Damage evolution in a tensile specimen of a ductile stainless steel

Abstract

This paper presents a study about the fracture mechanism of a ferritic stainless steel (UNS S44400 type) during a tensile test. The applied materials for the experimental procedures were 25 specimens of the steel, machined in the rolling direction. Each specimen was submitted to standard polishing procedures. One of the samples, in the original state, was structurally characterized by reflected light optical microscopy. The other samples were submitted to tensile tests with a constant displacement rate. Three samples were tested until failure (complete tests) and the others just until specific strain values, when the tests were interrupted and the samples were characterized by using optical and scanning electron microscopy. The main objective of these characterizations was to evaluate the structural damage evolution and to identify the fracture mechanism for the tested conditions. A methodology to quantify the damage evolution by surface roughness, identified by optical microscopy, was proposed. A new index-Damage by Diffuse Reflection Index (DRI)-was proposed to quantify the damage evolution in function of the specimen deformation. It was possible to confirm the ductile behavior of the studied steel and that the main fracture mechanism was the traditional dimpled rupture.

Influência da temperatura sobre o comportamento mecânico do aço inoxidável ferrítico ASTM A240 UNS S41003

“…A Figura 6 apresenta fractografias das amostras submetidas aos ensaios de tração nas três temperaturas avaliadas. Observou-se que o mecanismo de fratura atuante nas três condições é o de nucleação, crescimento e coalescimento de microcavidades, indicando fraturas dúcteis, o que está em acordo com a literatura [2,21]. Destaca-se que a amostra tracionada à temperatura ambiente apresenta delaminações no sentido de laminação da chapa.…”

“…Esse fenômeno pode ser causado por inclusões alinhadas, segregação química, ou precipitação preferencial de fases no sentido de laminação decorrentes do processamento termomecânico do aço. Durante o carregamento estático, essas regiões, como forma de promover alívio de tensões, propagam trincas secundárias [2,21]. Observa-se que a 600°C as microcavidades se apresentam maiores do que a 300°C, o que está coerente com o maior alongamento não uniforme verificado para a maior temperatura [21].…”