University of Oulu

Sumit Ghosh, Jukka Kömi, Suhrit Mula, Flow stress characteristics and design of innovative 3-steps multiphase control thermomechanical processing to produce ultrafine grained bulk steels, Materials & Design, Volume 186, 2020, 108297, ISSN 0264-1275,

Flow stress characteristics and design of innovative 3-steps multiphase control thermomechanical processing to produce ultrafine grained bulk steels

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Author: Ghosh, Sumit1,2; Kömi, Jukka1; Mula, Suhrit2
Organizations: 1Materials and Mechanical Engineering, Centre for Advanced Steels Research, University of Oulu, 90014, Oulun yliopisto, Finland
2Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Roorkee, 247667, Uttarakhand, India
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 8.3 MB)
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Language: English
Published: Elsevier, 2020
Publish Date: 2019-12-12


In the present study, at first flow behavior of Nb–Ti microalloyed and interstitial-free (IF) steels was investigated to know the effects of processing parameters on their microstructural evolution. Then, innovative 3-steps multiphase control rolling schedules have been designed to yield submicron size uniform grains structure and successfully achieved ultrafine ferrite+martensite (0.69–0.78 μm) and ferritic structure (0.83–0.88 μm), respectively, in microalloyed and IF steels. The good combination of yield strength and ductility was achieved for the microalloyed (924 MPa, 13.6% elongation) and IF steel (621 MPa, 19.4% elongation) after rolling as per the designed 3-steps multiphase control deformation schedules. Deformation induced ferrite transformation followed by continuous dynamic recrystallization of the dynamically transformed ferrite is found to be the key mechanism for the formation of the ultrafine grained structure. Due to application of high amount of strains specifically within α+γ phase regime, the α-phase subdivided into several subgrains. These α-subgrains are strongly pinned by the γ/α grain boundaries and thereby restrict the dynamic recovery of the ferrite through reknitting and unravelling subgrain boundaries. On the application of further straining, the misorientation angle between these subgrain boundaries increases continuously through accumulation of the dislocations and finally, ultrafine ferrite grain structure is developed through continuous dynamic recrystallization.

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Series: Materials & design
ISSN: 0264-1275
ISSN-E: 1873-4197
ISSN-L: 0264-1275
Volume: 186
Article number: 108297
DOI: 10.1016/j.matdes.2019.108297
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Funding: Authors are grateful and highly acknowledged Academy of Finland through Genome of Steel project (Grant no. #311934) for providing the financial support and Metallurgical and Materials Engineering Department, Indian Institute of Technology, Roorkee for providing the research facilities to carry out the present research work.
Copyright information: © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (