Such microstructure yielded substantial improvement in both the strength and ductility of the steel. The proposed treatment led to excellent elongation (24%) at fracture, combined with very high ultimate tensile strength and yield strength of 1345 MPa and 1163 MPa, respectively, of the steel, resulting in a product of strength and elongation that exceed 32 GPa%.

Original languageEnglish
Article number113377
Number of pages12
JournalMaterials Characterization
Volume205
DOIs
Publication statusPublished - 2023

Bibliographical note

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Keywords

  • Austenitization kinetics
  • Cold-worked ferrite
  • Medium‑manganese steel
  • Microstructure and mechanical properties
  • Quenching and partitioning process

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