Production of a non-stoichiometric Nb-Ti HSLA steel by thermomechanical processing on a Steckel mill.
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Date
2023
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Abstract
Obtaining high levels of mechanical properties in steels is directly linked to the use of
special mechanical forming processes and the addition of alloying elements during their manufacture. This work presents a study of a hot-rolled steel strip produced to achieve a yield strength
above 600 MPa, using a niobium microalloyed HSLA steel with non-stoichiometric titanium (titanium/nitrogen ratio above 3.42), and rolled on a Steckel mill. A major challenge imposed by
rolling on a Steckel mill is that the process is reversible, resulting in long interpass times, which
facilitates recrystallization and grain growth kinetics. Rolling parameters whose aim was to obtain
the maximum degree of microstructural refinement were determined by considering microstructural
evolution simulations performed in MicroSim-SM® software and studying the alloy through physical
simulations to obtain critical temperatures and determine the CCT diagram. Four ranges of coiling
temperatures (525–550 ◦C/550–600 ◦C/600–650 ◦ C/650–700 ◦C) were applied to evaluate their impact on microstructure, precipitation hardening, and mechanical properties, with the results showing
a very refined microstructure, with the highest yield strength observed at coiling temperatures of
600–650 ◦C. This scenario is explained by the maximum precipitation of titanium carbide observed
at this temperature, leading to a greater contribution of precipitation hardening provided by the
presence of a large volume of small-sized precipitates. This paper shows that the combination of
optimized industrial parameters based on metallurgical mechanisms and advanced modeling techniques opens up new possibilities for a robust production of high-strength steels using a Steckel
mill. The microstructural base for a stable production of high-strength hot-rolled products relies on
a consistent grain size refinement provided mainly by the effect of Nb together with appropriate
rolling parameters, and the fine precipitation of TiC during cooling provides the additional increase
to reach the requested yield strength values.
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Keywords
Controlled rolling, Thermomechanical processing, Accelerated cooling, High-strength low-alloy steels, Nb precipitation
Citation
MARTINS, C. A. et al. Production of a non-stoichiometric Nb-Ti HSLA steel by thermomechanical processing on a Steckel mill. Metals, v. 13, n. 2, artigo 405, fev. 2023. Disponível em: <https://www.mdpi.com/2075-4701/13/2/405>. Acesso em: 15 mar. 2023.