MECANISMOS DE ENDURECIMENTO EM AÇO MICROLIGADO Nb-Ti-V
STRENGTHENING MECHANISMS IN Nb-Ti-V MICROALLOYED STEEL
Martins, Vinícius Lopes Vieira; Vasconcelos, Felipe Pereira; Gallego, Juno
http://dx.doi.org/10.4322/tmm.2014.033
Tecnol. Metal. Mater. Min., vol.11, n3, p.222-228, 2014
Resumo
A elevada resistência mecânica e tenacidade dos aços microligados são resultantes da otimização dos diferentes mecanismos de endurecimento atuantes na liga. No presente trabalho a interação entre a microestrutura e o limite de escoamento de um aço comercial com baixo carbono e multimicroligado foi investigada. Amostras na condição laminada foram observadas por microscopia óptica e MET, quando parâmetros microestruturais que afetam a resistência mecânica - tais como tamanho de grão da ferrita, densidade de discordâncias e precipitação de carbonitretos - foram determinados. O incremento de resistência mecânica obtido com cada um dos mecanismos avaliados foi estimado com a aplicação de modelos empíricos coletados na literatura. O refino do grão ferrítico foi considerado o mecanismo de endurecimento mais efetivo. A precipitação de carbonitretos na austenita e durante a transformação de fase austenitaferrita (precipitação interfásica) também contribuíram com o aumento de resistência mecânica. Verificou-se que o limite de escoamento estimado pelo efeito cumulativo das diferentes contribuições analisadas foi bastante aproximado ao limite de escoamento determinado experimentalmente.
Palavras-chave
Aço microligado, Microestrutura, Mecanismos de endurecimento, Microscopia eletrônica de transmissão.
Abstract
Yield strength of Nb-Ti-V microalloyed steel has been investigated as a function of its microstructure obtained after industrial rolling on a hot strip mill. Optical (OM) and transmission electron microscopy (TEM) were used to reveal the ferrite grain structure, fine carbonitride precipitation and dislocation substructures. It was found that the effects of solid solution and grain size hardening were not sufficient to justify the results of tensile testing. Additional strengthening was attributed to carbonitride precipitation in austenite, interphase precipitation during transformation, and the formation of dislocations. All contributions of these microstructural features on mechanical property were estimated from empirical models available from literature. A global effect of both austenite and interphase carbonitride precipitation hardening was proposed. It was verified that yield strength calculated from cumulative effect of different strengthening mechanisms has presented good fitting with experimental tensile test.
Keywords
Microalloyed steel, Microstructure, Strengthening mechanisms, Transmission electron microscopy.
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