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Metals 2017, 7(9), 377; doi:10.3390/met7090377

The Influence of La and Ce Addition on Inclusion Modification in Cast Niobium Microalloyed Steels

1
School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, 111554563 Tehran, Iran
2
Materalia Research Group, National Center for Metallurgical Research (CENIM), Consejo Superior de Investigaciones Científicas (CSIC), E–28040 Madrid, Spain
3
Research Department of Nano‐Technology and Advanced Materials, Materials and Energy Research Center, 3177983634 Karaj, Iran
*
Authors to whom correspondence should be addressed.
Received: 7 August 2017 / Revised: 28 August 2017 / Accepted: 29 August 2017 / Published: 15 September 2017
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Abstract

The main role of Rare Earth (RE) elements in the steelmaking industry is to affect the nature of inclusions (composition, geometry, size and volume fraction), which can potentially lead to the improvement of some mechanical properties such as the toughness in steels. In this study, different amounts of RE were added to a niobium microalloyed steel in as-cast condition to investigate its influence on: (i) type of inclusions and (ii) precipitation of niobium carbides. The characterization of the microstructure by optical, scanning and transmission electron microscopy shows that: (1) the addition of RE elements change the inclusion formation route during solidification; RE > 200 ppm promote formation of complex inclusions with a (La,Ce)(S,O) matrix instead of Al2O3-MnS inclusions; (2) the roundness of inclusions increases with RE, whereas more than 200 ppm addition would increase the area fraction and size of the inclusions; (3) it was found that the presence of MnS in the base and low RE-added steel provide nucleation sites for the precipitation of coarse niobium carbides and/or carbonitrides at the matrix–MnS interface. Thermodynamic calculations show that temperatures of the order of 1200 °C would be necessary to dissolve these coarse Nb-rich carbides so as to reprecipitate them as nanoparticles in the matrix. View Full-Text
Keywords: niobium microalloyed steel; as-cast condition; inclusion; rare earth elements; precipitation. niobium microalloyed steel; as-cast condition; inclusion; rare earth elements; precipitation.
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Torkamani, H.; Raygan, S.; Mateo, C.G.; Rassizadehghani, J.; Vivas, J.; Palizdar, Y.; San-Martin, D. The Influence of La and Ce Addition on Inclusion Modification in Cast Niobium Microalloyed Steels. Metals 2017, 7, 377.

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