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Title

HOT ROLLING STRATEGIES TO MODULATE NB INTERACTION WITH MICROSTRUCTURE IN FLAT PRODUCTS

Authorship

Pereda, Beatriz; Uranga, Pello; Lopez, Beatriz; Rebellato, Marcelo; Rodriguez-Ibabe, J.M.

Pereda, Beatriz

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Uranga, Pello

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Lopez, Beatriz

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Rebellato, Marcelo

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Rodriguez-Ibabe, J.M.

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DOI

10.5151/9785-9785-32246

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Abstract

The classical application of Nb microalloying in the development of thermomechanical processes for flat products has been related to its suitability to enhance strain-induced precipitation and get a pancaked austenite prior to transformation. As new steel grades or new lay-outs are being developed, more complex metallurgical conditions need to be evaluated. In this context, Nb microalloying, alone or combined with other microadditions, needs to intervene in a more controlled way in additional steps of the thermomechanical process, besides its conventional strain-induced precipitation role. For example, the hardenability enhancement associated with Nb to properly achieve lower temperature transformation products, demands a proper balance of the Nb amount precipitated during rolling and the one remaining in solid solution. Similar effects are also sought when the final available Nb is used to increase strength through precipitation hardening. This manuscript evaluates how changes in the rolling strategies affect the interaction between Nb(C,N) precipitation and austenite recrystallization at different steps of the rolling process. As the possible interactions between parameters intervening simultaneously are quite complex, the application of microstructural models helps to properly define the best austenite conditioning combined with the convenient amount of Nb in solution, as a function of the final property requirements. Along the manuscript, several strategies will be discussed for the case of hot rolling of flat products comparing both normal and coarse initial austenite grain sizes.

Keywords

Nb microalloying; Thermomechanical processing; Pancaked austenite; Intragranular nucleation