Low Temperature Precipitation in Nb-Added Si- and Si-Free Bainitic Steels

Ian Zuazo; Sebastian Cobo

doi:10.4028/www.scientific.net/MSF.706-709.2384

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HomeMaterials Science ForumMaterials Science Forum Vols. 706-709Low Temperature Precipitation in Nb-Added Si- and...

Low Temperature Precipitation in Nb-Added Si- and Si-Free Bainitic Steels

Abstract:

Precipitation strengthening by fine Nb-rich particles represents an important element on the design of low carbon high strength steels. This is typically obtained on steel strips by thermal holding at temperatures above 600°C following the austenite to ferrite transformation. These conditions are beneficial to obtain a large precipitation of small Nb-rich precipitates. On the other hand, precipitation at lower temperatures, in a phase already hard, such as bainite, has been scarcely studied. In this work, the precipitation phenomena occurring during isothermal treatments following the austenite to bainite transformation at 450°C are investigated. For this purpose, two Nb-alloyed low carbon steels with and without silicon are studied and the evolution of the microstructure is determined by the use of transmission electron microscopy and followed by hardness measurements. The presence of a hardness peak is not detected until long isothermal times (150h). Preliminary atom probe tomography (APT) characterization provides insight on the possible presence of fine NbC precipitates at the peak hardness treatment. A comparison with a Nb-free alloy indicates a significant hardening effect of niobium on the bainitic structure.

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Periodical:

Materials Science Forum (Volumes 706-709)

Pages:

2384-2389

DOI:

https://doi.org/10.4028/www.scientific.net/MSF.706-709.2384

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Online since:

January 2012

Authors:

Ian Zuazo, Sebastian Cobo

Keywords:

Atom Probe Tomography, Bainite, NbC, Precipitation, TEM

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References

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