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Title

AUSTENITE PARTIAL RECRYSTALLIZATION IN THE FINISHING STAGE OF CONTROLLED ROLLING OF NIOBIUM MICROALLOYED STEELS WITH LOW MANGANESE

Authorship

Gorni, Antonio Augusto; Silveira, José Herbert Dolabela da; Camey, Kenji; Reis, Emanuelle Garcia

Gorni, Antonio Augusto

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Silveira, José Herbert Dolabela da

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Camey, Kenji

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Reis, Emanuelle Garcia

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DOI

10.5151/9785-9785-32284

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Abstract

In recent years, several studies have been developed on the use of Nb micro-alloyed steels with low Mn content in the controlled rolling of heavy plates. This unprecedent concept of alloy leads to some peculiarities in its thermomechanical processing. For example, its very low levels of C and Mn promote an increase in the temperature at the beginning of the ferrite formation (Ar3), while its Nb content raises the non-recrystallization temperature of austenite (Tnr). This restricts the proper temperature range at which the finishing phase of controlled rolling should be performed. Lower Mn contents should lead to the acceleration of the NbCN precipitation kinetics during rolling, leading to a reduction in the soluble niobium content in austenite that delays by dragging the recrystallization of austenite. This fact, plus the heavy and fast passes applied under virtually isothermal conditions in a heavy plate rolling mill with high power, increases the risk of partial recrystallization during the finishing phase of the controlled rolling mill, since the strain hardening of the austenite becomes significant and the interaction between precipitation and recrystallization of austenite is increasingly delayed due to the greater reduction in the dissolved niobium content that results from the intensification of its precipitation. The objective of this study was to analyze the evolution of the average values of mean flow stress during the finishing phase of the controlled rolling mill in these Nb microalloyed steels with low Mn content, in order to better understand the metallurgical mechanisms acting during the thermomechanical treatment of this specific steel.

Keywords

TMCP, Austenite, Recrystallization, Manganese, Niobium