Título

ENCRUAMENTO E TENACIDADE DO AÇO Nb-Ti DE GRÃO ULTRAFINO

ENCRUAMENTO E TENACIDADE DO AÇO Nb-Ti DE GRÃO ULTRAFINO

Autoria

Silva, Hezio Rosa da; Lourenço, Gustavo Gonçalves; Braga, Luciana Helena Reis; Rodrigues, Paulo César Matos; Santos, Dagoberto Brandão

DOI

10.5151/2594-5327-0365

Downloads

Baixar Artigo 16 Downloads

Resumo

A obtenção de aços de baixo teor de carbono microligados pelo processamento termomecânico visando uma alta resistência mecânica e alta tenacidade a baixas temperaturas, com boas características de ductilidade e soldabilidade, tem sido o grande objetivo da produção industrial desses materiais. Uma vez que a redução do tamanho de grão ferrítico é o único mecanismo capaz de aumentar a resistência mecânica e manter uma boa tenacidade, a produção de aços de grão ferrítico ultrafino torna-se importante. Por outro lado, o comportamento desses materiais de granulação ultrafina quando deformados plasticamente tem-se mostrado bastante interessante. Por exemplo, o alongamento uniforme aumenta com a redução do tamanho de grão ferrítico ao mesmo tempo em que se reduz a razão elástica. Assim, o objetivo deste trabalho foi avaliar o comportamento com relação ao encruamento e a tenacidade de um aço microligado baixo carbono (0,11% C, 1,41% Mn, 0,028%Nb e 0,012%Ti) de grão ferrítico ultrafino (~2

 

The ferritic grain refinement is a powerful mechanism to improve mechanical properties of low carbon steels providing steels with high strength and toughness at low temperatures and good weldability characteristics. The grain size refining is the unique mechanism capable of to increase both mechanical strength and toughness. The steel with an ultra-fine ferrite grained structure must shows a better relationship between mechanical strength, ductility and toughness, while the low carbon content enhances good welding characteristics. The objective of this work was to investigate the mechanical behavior of a microalloyed low carbon-manganese (0,11%C, 1,41%Mn, 0,028%Nb e 0,012%Ti) steel with ultra-fine grains produced through thermal treatment, warm rolling, followed by sub and intercritical annealing. After quenching in ice brine, steel samples were submitted to warm rolling at 700oC, with three pass of 0.23 true strain thickness reduction and air cooled. The following intercritical annealing treatment was done at 550 or 800oC for soaking times from 5 up to 120 min. The mechanical behavior of the steel was estimated using hardness tests. The mechanical strength and hardness obtained after all processing have shown a 20% increasing when compared with results from the steel in as hot rolling industrial condition. In order to investigate the work hardening, tensile testing and Vickers hardening have been carried out. Toughness was determined by subsize Charpy V-notched specimens impact tests, which were conducted at -20°C (253K). On the average ferrite grain size changing among 1,3 e 3,5μm has ben achieved, meaning an 87% refinement maximum around. It was possible to note the material annealed at 800°C (1073K) has shown the best toughness and strength characteristics, having presented good ductility yet. Besides that, for the material annealed at 800°C (1073K), the work hardening exponent has been around twice times bigger than another one annealed at 550°C (773 K).

Palavras-chave

Grão ultrafino; Recozimento intercrítico; Laminação a morno; Cementita.

Warm rolling; Ultra-fine grain; Hardness; Sub critical annealing.