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

Journal article (2023)

Authors

Jiayu Li Northeastern University China, Universiteit Gent
Yunbo Xu Northeastern University China
Yi Jing Northeastern University China
Yijing Gao Northeastern University China
Hongliang Liu Technology Research Institute of Bengang Steel Plates Co.
Yongmei Yu Shenyang University of Chemical Technology
Alexandros Banis Universiteit Gent
L.A.I. Kestens Universiteit Gent, Team Maria Santofimia Navarro - Mechanical, Maritime and Materials Engineering
R.H. Petrov Team Maria Santofimia Navarro - Mechanical, Maritime and Materials Engineering , Universiteit Gent
Research Group
Team Maria Santofimia Navarro (Mechanical, Maritime and Materials Engineering) (TU Delft)
Copyright: © 2023 Jiayu Li, Yunbo Xu, Yi Jing, Yijing Gao, Hongliang Liu, Yongmei Yu, Alexandros Banis, L.A.I. Kestens, R.H. Petrov
DOI
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https://doi.org/10.1016/j.matchar.2023.113377
Austenitization kinetics Cold-worked ferrite Medium‑manganese steel Microstructure and mechanical properties Quenching and partitioning process
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Published Date

2023

Language

English

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Faculty

Mechanical, Maritime and Materials Engineering

Department

Materials Science and Engineering

Research Group

Team Maria Santofimia Navarro

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%.