Influencia da taxa de resfriamento nas propriedades mecanicas e no micromecanismo de fratura de um aço microligado com niobio e titanio / The effect of cooling rate on the mechanical properties and fracture micromechanisms in a low carbon microalloyed niobium-titanium steel

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

In the last years the plain low-carbon steels have been replaced by the microalloyed steels in several applications as ship structure, pipeline, and several other applications in the automobile industry. Nowadays, a lot of effort has been pointed out to obtain steels with microstructures to improve the relationship between strength and ITacture toughness. The purpose of this work is to study the effect of the cooling rate, from complete austenization at 920º C and from intercritical zone at two different temperatures (710 and 770º C), on the microstructure, mechanical properties, and fracture micromechanisms, for the API 5L X65 steel - a niobium-titanium microalloyed steel. It was analyzed also the effect of austempering on the microstructure and mechanical properties. The mechanical properties analyzed are yield strength (S IND. y), tensile strength (S IND. u), total elongation (El IND. t), hardness (HV), and fracture toughness (crack tip opening displacement ( sigma IND. m). From changing the cooling rate, in different thermal treatment routes, several microstructures were obtained, some of them pointing out a better strength - fracture toughness relationship. The samples submitted to different cooling rates, from austenization at 920º C, showed the microstructure as follows: ferrite-perlite-MA constituent for the 7 º C/s cooling rate, ferrite-bainite-MA constituent for the 16 and 23 º C/s and ferrite-martensite for the 50 º C/s ... Note: The complete abstract is available with the full electronic digital thesis or dissertations

ASSUNTO(S)

aço-carbono - propriedades mecanicas mecanica de fratura aço - tratamento termico

ACESSO AO ARTIGO

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