University of Oulu

Ali, M.; Nyo, T.; Kaijalainen, A.; Hannula, J.; Porter, D.; Kömi, J. Influence of Chromium Content on the Microstructure and Mechanical Properties of Thermomechanically Hot-Rolled Low-Carbon Bainitic Steels Containing Niobium. Appl. Sci. 2020, 10, 344.

Influence of chromium content on the microstructure and mechanical properties of thermomechanically hot-rolled low-carbon bainitic steels containing niobium

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Author: Ali, Mohammed1,2; Nyo, Tun1; Kaijalainen, Antti1;
Organizations: 1Materials and Mechanical Engineering, Centre for Advanced Steels Research, University of Oulu, P.O. Box 4200, 90014 Oulu, Finland
2Steel Technology Department, Central Metallurgical Research and Development Institute (CMRDI), Helwan, Cairo 11421, Egypt
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 10.1 MB)
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Language: English
Published: Multidisciplinary Digital Publishing Institute, 2020
Publish Date: 2020-01-22


The effect of chromium content in the range of 1 wt.%–4 wt.% on the microstructure and mechanical properties of controlled-rolled and direct-quenched 12 mm thick low-carbon (0.04 wt.%) steel plates containing 0.06 wt.% Nb has been studied. In these microalloyed 700 MPa grade steels, the aim was to achieve a robust bainitic microstructure with a yield strength of 700 MPa combined with good tensile ductility and impact toughness. Continuous cooling transformation diagrams of deformed and non-deformed austenite were recorded to study the effect of Cr and hot deformation on the transformation behavior of the investigated steels. Depending on the cooling rate, the microstructures consist of one or more of the following microstructural constituents: bainitic ferrite, granular bainite, polygonal ferrite, and pearlite. The fraction of bainitic ferrite decreases with decreasing cooling rate, giving an increasing fraction of granular bainite and polygonal ferrite and a reduction in the hardness of the transformation products. Polygonal ferrite formation depends mainly on the Cr content and the cooling rate. In both deformed and non-deformed austenite, increasing the Cr content enhances the hardenability and refines the final microstructure, shifting the ferrite start curve to lower cooling rates. Preceding austenite deformation promotes the formation of polygonal ferrite at lower cooling rates, which leads to a decrease in hardness. In hot-rolled and direct-quenched plates, decreasing the Cr content promotes the formation of polygonal ferrite leading to an increase in the impact toughness and elongation but also a loss of yield strength.

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Series: Applied sciences
ISSN: 2076-3417
ISSN-E: 2076-3417
ISSN-L: 2076-3417
Volume: 10
Issue: 1
Article number: 344
DOI: 10.3390/app10010344
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Funding: This research was funded by CBMM (Companhia Brasileira de Metalurgia e Mineracao).
Copyright information: © 2020 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 (