University of Oulu

Sadeghpour, S.; Javaheri, V.; Somani, M.; Kömi, J.; Karjalainen, P. Heterogeneous Multiphase Microstructure Formation through Partial Recrystallization of a Warm-Deformed Medium Mn Steel during High-Temperature Partitioning. Materials 2022, 15, 7322.

Heterogeneous multiphase microstructure formation through partial recrystallization of a warm-deformed medium Mn steel during high-temperature partitioning

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Author: Sadeghpour, Saeed1; Javaheri, Vahid1; Somani, Mahesh1;
Organizations: 1Centre for Advanced Steels Research, Materials and Mechanical Engineering, University of Oulu, 90014 Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 8.5 MB)
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Language: English
Published: Multidisciplinary Digital Publishing Institute, 2022
Publish Date: 2023-04-18


A novel processing route is proposed to create a heterogeneous, multiphase structure in a medium Mn steel by incorporating partial quenching above the ambient, warm deformation, and partial recrystallization at high partitioning temperatures. The processing schedule was implemented in a Gleeble thermomechanical simulator and microstructures were examined by electron microscopy and X-ray diffraction. The hardness of the structures was measured as the preliminary mechanical property. Quenching of the reaustenitized sample to 120 °C provided a microstructure consisting of 73% martensite and balance (27%) untransformed austenite. Subsequent warm deformation at 500 °C enabled partially recrystallized ferrite and retained austenite during subsequent partitioning at 650 °C. The final microstructure consisted of a heterogeneous mixture of several phases and morphologies including lath-tempered martensite, partially recrystallized ferrite, lath and equiaxed austenite, and carbides. The volume fraction of retained austenite was 29% with a grain size of 200–300 nm and an estimated average stacking fault energy of 45 mJ/m2. The study indicates that desired novel microstructures can be imparted in these steels through suitable process design, whereby various hardening mechanisms, such as transformation-induced plasticity, bimodal grain size, phase boundary, strain partitioning, and precipitation hardening can be activated, resulting presumably in enhanced mechanical properties.

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Series: Materials
ISSN: 1996-1944
ISSN-E: 1996-1944
ISSN-L: 1996-1944
Volume: 15
Issue: 20
Article number: 7322
DOI: 10.3390/ma15207322
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Funding: This research was funded by Academy of Finland, grant number 311934.
Copyright information: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.