University of Oulu

Kumar, G., Ghosh, S., Pallaspuro, S., Somani, M. C., Kömi, J., Mishra, S. K., & Gokhale, A. A. (2022). Fracture toughness characteristics of thermo-mechanically rolled direct quenched and partitioned steels. Materials Science and Engineering: A, 840, 142788. https://doi.org/10.1016/j.msea.2022.142788

Fracture toughness characteristics of thermo-mechanically rolled direct quenched and partitioned steels

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Author: Kumar, Gaurav1; Ghosh, Sumit2; Pallaspuro, Sakari2;
Organizations: 1Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, 400076, India
2Materials and Mechanical Engineering, Centre for Advanced Steels Research, University of Oulu, 90014, Oulun Yliopisto, Finland
Format: article
Version: accepted version
Access: embargoed
Persistent link: http://urn.fi/urn:nbn:fi-fe2022061747386
Language: English
Published: Elsevier, 2022
Publish Date: 2024-04-18
Description:

Abstract

The propensity of the retained austenite to transform to martensite under external strain is known to induce plasticity (TRIP) in steels. If the retained austenite has a high volume fraction, it generally has blocky morphology and increases the tensile ductility via TRIP effect but can potentially deteriorate the yield strength. The present work demonstrates improved balance of strength and fracture toughness in a Si-containing 0.2%C steel having a refined martensitic matrix and evenly distributed and finely divided retained austenite (RA). Such a microstructure is obtained by thermo-mechanical rolling followed by direct quenching and partitioning (TMR-DQP) of the steel that results in establishing a constrained carbon equilibrium stabilising the austenite to room temperature. Transmission electron microscopy was used to characterise the nano-twinned martensite and the interlath nanometer thick austenite. An improved combination of yield strength, YS (1171 MPa), ultimate tensile strength, UTS (1419 MPa) and elastic-plastic fracture toughness, KJC (154 MPa √m) was achieved as compared to YS 1240 MPa, UTS 1654 MPa and KJC 111 MPa √m, respectively, for the fully martensitic counterpart. X-ray diffraction combined with Rietveld analysis revealed a reduction in the retained austenite from 9% away from the crack, which undergoes little strain, to 4 vol% near the crack, under higher strain, demonstrating strain induced martensitic transformation. The constrained nature of the austenite-to-martensite transformation within the rigid surrounding martensite is believed to increase the energy required to drive the crack forward, which raises the fracture toughness. Importantly, the results show that the uniformly distributed and nanoscale retained austenite is effective in imparting transformation-induced- plasticity at relatively small strength penalty.

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Series: Materials science & engineering. A, Structural materials: properties, microstructure and processing
ISSN: 0921-5093
ISSN-E: 1873-4936
ISSN-L: 0921-5093
Volume: 840
Article number: 142788
DOI: 10.1016/j.msea.2022.142788
OADOI: https://oadoi.org/10.1016/j.msea.2022.142788
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Subjects:
Funding: The authors express their sincere thanks to the Academy of Finland for providing necessary resources to conduct this research work under the Genome of Steel (Profi3) project #311934.
Academy of Finland Grant Number: 311934
Detailed Information: 311934 (Academy of Finland Funding decision)
Copyright information: © 2022. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http:/creativecommons.org/licenses/by-nc-nd/4.0/
  https://creativecommons.org/licenses/by-nc-nd/4.0/